OF  THE 

U N I VERS  ITY 
or  ILLI  NOIS 


PRESENTED  5Y 
Luther  L.  Gordon 
Rushville,  Illinois 
1938 

sao 

TSSe 

1852. 


ELEMENTS 

or 

CHEMISTRY, 

INCLUDING  THE 

RECENT  DISCOVERIES  AND  DOCTRINES  OF  THE  SCIENCE. 


BX 


EDWARD  TURNER,  M.D.  F.R.S.  L.  &E.  Sec.  G.S. 

PBOrSSSOB  OF  CHElttlSTRT  IN  THE  UNIVERSITY  OF  LONDON. 


Fellow  of  the  Royal  College  of  Physicians  of  Edinburgh ; Corresponding  Mem- 
ber of  the  Royal  Society  of  Gottingen  ; Honorary  Member  of  the 
Plinian  Society  of  Edinburgh  ; and  Member,  and  formerly 
President,  of  the  Royal  Medical  Society  of  Edinburgh. 


Fourth  American^  from  the  Third  Londmi  Edition, 

WITH  NOTES  AND  EMENDATIONS, 

BY  FRANKLIN  BACHE,  M.D. 


Profejsor  of  Chemistry  in  the  Franklin  Institute  of  the  State  of  Pennsylvatiia,  and 
in  the  Philadelphia  College  of  Pharmacy  ; one  of  the  Secretaries 
of  the  American  Philosophical  Society,  &c. 


PHILADELPHIA  : 

GIUGG  & ELLIOT,  NO.  9,  NORTH  FOURTH  STREET. 

1832. 


Entered  according  to  the  Act  of  Congress,  in  the  year  1831,  by 
Grlgg  & Elliott,  of  the  state  of  Pennsylvania,  in  the  office  of  the  Clerk 
of  the  District  Court  of  the  Eastern  District  of  Pennsylvania. 


Mifflin  8c  Parry,  Printers, 
No.  59,  Locust  Street. 


■> 


N 


■ '2  "') 


/.  . V. 


TO 


FREDERICK  STROMEYER,  M.D.  F.R.S.  L.  & E. 

PROFESSOR  OF  CHEMISTRY  IN  THE  UNIVERSITY  OF  GOTTINGEN, 

ETC.  ETC. 

X^*My  Dear  Sir, 

^ The  feelings  of  respect  and  regard  which  prompted  me  to  dedi- 
^ |oate  to  you  the  former  editions  of  this  Treatise,  continue  unahered. 
Increasing  experience,  indeed,  has  served  but  to  enhance  the  value 
"which  I ever  attached  to  the  instruction  received  in  your  laboratory, 
"^nd  to  the  habits  of  accuracy  in  research  inculcated  by  your  pre- 
"^cept,  and  enforced  by  your  example.  To  you,  therefore,  permit 
still  to  inscribe  a work  intended  to  promote  the  study  of  that 
^ Science,  which  you  cultivate  with  so  much  zeal  and  success;  and 
^ye  assured  that  the  opportunity  of  again  publicly  expressing  grati- 
tude for  your  kindness,  and  admiration  of  your  distinguished  ana- 
lytical attainments,  is  a source  of  much  pride  and  pleasure  to  your 


Friend  and  former  Pupil, 

A| 

Upper  Gower-street, 
October  1,  1830. 


EDWARD  TURNER. 


h ^ 


Digitized  by  the  internet  Archive 
in  2017  with  funding  from 

University  of  liiinois  Urbana-Champaign  Aiternates  • 


https://archive.org/detaiis/eiementsofchemis00turn_0 


PREFACE 


TO 

THE  THIRD  EDITION. 


The  remarks  with  which  the  second  edition  of  these  Elements 
was  prefaced,  may  with  equal  propriety  be  applied  to  the  present. 
Every  part  of  the  Treatise  has  been  carefully  revised; — redun- 
dancies have  been  retrenched, — inaccuracies,  as  far  as  possible^ 
corrected, — obscurities,  it  is  hoped,  removed, — and  deficiencies 
supplied.  It  has  been  attempted,  by  the  careful  perusal  of  origi- 
nal essays,  to  give  the  latest  and  most  correct  information  in  every 
department  of  the  Science.  On  the  writings  of  Berzelius,  espe- 
cially on  his  Lehrbuch  der  Chemie,  I have  drawn  more  freely  than 
in  the  former  editions ; partly  from  having  become  better  ac- 
quainted with  the  work  itself,  and  partly  because  my  own  expe- 
rience, in  enabling  me  more  fully  to  appreciate  the  accuracy  of  its 
author,  has  induced  me  to  attach  a higher  interest  to  his  observa- 
tions. 

The  most  material  change  in  the  present  edition  will  be  found 
in  the  article  on  Galvanism,  in  the  theory  of  which  some  modifica- 
tion has  become  necessary.  An  outline  of  tlie  views  of  Berzelius 
on  the  Haloid  and  Sulfiho-salts  has  also  been  introduced.  Some 
changes  have  been  made,  of  a nature  not  to  require  particular 
mention,  and  too  numerous  to  admit  of  it.  The  plan  of  the  work  re- 
mains precisely  the  same  as  it  was  explained  in  the  original  pre- 
face, The  size  of  the  volume  has,  indeed,  been  somewhat  en- 
larged; but  the  additions,  which  were  required  by  the  state  of  the 
science,  will  render  the  work  a safer  and  a more  useful  gn.icje  fo  the 
student  of  Chemistry. 

Upper  Gower^btreet,  October  1,  1830. 


1* 


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ADVERTISEMENT 


OP 

THE  AMERICAN  EDITOR. 


The  American  Editor,  in  superintending  a new  impression  of 
Dr.  Turner’s  Elements,  from  the  third  London  edition,  enlarged 
and  revised  by  the  Author,  has  restricted  himself,  as  on  the  for- 
mer occasion,  to  the  task  of  revising  the  text,  and  supplying  a 
few  notes.  Several  additional  inaccuracies  have  been  detected  in 
the  original  text,  and  some  also  in  the  matter  which  has  been 
newly  introduced  by  the  Author. 

The  notes  of  the  Editor  are  distinguished  by  the  letter  B.  A 
few  have  been  added  to  those  which  appeared  im  the  former  edi- 
tion ; and  about  an  equal  number  have  been  omitted,  chiefly  re- 
lating to  inaccuracies  and  omissions,  which  have  since  been  either 
corrected  or  supplied  by  the  Author  himself.  These  notes  will 
be  found,  for  the  most  part,  explanatory  or  supplementary,  though 
occasionally  critical.  It  has,  however,  been  rarely  necessary  to 
differ  from  the  Author,  who  has  certainly  exhibited,  in  the  com- 
position of  his  treatise,  the  qualities  of  an  accurate  Chemist,  and 
neat  and  perspicuous  writer. 

Philabbiphia,  December  1831, 


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CON  TEN  T S. 


IifTRODUCTiON  . Page  13 

PART  I. 

IMPONDERABLE  SUBSTANCES. 

Sect*  I.— Caloric,  * 19 

Communicationof  Caloric,  20 
Radiation,  23 

Cooling“  of  Bodies,  28 

Effects  of  Caloric,  28 

Expansion,  29 

Thermometer,  37 

Liquefaction,  50 

Vaporization,  56 

Ebullition,  57 

Evaijoration,  60 

Constitution  of  Gases 

Avith  respect  to  Caloric,  67 
Sources  of  Caloric,  68 

Sect*  II. — Light,  68 

Sect*  III. — Electricity,  73 

Se<^*  IV.— Galvanism,  84 

PART  II. 

INORGANIC  CHEMISTRY. 
PRELIMINARY  REMARKS,  106 

Sect*  I.— Affinity,  109 

Changes  that  accompany 

Chemical  Action,  113 

Circumstances  that  modi- 
fy and  influence  the 
Operation  of  Affinity,  114 
Measure  of  Affinity,  121 


Sect*  II.— Proportions  in  Avliich  Bo- 
dies unite,  and  the 
Laws  of  Combination,  121 
Atomic  Theory  of  Mr. 


Dalton,  129 

Theory  of  Volumes,  132 

Theory  of  Berzelius,  137 

Sect*  III.— Oxygen,  140 

Theory  of  Combustion,  143 
Sect*  IV.— Hydrogen,— Water,  146 

Deutoxide  of  Hydrogen,  151 
Sect*  V.— Nitrogen,  154 

Atmosphere,  155 

Compounds  of  Nitro- 
gen and  Oxygen.— 
Protoxide,  163 


Deutoxide  of  Nitrogen,  165 


Hyponitrous  Acid,  168 

Nitrous  Acid,  168 

Nitric  Acid,  170 

Sect.  VI.— Carbon,  174 

Carbonic  Acid,  177 


Carbonic  Oxide  Gas, 
Sect*  VIL— Sulphur, 

Compounds  of  Sulphur 
and  Oxygen.— Sul- 


pliurous  Acid,  184 

Sulphuric  Acid,  186 

Hyposulphurous  Acid,  189 

Hyposulphuric  Acid,  190 

Sect*  Vill.— Phosphorus,  I9l 

Compounds  of  Phos- 
phorus and  Oxy- 
gen.—Phosphoric 
Acid,  193 

Phosi)horous  Acid,  196 
Hypophosphorous  Acid.  197 
Oxides  of  Phosphorus,  198 
Sect*  IX.— Boron,  198 

Boracic  Acid,  199 

Sect*  X.— Selenium,  200 

Oxide  of  Selenium,  201 

Selenious  and  Selenie 

Acids,  201 

Sect*  Xl.-Chlorine,  203 

Muriatic  Acid,  206 

Compounds  of  Chlorine 

and  Oxygen,  210 

Protoxide  of  Chlorine,  211 
Peroxide  of  Chlorine,  211 
Chloric  Acid,  212 

Perchloric  Acid,  213 

Chloride  of  Nitrogen,  213 
Compounds  of  Chlorine 
and  Carbon,  214 

Chloride  of  Sulphur,  215 
Chlorides  of  Phosidiorus,  216 
Chlorocarbonic  Acid,  216 
Chloride  of  Boron,  217 

Nature  of  Chlorine,  217 
Sect.  Xll.-Iodine,  220 

Hydriodic  Acid,  221 

Iodic  Acid,  223 

lodous  Acid,  224 

Chloriodic  Acid,  225 


X 


CONTENTS 


Iodide  of  Nitrogen,  225 

Sect,  XIII. — Bromine,  226 

Hydrobromic  Acid,  229 

Bromic  Acid,  230 

Chloride  and  Iodide 

of  Bromine,  231 

• Bromide  of  Sulphur,  231 
Bromide  of  Phosphorus,  232 
Sect,  XIV. — Fluorine,  232 

Hydrofluoric  Acid,  233 

Fluoboric  Acid  Gas,  235 


COMPOUNDS  OF  THE  SIMPLE  NON-ME- 
TALLIC  ACIDIFIABLE  COMBUSTI- 
BLES WITH  EACH  OTHEB,  238 

Sect.  I. — Hydrogen  with  Nitrogen.— 

Ammonia,  238 

Sect,  II. — Hydrogen  with  Carbon,  240 
Light  carbu retted  Hy- 
drogen, 241 

Olefiant  Gas,  243 

New  Carburets  of  Hy- 
drogen, discovered  by 
Mr.  Faraday,  246 

Naphtha  from  Coal  Tar. 

Naphthaline,  248 

Coal  and  Oil  Gas,  250 

Sect,  III.— Hydrogen  with  Sulphur,  252 
Sulphuretted  Hydrogen,  252 
Bisulphuretted  Hydro- 
gen, 254 

Sect,  IV.— -Hydrogen  with  Selenium.— 

Hydroselenic  Acid,  255 
Sect,  V. — Hydrogen  with  Phospliorus,  255 
Protophosphuretted  Hy- 
drogen, 256 

Perphosphurettcd  Hy- 
drogen, 25’7 

Sect,  VI.— Nitrogen  with  Carbon.— 

Cjanogen,  259 

Cyanogen  with  Hydrogen. 

Hydrocyanic  Acid,  260 

Cyanic  Acid,  264 

Cyanous  Acids,  265 

Chloride  of  Cyanogen,  266 

Iodide  of  Cyanogen,  268 

Bromide  of  Cyanogen,  268 

Ferrocyanic  Acid,  269 

Sulphocyanic  Acid,  271 

Sect,  VII.— Compounds  of  Sulphur 
with  Carbon  and 
Phosphorus,  272 

Bisulphuret  of  Carbon,  272 
Sulphuretof  Phospho- 
rus, 273 

Sect,  VIII.— Compounds  of  Selenium 
with  Sulphur  and 
Pliosphorus.  274 

METALS. — OENEllAL  PBOPERTIES, 

275 

Sect.  I.r-Potassiiim  and  its  Oxides, 
Chloride,  Sulj)hu- 
reti,  8cc.  201 


Sect.  II.— Sodium  and  its  Oxides, 

Chloride,  &c.  t06 

Sect.  III.— Lithium  and  Lithia,  JOO 

Sect.  IV. — Barium  and  its  Oxides, 

Chloride,  and  Sulphui*et,  301 
Sect.  V.— Strontium  and  its  Oxides, 

Chloride,  and  Sulphuret,  303 
Sect,  VI.— Calcium  and  its  Oxides, 

Chloride,  &c.  305 

Chloride  of  Lime,  or 

Bleaching  Powder,  306 
Sect.  VII. — Magnesium  and  Magnesia,  308 
Sect.  VlII. — Aluminium,  and  Alumina,  309 


Sect.  IX.— Glucinium,  Yttrium,  Tho- 
rium, Zirconium,  and 
their  Oxides,  3 13 

Sect.  X.— Silicium  and  Silica  Sl7 

Fluosilicic  Acid  Gas,  320 

Sect,  XI.— Manganese  and  its  Oxides, 

Chlorides,  &c.  322 

Sect.  ^11.  — Iron  and  its  Oxides,  Chlo- 
rides, Sulphurets,  SiC.  328 
Carburets  of  Iron.— 
Graphite,  Cast  Iron, 

Steel,  333 


Sect.  XIII.— Zinc  and  its  Oxide,  Chlo- 
ride, and  Sulphuret,  335 
Cadmium,  and  its  Oxide,  336 
Sect.  XIV.— Tin  and  its  Oxides,  Chlo- 
rides, &c.  338 

Sect.  XV.— Cobalt  and  its  Oxides,  340 
Nickel  and  its  Oxides,  342 
Sect.  XVI.— Arsenic  and  its  compounds 
with  Oxygen,  Chlo- 
rine, &c.  344 

Tests  for  Arsenious  Acid,  346 
Sect.  XVII.— Chromium  and  its  com- 
pounds with  Oxygen,  351 
Fluochromic  Acid  Gas,  353 
Chlorochromic  Acid 
Gas,  353 

Molybdenum  and  its 
compounds  with  Oxy- 
gen, 354 

Tungsten  and  its  com- 
pounds with  Oxygen,  355 
Columbium  and  its 
compounds  with  Oxy- 
gen, 357 

Sect.  XVIII.— Antimony  and  irt  Ox- 
ides, Chlorides,  ami 
Sulphurets,  358 

Sect.  XIX.— Uranium  and  its  Oxides,  362 
Cerium  and  its  Oxides,  364 
Sect.  XX.— Bismuth  and  its  Oxide, 

Chloride,  and  Sulphuret,  365 
Titanium  and  its  Oxides,  366 
Tellurium  and  its  Oxide,  368 
Sect.  XXL— Copper  and  its  .Oxides, 
Chlorides,  and  Sul- 
pburets,  369 

Sect.  XXII.— Lead  and  its  Oxides, Chlo- 
ride, and  Sulphuret.  372 
Sect.  XXIIL— Mercury  aiul  its  Oxides,  376 
Chlorides.— Calomel 


CONTENTS. 


XI 


and  Corrosive  Sub- 
limate, 378 

Iodides,  Cyanuret, 
and  Sulphurets,  380 

Sect,  XXIV.— Silver  and  its  Oxide, 

Chloride,  &c,  381 

Sect.  XXV.— Gold  and  its  Oxides, 
Chlorides,  and  Sul- 
phurets, 384 

Sect.  XXVI.— Platinum  and  its  Ox^ 

ides,  Chlorides,  &c.  387 

Sect.  XXVII.— Palladium,  Rhodium, 

Osmium,  and  Iridium,  389 
Piuranium  and  Rhu- 


tenium,  394 

Sect,  XXVIII.— Metallic  Combinations,  395 

SALTS — GENERAL  REMARKS,  400 

Crystallization,  404 

Sect,  L— Sulphates,  4l3 

Sulphites,  420 

Hyposulphates  and  Hy- 
posulphites, 420 

Sect.  II.— Nitrates,  421 

Nitrites,  424 

Chlorates,  425 

lodates,  ’426 

Sect.  III. — Phosphates,  427 

Pyrophosphates,  429 

Phosphites  and  Hypo- 
phosphites,  430 

Arseniates,  430 

Arsenites,  430 

Sect,  IV^Chromates,  43 1 

Borates,  432 

Fluoborates,  433 

Sect.  V.— Carbonates,  433 

Sect.  VI.— Salts  of  the  Hydracids,  438 

Muriates  or  Hydrochlo- 
rates, 439 

Hydriodates,  441 

Hydrobromates,  442 

Hydroftnates,  443 

Hydros ulphurets  or  Hy- 
'drosulphates,  444 

Hydrocyanates,  445 

Ferroeyanates,  446 

Sulphocyanates,  449 

Sect.  VII. — Haloid  Salts,  and  Sul- 

plio-salts,  449 

PART  III. 

ORGANIC  CHEMISTRY. 
VEGETABLE  CHEMISTRY,  455 

S€>'t.  I. — Vegetable  Acids,  457 

Acetic  Acid  and  its  Salts,  457 
Oxalic  Acid  and  its  Salts,  461 


Tartaric  Acid  and  its  Salts,  464 
Citric  Acid  and  its  Salts,  467 
Malic  Acid  and  its  S alts,  468 
Benzoic  Acid  and  its  Salts,  469 
Gallic  Acid  and  its  Salts,  470 
Succinic  Acid  and  its  Salts,  471 
Camphoric  Acid,  471 


Saccholactic,  Moroxylic,  Hy- 
drocyanic, Rheumic,  Bo- 
letic,  Igasuric,  and  Mel- 
litic  Acids,  472 

Suberic,  Zumic,  Kinic,  Me- 
conic,  Pectic,  Carbazotic, 
and  Indigotic  Acids.  473 

Sect.  II.— Vegetable  Alkalies,  475 

Morphia.— Narcotine,  476 

Cinchonia  and  Quinia,  479 

Strychnia  and  Brucia,  480 

Veratria,  Emetia,  Picro- 
toxia,  Solania,  Del- 
phia,  &c.  481 

Sect.  III.— Substances  which,  in  rela- 
tion to  Oxygen,  con- 
tain an  excess  of  Hy- 
drogen, 484 

Fixed  Oils,— Elaine  and 

Stearine,  484 

Volatile  Oils,  485 

Camphor,  486 

Resins,  487 

Amber,  48  S 

Balsams,  Gum-resins, 

Caoutchouc,  489 

Wax,  490 

Alcohol,  491 

Ether,  494 

Sulphuric  Ether,  494 

Nitrous  Ether,  497 

Acetic,  Muriatic,  and 
Hydriodic  Ethers,  497 

Bituminous  substances,  498 

Naphtha.  498 

Petroleum,  Asphaltum, 
Mineral  Pitch,  Reti- 
nasphaltum,  Coal,  499 

Sect,  IV.— Substances,  the  Oxygen 
and  Hydrogen  of  which 
are  in  exact  proportion 
for  forming  water,  501 

Sugar,  Molasses,  Honey, 
Manna,  501 

Starch— Amidine,  Hor- 
dein,  503 

Gum — Mucilage,  505 

Lignin  or  Woody  Fibre. 
Pyroxylic  and  Pyro- 
acetic  spirit,  506 

Seet.  V.— Substances  which,  so  far  as 
is  known,  do  not  belong 
to  either  of  the  preced- 
ing Sections,  507 

Colouring  Matter — Dyes,  507 

Tannin— Artificial  Tannin,  513 
Vegetable  Albumen,  514 

Gluten— Gliadine,  Zymome,  515 
Yeast,  515 

Asparagin,  Rassorin,  Caf- 
fein,  Cathartin,  Fungin, 
Suberin,  Ulmin,  Lupu- 
lin,  Inulin,  Medullin, 


CONTENTS 


xli 


Pollenin,  Piperin,  Olivile, 
Sarcocoll,  &c.  516 

Sect*  VI.— Spontaneous  changes  of 

Vegetable  Matter,  520 

Saccharine  Fermentation,  520 
Vinous  Fermentation,  521 

Acetous  Fermentation,  523 

Putrefactive  Fermenta- 
tion, 524 

Sect.  VII.— Chemical  Phenomena  of 
Germination  and  Veg- 
etation, 526 

Germination,  526 

Growth  of  Plants,  5J8 

Food  of  Plants,  530 

animal  CHEMISTHY.  532 

Proximate  Animal  Principles,  532 

Sect.  I.— Substances  which  are  nei- 
ther acid  nor  oleagi- 
nous, 533 

Fibrin,  533 

Albumen,  534 

Gelatin,  536 

Urea,  537 

Sugar  of  Milk,  and  Su- 
gar of  Diabetes,  539 

II. —Animal  Acids,  539 

Uric  Acid  and  its  Salts,  539 

Purpuric  Acid,  541 

Erythric  and  Rosacic 
Acids— Lateritious 
Sediment,  541 

Hipp  uric.  Formic,  Lactic, 
and  Amniotic  Acids,  542 

Sect.  III.— Oleaginous  substances,  543 

Animal  Oils  and  Fats,  543 

Spermaceti,  545 

Adipocire,  Cholesterine,  546 

Ambergris,  547 

MORE  COMPLEX  ANIMAL  SUB- 
STANCES, AND  SOME  FUNC- 
TIONS OF  ANIMAL  BODIES,  547 


Sect.  L— Blood,  547 

Respiration,  552 

Animal  Heat,  550 

Sect,  II.— Secreted  Fluids  subservient 

to  Digestion,  559 

Saliva,  559 

Pancreatic  and  Gastric 
Juices,  559 

Bile  and  Biliary  Concretions,  561 
Sect.  III.— Chyle,  Milk,  Eggs,  563 

Sect,  IV.— Liquids  of  Serous  and  Mu- 
cous Surfaces,  and  Puru- 
lent Matter,  567 

Sect,  V . — Urine  and  Urinary  Concre- 
tions, 509 

Veef.  VI.— Solid  parts  of  Animals; 

Bones,  Horn,  Muscle,  &c.  576 
Sect.  VII.— Putrefaction,  578 

PART  IV. 

ANALYTICAL  CHEMISTRY. 

Sect.  I.— Analysis  of  Mixed  Gases,  580 
Sect.  II.—  Analysis  of  Minerals,  584 

Sect,  III.— Analysis  of  Mineral  Waters,  589 
Composition  of  Mineral 

Waters.  593 

APPENDIX. 

Table  of  Chemical  Equivalents  or 

Atomic  Weights,  597 

of  the  Elastic  Force  of  Aque- 
ous Vapour,  603 

of  the  Elastic  Force  of  the  Va- 
pour of  Alcohol,&c.  606 

of  the  strength  of  Sulphuric 
Acid,  607 

of  the  strength  of  Nitric  Acid,  608 
of  the  strength  of  Alcohol  609 
of  Specific  Gravities,  indicated 
by  Baum^’s  Hydrometer,  610 

INDEX,  611 


INTRODUCTION, 


Material  substances  are  endowed  with  two  kinds  of  properties, 
physical  and  chemical;  and  the  study  of  the  phenomena  occasioned 
by  them  has  given  rise  to  two  corresponding  branches  of  knowledge, 
Natural  Philosophy  and  Chemistry, 

The  physical  properties  are  either  general  or  secondar3%  The  general 
are  so  called  because  they  are  common  to  all  bodies;  the  secondary, 
from  being  observable  in  some  substances  only.  Among  the  general 
may  be  enumerated  extension,  impenetrability,  mobility,  extreme  di- 
visibility, gravitation,  porosity,  and  indestructibility. 

Extension  is  the  property  of  occupying  a certain  portion  of  space.  A 
substance  is  said  to  be  extended  when  it  possesses  length,  breadth,  and 
thickness.  By  impenetrahility  is  meant  that  no  two  portions  of  matter 
can  occupy  the  same  space  at  the  same  moment.  Every  thing  that  pos- 
sesses extension  and  impenetrability  is  matter. 

Matter,  though  susceptible  of  motion,  has  no  power  either  to  move 
itself,  or  to  arrest  its  own  progress  when  an  impulse  is  once  communi- 
cated to  it.  This  indifference  to  rest  or  motion  has  been  expressed  by 
the  term  vis  inertige,  as  if  it  depended  on  some  specific  force  resident  in 
matter;  but  it  may  with  greater  propriety  be  regarded  as  a negative 
character,  in  consequence  of  wdiich,  matter  is  wholly  given  up  to  the 
operation  of  the  various  forces  which  are  constantly  acting  upon  it. 

Matter  is  divisible  to  an  extreme  degree  of  minuteness.  A grain  f 
gold  may  be  so  extended  by  hammering  that  it  will  cover  50  square 
inches  of  surface,  and  contain  two  millions  of  visible  points;  yet  the 
gold  which  covers  the  silver  wire,  used  in  making  gold  lace,  is  spread 
over  a surface  twelve  times  as  great.  (Nicholson’s  Introduction  to  Na- 
tural Philosophy,  vol,  i.)  A grain  of ‘iron,  dissolved  in  nitro-muriatic 
acid,  and  mixed  with  3137  pints  of  water,  will  be  diffused  through  the 
whole  mass,  and  by  means  of  the  ferrocyanate  of  potassa,  which  strikdb 
a uniform  blue  tint,  some  portion  of  iron  may  be  detected  in  every  part 
of  the  liquid.  This  experiment  proves  the  grain  of  iron  to  have  been 
divided  into  rather  more  than  24  millions  of  parts;  and  if  the  same  quan- 
tity of  iron  were  still  further  diluted,  its  diffusion  though  the  whole 
liquid  might  be  proved  by  concentrating  any  portion  of  it  by  evapora- 
tion, and  detecting  the  metal  by  its  appropriate  tests. 

A keen  controversy  existed  at  one  time  concerning  the  divisibility  of 
matter;  some  philosophers  affirming  it  to  be  infinitely  divisible,  wffiile 
others  maintained  an  opposite  opinion.  Owing  to  the  imperfection  of 
our  senses  the  question  cannot  be  determined  by  direct  experiment, 
because  matter  certainly  continues  to  be  divisible  long  after  it  has  ceased 
to  be  an  object  of  sense.  The  decision,  if  effected  at  all,  can  only  be 
accomplished  by  indirect  means.  In  favour  of  the  former  view  it  was 
urged,  that  to  whatever  degree  matter  is  divided,  it  may  still  be  con- 
ceived, in  possessing  extension,  to  be  divisible  into  two  parts;  and  the 
minuteness  to  which  matter  may  actually  be  reduced,  gave  additional 


14 


INTRODUCTION. 


weight  to  this  argument.  Plausible,  however,  as  this  mode  of  reasoning 
may  appear,  the  opposite  opinion  is  daily  becoming  more  general.  It 
is  now  commonly  believed  that  matter  consists  of  ultimate  particles  or 
molecules,  which  are  thought  to  be  indivisible;  and  according  to  this 
belief  have  received  the  appellation  of  atoms,  (From  the  privative  a 
and  TcfA^Mca  Icut.^  T'he  arguments  adduced  in  favour  of  this  opinion  are 
derived  from  certain  astronomical  phenomena,  from  the  laws  of  cbem  - 
cal  union,  and  the  relations  which  have  been  observed  to  exist  between 
the  composition  and  form  of  crystallized  bodies.  These  subjects  will  bo 
considered  in  their  proper  place;  but  I may  observe  here,  in  order  to 
show  the  nature  of  the  argument,  that  the  supposed  existence  of  atoms 
accounts  for  numerous  facts,  which  do  not  admit  of  a satisfactory  ex- 
planation on  any  other  principle. 

All  bodies  descend  in  straight  lines  towards  the  centre  of  the  earth, 
when  left  at  liberty  at  a distance  from  its  surface.  The  power  which 
produces  this  eff  ect  is  termed  gravity,  attraction  of  gravitation,  or  ter- 
restrial attraction;  and  the  force  required  to  separate  a body  from  the 
surface  of  the  earth,  or  prevent  it  from  descending  towards  it,  is  called 
its  wtiglit.  Every  particle  of  matter  is  equally  affected  by  gravity;  and 
therefore  the  weiglit  of  any  body  will  be  proportionate  to  the  number 
of  ponderable  particles  which  it  contains. 

The  minute  particles,  of  which  bodies  consist,  are  disposed  in  such  a 
manner  as  to  leave  certain  intervals  or  spaces  between  them,  and  this 
arrangement  is  called  porosity.  These  interstices  may  sometimes  bo 
seen  by  the  naked  eye,  and  frequently  by  the  aid  of  glasses.  But  were 
“^hey  wholly  invisible,  it  would  still  be  certain  that  they  exist.  All 
substances,  even  the  most  compact,  may  be  diminished  in  bulk  either 
by  mechanical  force  or  a reduction  of  temperature.  It  hence  follows 
that  their  particles  must  touch  each  other  at  a very  few  points  only,  if 
at  all;  for  if  their  contact  were  so  perfect  as  to  leave  no  interstitial  spaces, 
tken  would  it  be  impossible  to  diminish  the  dimensions  of  a body,  be- 
cause matter  is  incompressible  and  cannot  yield.  When  therefore  a 
body  expands,  the  distance  between  its  particles  is  increased;  and,  con- 
vei-sely,  when  it  contracts  or  diminishes  in  size,  its  particles  approach 
each  other. 

By  indestnictihility  is  meant,  that,  according  to  the  present  laws  of  na- 
ture, matter  never  ceases  to  exist.  T'his  statement  seems  at  first  view  con- 
trary to  fact.  Water  and  volatile  substances  are  dissipated  by  heat,  and 
lost;  coals  and  wood  are  consumed  in  the  fire,  and  disappear.  But  in 
these  and  all  similar  phenomena  not  a particle  of  matter  is  annihilated. 
The  apparent  destruction  is  owing  merely  to  a change  of  form -or  com- 
position; for  the  same  material  particles,  after  having  undergone  any 
number  of  such  changes,  may  still  be  proved  to  possess  the  characteristic 
properties  of  matter. 

The  secondary  properties  of  matter  are  opacity,  transparency,  soft- 
ness, hardness,  elasticity,  colour,  density,  solidi^,  fluidity,  and  others 
of  a like  nature.  The  condition  of  bodies  with  respect  to  several  of 
these  properties  seems  dependent  on  the  operations  of  two  opposite 
forces — cohesion  and  repulsion.  It  is  inferred,  from  the  divisibility  of 
matter,  that  the  siibstance  of  solids  and  liquids  is  made  up  of  an  infinity 
of  minute  particles  adhering  together  so  as  to  constitute  larger  masses; 
and  in  order  that  these  particles  should  thus  cohere,  they'must  possess 
a power  of  reciprocal  attraction.  T'his  force  is  called  cohesion,  cohesive 
attraction,  or  the  attraction  of  aggregation,  in  order  to  distinguish  it  from 
terrestrial  attraction.  Gravity  is  exerted  between  different  masses  of 
matter,  and  acts  at  sensible  and  frequently  at  very  great  distances;  while 
cohesion  exerts  its  influence  only  at  insensible  and  infinitely  small  dis- 


INTRODUCTION. 


15 


tnnces.  It  enables  similar  molecules  to  cohere,  and  tends  to  keep  them 
in  that  condition.  It  is  best  exemplified  by  the  force  required  to  se- 
parate a hard  body,  such  as  iron  or  marble,  into  smaller  fragments,  or  by 
the  weig'ht  which  twine  or  metallic  wire  will  sujiport  without  breaking. 

'fhe  tendency  of  cohesion  is  manifestly  to  bring  the  ultimate  particles 
of  bodies  into  immediate  contact;  and  such  would  be  the  result  of  its  in- 
fluence, were  it  not  counteracted  by  an  opposing  force,  a principle  of  re- 
pulsion, which  prevents  their  approximation.  It  is  a general  opinion 
among  philosophers,  supported  by  very  strong  facts,  that  this  repul- 
sion is  owing  to  the  agency  of  caloric,  which  is  somehow  attached  to 
the  elementary  molecules  of  matter,  causing  them  to  repel  one  another. 
Material  substances  are  therefore  subject  to  the  action  of  two  contrary 
and  antagonizing  forces,  one  tending  to  separate  their  particles,  the 
other  to  bring  them  into  closer  proximity,*  The  form  of  bodies,  as  to 
solidity  and  fluidity,  is  determined  by  the  relative  intensity  of  these' 
powers.  Cohesion  predominates  in  solids,in  consequence  of  which 
their  particles  are  prevented  from  moving  freely  on  one  another.  I'he 
])articles  of  a fluid,  on  the  contrary,  are  far  less  influenced  by  cohesion, 
being  free  to  move  on  each  other  with  very  slight  friction.  Tluids  are 
of  two  kinds,  elastic  fluids  or  aeriform  substances,  and  inelastic  fluids 
or  liquids.  Cohesion  seems  wholly  wanting  in  the  former;  they  yield 
readily  to  compression,  and  expand  when  the  pressure  is  removed;  in- 
deed, the  space  they  occupy  is  chiefly  determined  by  the  force  which 
compresses  them.  The  latter,  on  the  contrary,  do  not  yield  perceptibly 
to  ordinary  degrees  of  compression,  nor  does  an  appreciable  dilatation 
ensue  from  the  removal  of  pressure,  the  tendency  of  repulsion  being  in 
them  counterbalanced  by  cohesion. 

Matter  is  subject  to  another  kind  of  attraction  different  from  those  yet 
mentioned,  termed  chemical  attraction  or  affiiiity.  Like  cohesion  it  acts 
only  at  insensible  distances,  and  thus  differs  entirely  from  gravity.  It 
is  distinguished  from  cohesion  by  being  exerted  between  dissimilar  par- 
ticles only,  while  the  attraction  of  cohesion  unites  similar  particles. — 
Thus,  a piece  of  marble  is  an  aggregate  of  smaller  portions  attached  to 
one  another  by  cohesion,  and  the  parts  so  attached  are  called  integi'ant 
particles;  each  of  which,  however  minute,  being  as  perfect  marble  as 
the  mass  itself.  But  the  integrant  particles  consist  of  two  substances, 
lime  and  carbonic  acid,  which  are  different  from  one  another  as  well  as 
from  marble,  and  are  united  by  chemical  attraction.  They  are  the  com- 
poyient  or  constituent  parts  of  marble.  The  integrant  particles  of  a body 
are  therefore  aggregated  together  by  cohesion;  the  component  parts 
are  united  by  affi  nity , 

The  cliemical  properties  of  bodies  are  owing  to  affinity,  and  every 
chemical  phenomenon  is  produced  by  the  operation  of  this  principle. 
Though  it  extends  its  influence  over  all  substances,  yet  it  affects  them 
in  very  different  degrees,  and  is  subject  to  peculiar  modifications.  Of 
three  bodies,  A,  B,  and  C,  it  is  often  found  that  B and  C evince  no  af- 
finity for  one  another,  and  therefore  do  not  combine;  that  A,  oil  the 
contrary,  has  an  affinity  for  B and  C,  and  can  enter  int6  separate  com- 


* It  should  be  borne  in  mind,  however,  that  the  force  which  tends  to 
bring  the  elementary  molecules  into  closer  proximity,  is  derived  from 
an  innate  property  of  ponderable  matter;  while  the  force  which  tends  to 
separate  them  is  dependent  on  the  operation  of  a distinct  principle, 
caloric,  whose  particles,  being  self  repellent,  force  the  ponderable  parti- 
cles apart.  In  order  to  explain  why  the  caloric  remains  attached  to 
the  ponderable  molecules,  it  is  necessary  to  suppose  that  its  .particles, 
though  self-repellent,  have  an  attraction  for  ponderable  matter.  B. 


16 


INTRODUCTION. 


bination  witli  each  of  them;  but  that  A has  a greater  attraction  for  C than 
for  Ij,  so  that  if  we  bring  C in  contact  with  a compound  of  A and  B,  A 
will  quit  B and  unite  by  preference  with  C.  The  union  of  two  sub- 
stances is  called  combination and  its  result  is  the  formation  of  a new 
body  endowed  with  properties  peculiar  to  itself,  and  different  from  those 
of  its  constituents.  Tlie  change  is  frequently  attended  by  the  destruc- 
tion of  a previously  existing  compound,  and  in  that  case  decomposition  is 
said  to  be  effected. 

The  operation  of  chemical  attraction,  as  thus  explained,  lays  open  a 
wide  and  interesting  field  of  inquiry.  One  may  study,  for  example,  the 
affinity  existing  between  difierent  substances;  an  attempt  may  be  made 
to  discover  the  proportion  in  which  they  unite;  and  finally,  after  collec- 
ting and  arranging  an  extensive  series  of  insulated  facts,  general  con- 
clusions may  be  deduced  from  them.  Hence  chemistry  may-  be  de- 
fined the  science,  the  object  of  which  is  to  examine  the  relations  that 
affinity  establishes  between  bodies,  ascertain  with  precision  the  nature 
and  constitution  of  the  compounds  it  produces,  and  determine  the  laws 
by  which  its  action  is  regulated. 

Material  substances  are  divided  by  the  chemist  into  simple  and  com- 
pound. He  regards  those  bodies  as  compound,  which  may  be  resolved 
into  two  or  more  parts;  and  those  as  simple  or  elementary,  which  con- 
tain but  one  kind  of  ponderable  matter.  The  number  of  the  latter 
amounts  only  to  fifty -three;  and  of  these  all  the  bodies  in  the  earth,  as 
lar  as  our  knowledge  extends,  are  composed.  The  list,  a few  years 
ago,  was  somewhat  different  from  what  it  is  at  present;  for  the  acquisi- 
tion of  improved  methods  of  analysis  has  enabled  chemists  to  demon- 
strate that  some  substances,  which  were  once  supposed  to  be  simple, 
are  in  reality  compound;  and  it  is  probable  that  a similar  fate  awaits 
some  of  those  which  are  at  present  regarded  as  simple. 

The  composition  of  a body  may  be  determined  in  two  ways,  analyti- 
cally or  synthetically.  By  the  former  method,  the  elements  of  a com- 
pound are  separated  from  one  another,  as  when  water  is  resolved  by 
the  agency  of  galvanism  into  oxygen  and  hydrogen;  by  synthesis  they 
are  made  to  combine,  as  when  oxygen  and  hydrogen  unite  by  the  elec- 
tric spark,  and  generate  a portion  of  water.  Each  of  these  kinds 
proof  is  satisfactory;  but  when  they  are  conjoined — when  we  first  re- 
solve a particle  of  water  into  its  elements,  and  then  reproduce  it  by  caus- 
ing them  to  unite — the  evidence  is  in  the  highest  degree  conclusive. 

I have  followed,  in  the  composition  of  this  treatise,  the  same  general 
arrangement  which  I adopt  in  my  lectures.  It  is  divided  into  four  prin- 
cipal parts.  The  first  comprehends  an  account  of  the  nature  and  pro- 
perties oi  Heat,  Light,  and  agents  so  diffusive  and  subtile, 

that  the  common  attributes  of  matter  cannot  be  perceived  in  them.  They 
are  altogether  destitute  of  weight;  at  least,  if  they  possess  any,  it  can- 
not be  discovered  by  our  most  delicate  balances,  and  hence  they  have 
received  the  appellation  of  Imponderables.  They  cannot  be  confined 
and  exhibited  in  a mass  like  ordinary  bodies;  they  can  be  collected  only 
tliroiigh  tlie  intei’vention  of  other  substances.  Their  title  to  be  con- 
sidered material  is,  therefore,  questionable,  and  the  effects  produced 
by  them  have  accordingly  been  attributed  by  some  to  certain  motions 
or  affections  of  common  matter.  It  must  be  admitted,  howevp,  that 
tfu;y  api)car  to  be  subject  to  the  same  powers  that  act  on  inatter  in  gen- 
eral, and  that  some  of  the  laws  which  have  been  determined  concern- 
ing them,  arc  exactly  such  as  might  have  been  anticipated  on  the  sup- 
position of  tlieir  materiality.  It  hence  follows,  that  we  need  only  re- 
gard them  as  subtile  species  of  matter,  in  order  that  the  phenomena  to 
which  they  give  rise  may  be  explained  in  the  language,  and  according 


INTRODUCTION. 


to  the  principles,  which  are  applied  to  moterial  substances  in  g*enerrJ^ 
and  I shall,  therefore,  consider  them  as  such  in  my  subsequent  remarks. 

The  second  part  comprises  Inorganic  Chemistry.  It  includes  the 
doctrine  of  affinity,  and  the  laws  of  combination,  together  with  the  chem- 
ical history  of  all  the  elementary  principles  hitherto  discovered,  and 
of  those  compound  bodies  which  are  not  the  product  of  organization. 
Elementary  bodies  are  divided  into  the  non-metallic  and  metallic  ^ and  the 
substances  contained  in  each  division  are  treated  in  the  order  which,  it  is 
conceived,  will  be  most  convenient  for  the  purposes  of  teacijing.  From 
the  important  part  which  oxygen  plays  in  the  economy  of  nature,  it  is 
necessary  to  begin  with  the  description  of  that  principle;  and  from  the 
tendency  it  has  to  unite  with  other  bodies,  as  well  as  the  importance  of 
the  compounds  it  forms  with  them,  it  will  be  useful,  in  studying  the 
history  of  each  elementary  body,  to  describe  the  combinations  into 
wliich  it  enters  with  oxygen  gas.  The  remaining  compounds  which 
the  non  metallic  substances  form  with  each  other,  will  next  be  con- 
sidered. The  description  of  the  individual  metals  will  be  accompanied 
by  a history  of  their  combinations,  first  vvith  the  simple  non-metallic 
bodies,  and  afterwards  with  each  other.  The  last  division  of  this  part 
\vill  comprise  a history  of  the  salts. 

The  third  general  division  of  the  work  is  Organic  Chemistry,  a sub- 
ject which  will  be  conveniently  discussed  under  two  heads,  the  one 
comprehending  the  products  of  vegetable,  the  other  of  animal  life. 

The  fourth  part  contains  brief  directions  for  the  performunce'  cf 
analysis. 


w'. 


■ -■  ,-■  \- 

'.  ri,\ 


.-,i.--  ' -w 


\ 


■-  . V,  ■ ' ^ ■'-.  ..W',  -v"*'  '-  -■, 

. , ■ .:  ■ V ; . _ -''i'-  -'■  ♦ ■•;■'  ' ' 

wr- ■:'■  '^■,  '-,■ 

r - -v’  ;i< 


Ik  ■;  V-: “•■■  '■ 


ELEMENTS 


OF 

CHEMISTRY. 


PART  I. 

IMPONDERABLE  SUBSTANCES, 


SECTION  1. 

CALORIC. 

The  term  Heat,  in  common  language,  has  two  meanings:  in  the  one 
case,  it  implies  the  sensation  experienced  on  touching  a hot  body,-  in  the 
other,  it  expresses  the  cause  of  that  sensation.  To  avoid  any  ambiguity 
that  may  arise  from  the  use  of  the  same  expression  in  two  such  different 
senses,  it  has  been  proposed  to  employ  the  word  Caloric  to  signify  ex- 
clusively the  principle  or  cause  of  the  feeling  of  heat;  and  the  use  of 
this  term  has  now  become  so  general,  that  I have  adopted  it  in  the  pre- 
sent treatise. 

Caloric,  on  the  supposition  of  its  being  material,  is  a subtile  fluid, 
the  particles  of  which  repel  one  another,  and  are  attracted  by  all  other 
substances.  It  is  imponderable:  that  is,  it  is  so  exceedingly  light,  that 
a body  undergoes  no  appreciable  change  of  weight,  either  by  the  ad- 
dition or  abstraction  of  caloric.  It  is  present  in  all  bodies,  and  cannot  be 
wholly  separated  from  them.  For  if  we  take  any  substance  whatever, 
at  any  temperature,  however  low,  and  transfer  it  into  an  atmosphere, 
whose  temperature  is  still  lower,  a thermometer  will  indicate  that  cal- 
oric is  escaping  from  it.  That  its  particles  repel  one  another,  is  proved 
by  observing  that  it  flies  off  from  a heated  body;  and  that  it  is  at- 
tracted by  other  substances,  is  inferred  from  the  tendency  it  has  to  pe- 
netrate their  particles,  and  to  be  retained  by  them. 

Caloric  may  be  transferred  from  one  body  to  another.  Thus  if  a cup 
of  mercury  at  60°  be  plunged  into  hot  water,  caloric  passes  rapidly 
from  one  to  the  other,  until  the  temperature  in  both  is  the  same;  that 
is,  till  a thermometer  placed  in  each  stands  at  the  same  height.  All 
bodies  on  the  earth  are  constantly  tending  to  attain  an  equality,  or 
what  is  technically  called  an  equilibrium  of  temperature.  If,  for  exam- 
ple, a number  of  substances  of  different  temperatures  be  enclosed  in  an 
apartment,  in  whicli  there  is  no  actual  source  of  caloric,  they  will  very 
soon  acquire  an  equilibrium,  so  that  a thermometer  will  stand  at  the 
same  point  in  all  of  them.  The  varying  sensations  of  heat  and  cold, 
which  we  experience,  are  owing  to  a like  cause.  On  touching  a hot 
body,  caloric  passes  from  it  into  the  hand,  and  excites  the  feeling  of 
warmth;  when  we  touch  a cold  body,  caloric  is  communicated  to  it 
from  the  hand,  and  thus  arises  the  sensation  of  cold. 

As  the  transportation  of  caloric  is  constantly  going  forward,  it  is  im- 


20 


CALOinC. 


portant  to  determine  by  what  means,  and  according-  to  wliat  laws,  the 
equilibrium  is  established.  When  any  substance  is  brought  into  con- 
tact with  another,  which  differs  from  it  in  temperature — if,  for  exam- 
ple, a bar  of  cold  iron  be  thrust  among  glowing  embers,  or  a hot  ball  of 
the  same  metal  be  plunged  into  a basin  of  cold  water — the  excess  of 
caloric  in  tlie  hot  body  passes  rapidly  to  the  particles  on  the  surface  of 
the  other;  from  them  it  is  transferred  to  those  situated  more  internally, 
and  so  forth,  till  the  bar  in  the  one  case,  and  the  ball  in  the  other  arrive 
at  the  same  temperature  as  the  embers  or  the  water  with  which  they  are 
in  contact.  In  such  instances,  caloric  is  said  to  ])ass  by  communicatim^ 
or  to  be  communicated  from  one  body  to  another;  and  in  its  passage 
through  any  one  of  those  bodies,  it  is  said  to  be  conducted  by  them. 

But  when  a heated  substance  is  placed  under  such  circumstances  as 
to  preclude  the  possibility  of  its  caloric  being  communicated — for  in- 
stance, when  a glass  globe  full  of  hot  water  is  suspended  in  the  vacuum 
of  an  air-pump — the  excess  of  its  caloric  still  passes  away,  and  in  a very 
short  time  it  w ill  have  acquired  the  temperature  of  the  surrounding  ob- 
jects. It  must  then  be  capable  of  passing  from  one  body  to  another  sit- 
uated at  a sensible  distance;  it  is  projected  as  it  were  from  one  to  the 
other.  In  order  that  its  passage  should  take  place  in  this  manner,  it  is 
not  nece.ssary  that  the  body  should  be  in  vacuo;  it  passes,  to  all  appear- 
ance, with  equal  facility  through  the  air  as  through  a vacuum. 

It  follows,  therefore,  that  in  establishing  an  equilibrium  'of  tempera- 
ture, caloric  is  distributed  among  the  surrounding  objects  in  two  w’nys; 
partly  through  the  means  of  intermediate  bodies,  or  by  communication, 
partly  in  consequence  of  an  interchange  established  from  a distance,  or 
by  radiation. 

Communication  of  Caloric, 

Caloric  passes  through  bodies  with  different  degrees  of  velocity. 
Some  substances  oppose  very  little  impediment  to  its  passage,  while 
it  is  transmitted  slowly  by  otliers.  Daily  experience  teaches,  that 
though  w'e  cannot  leave  one  end  of  a rod  of  iron  for  some  time  in  the 
fire,  and  then  touch  its  other  extremity,  w ithout  danger  of  being  burnt; 
yet  this  may  be  done  with  perfect  safety  with  a rod  of  glass  or  of  w ood. 
The  caloric  will  speedily  traverse  the  iron  bar,  so  that,  at  the  distance 
of  a foot  from  the  fire,  it  is  impossible  to  su])port  its  heat;  while  W'e  may 
hold  a piece  of  red  hot  glass  two  or  three  inches  from  its  extremity,  or 
keep  a piece  of  burning  charcoal  in  the  hand,  though  the  part  in  com- 
bustion is  only  a few  lines  removed  from  the  skin.  The  observation  of 
these  and  similar  facts,  has  led  to  the  division  of  bodies  into  conductor* 
and  non-conductors  of  caloric.  The  former  division,  of  course,  include.^ 
those  bodies,  such  as  metals,  wdiich  allow  caloric  to  pass  freely  through 
their  substance;  and  the  latter  comprises  those  which  do  not  give  an 
easy  passage  to  it,  such  as  stones,  glass,  wood,  and  charcoal. 

Various  methods  have  been  adopted  for  determining  the  relative 
conducting  power  of  different  substances.  I'he  mode  adopted  by 
Ingenhouz,*  who  made  experiments  on  this  subject,  is  the  follow  ing. 
He  covered  small  rods  of  the  same  form,  size,  and  length,  but  of  dif- 
ferent materials,  with  a layer  of  wax,  plunged  their  extremities  into 
heated  oil,  and  noted  to  what  distance  the  wax  was  melted  on  each  dur- 
ing the  same  interval.  The  metals  were  found,  by  this  method,  to  con- 
duct caloric  better  than  any  other  substances;  and  of  the  metals,  silver 
is  the  best  conductor;  gold  comes  next;  then  tin  and  copper,  which  ar« 
neaMy  equal;  then  iron,  platinum,  and  lead. 


Ingenhouz,  Journal  de  Phys.  ir89,  p,  68, 


CALORIC. 


21 


Some  experiments  have  lately  been  made  by  M.  Despretz,  apparent- 
ly with  great  care,  on  the  relative  conducting  power  of  the  metals  and 
some  other  substances,  and  the  results  are  contained  in  the  following 
table.  (An.  de  Ch,  et  de  Ph.  xxxvi.  422.) 


Gold  . . . 

. 1000 

Tin  . . 

. , 303.9 

Platinum  . 

. . 981 

Lead  . . 

. . 179.6 

Silver  . . . 

. 973 

Marble  . . 

23.6 

Copper  . . 

. . 898.2 

Porcelain 

. . 12.2 

Iron  . . . 

. .374.3 

Fine  clay  , 

• . 11.4 

Zinc  . . 

. 363 

The  substances  employed  for  these  experiments  were  made  into 
prisms  of  the  same  form  and  size.  To  one  extremity  a regular  source 
of  heat  was  applied,  and  the  passage  of  caloric  along  the  bar  was  esti- 
mated by  small  thermometers  placed  at  regular  distances,  with  their 
bulbs  fixed  in  the  substance  of  the  prism.  According  to  the  table,  the 
conducting  power  of  platinum  is  superior  even  to  that  of  silver,  while 
Ingenhouz  places  it  after  copper.  There  must  certainly  be  sotne  mis- 
take either  in  the  experiments  or  calculations  of  M.  Despretz,  or  in  the 
report  of  them.  From  my  own  observation  I agree  with  Ingenhouz  in 
considering  platinum  as  a much  less  perfect  conductor  than  most  of  the 
metals  in  general  use,  and  am  satisfied  from  frequent  experiment  that 
it  is  much  inferior  to  silver.* 

An  ingenious  plan  was  adopted  by  Count  Rumfordf  for  ascertaining 
the  relative  conducting  power  of  the  different  materials  employed  for 
clothing.  He  enveloped  a thermometer  in  a glass  cylinder  blown  into 
a ball  at  its  extremity,  and  filled  the  interstices  with  the  substance  to 
be  examined.  Having  heated  the  apparatus  to  the  same  temperature 
in  every  instance  by  immersing  it  in  boiling  water,  he  transferred  it 
into  melting  ice,  and  observed  carefully  the  number  of  seconds  which 
elapsed  during  the  passage  of  the  thermometer  through  135  degrees. 
When  there  was  air  between  the  thermometer  and  cylinder,  the  cooling 
took  place  in  576  seconds;  when  the  interstice  was  filled  with  fine  lint, 
it  took  place  in  1032";  with  cotton  wool  in  1046";  with  sheep’s  woolin 
1118";  with  raw  silk  in  1284";  with  beaver’s  fur  in  1296";  with  eider 
down  in  1305";  and  with  hare’s  fur  in  1315".  The  general  practice  of 
mankind  is  therefore  fully  justified  by  experiment.  In  winter  we  re- 
tain the  animal  heat  as  much  as  possible  by  covering  the  body  with  bad 
conductors,  such  as  silk  or  woollen  stuffs;  and  in  summer,  cotton  or 
linen  articles  are  employed  with  an  opposite  intention. 

A variety  of  familiar  phenomena  arise  from  difference  of  conducting 
power.  Thus  if  a piece  of  iron  and  glass  be  heated  to  the  same  degree, 
the  sensation  they  communicate  to  the  hand  is  very  different,  the  iron 
will  give  the  sensation  of  burning,  while  the  glass  feels  but  moderately 
warm.  The  quantity  of  caloric,  which  in  a given  time  maybe  brought 
to  the  surface  of  the  heated  body,  so  as  to  pass  into  the  skin,  is  much 
greater  in  the  iron  than  in  the  glass,  and  therefore  in  the  former  case 
the  sensation  must  be  more  acute.  This  proves  that  the  sense  of  touch 
is  a very  fallacious  test  of  heat  and  cold;  and  hence,  on  applying  the  hand 


• Dr.  Turner  is  undoubtedly  correct  in  his  conjecture  that  there  is 
some  mistake  in  the  number  given  in  the  above  table  for  the  conducti- 
bility  of  platinum.  Berzelius  gives  the  same  table  on  the  authority  of 
Despretz  in  his  Traiii  de  ChimiCy  but  places  platinum  after  silver  and 
copper,  with  the  number  381.  It  is  probable,  therefore,  that  981  is  a 
misprint,  and  that  381  is  the  correct  number.  13. 
t Rumford,  Phil.  Tr.  1792. 


!22 


CALORIC. 


to  various  contig*uous  objects,  we  are  very  apt  to  form  wrong*  notions  of 
their  temperature.  The  carpet  will  feel  nearly  as  warm  as  the  h ind; 
a book  will  feel  cool,  the  table  cold,  the  marble  chimney-piece  colder, 
and  the  candlestick  colder  still;  yet,  a thermometer  applied  to  them  will 
stand  in  all  at  exactly  the  same  elevation.  Tliey  are  all  colder  than  the 
hand;  but  those  that  carry  away  caloric  most  rapidly,  excite  the  strongest 
sensation  of  cold. 

The  conducting  power  of  solid  bodies  does  not  seem  to  be  related  to 
any  of  the  other  properties  of  matter;  but  it  approaches  nearer  to  the 
ratio  of  their  densities  than  to  that  of  any  other  property.  Count  Rum- 
ford  found  a considerable  difference  in  the  conducting  power  even  of 
the  same  material,  according  to  the  state  in  which  it  was  employed. 
His  observations  seem  to  warrant  the  conclusion,  that  in  the  same  sub- 
stance the  conducting  power  increases  with  the  compactness  of  struc- 
ture. 

Liquids  may  be  said,  in  one  sense  of  the  word,  to  have  the  power  of 
communicating  caloric  with  great  rapidity,  and  yet  they  are  very  im- 
perfect conductors.  The  transmission  of  caloric  from  particle  to  parti- 
cle does  in  reality  take  place  very  slowly;  but  in  consequence  of  the 
mobility  of  their  particles  upon  each  other,  there  are  peculiar  internal 
movements,  which  under  certain  circumstances  may  be  occasioned  in 
them  by  increase  of  temperature,  and  which  do  more  than  compensate 
for  the  imperfect  conducting  power  with  which  they  are  really  endowed. 

When  certain  particles  of  a liquid  are  heated  they  expand,  and  thus 
become  specifically  lighter  than  those  which  have  not  yet  received  an 
increase  of  temperature;  and  consequently,  according  to  a well  known 
law  in  physics,  the  colder  and  denser  particles  descend, . while  the 
warmer  ones  are  pressed  upwards.  It  therefore  follows  that  if  caloric 
enter  at  the  bottom  of  a vessel  containing  any  liquid,  a double  set  of  cur- 
rents must  be  immediately  established,  the  one  of  hot  particles  rising 
towards  the  surface,  and  the  other  of  colder  particles  descending  to  the 
bottom.  Now  these  currents  take  place  with  such,  rapidity,  that  if  a 
thermometer  be  placed  at  the  bottom,  and  another  at  the  top  of  a long 
jar,  the  fire  being  applied  below,  the  upper  one  will  begin  to  rise  al- 
most as  soon  as  the  lower.  Hence,  under  certain  circumstances,  caloric 
is  rapidly  communicated  through  liquids. 

But  if,  instead  of  heating  the  bottom  of  the  jar,  the  caloric  is  made 
to  enter  by  the  upper  surface,  vet^y  different  phenomena  will  be  ob- 
served. The  intestine  movements  cannot  now  be  formed,  because  the 
heated  particles  have  a tendency  to  remain  constantly  at  the  top;  the 
caloric  can  descend  through  the  fluid  only  by  transmission  from  particle 
to  particle,  a process  which  takes  place  so  very  tardily,  as  to  have  in- 
duced Count  Rumford  to  deny  tliat  water  can  conduct  at  all.  In  this 
he  was  mistaken;  for  the  opposite  opinion  has  been  successfully  sup- 
ported by  Dr.  Hope,  Dr.  Thomson,  and  the  late  Dr.  Murray,  though 
they  all  admit  that  water,  and  liquids  in  general,  mercury  excepted, 
possess  the  power  of  conducting  caloric  in  a very  slight  degree. 

It  is  extremely  difficult  to  estimate  the  conducting  power  of  aeriform 
fluids.  Their  particles  move  so  freely  on  each  other,  that  the  moment 
a particle  is  dilated  by  caloric,  it  is  pressed  upwards  with  great  velocity 
by  the  descent  of  colder  and  lieavier  particles,  so  that  an  ascending  and 
de.scending  current  is  instantly  established.  Besides,  these  bodies 
allow  a passage  through  them  by  radiation.  Now  the  quantity  of  caloric 
which  passes  l)y  these  two  channels  is  so  much  greater  than  that  which 
is  conducted  from  ])urticlc  to  particle,  that  we  possess  no  means  of 
determining  their  proportion.  It  is  certain,  however,  that  the  conduct- 
ing power  of  gaseous  fluiils  is  exceedingly  imperfect,  probably  even 
more  so  thaji  tliat  of  liquids. 


CALORIC. 


23 


Radiation. 

When  the  hand  Is  placed  beneath  a hot  body  suspended  in  the  air,  a 
distinct  sensation  of  warmth  is  perceived,  thong'll  from  a considerable 
distance.  This  effect  does  not  arise  from  the  caloric  being  conveyed 
by  means  of  a hot  current;  for  all  the  heated  particles  have  a uniform 
tendency  to  rise.  Neither  can  it  depend  upon  the  conducting  power  of 
the  air;  since  aerial  substances  possess  that  power  in  a very  low  degree, 
while  the  sensation  in  the  present  case  is  excited  almost  on  the  instant. 
There  is  yet  another  mode  by  which  caloric  passes  from  one  body  to 
another;  and  as  it  takes  place  in  all  gases,  and  even  in  vacuo,  it  is  infer- 
red that  tlie  presence  of  a medium  is  not  necessary  to  its  passage.  This 
mode  of  transmission  is  called  Radiation  of  caloric,  and  the  fluid  so 
transmitted  is  called  Radiant  or  Radiated  Caloric.  It  appears,  therefore, 
that  a heated  body  suspended  in  the  air  cools,  or  is  brought  down  to  an 
equilibrium  with  surrounding  bodies,  in  three  ways;  first,  by  the  con- 
ducting power  of  the  air,  the  influence  of  which  is  very  trifling;  second- 
ly, by  the  mobility  of  the  air  in  contact  with  it;  and  thirdly,  by  radiation. 

Caloric  is  emitted  from  the  surface  of  a hot  body  equally  in  all  direc- 
tions, and  in  right  lines,  like  radii  drawn  from  the  centre  to  the  circum- 
ference of  a circle;  so  that  a thermometer  placed  at  the  same  distance 
on  any  side  would  stand  at  the  same  point,  if  the  effect  of  the  ascending 
current  of  hot  air  could  be  averted.  The  calorific  rays,  thus  distributed, 
pass  freely  t]  ; ough  a vacuum  and  the  air,  without  being  arrested  by 
the  latter  or  in  any  way  affecting  its  temperature.  When  they  fall 
upon  the  surface  of  a solid  or  liquid  substance,  they  are  either  reflected 
from  it,  and  thus  receive  a new  direction,  or  they  lose  their  radiant  form 
altogether,  and  are  absorbed.  In  the  latter  case,  the  temperature  of 
the  receiving  substance  is  increased;  in  the  former  it  is  unchanged. 

The  absorption  of  radiant  caloric  may  be  proved  b}^  placing  a ther- 
mometer before  the  fire,  or  any  heated  body,  when  the  mercury  will  be 
seen  to  rise  in  the  stem.  It  has  been  ascertained  by  accurate  experi- 
ment, and  may  be  demonstrated  mathematically,  that  the  intensity  of 
eft'ect  diminishes  according  to  the  squares  of  the  distance  from  the  ra- 
diating point.  Thus  the  thermometer  will  indicate  four  times  less  heat  at 
two  inches,  nine  times  less  at  three  inches,  and  sixteen  times  less  at  four 
inches,  than  it  did  when  it  was  only  one  inch  from  the  heated  substance. 

The  existence  of  a reflecting  power  may  be  shown  in  a familiar  man- 
ner, by  standing  at  the  side  of  a fire  in  such  a position  that  the  caloric 
cannot  reach  the  face  directly,  and  then  placing  a large  plate  of  tinned 
iron  opposite  the  grate,  and  at  such  an  inclination  as  permits  the  ob- 
server to  see  in  it  the  reflection  of  the  fire;  as  soon  as  it  is  brought  to 
this  inclination,  a distinct  impression  of  heat  will  be  perceived  upon  the 
face.  If  a line  be  drawn  from  the  heated  substance  to  the  point  of  a 
plane  surface  from  which  it  is  reflected,  and  a second  line  from  that 
point  to  the  spot  where  it  produces  its  effect,  the  angles  which  these 
lines  form  with  a line  perpendicular  to  the  reflecting  plane  are  equal  to 
each  other,  or,  in  philosophical  language,  the  angle  of  incidence  is 
equal  to  the  angle  of  reflection.  It  follows  from  the  operation  of  this 
law,  that  when  a heated  body  is  placed  in  the  focus  of  a concave  para- 
bolic reflector,  the  diverging  rays  which  strike  upon  it  assume  a paral- 
lel direction  with  respect  to  each  other;  and  when  these  parallel  rays 
impinge  upon  a second  concave  reflector,  standing  opposite  to  the  for- 
mer, they  are  made  to  converge,  so  as  to  meet  in  its  focus,  where  a 
great  degree  of  heat  is  developed.  This  fact,  as  applied  to  the  sun’s 
rays  or  red-hot  bodies,  has  been  long  known.  But  it  is  a modern  dis- 
covery that  caloric  emanates  in  invisible  rays,  which  are  subject  to  the 
same  laws  of  reflection  as  those  that  are  accompanied  by  light. 


24 


CALORIC. 


This  fact  may  be  inferred  from  the  experiments  of  the  Florentine 
Academicians,  and  Lambert  observed  the  reflection  of  non-luminous 
caloric;  but  the  honour  of  establishing*  it  in  a decisive  and  unequivocal 
manner  is  due  to  Messrs.  Saiissure  and  Pictet*  of  Geneva,  the  latter  of 
whom,  at  the  suggestion  of  the  former,  first  proved  it  of  an  iron  ball 
heated  so  a3  not  to  be  luminous  even  in  the  dark,  and  afterwards  of  a 
vessel  of  boiling  water.  For  a knowledge  of  the  laws  of  radiation  in 
general,  however,  we  are  indebted  to  the  researches  of  Professor  Leslie, 
described  in  his  Essay  on  Heat. 

Mr.  Leslie  employed  a hollow  tin  cube  filled  with  hot  water  as  the 
radiating  substance.  The  rays  proceeding  from  it  were  brought,  by 
means  of  a concave  mirror,  into  a focus,  in  which  the  bulb  of  a differ- 
ential thermometer  was  placed.  Fie  found  that  certain  substances  ra- 
diate caloric  much  more  rapidly  than  others,  and  that  the  nature  of  the 
surface  of  a heated  body  has  a singular  influence  upon  its  radiation.  By 
adapting  thin  plates  of  different  metals  to  the  sides  of  the  tin  cube,  and 
turning  them  successively  towards  the  mirror,  he  found  a very  variable 
effect  produced  upon  the  thermometer.  A bright  smooth  polished 
metallic  surface  radiated  caloric  very  imperfectly;  but  if  the  surface  was 
in  the  least  degree  dull  or  rough,  the  radiating  power  was  immediately 
augmented.  By  covering  the  tin  surface  with  a thin  layer  of  isinglass, 
paper,  wax,  or  resin,  its  power  of  radiation  increased  surprisingly. 
Metallic  substances  were  observed  to  be  the  worst  possible  radiators, 
particularly  such  as  are  susceptible  of  a high  polish,  as  gC'ld,  silver,  tin, 
and  brass;  but  it  is  easy  to  make  them  radiate  well  by  giving  them  the  op- 
posite properties,  either  by  scratching  their  surface,  or  covering  it  with 
whiting,  lampblack,  or  any  other  convenient  substance.  It  is  commonly 
supposed  that  black  surfaces  radiate  better  than  white  ones,  but  I am 
not  acquainted  with  any  conclusive  experiments  in  proof  of  this  opinion. 

Mr.  Leslie  next  examined  the  power  of  different  substances  in  reflect- 
ing caloric,  and  he  soon  arrived  at  the  interesting  conclusion,  that  those 
surfaces  which  radiate  least  reflect  most  powerfully.  A polished  plate 
of  tin  or  brass  is  an  excellent  reflecting  surface,  but  a bad  radiating  one: 
by  removing  the  polish  in  any  way,  its  reflecting  power  is  diminished 
in  the  same  proportion  as  its  radiating  power  is  increased.  His  experi- 
ments, indeed,  justify  the  conclusion,  that  the  faculty  of  radiation  is 
inversely  as  that  of  reflection. 

There  are  only  two  modes  by  which  calorific  rays,  falling  upon  a 
solid  opake  body,  can  dispose  of  themselves;  they  must  either  be  re- 
flected from  it,  or  enter  into  its  substance.  In  the  latter  case  caloric  is 
said  to  be  absorbed.  Now  it  is  manifest,  that  those  rays  which  are  re- 
flected cannot  be  absorbed,  and  those  which  are  not  reflected  must  be 
absorbed.  Hence  it  follows  that  the  absorption  of  caloric  in  the  same 
body  is  inversely  as  its  reflection;  and  since  the  property  of  radiation  is 
likewise  inversely  as  that  of  reflection,  the  power  of  radiating  and  ab- 
sorbing caloric  must  be  proportional  and  equal.f 


* Pictet’s  F.ssai  sur  le  Feu,  p.  65.  (1790.) 

j-  The  remarks  of  the  author  on  the  passage  of  caloric  through  sur- 
faces, may,  perhaps,  be  extended  with  advantage.  Surfaces,  as  to  the 
transmission  of  caloric,  may  be  divided  into  two  sets;  1st,  those  which 
offer  an  easy  passage  to  caloric,  either  inwards  or  outwards;  and  2d, 
those  through  which  caloric  passes  with  difficulty.  The  first  set  of 
surfaces  are  at  the  same  time  good  a])sorbers  and  radiators;  the  second 
set  combine  the  qualities  of  good  reflectors  and  retainers.  The  absorb- 
ing and  radiating  power  on  the  one  hand,  and  tlie  reflecting  and  retain- 
ing power  on  tlie  other,  would,  tliercfore,  seem  to  be  common  proper- 
ties, belonging  to  two  distinct  sets  of  surfaces.  B. 


CALORIC. 


25 


In  speaking  of  radiant  caloric,  it  is  necessary  to  distinguish  calorific 
rays  accompanied  by  light  from  those  which  are  emitted  by  a non-lumi- 
nous  body,  since  their  properties  are  not  exactly  similar.  Thus  tlie 
absorption  of  luminous  caloric,  whether  proceeding  from  the  sun  or  a 
common  fire,  is  very  much  influenced  by  colour;  it  is  most  considerable 
in  black  and  dark-coloured  surfaces,  while  it  is  much  less  in  wliite  ones. 
The  influence  of  colour,  on  the  contrary,  over  the  absorption  of  non- 
luminous  caloric  is  exceeding’ly  slight;  it  remains  to  be  proved,  indeed, 
whether  any  effect  can  fairly  be  attributed  to  this  cause. 

It  may  be  asked,  since  radiant  caloric  passes  without  interruption 
tlirough  the  air,  whether  it  can  pass  in  a similar  manner  through  solid 
transparent  media,  such  as  glass  or  rock  crystal.  The  only  point  of 
view  under  which  this  subject  can  be  considered  at  present,  is  with  re- 
spect to  radiant  caloric  emitted  by  a warm  body  that  is  not  luminous. 
When  a piece  of  clear  glass  is  placed  between  such  a body  and  a ther- 
mometer, the  latter  is  not  nearly  so  much  affected  as  it  would  be  were 
no  screen  interposed;  and  the  glass  itself  becomes  warm.  These  facts 
prove  that  at  least  the  greater  part  of  the  calorific  rays  is  intercepted  by 
the  glass.  But  the  thermometer  is  affected  to  a certain  degree;  and 
the  question  is,  by  what  means  do  the  rays  reach  it?  Professor  Leslie 
contends  that  all  the  rays  which  fall  upon  the  glass  are  absorbed  by  it, 
pass  through  its  substance  by  its  conducting  power,  and  are  then  ra- 
diated from  the  other  side  of  the  glass  towards  the  thermometer,  an 
opinion  which  Dr.  Brewster  has  ably  supported  by  an,  argument  sug- 
gested by  his  optical  researches.  (Phil.  Trans,  for  1816,  p.  106.)  The 
experiments  of  Delaroche,  on  the  contrary,  (Biot,  Traite  de  Physique, 
V.  4.)  lead  to  the  conclusion  that  glass  does  transmit  some  calorific  rays, 
tlie  number  of  which,  in  relation  to  the  quantity  absorbed,  is  greater  as 
the  intensity  of  the  heat  increases;  and  the  general  result  obtained  by 
that  philosopher  agrees  with  some  experiments  which  Dr.  Christison 
and  myself  performed  in  the  year  1824  on  the  same  subject. 

I'he  facts  that  have  been  determined  concerning  the  laws  of  radiant 
caloric  have  given  rise  to  two  ingenious  modes  of  accounting  for  the  ten- 
dency of  bodies  to  acquire  an  equilibrium  of  temperature.  This  takes 
place,  according  to  M.  Pictet,  in  consequence  of  the  hot  bod}"  giving 
calorific  rays  to  the  surrounding  colder  ones  till  an  equilibrium  is  estab- 
lished, at  which  moment  the  radiation  ceases.  M.  Prevcrst*,  on  the 
contrary,  contends  that  radiation  goes  on  at  all  times,  and  from  all 
bodies,  whether  their  temperature  is  the  same  or  different  from  those 
that  surround  them.  According  to  this  view,  the  temperature  of  a body 
falls  whenever  it  radiates  more  caloric  than  it  absorbs;  its  temperature 
is  stationary  when  the  quantities  emitted  and  received  are  equal;  and  it 
becomes  warm  when  the  absorption  exceeds  the  radiation.  A hot  body, 
surrounded  by  others  colder  than  itself,  is  an  example  of  the  first  case; 
the  second  happens  when  all  the  substances  which  are  near  one  another 
have  the  same  temperature;  and  the  third  occurs  when  a cold  body  is 
brought  into  a warm  room. 

I'hough  neither  of  these  theories  has  been  proved  to  be  true,  and 
both  of  them  have  the  merit  of  accounting  for  the  phenomena  of  radia- 
tion, the  preference  is  commonly  given  to  the  latter.  The  theory  of 
M.  Prevost  affords  a more  satisfactory  explanation  of  the  phenomena  of 
radiant  caloric  than  that  of  M.  Pictet;  but  the  chief  argument  in  its  fa- 
vour is  drawn  from  the  close  analogy  between  the  laws  of  light  and  ca- 
loric. Luminous  bodies  certainly  exchange  rays  with  one  another;  a 


* llecherches  sur  la  Chalcur. 
3 


25 


CALORIC. 


less  intense  lig-ht  sends  rays  to  one  of  greater  intensity,  and  the  quan- 
tity of  light  emitted  by  either  does  not  seem  to  be  at  all  affected  by  the 
vicinity  of  tlie  other.  As,  therefore,  tlie  radiation  of  light  is  not  pre- 
vented by  other  luminous  bodies,  it  is  probable  that  the  radiation  of 
beat,  the  laws  of  which  are  so  similar  to  those  of  light,  is  equally  unin- 
ffuenced  by  the  proximity  of  other  radiating  substances. 

This  ingenious  theory  applies  equally  well  to  the  experiments  with 
the  conjugate  mirrors,  as  to  the  phenomena  of  ordinary  radiation.  If  a 
metallic  ball  in  the  focus  of  one  mirror,  and  a thermometer  in  that  of 
the  other,  are  both  of  the  same  temperature  as  the  surrounding  objects, 
(say  at  60^  F.)  the  thermometer  remains  stationary.  It  does  indeed  re- 
ceive rays  from  the  ball;  but  its  temperature  is  not  affected  by  them, 
because  it  gives  back  an  equal  number  in  return.  If  the  ball  is  above 
60°  the  thermometer  begins  to  rise,  because  it  now  receives  a greater 
number  of  rays  than  it  gives  out.  If,  on  the  contrary,  the. ball  is  below 
60°,  then  the  thermometer,  being  the  warmer  of  the  two  bodies,  emits 
more  rays  than  it  receives,  and  its  temperature  falls. 

The  same  mode  of  reasoning  accounts  very  happily  for  an  experi- 
ment originally  performed  by  the  Florentine  Academicians,  and  since 
carefully  repeated  by  M.  Pictet,  the  result  of  which  at  first  appeared 
quite  anomalous.  Pie  placed  a piece  of  ice  instead  of  the  metallic  ball 
in  the  focus  of  his  mirror,  and  observed  that  the  thermometer  in  the  op- 
posite focus  immediately  descended,  but  rose  again  as  soon  as  the  ice 
was  removed.  On  replacing  the  ice  in  the  focus,  the  thermometer 
again  fell,  and  reascended  when  it  was  withdrawn.  It  was  supposed  by 
some  philosophers  that  this  experiment  proved  the  existence  of  frigo- 
rific  rays,  endowed  with  the  property  of  communicating  coldness  ; 
whereas,  all  the  preceding  remarks  are  made  on  the  supposition  that 
cold  is  merely  a negative  quality  arising  from  the  diminution  of  caloric. 
If,  indeed,  the  result  of  M.  Pictet’s  experiment  could  not  be  explained 
on  the  latter  supposition,  w^e  should  be  obliged  to  adopt  the  former  ; 
but  as  we  are  not  driven  to  that  alternative,  it  is  in  nowise  necessary  to 
modify  our  views.  The  same  mode  of  reasoning,  hitherto  employed, 
will  account  for  this  as  w^ell  as  the  preceding  phenomena  ; for,  in  fact, 
as  the  thermometer  gives  more  rays  to  the  ice  than  it  receives  in  return, 
it  must  necessarily  become  colder.  It  rises  again  when  the  ice  is  re- 
moved, because  it  then  receives  a number  of  calorific  rays  proceeding 
from  the  warmer  surrounding  objects,  which  were  intercepted  by  the 
ice  while  it  was  in  the  focus.  Whence  it  appears  that  the  result  of  this 
experiment  flows  naturally  out  of  the  theory  of  Prevost.* 


* It  flows  no  less  naturally  out  of  M.  Pictet’s  views.  In  explaining 
the  experiment  of  the  apparent  radiation  of  cold,  it  is  necessary  to  dis- 
tinguish two  cases  in  whicli  the  equilibrium  of  temperature  is  disturbed; 
1st,  where  a body  is  raised  above  the  temperature  of  the  surrounding 
medium  ; and  2d,  where  it  is  below  the  temperature  of  such  medium. 
If  a thermometer,  after  being  heated  to  the  boiling  point,  be  held  in 
the  air,  it  immediately  commences  to  project  its  caloric  into  the  sur- 
rounding colder  medium.  If,  however,  we  hold  a ball  of  snow  near  the. 
bulb  of  a thermometer  which  has  been  standing  in  a temperate  apart- 
ment, the  mercury  falls,  not  because  the  caloric  is  projected  from  the  in- 
strument, but  rather  because  the  caloric  is  drawn  into  the  snow.  The 
calorific  tension  of  the  space  occupied  by  the  snow  is  diminished,  and  the 
caloric  of  the  surrounding  medium  is  drawn  in  by  what  might  be  con- 
veniently culled  calorific  induction.  The  effect,  at  first,  is  felt  in  the 
immediate  vicinity  of  the  cold  body,  and  is  thence  propagated  in  right 


CALORIC. 


27 


A very  elegant  application  of  this  theory  was  made  by  the  late  Dr. 
Wells  to  account  for  the  formation  of  dew.*  The  most  copious  depo- 
sition of  dew  takes  place  when  the  weather  is  clear  and  serene;  and 
the  substances  that  are  covered  with  it  are  always  colder  than  the  con- 
tiguous strata  of  air,  or  than  those  bodies  on  which  dew  is  not  deposited. 
In  fact,  dew  is  a deposition  of  water  previously  existing  in  the  air  as  va- 
pour, and  which  loses  its  gaseous  form  only  in  consequence  of  being 
chilled  by  contact  with  colder  bodies.  In  speculating,  therefore,  about 
the  cause  of  this  interesting  and  important  phenomenon,  the  chief  ob- 
ject is  to  discover  the  principle  by  which  the  reduction  of  temperature 
is  effected.  The  explanation  proposed  by  Dr.  Wells,  and  now  almost 
universally  adopted,  is  founded  on  the  theory  of  M.  Prevost.  If  it  be 
admitted  that  bodies  radiate  at  all  times,  their  temperature  can  remain 
stationary  only  by  their  receiving  from  surrounding  objects  as  many  rays 
as  they  emit;  and  should  a substance  be  so  situated  that  its  own  radia- 
tion may  continue  uninterruptedly  without  an  equivalent  being  returned 
to  it,  its  temperature  must  necessarily  fall.  Such  is  believed  to  be  the 
condition  of  the  ground  in  a calm  starlight  evening.  The  calorific  rays 
which  are  then  emitted  by  substances  on  the  surface  of  the  earth,  are 
dispersed  through  free  space  and  lost;  nothing  is  present  in  the  atmos- 
phere to  exchange  rays  with  them,  and  their  temperature  consequently 
diminishes.  If,  on  the  contrary,  the  weather  is  cloudy,  the  radiant  ca. 
loric  proceeding  from  the  earth  is  intercepted  by  the  clouds,  an  inter- 
change is  established,  and  the  ground  retains  nearly,  if  not  quite,  the 
same  temperature  as  the  adjacent  portions  of  air. 

All  the  facts  hitherto  observed  concerning  the  formation  of  dew,  tend 
to  confirm  this  explanation.  It  is  found  that  dew  is  deposited  sparingly 
or  not  at  all  in  cloudy  weather;  that  all  circumstances  which  promote 
free  radiation  are  favourable  to  the  formation  of  dew;  that  good  radia- 
tors of  caloric,  such  as  grass,  wood,  the  leaves  of  plants,  and  filamentous 
substances  in  general,  reduce  their  temperature,  in  favourable  states  of 


lines  successively  to  greater  and  greater  distances.  If  these  views  be 
admitted  as  probable,  it  will  not  be  difficult  to  conceive  how  the  direc- 
tion of  this  motion  of  caloric  by  induction  may  be  changed  by  the  inter- 
position of  mirrors.  There  can  be  little  doubt,  that  caloric  constitutes 
a medium  which  pervades  all  space,  and  that  rows  of  calorific  particles 
in  right  lines  must  exist  in  every  conceivable  direction.  In  the  experi- 
ment cited  in  the  text,  the  ice  in  the  focus  of  one  mirror  produces,  by 
induction,  a deficiency  of  caloric  in  its  surface;  a number  of  pre-exist- 
ing rays  are  drawn  into  the  ice,  which  are  continuous  with  an  equal 
number  parallel  with  the  axis  of  the  mirror.  Let  it  be  supposed  that  a 
particular  row  of  particles  is  put  in  motion  by  induction,  it  is  clear  that 
a deficiency  of  caloric  will  be  the,  consequence  at  some  point  on  the 
surface  of  the  mirror.  This  cannot  be  supplied  by  the  mirror  itself, 
and  hence  it  will  be  made  up  by  the  first  particle  in  the  continuous 
parallel  row.  This  produces  an  induction  in  the  parallel  row,  which 
results  in  creating  a deficiency  of  caloric  in  some  point  of  the  surface  of 
the  second  mirror.  Finally,  a similar  induction  of  caloric  is  created  in 
the  corresponding  row  of  particles,  leading  to  the  focus  of  the  second 
mirror  where  the  thermometer  is  placed,  which  necessarily  indicates  a 
reduction  of  temperature.  In  this  way  we  think  the  experiment  of  the 
radiation  of  cold  may  be  explained,  without  the  aid  of  M.  Prevost’s 
theory,  which  we  conceive,  on  the  whole,  to  be  less  simple  than  that 
of  M.  Pictet.  B. 

* Wells  on  Dew. 


28 


CALORIC. 


t he  weathei-,  to  an  extent  of  ten,  twelve,  or  even  fifteen  degrees  below 
that  of  the  eircumambient  air;  and  that  while  these  are  drenched  with 
dew,  pieces  of  polished  metal,  smooth  stones,  and  other  imperfect  ra- 
<tiators,  are  barely  moistened,  and  are  nearly  as  warm  as  the  air  in  their 

^ iCl lilt  V • 


Cooling  of  Bodies, 

K appears  from  the  preceding  remarks  on  the  passage  of  caloric,  that 
the  cooling  of  bodies  takes  place  by  two  very  different  methods.  W hen 
a hot  body  is  enveloped  in  solid  substances,  its  caloric  is  withdrawn 
solely  by  means  of  communication,  and  the  rapidity  of  cooling  is  depen- 
dent on  the  conducting  power.  The  refrigeration  is  effected  in  a simi- 
lar  manner  when  the  heated  body  is  immersed  in  a liquid;  but  the  ra- 
pidity of  cooling  depends  partly  on  the  conducting  power  of  the  liquid, 
and  partly  on  the  mobility  of  its  particles.  In  elastic  fluids  the  cooling 
takes  place  both  by  communication  and  radiation;  and  in  a vacuum  it  is 
produced  solely  by  radiation. 

The  first  attempt  to  fix  the  rate  of  cooling  was  by  Newton.  He  con- 
ceived that  a hot  body  exposed  to  a uniform  cause  of  refrigeration,  as 
by  exposure  to  the  air,  loses  at  each  instant  a quantity  of  caloric  which 
always  bears  the  same  proportion  to  its  excess.  Thus  if  a hot  body  is 
deprived  of  1-lOth  of  its  excess  of  caloric  in  one  second,  it  should  lose 
1-lOth  of  the  remaining  Q-lOths,  or  9-lOOths  in  the  next  second,  and  in 
the  third  second  it  will  lose  1-lOth  of  the  remaining  81-lOOths,  or 
81-lOOOths,  &c.  In  this  way  the  following  series  of  numbers  may  be 
obtained,  expressing  the  proportion  of  the  excess  of  caloric  lost  in 
equal  intervals  of  time; 

IQQQ  900  810  729  656  590*5  531*6 

10,000’  10,000’  10,000’  10,000’  10,000’  10,000’  10,000’ 

and  the  excess  remaining  after  each  interval  is, 

9000  8100  7290  6560  5905  5316 

10,000’  10,000’  lO^^O’  10,000’  10,000’  10^’ 

It  is  obvious  that  the  numerators  of  these  fractions  constitute  a geome- 
trical series,  of  which  1*111  is  the  ratio;  for  5316x1*111=5905,  5315 
Xl*lll^=0559,  5316xl‘f  11^=7286,  &c.  Hence  it  was  inferred  by 
Newton,  that  while  the  times  of  cooling  are  in  arithmetical  progression, 
the  refrigeration  proceeds  according  to  a geometrical  progression. 

This  subject  has  been  experimentally  investigated  with  remarkable 
ingenuity  and  success  by  MM.  Dulong  and  Petit.  (An.  de  Ch.  et  de 
Ph.vii.225.)  They  have  demonstrated  that  Newton’s  law  of  refrige- 
ration may  be  adopted  when  the  temperature  is  inconsiderable;  but 
that  when  a body  cools  through  an  extensive  rawge  of  temperature,  as 
when  the  excess  of  caloric  is  great,  the  law  is  then  found  to  be  erro- 
neous. They  have  examined  with  consummate  skill  the  various  cir- 
cumstances by  which  the  cooling  of  a hot  body  in  vacuo,  or  when 
surrounded  by  an  elastic  fluid,  is  influenced;  but  their  inquiry  is  too 
mathematical  and  abstruse  for  the  purposes  of  an  elementary  treatise. 

Effects  of  Caloric^ 

The  phenomena  that  may  be  ascribed  to  the  agency  of  caloric,  and 
which  may  tliercfore  be  enumerated  as  its  eflccts,  are  numerous.  With 
respect  to  animals,  it  is  the  cause  of  the  feelings  of  cold,  agreeable 
warmth,  and  l)urning,  according  to  its  intensity.  It  excites  the  system 
powerfully,  and  without  a certain  degree  of  it  the  vital  actions  would 


CALORIC. 


2^ 


entirely  cease.  Over  the  vegetable  world  its  influence  is  obvious  to  ’ 
every  eye.  By  its  stimulus,  co-operating  with  air  and  moisture,  the 
seed  bursts  its  envelope  and  yields  a new  plant,  the  buds  open,  the 
leaves  expand,  and  the  fruit  arrives  at  maturity.  With  the  declining 
temperature  of  the  seasons  the  circulation  of  the  sap  ceases,  and  the 
plant  remains  torpid  till  it  is  again  excited  by  the  stimulus  of  caloric. 

The  dimensions  of  every  kind  of  matter  are  regulated  by  this  princi- 
ple. Its  increase,  with  few  exceptions,  separates  the  particles  of  bo- 
dies to  a greater  distance  from  one  another,  producing  expansion,  so 
that  the  same  quantity  of  matter  is  thus  made  to  occupy  a larger  space; 
and  the  diminution  of  caloric  has  an  opposite  effect.  Were  the  repul- 
sion occasioned  by  this  agent  to  cease  entirely,  the  atoms  of  bodies 
would  come  into  absolute  contact. 

The  form  of  bodies  is  dependent  on  caloric.  By  its  increase  solids 
are  converted  into  liquids,  and  liquids  are  dissipated  in  vapour;  by  its 
decrease  vapours  are  condensed  into  liquids,  and  these  become  solid. 
If  matter  ceased  to  be  under  the  influence  of  caloric,  all  liquids,  va- 
pours, and  doubtless  even  gases,  would  become  permanently  solid;  and 
all  motion  on  the  surface  of  the  earth  would  be  arrested. 

When  caloric  is  accumulated  to  a certain  extent  in  bodies,  they  shine 
or  become  incandescent.  On  this  important  property  depend  all  our 
methods  of  artificial  illumination. 

Caloric  exerts  a powerful  influence  over  chemical  phenomena. 
There  is,  indeed,  scarcely  any  chemical  action  which  is  not  in  some 
degree  modified  by  this  pri'nciple;  and  hence  a knowledge  of  the  laws 
of  caloric  is  indispensable  to  the  chemist.  By  its  means,  bodies  pre- 
viously separate  are  made  to  combine,  and  the  elements  of  compounda 
are  disunited.  An  undue  proportion  of  it  is  destructive  to  all  or- 
ganic and  many  mineral  compounds;  and  it  is  essentially  concerned 
in  combustion,  a process  so  necessary  to  the  wants  and  comforts  of 
man. 

Of  the  various  effects  of  caloric  above  enumerated,  several  will  be 
discussed  in  other  parts  of  the  work.  In  this  place  it  is  proposed  to 
treat  only  of  the  influence  of  caloric  over  the  dimensions  and  form  of 
bodies;  and  this  subject  will  be  conveniently  studied  under  the  three 
heads  of  expansion,  liquefaction,  and  vaporization. 

Expansion. 

One  of  the  most  remarkable  properties  of  caloric  is  the  repulsion 
which  exists  among  its  particles:  hence  it  happens,  that  when  this  prin- 
ciple enters  into  a body,  its  first  effect  is  to  remove  the  integrant  mole- 
cules of  the  substance  to  a greater  distance  from  one  another.  The 
body,  therefore,  becomes  less  compact  than  before,  occupies  a greater 
space,  or,  in  other  words,  expands.  Now  this  effect  of  caloric  is  ma- 
nifestly in  opposition  to  cohesion — that  force  which  tends  to  make  the 
particles  of  matter  approximate,  and  which  must  be  overcome  before  any 
expansion  can  ensue.  It  may  be  expected,  therefore,  that  a small  ad- 
dition of  caloric  will  occasion  a small  expansion,  and  a greater  addi- 
tion of  caloric  a greater  expansion;  because  in  the  latter  case,  the  co- 
hesion will  be  more  overcome  than  in  the  former.  It  may  be  anticipated 
also,  that  whenever  caloric  passes  out  of  a body,  the  cohesion  being 
then  left  to  act  freely,  a contraction  will  necessarily  follow;  so  that  ex- 
pansion is  only  a transient  effect,  occasioned  solely  by  the  accumula- 
tion of  caloric.  It  follows,  moreover,  from  this  view,  that  caloric  must 
produce  the  greatest  expansion  in  those  bodies,  the  cohesive  power  of 
which  is  least;  and  the  inference  is  fully  justified  by  observation.  Thus 
the  force  of  cohesion  is  greatest  in  solids,  less  in  liquids,  and  least  of  all 

3* 


50 


CALORIC. 


*3n  aeriform  substances;  while  the  expansion  of  solids  is  trifling,  that  of 
liquids  much  more  considerable,  and  that  of  elastic  fluids  far  greater. 

It  may  be  laid  down  as  a rule,  the  reason  of  which  is  now  obvious,  that 
all  bodies  are  expanded  by  heat,  and  that  the  expansion  of  the  same 
body  increases  with  the  quantity  of  caloric  which  enters  it.  But  this  law 
does  not  apply,  unless  the  form  and  chemical  constitution  of  the  body 
be  preserved.  For  if  a change  in  either  of  these  respects  be  occasioned, 
then  the  reverse  of  expansion  may  ensue  ; not,  however,  as  the  direct 
consequence  of  an  augmented  temperature,  but  as  the  result  of  a change 
in  form  or  composition. 

In  proof  of  the  expansion  of  solids,  we  need  only  take  the  exact  di- 
mensions in  length,  breadth  and  thickness  of  any  substance  when  cold, 
and  measure  it  again  while  strongly  heated,  when  it  will  be  found  to 
have  increased  in  every  direction.  A familiar  demonstration  of  the  fact 
may  be  afforded  by  adapting  a ring  to  an  iron  rod,  the  former  being 
just  large  enough  to  permit  tlie  latter  to  pass  through  it  while  cold. 
'The  rod  is  next  heated,  and  will  then  no  longer  pass  through  the  ring. 
This  dilatation  from  heat  and  consequent  contraction  in  cooling  take 
place  with  a force  which  appears  to  be  irresistible. 

The  expansion  of  solids  has  engaged  the  attention  of  several  experi- 
menters, whose  efforts  have  been  chiefly  directed  towards  ascertaining 
the  exact  quantity  by  which  different  substances  are  lengthened  by  a 
given  increase  of  heat,  and  determining  whether  or  not  their  expan- 
sion is  equable  at  different  temperatures.  The  Philosophical  Transac- 
tions of  London  contain  various  dissertations  on  the  subject  by  Eilicot, 
Smeaton,  Troiighton,  and  General  Roy;  and  M.  Biot,  in  his  Traiii  de 
Physique,  has  given  the  results  of  experiments  performed  with  great 
care  by  Lavoisier  and  Laplace.  Their  experiments  establish  the  fol- 
lowing points  : 1.  Different  solids  do  not  expand  to  the  same  degree 
from  equal  additions  of  caloric.  2.  A body  which  has  been  heated 
from  the  temperature  of  freezing  to  that  of  boiling  water,  and  again  al- 
lowed to  cool  to  32®  F.,  recovers  precisely  the  same  volume  which  it 
possessed  at  first.  3.  The  dilatation  of  the  more  permanent  or  infusi- 
ble solids  is  very  uniform  within  certain  limits;  their  expansion,  for  ex- 
ample, from  the  freezing  point  of  water  to  122®,  is  equal  to  what  takes 
place  betwixt  122®  and  212®.  The  subsequent  researches  of  Dulong  and 
Petit,  (Annales  de  Ch.  et  de  Ph.  vol.  vii.)  prove  that  solids  do  not  dilate 
uniformly  at  high  temperatures,  but  expand  in  an  increasing  ratio;  that  is, 
the  higher  the  temperature  beyond  212®  the  greater  tlie  expansion  for 
equal  additions  of  caloric.  It  is  manifest,  indeed,  from  their  experi- 
ments, that  the  rate  of  expansion  is  an  increasing  one  even  between  32® 
and  212®;  but  the  differences  which  exist  within  this  small  range  are  so 
inconsiderable  as  to  escape  observation,  and,  therefore,  for  all  practical 
purposes  may  be  disregarded. 

The  subjoined  table  includes  the  most  interesting  results  of  Lavoisier 
and  Laplace.  (Biot,  vol,  i.  p.  Ia8.) 


Names  of  Suhstances. 

(ilass  tube  without  lead,  a mean  of  three 
specimens  ..... 
Kng’llsh  flint  glass  .... 
(.’opper  ....  . . 

Hr  iss — mean  of  two  sfiecimens 

Soft  iron  forged 

iron  wire  ..... 

Uiin.  iiipercd  steel  . ... 


Elone^alion  when  heated 
from  32^  /o  212®. 

1-11 15  of  its  length. 
M248 
1-581 
1-532 
1-819 
1-812 
1-927 


CALORIC. 


31 


Names  of  Substances* 

Elongation  when  heated 
. from  32®  to  212®. 

Tempered  steel  .... 

. 1-807  of  its  length. 

Lead  

1-351 

Tin  of  India  . . . • . 

1-516 

Tin  of  Falmouth  .... 

1-462 

Silver 

1-524 

Gold,  mean  of  three  specimens  . 

1-602 

Platinum,  determined  by  Borda 

1-1167 

Knowing  the  elongation  of  any  substance  for  a given  number  of  de- 
grees of  the  thermometer/  it  is  easy  to  calculate  its  total  increase  in 
bulk,  by  trebling  the  number  which  expresses  its  increase  in  length. 
Thus  if  a tube  of  flint  glass  elongates  by  1-1248,  when  heated  from 
the  freezing  to  the  boiling  point  of  water,  its  cubic  space  will  have  in- 
creased by  3-1248  or  1-416  of  its  former  capacity. 

The  expansion  of  glass,  iron,  copper,  and  platinum,  has  been  par- 
ticularly investigated  by  MM.  Dulong  and  Petit.  The  following  table 
contains  the  result  of  their  observations  on  glass.  (An.  de  Ch.  et  de 
Ph.  vii.  138.)  It  appears  from  the  third  column  that  at  temperatures 
beyond  212®  glass  expands  in  a greater  ratio  than  mercury. 


Temperature  by 
an  air  thermo- 
meter. 

Mean  Absolute  Di- 
latation of  glass  for 
each  degree. 

Temperature  by 
a thermometer 
made  of  glass. 

Fahr. 

Fahr. 

Fahr. 

From  32°  to  212° 

1-69660 

212® 

32  to  392 

1-65340 

415.3 

32  to  572 

1-59220 

667.2 

The  second,  fourth,  and  sixth  columns  of  the  following  table  show 
the  mean  total  expansion  of  iron,  copper,  and  platinum,  when  heated 
from  32®  to  212®  and  from  32®  to  572®,  for  each  degree.  The  third, 
fifth,  and  seventh  columns  indicate  the  degrees  on  a thermometer  of  iron, 
copper,  and  platinum,  corresponding  to  a temperature  of  572®'*on  an 
air  thermometer.  It  is  obvious  that  platinum  is  much  more  uniform  in 
its  expansion  than  either  of  the  other  metals. 


Temp,  by  air 
thermome- 
ter. 

1 Mean  Dilat* 

1 of  iron  in 

1 volume  for 

1 each  deg. 

Temperature 
by  iron  7'od 
thei'mom. 

1 Mean  Diat, 

1 of  Copper  in 

1 volume  for 

1 each  degree. 

Temp.  by 
copper  rod 
therm  cm,. 

1 Meant  Dilat 

of  Platinum 

1 in  vol.  for 

1 each  degree. 

Temp. by  pla- 
tinum rod 
thermom. 

Fahr. 

Fahr. 

Fahr. 

Fahr. 

Fahr. 

Fahr. 

Fahr. 

212® 

h-50760 

212® 

1-34920 

212® 

1-67860 

212® 

572® 

1-40678 

702.5 

1-31860 

623.8 

1-65340 

592.9 

The  simplest  method  of  proving  the  expansion  of  liquids  is  by  put- 
ting a common  thermometer,  made  with  mercury  or  alcohol,  into  warm 
water,  when  the  dilatation  of  the  liquid  will  be  shown  by  its  ascent  in  the 
stem.  'I  he  experiment  is  indeed  illustrative  of  two  other  facts.  It  proves 
first,  that  the  dilatation  increases  with  the  temperature  ; for  if  the  ther- 
mometer is  plunged  into  several  portions  of  water  heated  to  different  de- 
grees the  ascent  will  be  the  greatest  in  the  hottest  water,  and  least  in  the 


32 


CALORIC. 


coolest  portions.  It  demonstrates,  secondly,  that  liquids  expand  more 
than  solids.  The  glass  bulb  of  the  thermometer  is  itself  expanded  by 
the  hot  water,  and  therefore  is  enabled  to  contain  more  mercury  than 
before  ; but  the  mercury  being  dilated  to  a much  greater  extent,  not 
only  occupies  the  additional  space  in  the  bulb,  but  likewise  rises  in  the 
stem.  Its  ascent  marks  the  difference  between  its  own  dilatation  and 
that  of  the  glass,  and  is  only  the  apparent,  not  the  actual  expansion  of 
the  li^id, 

Diffte’ent  liquids  do  not  expand  to  the  same  degree  from  an  equal 
increase  of  temperature.  Alcohol  expands  much  more  than  water,  and 
water  than  mercury.  From  the  frequency  with  which  the  latter  is  em- 
ployed in  philosophical  experiments,  it  is  important  to  know  the  exact 
amount  of  its  expansion.  This  subject  has  been  investigated  by  several 
philosophers,  but  the  experiments  of  Lavoisier  and  Laplace,  and  espe- 
cially of  Dulong  and  Petit,  from  the  extreme  care  with  which  they  were 
made,  are  entitled  to  the  greatest  confidence.  According  to  the  former 
the  actual  dilatation  of  mercury,  in  passing  from  the  freezing  to  the  boil- 
ing point  of  water,  amounts  to  100-5412  of  its  volume;  but  the  result  ob- 
tained by  Dulong  and  Petit,  who  found  it  100-5550,  is  probably  still 
nearer  the  truth.  Adopting  the  last  estimate,  this  metal  dilates,  for 
every  degree  of  Fahrenheit’s  thermometer,  1-9990  of  the  bulk  which 
it  occupied  at  the  temperature  of  32^^.  If  the  barometer,  for  instance, 
stands  at  30  inches  when  the  thermometer  is  at  32^,  we  may  calculate 
what  its  elevation  ought  to  be  when  the  latter  is  at  60®,  or  at  any  other 
temperature.*  The  apparent  expansion  of  mercury  contained  in  glass 
is  of  course  less  than  the  absolute  expansion.  Between  the  limits  of 
32®  and  212®  F.,  Lavoisier  and  Laplace  estimate  the  apparent  expan- 
sion at  1-63,  and  Dulong  and  Petit  at  1-64.8  of  its  volume,  being  1-11664 
for  each  degree  of  Fahrenheit’s  thermometer.  Dulong  and  Petit  state 
that  the  mean  total  expansion  of  mercury  from  32®  to  572®  F.  for  each 
degree  is  1-9540;  and  that  the  mean  apparent  expansion  in  glass  from 
32®  to  572°  F.  for  each  degree  is  1-11372.  The  temperature  in  their 
experiments  was  estimated  by  an  air  thermometer,  which  they  consider 
more  uniform  in  its  rate  of  expansion  than  one  of  mercury.  The  tem- 
perature of  572®  F.  on  the  air  thermometer  corresponds  to  586®  in  the 
mercurial  one. 

All  experimenters  agree  that  liquids  expand  in  an  increasing  ratio, 
or  that  equal  increments  of  caloric  cause  a greater  dilatation  at  high 


* The  general  formula  is  as  follows:  Let  H be  the  height  of  the  baro- 
meter when  the  thermometer  is  at  32®  F.;  H'  its  elevation  at  any  tem- 
perature above  32°,  and  let  T express  the  number  of  degrees  of  Fah- 


renheit’s therm,  above  that  point.  Then  H'=x 


hence 


H'9990=II(9990+T);  and  H'=H  or  if  H is  unknown,  it 

may  be  calculated  by  the  formula  ^ 9990  , 

9990+ T 

first  formula  substitute  their  value,  as  stated  in  the  text,  and  perform 

llie  calculation.  1 F=3Q^-‘^.^^~^--r=s3Q.Q84.  The  rate  of  actual  and 
9990 


not  apparent  expansion  is  employed  in  this  calculation;  because  the 
length  of  the  mercurial  column,  being  determined  by  the  atmosphe- 
ric pressure,  is  not  affected  by  the  expansion  or  contraction  of  the 
tube. 


CALORIC. 


33 


than  at  !ow  temperatures.  Thus,  if  a fluid  is  heated  from  32^^  to  122^^  it 
’W  ill  not  expand  so  much  as  it  would  do  in  being*  heated  from  122°  to 
212®,  though  an  equal  number  of  degrees  is  added  in  both  cases.  In 
mercury  the  first  expansion,  according  to  Deluc,  is  to  the  second  as  14 
to  15;  in  olive  oil  as  13.4  to  15;  in  alcohol  as  10.9  to  15;  and  in  pure  wa- 
ter 4.7  to  15.  Attempts  have  been  made  to  discover  a general  law  by 
wliich  this  progression  is  regulated,  and  Mr.  Dalton  conceives  that  the 
expansion  observes  the  ratio  of  the  square  of  the  temperature  estimated 
from  the  point  of  congelation,  or  of  greatest  density;  but  this  opinion  is 
merely  hypothetical,  and  has  been  shown  by  Dulong  and  Petit  to  be  in- 
consistent with  the  facts  established  by  their  experiments. 

There  is  a peculiarity  in  the  effect  of  caloric  upon  the  bulk  of  some 
fluids;  namely,  that  at  a certain  temperature  an  increase  of  heat  causes 
them  to  contract,  and  its  diminution  makes  them  expand.  This  singu- 
lar exception  to  the  general  effect  of  caloric  is  only  observable  in  those 
liquids  which  acquire  an  increase  of  bulk  in  passing  from  the  liquid  to 
the  solid  state,  and  is  remarked  only  within  a few  degrees  of  tempera- 
ture above  their  point  of  congelation.  Water  is  a noted  example  of  it. 
Ice,  as  every  one  knows,  swims  upon  the  surface  of  water,  and  there- 
fore must  be  lighter  than  it,  which  is  a convincing  proof  that  water,  at 
the  moment  of  freezing,  must  expand.  The  increase  is  estimated  by 
Boyle  at  about  l-9tli  of  its  volume.  (Experiments  on  Cold.) 

The  most  remarkable  circumstance  attending  this  expansion,  is  the 
prodigious  force  with  which  it  is  effected.  Mr.  Boyle  filled  a brass  tube, 
three  inches  in  diameter,  with  water,  and  confined  it  by  means  of  a 
moveable  plug:  the  expansion,  when  it  froze,  took  place  with  such  vio- 
lence as  to  push  out  the  plug,  though  preserved  in  its  situation  by  a 
weight  equal  to  74  pounds.  The  Florentine  Academicians  burst  a hol- 
low brass  globe,  whose  cavity  was  only  an  inch  in  diameter,  by  freez- 
ing the  water  with  which  it  was  filled;  and  it  has  been  estimated  that 
the  expansive  power  necessary  to  produce  such  an  effect  was  equal  to 
a pressure  of  27,720  pounds  weight.  Major  Williams  gave  ample  con- 
firmation of  the  same  fact  by  some  experiments  which  he  performed  at 
Quebec  in  the  years  1784  and  1785.  (Philosophical  Transactions  of  Ed. 
ii.  23.) 

But  it  is  not  merely  during  the  act  of  congelation  that  water  expands; 
for  it  begins  to  dilate  considerably  before  it  actually  freezes.  Dr. 
Croune  noticed  this  phenomenon  so  early  as  the  year  1683,  and  it  has 
since  been  observed  by  various  philosophers.  It  may  be  rendered  ob- 
vious to  any  one  by  the  following  experiment.  Fill  a flask,  capable  of 
holding  three  or  four  ounces,  with  water  at  the  temperature  of  60®  F. 
and  adapt  to  it  a cork,  through  which  passes  a glass  tube  open  at  both 
ends,  about  the  eighth  of  an  inch  wide,  and  ten  inches  long.  After 
having  filled  the  flask,  insert  the  cork  and  tube,  and  pour  a little  water 
into  the  latter  till  the  liquid  rises  to  the  middle  of  it.  On  immersing 
the  flask  into  a mixture  of  pounded  ice  and  salt,  the  water  will  fall  in 
the  tube,  marking  contraction;  but  in  a short  time  an  opposite  move- 
ment will  be  perceived,  indicating  that  dilatation  is  taking  place,  while 
the^  water  within  the  flask  is  at  the  same  time  yielding  caloric  to  the 
freezing  mixture  in  which  it  is  immersed. 

To  the  inference  deduced  from  this  experiment  it  was  objected  by 
some  philosophers,  that  ihe  ascent  of  the  water  in  the  tube  did  not  arise 
from  any  expansion  in  the  liquid  itself,  but  from  a contraction  of  the 
flask,  by  which  its  capacity  was  diminished.  In  fact,  this  cause  does 
operate  to  a certain  extent,  but  it  is  by  no  means  sufiicient  to  account 
for  the  whole  eflect  ; and,  accordingly,  it  has  been  proved  by  an  cle- 


34 


CALORIC. 


gant  and  decisive  experiment  by  Dr.  Hope,  that  water  does  really  ex- 
pand previous  to  congelation.*  He  believes  the  greatest  density  of  wa- 
ter to  be  between  thirty-nine  and  a half  and  forty  degrees  of  Fahrenheit’s 
thermometer?  that  is,  boiling  water  obeys  the  usual  law  till  it  has  cooled 
to  the  temperature  of  about  40*^,  after  which  the  abstraction  of  caloric 
produces  increase  instead  of  diminution  of  volume.  According  to  M. 
Hallstrbm,  whose  experiments  are  the  most  recent,  and  appear  to  have 
been  conducted  with  great  care,  the  maximum  density  of  water  is  39.39^ 
F.  (An.  de  Ch.  et  de  Ph.  xxviii.  90.) 

The  cause  of  the  expansion  of  water  at  the  moment  of  freezing  is  at- 
tributed to  a new  and  peculiar  arrangement  of  its  particles.  Ice  is  in 
reality  crystallized  water,  and  during  its  formation  the  particles  arrange 
themselves  in  ranks  and  lines,  which  cross  each  other  at  angles  of  60^ 
and  120°,  and  consequently  occupy  more  space  than  when  liquid.  This 
may  be  seen  by  examining  the  surface  of  water  while  freezing  in  a saucer. 
No  very  satisfactory  reason  can  be  assigned  for  the  expansion  which 
takes  place  previous  to  congelation.  It  is  supposed,  indeed,  that  the 
water  begins  to  arrange  itself  in  the  order  it  will  assume  in  the  solid 
state  before  actually  laying  aside  the  liquid  form?  and  this  explanation 
is  generally  admitted,  not  so  much  because  it  has  been  proved  to  be  true» 
but  because  no  better  one  has  been  offered. 

Water  is  not  the  only  liquid  which  expands  under  reduction  of  tem- 
perature, as  the  same  effect  has  been  observed  in  a few  others  which 
assume  a highly  crystalline  structure  on  becoming  solid; — fused  iron, 
antimony,  zinc,  and  bismuth,  are  examples  of  it.  Mercury  is  a remarka- 
ble instance  of  the  reverse;  for  when  it  freezes,  it  suffers  a very  great 
contraction. 

As  the  particles  of  air  and  aeriform  substances  are  not  held  together 
by  cohesion,  it  follows  that  increase  of  temperature  must  occasion  a 
considerable  dilatation  of  them;  and,  accordingly,  they  are  found  to  di- 
late from  equal  additions  of  caloric  much  more  than  solids  or  liquids. 
Now,  chemists  are  in  the  habit  of  estimating  the  quantity  of  the  gases 
employed  in  their  experiments  by  measuring  them;  and  since  the  vol- 
ume occupied  by  any  gas  is  so  much  influenced  by  temperature,  it  is 
essential  to  accuracy  that  a due  correction  be  made  for  the  variations 
arising  from  this  cause;  that  they  should  know  how  much  dilatation  is 
produced  by  each  degree  of  the  thermometer,  whether  the  rate  of  ex- 
pansion is  uniform  at  all  temperatures,  and  whether  that  ratio  is  the 
same  in  all  gases. 

This  subject  had  been  unsuccessfully  investigated  by  several  philoso- 
phers, who  failed  in  their  object  chiefly  because  they  neglected  the 
precaution  of  drying  the  gases  upon  which  they  operated  ; but  at  last 
the  law  of  dilatation  was  detected  by  Dalton  and  Gay-Lussac  nearly  at 
the  same  time.  Mr.  Dalton’s  method  of  operating  (Manchester  Me- 
moirs, vol.  V.)  was  exceedingly  simple.  He  filled  with  dry  mercury  a 
graduated  tube,  closed  at  one  end  and  carefully  dried  ; and  then  plung- 
ing the  open  end  of  the  tube  into  a mercurial  trough,  introduced  a por- 
tion of  dry  air.  After  having  marked  the  bulk  and  temperatvire  of  the 
air,  he  exposed  it  to  a gradually  increasing  heat,  the  exact  amount  of 
which  was  regulated  by  a thcnnoineter,  and  observed  the  dilatation  oc- 
casioned by  each  increase  of  temperature.  The  apparatus  of  M.  Gay- 
Lussac(An.  de  Chirnie,  v.  43)  was  the  same  in  principle,  but  more  com- 


Philosophical  Transactions  of  Edinburgh,  v.  379. 


CALORIC. 


35 


plicated,  in  consequence  of  the  precautions  he  took  to  avoid  every  pos- 
sible source  of  fallacy. 

It  is  proved  by  the  researches  of  these  philosophers,  that  all  gases 
undergo  equal  expansions  by  the  same  addition  of  caloric,  supposing 
them  placed  under  the  same  circumstances;  so  that  it  is  sufficient  to 
ascertain  the  law  of  expansion  observed  by  any  one  gas,  in  order  to 
know  the  law  for  all.  Now  it  appears  from  the  experiments  of  Gay- 
Lussac,  that  100  parts  of  air  in  being  heated  from  32^  to  212^  F.  expand 
to  137*5  parts.  The  increase  for  180  degrees  is  therefore  0*375  or 
S7*5-100th  of  its  bulk;  and  by  dividing  this  number  by  180  it  is  found 
that  a given  quantity  of  dry  air  dilates  to  1 -480th  of  the  volume  it  occu- 
pied at  32®,  for  every  degree  of  Fahrenheit’s  thermometer.  The  re-, 
suit  of  Dalton’s  experiments  corresponds  very  nearly  with  the  foregoing. 

This  point  being  established,  it  is  easy  to  ascertain  what  volume 
any  given  quantity  of  gas  should  occupy  at  any  given  temperature. 
Suppose  a certain  quantity  of  gas  occupies  20  measures  of  a graduated 
tube  at  32®,  it  may  be  desirable  to  determine  what  would  be  its  bulk  at 
42®  F.  For  every  degree  of  heat  it  has  increased  by  l-480th  of  its  ori- 
ginal volume,  and  therefore,  since  the  increase  amounts  to  ten  degrees, 
the  20  measures  will  have  dilated  by  10-480ths.  The  expression  will 
therefore  be  20-[-20Xl0-480=20*41 6.  It  must  not  be  forgotten  that 
the  volume  which  the  gas  occupies  at  32®  is  a necessary  element  in  all 
such  calculations.  Thus,  having  20*416  measures  of  gas  at  42®  F.  the 
corresponding  bulk  for  52®  F.  cannot  be  calculated  by  the  formula 
20*416-[~20 *41 6x10-480;  the  real  expression  is  20*4164-20x10-480,  be- 
cause the  increase  is  only  10-480tli  of  the  space  occupied  at  32®  F., 
which  is  20  measures.*  A similar  remark  applies  to  the  formula  for 
estimating  the  effect  of  heat  on  the  height  of  the  barometer. 


* Convenient  formulae  for  such  calculations  may  be  thus  deduced : 
Let  P'  be  the  volume  of  gas  at  any  temperature  above  32®,  T the  num- 
ber of  degrees  above  that  point,  and  P its  volume  at  32®.  Then  P'= 

^ 0+5o)’  O80+T);  and  P'= 

P (480+T) 

480 

P'480 

Or  if  P is  unknown,  it  may  be  calculated  by  the  formula 

It  frequently  happens,  in  the  employment  of  Fahrenheit’s  thermome- 
ter, that  when  P'^  for  the  above  formula  is  known,  it  is  not  P itself 
which  is  wanted,  but  the  volume  of  gas  at  some  other  temperature,  as 
at  60®  F.  This  value  may  be  obtained  without  first  calculating  what 
P is.  Let  P',  for  instance,  be  any  known  quantity  of  gas  at  a certain 
temperature;  and  let  P"  be  the  quantity  sought  at  some  other  temper- 
ature, the  degrees  of  which  above  32®  may  be  expressed  by  T'.  Now 


P" 


(480 4- T') 
480 


XP)  but  as  P is  unknown,  let  its  value  be  substituted 


/4804-T'\  /P'480\ 

according  to  the  above  formula.  Thus,  P"  c=3  — 480~  ) ^ \480-(~T/  ^ 

4802  p'4-480  T'  P'  P'  480  (4804-T')  P'(4804T') 

4804-T. 


which  gives  P"  =- 


480^4-480  T 480  (480+T) 

Suppose,  for  example,  a portion  of  gas  occupies  100  divisions  of  » 


36 


CALOHIC. 


The  rate  of  expansion  of  atmospheric  air  at  temperatures  exceeding 
212®  has  been  examined  by  MM.  Dulong  and  Petit,  and  the  following 
Table  contains  the  result  of  their  observations.  {Jin,  de  Ch.  ci  dt  Ph. 
vii.  120.) 


Temperature  hy  the 
Mercurial  Thermometer. 

Fahrenheit.  Centigrade. 

Corre.^pondhtg 
volumes  of  a 
given  volume 
of  air. 

— 33® 

— 36® 

0.8650 

32 

0 

1.0000 

212 

100 

1.3750 

302 

150 

1.5576 

392 

200 

1.7389 

482 

250 

1.9189 

572 

300 

2.0976 

Mercury  boils  680 

360 

2.3125 

Hydrogen  gas  was  found  to  expand  in  the  same  proportion;  so  that 
all  gases  may  be  inferred  to  expand  to  the  same  extent,  for  equal  in- 


graduated  tube  at  48®  F.,  how  many  will  it  fill  at  60®  F?  Here  P'  = 
100;  T=48— 32  or  16;  T'==  60—32,  or  28.  The  number  sought,  or  the 


100x508_ 
496  ” 


102.42.* * 


* To  those  who  are  not  algebraists,  the  following  explanation  and  cal- 
culation may  be  useful.  As  every  gas  expands  l-480th  of  the  volume 
it  would  occupy  at  32®,  for  every  degree  of  Fahrenheit’s  thermometer, 
it  is  clear  that  it  will  expand  1-481  st  part  of  its  volume  at  33®,  l-482d 
part  of  its  volume  at  34*^^,  and  so  on  for  each  successive  addition  of  one 
degree  of  caloric.  In  order  to  know,  therefore,  the  fractional  dilatation 
of  a gas  at  any  temperature  above  32®,  for  a single  degree,  it  is  only 
necessary  to  add  to  the  denominator  of  the  fraction  1-480,  a number  of 
units  equal  to  the  number  of  degrees  that  the  gas  exceeds  the  tempe- 
rature of  32®.  Thus  a gas  at  the  temperature  of  42®  will  expand  l-490th, 
at  52?  1-500,  of  its  volume,  for  every  increment  of  heat  equal  to  one 
degree.  Knowing  in  this  simple  manner  the  fractional  amount  of  ex- 
pansion of  a gas  at  any  temperature  for  one  degree,  we  multiply  this 
amount  by  the  difference  between  the  existing  temperature  and  the 
temperature  to  which  it  is  desired  to  reduce  the  volume.  If  the  reduc- 
tion is  to  a higher  temperature,  this  product  is  added  to  the  existing 
volume;  if  to  a lower,  subtracted.  Thus,  to  calculate  the  example 
which  Dr.  Turner  has  selected,  namely,  100  measures  of  a gas  at  48®, 
what  will  be  its  bulk  at  60®,  we  proceed  as  follows:  as  the  existing 
temperature  is  16®  above  32®,  its  fractional  expansion  for  one  degree 
will  be  l-480-]-16  = 1-496.  Taking  the  496th  part  of  one  hundred,  the 
given  volume,  wc  have  the  actual  expansion  for  one  degree.  This,  up- 
on calculation,  will  be  found  to  be  .2016,  which  multiplied  by  12,  the 
difference  between  the  actual  temperature  and  the  temperature  of  the 
volume  sought,  will  give  2-419,  as  the  actual  expansion,  corresponding 
to  12  degrees.  As  the  temperature  of  the  volume  sought  is  above  the 
original  temperature,  this  number  must  be  added  to  the  given  volume. 
So  that  100-[-2*419-=*102'419  will  be  the  volume  sought.  13. 


CALOmC. 


37 


crcments  of  caloric,  between  — 33°  F.  and  680°;  and  the  same  law  pro- 
bably prevails  at  all  temperatures.* 

On  the  Thermometer, 

The  influence  of  caloric  over. the  bulk  of  bodies  is  better  fitted  for 
estimating’  a change  in  the  quantity  of  that  agent  than  any  other  of  its 
properties;  for  substances  not  only  expand  more  and  more  as  the  tem- 
perature increases,  but  in  general  return  exactly  to  tlieir  original  volume 
when  the  heat  is  withdrawn.  The  first  attempt  to  measure  the  inten- 
sity of  heat  on  this  principle  was  made  early  in  the  seventeenth  cen- 
tury, and  the  honour  of  the  invention  k by  some  bestowed  on  Sancto- 
rius,  by  others  on  Cornelius  Drebel,  and  by  others  on  the  celebrated 
Galileo.  The  material  used  by  Sanctorius  was  atmospheric  air.  The 
construction  of  the  thermometer  itself,  or  thermoscope  as  it  was  some- 
times called,  is  exceedingly  simple.  A glass  tube  is  to  be  selected  for 
the  purpose,  and  one  end  of  it  is  blown  out  into  a spherical  cavity, 
while  its  other  extremity  is  left  open.  After  expelling  a small  quan- 
tity of  air  by  heating  the  ball  gently,  the  open  end  of  the  tube  is  plunged 
into  coloured  water,  and  a portion  of  the  liquid  is  forced  up  into  the 
tube  by  the  pressure  of  the  atmosphere,  as  the  air  within  the  ball  con- 
tracts. In  this  state  it  marks  changes  of  temperature  with  extreme  de- 
licacy, the  alternate  expansion  and  contraction  of  the  confined  air  being 
rendered  visible  by  the  corresponding  descent  and  ascent  of  the  colour- 
ed water  in  tlie  stem;  and  in  point  of  sensibility,  indeed,  it  yields  to  no 
instrument.  The  material  used  in  its  construction,  also,  is  peculiarly 
appropriate,  because  air,  like  all  gases,  expands  uniformly  by  equal  in. 
crements  of  caloric;  but  nevertheless,  independently  of  these  advan- 
tages, there  are  two  forcible  objections  to  the  employment  of  this  ther- 
mometer. For,  in  the  first  place,  its  dilatations  and  contractions  are  so 
great,  that  it  will  be  inconvenient  to  measure  them  when  the  change  of 
temperature  is  considerable;  and,  secondly,  its  movements  are  influ- 
enced by  pressure  as  wxil  as  by  caloric,  so  that  the  instrument  would 
be  affected  by  variations  of  the  barometer,  though  the  temperature 
sh.ould  be  quite  stationary. 

For  the  reasons  just  stated,  the  common  air  thermometer  is  rarely  em- 
ployed; but  a modification  of  it,  described  in  1804  by  Professor  Leslie  in 
his  Essay  on  Heat,  under  the  name  of  Differential  Thermometer^  is  entire- 
ly free  from  the  last  objection,  and  is  admirably  fitted  for  some  special 
purposes.  This  instrument  was  invented  a century  and  a half  ago  by  Stur- 
mius,  Professor  of  Mathematics  at  Altdorff,  who  has  left  a description 
and  sketch  of  it  in  his  Collegium  Curiosum.  p.  54,  published  in  the  year 
1676;  but  like  other  air  thermometers  it  had  fallen  into  disuse,  till  it 
w'as  again  brought  into  notice  by  Professor  Leslie.  As  now  made  it 
consists  of  two  thin  glass  balls  joined  together  by  a tube,  bent  twdee  at 


* The  law  of  the  equable  expansion  or  contraction  of  gases  by  equal 
increments  or  decrements  of  heat  is  a very  curious  one;  but  it  becomes 
particularly  so  W'hen  viewed  in  connexion  with  a descending  tempera- 
ture. If  gases  expand  or  contract  1.480th  of  the  volume  they  occupy 
at  tlie  freezing  point,  for  every  alteration  of  temperature  equal  to  one 
degree,  it  is  obvious  that  a given  volume  of  any  gas  at  32°  will  be  ex- 
panded by  a volume  equal  to  itself,  by  having  its  temperature  raised 
480^.  Rut  the  converse  of  the  proposition  would  seem  to  involve  a par- 
adox; forby  the  a[)plication  of  the  same  law,  a given  volume  of  any 
gas  at  32°,  if  cooled  down  480°,  would  be  contracted  by  a volume  equal 
to  itself,  that  is,  reduced  to  nothing!  B. 

4 


38 


CALORIC. 


a rig'ht  angle,  as  represented  in  the  annexed  figure.  Both  balls  con- 
tain air,  but  the  greater  part  of  tlie  tube  is  . 
filled  with  sulphuric  acid  coloured  with  card 
mine.  It  is  obvious  that  this  instrument  can-> 
not  be  affected  by  any  change  of  temperature 
acting  ecjually  on  both  balls;  for  as  long  as  the 
air  within  them  expands  or  contracts  to  the 
same  extent,  the  pressure  on  the  opposite  sur- 
faces of  the  liquid,  and  consequently  its  posi- 
tion, will  continue  unchanged.  Hence  the 
differential  thermometer  stands  at  the  same 
point,  however  different  may  be  the  tempera- 
ture of  the  medium.  But  the  slightest  differ- 
ence between  the  temperature  of  the  two 
balls  will  instantly  be  detected;  for  the  elas- 
ticity of  the  air  on  one  side  being  then  greater 
than  that  on  the  other,  the  liquid  will  retreat 
towards  the  ball  whose  temperature  is  lowest. 

Solid  substances  are  not  better  suited  to  the 
construction  of  a thermometer  than  gases;  for 
while  the  expansion  of  the  latter  is  too  great, 
that  of  the  former  is  so  small  that  it  cannot  be 
measured  except  by  the  adaptation  of  compli- 
cated machinery.  Liquids  which  expand 
more  than  the  one  and  less  than  the  other, 
are  exempt  from  both  extremes;  and,  consequently,  we  must  search 
among  them  for  a material  with  which  to  construct  a thermometer. 
The  principle  of  selection  is  plain.  A material  is  required  whose  ex- 
pansions are  uniform,  and  whose  boiling  and  freezing  points  are  very 
remote  from  one  another.  Mercury  fulfils  these  conditions  better  than 
any  other  liquid.  No  fluid  can  support  a greater  degree  of  heat  with- 
out  boiling  than  mercury,  and  none,  except  alcohol  and  ether,  can  en- 
dure a more  intense  cold  without  freezing.  It  has,  besides,  the  addi- 
tional advantage  of  being  more  sensible  to  the  action  of  caloric  than 
other  liquids,  while  its  dilatations  between  32®  and  212®  are  almost  per- 
fectly uniform.  Strictly  speaking,  the  same  quantity  of  caloric  does 
occasion  a greater  dilatation  at  high  than  at  low  temperatures,  so  that, 
like  other  fluids,  it  expands  in  an  increasing  ratio.  But  it  is  remarkable 
that  this  ratio,  within  the  limits  assigned,  is  exactly  the  same  as  that  of 
glass;  and  therefore,  if  contained  in  a glass  tube,  the  increasing  expan-, 
sion  of  the  vessel  compensates  for  that  of  the  mercury. 

The  first  object  in  constructing  a thermometer  is  to  select  a tube 
with  a very  small  bore,  which  is  of  the  same  diameter  through  its  whole 
length  ; and  then,  by  melting  the  glass,  to  blow  a small  ball  at  one  end 
of  it.  The  mercury  is  introduced  by  rarefying  the  air  within  the  ball 
and  then  dipping  the  open  end  of  the  tube  into  that  liquid.  As  the 
air  cools  and  contracts,  the  mercury  is  forced  up,  entering  the  bulb  to 
supply  the  place  of  the  air  which  had  been  expelled  from  it.  Only  a 
part  of  the  air,  however,  is  removed  by  this  means ; the  remainder  is 
di’iven  out  by  the  ebullition  of  the  mercury. 

Having  thus  contrived  that  the  bulb  and  about  one-third  of  the  tube 
shall  be  fidl  of  mercury,  the  next  step  is  to  seal  the  open  end  hermeti- 
cally. This  is  done  by  heating  the  bulb  till  the  mercury  rises  very  near 
the  summit,  and  then  suddenly  darting  a fine  pointed  flame  from  a 
blow-pipe  across  the  opening,  so  as  to  Rise  the  glass  and  close  the  ap- 
erture liefore  the  mercury  has  had  time  to  recede  from  it 

The  construction  of  a thermometer  is  now  so  far  complete  that  it  af- 


CALOKIC. 


39 


fords  a means  of  ascertaining*  the  comparative  temperature  of  bodies; 
but  it  is  deficient  in  one  essential  point,  namely,  the  observations  made 
with  different  instruments  cannot  be  compared  together.  To  effect 
this  object,  the  thermometer  must  be  graduated,  a process  which  con- 
sists of  two  parts.  The  first  and  most  important,  is  to  obtain  two  fixed 
points  which  shall  be  the  same  in  every  thermometer.  The  practice 
now  generally  followed  for  this  purpose  was  introduced  by  Sir  Isaac 
Newton,  and  is  founded  on  the  fact,  that  when  a thermometer  is  plunged 
into  ice  that  is  dissolving,  or  into  water  that  is  boiling,  it  constantly 
stands  at  the  same  elevations  in  all  countries,  provided  there  is  a cer- 
tain conformity  of  circumstances.  The  point  of  congelation  is  easily 
determined.  The  instrument  is  to  be  immersed  in  snow  or  pounded 
ice,  liquefying  in  a moderately  warm  atmosphere,  till  the  mercury  be- 
comes stationary.  To  fix  the  boiling  point  is  a more  delicate  opera- 
tion, since  the  temperature  at  which  water  boils  is  affected  by  various 
circumstances  which  will  be  more  particularly  mentioned  hereafter.  It 
is  sufficient  to  state  the  general  directions  at  present; — that  the  water 
be  perfectly  pure,  free  from  any  foreign  particles,  and  not  above  an  inch  in 
depth, — the  ebullition  brisk,  and  conducted  in  a deep  metallic  vessel,  so 
that  the  stem  of  the  thermometer  may  be  surrounded  by  an  atmosphei’C 
of  steam,  and  thus  exposed  to  the  same  tQjnperature  as  the  bulb, — the 
vapour  be  allowed  to  escape  freely, — and  the  barometer  stand  at  30 
inches. 

The  second  part  of  the  process  of  graduation  consists  in  dividing 
the  interval  between  the  freezing  and  boiling  points  of  water,  into  any 
number  of  equal  parts  or  degrees,  which  may  be  either  marked  on  the 
tube  itself,  by  means  of  a diamond,  or  first  drawn  upon  a piece  of  paper, 
ivory,  or  metal,  and  afterwards  attached  to  the  thermometer.  The 
exact  number  of  degrees  into  which  the  space  is  divided,  is  not  very 
material,  though  it  would  be  more  convenient  did  all  thermometers  cor- 
respond in  this  respect.  Unfortunately  this  is  not  the  case.  In  Britain 
we  use  Fahrenheit’s  scale,  while  the  continental  philosophers  employ 
either  the  centigrade,  or  that  of  Reaumur.  The  centigrade  is  the  most 
convenient  in  practice;  its  boiling  point  is  100,  that  of  melting  snow  is 
the  zero,  or  beginning  of  the  scale,  and  the  interval  is  divided  into  100 
equal  parts.  The  interval  in  the  scale  of  Reaumur  is  divided  into  80 
parts,  and  in  that  of  Fahrenheit  into  180;  but  the  zero  of  Fahrenheit  is 
placed  32  degrees  below  the  temperature  of  melting  snow,  and  on  this 
account  the  point  of  ebullition  is  212®. 

It  is  easy  to  reduce  the  temperature  expressed  by  one  thermometer 
to  that  of  another,  by  knowing  the  relation  which  exists  between  their 
degrees.  Thus,  180  is  to  100  as  9 to  5,  and  to  80  as  9 to  4;  so  that  nine 
degrees  of  Fahrenheit  are  equal  to  five  of  the  centigrade,  and  four 
of  Reaumur’s  thermometer.  Fahrenheit’s  is,  therefore,  reduced  to  the 
centigrade  scale,  by  multiplying  by  five,  and  dividing  by  nine,  or  to 
that  of  Reaumur,  by  multiplying  by  four  instead  of  five.  Either  of  these 
may  be  reduced  to  Fahrenheit  by  reversing  the  process;  the  multiplier 
is  nine  in  both  cases,  and  the  divisor  four  in  the  one  and  five  in  the  other. 
But  it  must  be  remembered  in  these  reductions,  that  the  zero  of  Fahren- 
heit’s thermometer  is  32  degrees  lower  than  that  of  the  centigrade  or 
Reaumur,  and  a due  allowance  must  be  made  for  this  circumstance.  An 
example  will  best  show  how  this  is  done.  To  reduce  212®  F.  to  the  cen- 
tigrade, first  subtract  32,  which  leaves  180;  and  this  number  multiplied 
gives  the  corresponding  expression  in  the  centigrade  scale.  Or 
to  reduce  100®  C.  to  Fahrenheit,  multiply  by  9-5,  and  then  add  32.  To 
save  the  trouble  of  such  reductions,  I have  subjoined  a table,  which 
shows  the  degrees  on  the  centigrade  scale  and  that  of  Reaumui*,  corres- 
ponding to  the  degrees  of  Fahrenheit’s  thermometer. 


to 


CALOmC. 


Fahrenheit, 

212 

200 

190 

180 

170 

160 

150 

140 

130 

120 

110 

100 

90 

80 

70 

60 

50 

40 

32 

20 

10 

0 


Centigrade, 

100 

93.3:3 

87.77 
82.22 

76.66 

71.11 

65.55 
60 

54.44 

48.88 

43.33 

37.77 
32  22 

26.66 

21.11 

15.55 
10 

4.44 

0 

—6.66 

—12.22 

—17.77 


Reaumur 

80 

74.66 

70.22 

65.77 

61.33 

56.88 

52.44 
48 

43.55 

39.11 

34.66 

30.22 

25.77 

21.33 

16.88 

12.44 
8 

3.55 

0 

—5.33 

—9.77 

—14.22 


The  mercurial  thermometer,  may  be  made  to  indicate  temperatui’cs 
which  exceed  212*^,  or  fall  below  zero,  by  continuing*  the  degrees  above 
and  below  those  points.  But  as  mercury  freezes  at  39  degrees  below 
zero,  it  cannot  indicate  temperatures  below  that  point;  and  indeed  the 
only  liquid  which  can  be  used  for  such  purposes  is  alcohol.  Our  means 
of  estimating  high  degrees  of  heat  are  as  yet  very  unsatisfactory.  Mer- 
cury is  preferable  to  any  other  liquid;  but  even  its  indications  cannot 
be  altogether  relied  on.  For,  in  the  first  place,  its  expansion  for  equal 
increments  of  caloric  is  greater  at  high  than  at  low  temperatures;  and, 
.secondly,  glass  expands  at  temperatures  beyond  112*^  F,  in  a more  rapid 
ratio  than  mercuiy,  and  consequently,  from  the  proportionally  greater 
capacity  of  the  bulb,  the  apparent  expansion  of  the  metal  is  consider- 
ably less  than  its  actual  dilatation.  Thus  MM.  Dulong  and  Petit  observed 
that  when  the  air  thermometer  is  at  572^^  F.,  the  common  mercurial 
thermometer  stands  at  586^;  but  when  corrected  for  the  error  caused 
by  the  glass,  it  indicates  a temperature  of  597.5®  F.  No  liquid  can  be 
employed  for  temperatures  which  exceed  680®  F.,  since  all  of  them  are 
then  eitlier  dissipated  in  vapour,  or  decomposed. 

The  instruments  for  measuring  intense  degrees  of  heat  are  called 
pyrometers^  and  must  be  formed  either  of  solid  or  gaseous  substances. 
The  former  alone  have  been  hitherto  employed,  thougli  the  latter,  from 
the  greater  uniformity  with  which  they  expand,  are  better  calculated 
for  tlie  purpose.  The  pyrometer  invented  by  Mr.  Wedgwood  is  best 
known.  It  is  founded  on  the  property  which  clay  possesses  of  contract- 
ing when  .strongly  heated,  without  returning  to  its  former  dimensions 
as  it  cools.  3'lie  earth  alumina,  whether  precipitated  from  a solution 
by  reagents,  or  found  more  or  less  pure  in  the  earth  as  clay,  is  always 
in  a state  of  chemical  combination  with  water.  On  heating  it  to  red- 
ness, part  of  the  water  is  expelled;  but  some  remains,  which  requires 
a very  strong  heat  before  it  is  dis.sipated;  and  in  proportion  as  these 
lii.st  portions  escape,  tlie  eartli  contracts.  The  contraction  even  con- 
tinues after  every  trace  of  water  has  been  removed,  owing  to  partial 
vitrification  taking  place,  which  tends  to  bring  the  particles  of  the  clay 


CALORIC. 


41 


into  nearer  proximity.  The  intensity  of  the  heat  may,  therefore,  in 
some  measure  be  estimated  by  the  degree  of  contraction  which  it  has 
occasioned. 

The  apparatus  consists  of  a metallic  groove,  24  inches  long,  the 
sides  of  which  converge,  being  half  an  incli  wide  above,  and  three- 
tenths  below.  The  clay,  well  washed,  is  made  up  into  little  cubes* 
that  fit  the  commencement  of  the  groove,  after  having  been  heated  to 
redness;  and  their  subsequent  contraction  by  heat  is  determined  by  al- 
lowing them  to  slide  from  the  top  of  the  groove  downwards,  till  they 
arrive  at  a part  of  it  through  which  they  cannot  pass.  Mr.  Wedgwood 
divides  the  whole  length  of  the  groove  into  240  degrees,  each  of  which 
he  supposes  equal  to  130^  F.  The  zero  of  his  scale  corresponds  to  the 
1077th  degree  of  Fahrenheit. 

Wedgwood’s  pyrometer  is  rarely  employed  at  present,  because  its 
indications  cannot  be  relied  on.  Every  observation  requires  a separate 
piece  of  clay,  and  the  observer  is  never  sure  that  the  contraction  of  the 
second  cube,  from  the  same  heat,  will  be  exactly  similar  to  that  of  the 
first;  especially  as  it  is  difficult  to  procure  specimens  of  the  earth,  the 
composition  of  which  is  in  every  respect  the  same. 

Other  pyrometers  have  been  proposed,  which  act  on  the  usual  prin- 
ciple of  dilatation.  They  consist  of  a metallic  bar,  the  elongation  of 
which  from  heat  is  rendered  sensible  by  an  index  being  attached  to  one 
end,  while  the  other  is  fixed.  The  experiments  of  Lavoisier  and  La- 
place on  the  expansion  of  solids  were  made  with  an  apparatus  of  this 
kind,  and  Mr.  Daniell  has  described  a similar  one  in  the  1 1th  volume  of 
the  Quarterly  Journal  of  Science.  These  instruments  are  in  general 
too  complicated  for  common  use;  and,  moreover,  scientific  men  have 
hitherto  placed  little  confidence  in  them,  in  consequence  of  the  irregu- 
larity with  which  solids  expand  at  high  temperatures. 

For  some  purposes,  especially  in  making  meteorological  observations, 
it  is  a very  desirable  object  to  ascertain  the  highest  and  lowest  temper- 
ature which  has  occurred  in  a given  interval  of  time,  during  the  ab- 
sence of  the  observer.  The  instrument  employed  with  this  intention 
is  called  a Register  Thermometer,  and  the  most  convenient  kind,  with 
which  I am  acquainted,  is  that  described  in  the  Philosophical  Transac- 
tions of  Edinburgh,  iii.  245,  by  Dr.  John  Rutherford.  The  thermometer 
for  ascertaining  the  most  intense  cold  is  made  with  alcohol,  and  the  bulb 
is  bent  at  a right  angle  to  the  stem,  so  that  the  latter  may  conveniently 
be  placed  in  a horizontal  position.  In  the  spirit  is  immersed  a cylin- 
drical piece  of  black  enamel,  of  such  size  as  to  move  freely  within  the 
tube.  In  order  to  make  an  observation,  the  enamel  should  be  brought 
down  to  the  surface  of  the  spirit,  an  object  easily  effected  by  slight  per- 
cussions while  the  bulb  is  inclined  upwards.  When  the  thermometer 
sinks  by  exposure  to  cold,  the  enamel  likewise  retreats  towards  the  bulb, 
owing  to  its  adhesion  to  the  spirit;  but,  on  expanding,  the  spirit  passes 
readily  beyond  the  enamel,  leaving  it  at  the  extreme  point  to  which  it 
had  been  conveyed  by  the  previous  contraction. 

For  registering  the  highest  temperature,  a common  mercurial  ther- 
mometer of  the  same  form  as  the  preceding  is  employed,  having  a small 
cylindrical  piece  of  black  enamel  at  the  surface  of  the  mercury.  When 
the  mercury  expands,  the  enamel  is  pushed  forward;  and  as  the  stem  of 


* In  this  statement,  Dr.  Turner  is  slightly  inaccurate;  for  strictly 
speaking  the  pieces  of  clay  are  little  truncated  cones,  the  sides  of  which 
have  the  same  inclination  to  each  other  as  the  sides  of  the  metallic 
groove,  B. 


4* 


42 


CALORIC. 


the  thermometer  is  placed  horizontally,  it  does  not  recede  A^hcn  the 
mercury  contracts,  but  remains  at  tlie  spot  to  which  it  had  been  con- 
veyed by  the  previous  dilatation.  'I’he  enamel  is  easily  restored  to  the 
surface  of  the  mercury  by  slight  percussion  while  the  bulb  is  inclined 
downwards;  but  this  should  be  performed  with  care,  lest  the  enamel, 
in  falling  abruptly,  should  interrupt  the  continuity  of  the  mercurial  col- 
umn, and  interfere  with  the  indication  of  the  instrument.  This  accident 
is  prevented  by  putting  some  pure  naphtha  in  the  tube  beyond  the  mer- 
cury, and  its  presence  is  likewise  of  use  in  preventing  the  oxidation  of 
the  mercury. — The  above  description  applies  to  an  improvement  on  Dr. 
Rutherford’s  thermometer,  made  by  Mr.  Adie  of  Edinburgh. 

Though  the  thermometer  is  one  of  the  most  valuable  instruments  of 
philosophical  research,  it  must  be  confessed  that  the  sum  of  informa- 
tion which  it  conveys  is  very  small.  It  does  indeed  point  out  a differ- 
ence in  the  temperature  of  two  or  more  substances  with  great  nicety; 
but  it  does  not  indicate  how  much  caloric  any  body  contains.  It  does 
not  follow,  because  the  thermometer  stands  at  the  same  elevation  in  any 
two  bodies,  that  they  contain  equal  quantities  of  caloric;  nor  is  it  right 
to  infer  that  the  warmer  possesses  more  of  this  principle  than  the  cold- 
er. The  thermometer  gives  the  same  kind  of  information  which  may 
be  discovered,  though  less  accurately,  by  the  feelings;  it  recognizes  in 
bodies  that  state  of  caloric  alone,  which  affects  the  senses  with  an  im- 
pression of  heat  or  cold;  the  condition  expressed  by  the  word  temperature. 
All  we  learn  by  this  instrument  is,  whether  the  temperature  of  one  body 
is  greater  or  less  than  that  of  another;  and  if  there  is  a difference,  it 
is  expressed  numerically,  namely,  by  the  degrees  of  the  thermometer. 
But  it  must  be  remembered  that  these  degrees  are  parts  of  an  arbitrary 
scale,  selected  for  convenience,  without  any  reference  whatever  to  the 
actual  quantity  of  caloric  present  in  bodies. 

Very  little  reflection  will  evince  the  propriety  of  these  remarks.  If 
two  glasses  of  unequal  size  be  filled  with  water  just  taken  frorn^  the 
same  spring*,  the  thermometer  will  stand  in  each  at  the  same  height, 
though  their  quantities  of  caloric  are  certainly  unequal.  This  observa- 
tion naturally  suggests  the  inquiry,  whether  different  kinds  of  sub- 
stances, whose  temperatures  as  estimated  by  the  thermometer  are  the 
same,  contain  equal  quantities  of  caloric; — if,  for  example,  a pound  of 
iron  contains  as  much  caloric  as  a pound  of  water  or  mercury.  The 
foregoing  remark  shows  that  equality  in  temperature  is  not  necessarily 
connected  with  equality  in  quantity  of  caloric,  and  the  inference  has  been 
amply  confirmed  by  experiment.  If  equal  quantities  of  water  are  mixed 
together,  one  portion  being  at  100^  F.,  and  the  other  at  50®,  the  tem- 
perature of  the  mixture  will  be  the  arithmetical  mean  or  75®;  that  is, 
the  25  degrees  lost  by  the  warm  water,  have  just  sufficed  to  heat  the 
cold  water  by  the  same  number  of  degrees.  It  is  hence  inferred,  that 
equal  weights  or  measures  of  water  of  the  same  temperature  contain 
equal  quantities  of  caloric;  and  the  same  is  found  to  be  true  of  other 
bodies.  But  if  equal  weights,  or  equal  bulks,  of  different  substances 
are  employed,  the  result  will  be  diflerent.  Thus  if  a pint  of  mercury 
at  100®  F.  be  mixed  witliapint  of  water  at  40®,  the  mixture  will  have  a 
temperature  of  60®,  so  that  the  40  degrees  lost  by  the  former  have  heat- 
ed the  latter  by  20  degrees  only;  and  when,  reversing  the  experiment, 
tlie  water  is  at  100®  and  the  mercury  at  40®,  the  mixture  wdll  be  at  80®, 
the  20  degrees  lost  by  the  former  causing  a rise  of  40  degrees  in  the 
iaiter.  'I'lie  fact  is  still  more  strikingly  displayed  by  substituting  equal 
weights  for  measures.  For  instance,  on  mixing  a pound  of  mercury  at 
160®  with  a pound  of  water  at  40®,  a thermometer  placed  in  the  mixture 
will  stand  at  45®;  but  if  the  mercury  be  at  40®  and  the  water  at  160®,  the 


CALORIC. 


43 


mixture  will  have  a temperature  of  155*^.  If  water  at  100*^  be  mixed 
with  an  equal  weight  of  spermaceti  oil  at  40®,  the  mixture  will  be  found 
at  80®;  and  when  the  oil  is  at  100®  and  the  water  at  40®,  the  tempera- 
ture of  the  mixture  will  be  only  60®. 

It  appears  from  the  facts  just  stated,  that  the  same  quantity  of  caloric 
imparts  twice  as  high  a temperature  to  mercury  as  to  an  equal  volume 
of  water;  that  a similar  proportion  is  observed  with  respect  to  equal 
weights  of  spermaceti  oil  and  water;  and  that  the  heat  which  gives  5 
degrees  to  water  will  raise  an  equal  weight  of  mercury  by  115®,  being 
the  ratio  of  1 to  23’*'.  Hence  if  equal  quantities  of  caloric  be  added  to 
equal  weights  of  water,  spermaceti  oil,  and  mercury,  their  temperatures 
in  relation  to  each  other  will  be  expressed  by  the  numbers  1,  2,  and  23; 
or  what  amounts  to  the  same,  in  order  to  increase  the  temperature  of 
equal  weights  of  those  substances  to  the  same  extent,  the  water  will  re- 
quire 23  times  as  much  caloric  as  the  mercury,  and  twice  as  much  as  the 
oil.  The  peculiarity  exemplified  by  these  substances,  and  which  it 
would  be  easy  to  illustrate  by  other  examples,  was  first  noticed  by  Dr. 
Black.  It  is  a law  admitted  to  be  universal,  and  may  be  thus  expressed; 
that  similar  quantities  of  different  bodies  require  unequal  quantities  of 
caloric  to  heat  them  equally.  This  difference  in  bodies  was  expressed 
in  the  language  of  Dr.  Black  by  the  term  capacity  for  caloric,  a word  ap- 
parently suggested  by  the  idea  that  the  heat  present  in  any  substance  is 
contained  in  its  pores,  or  the  spaces  left  between  its  particles,  and  that 
the  quantity  of  heat  is  regulated  by  the  size  of  the  pores.  And,  indeed, 
at  first  view  there  appear  sufficient  grounds  for  this  opinion;  for  it  is  ob- 
served, that  very  compact  bodies  have  the  smallest  capacities  for  caloric, 
and  that  the  capacity  of  the  same  substance  often  increases  as  its  density 
becomes  less.  But,  as  Dr.  Black  himself  pointed  out,  if  this  were  the 
real  cause  of  the  difference,  the  capacity  of  bodies  for  caloric  should  be 
inversely  as  their  densities.  Thus,  since  mercury  is  thirteen  times  and 
a half  denser  than  water,  the  capacity  of  the  latter  for  caloric  ought 
to  be  only  thirteen  times  and  a half  greater  than  the  former,  where- 
as it  is  twenty-three  times  as  great.  Oil  occupies  more  space  than  an 
equal  weight  of  water,  and  yet  the  capacity  of  the  latter  for  caloric  is 
double  that  of  the  former.  The  word  capacity,  therefore,  is  apt  to  ex- 
cite a wrong  notion,  unless  it  is  carefully  borne  in  mind,  that  it  is  mere- 
ly an  expression  of  the  fact  without  allusion  to  its  cause;  and  to  avoid 
the  chance  of  error  from  this  source,  the  term  specific  caloric  has  been 
proposed  as  a substitute  for  it,  and  is  now  very  generally  employed. 

The  singular  fact  of  substances  of  equal  temperature  containing  unequal 
quantities  of  heat  naturally  excites  speculation  about  its  cause,  and  various 
attempts  have  been  made  to  account  for  it.  The  explanation  deduced 
from  the  views  of  Dr.  Black  is  the  following:  He  conceived  that  caloric 
exists  in  bodies  under  two  opposite  conditions:  in  one  it  is  supposed  to  be 
in  a state  of  chemical  combination,  when  it  lays  aside  its  prominent  charac- 
ters, and  remains  as  it  were  concealed,  without  evincing  any  signs  of  its 
presence;  in  the  other,  it  is  free  and  uncombined,  passing  readily  from 
one  substance  to  another,  affecting  the  senses  in  its  passage,  determining 
the  heig'ht  of  the  thermometer,  and  in  a word  giving  rise  to  all  the  phe- 
nomena which  are  attributed  to  this  active  principle. 

Though  it  would  be  easy  to  start  objections  to  this  ingenious  conjec- 
tiire,  it  has  tlie  merit  of  explaining  phenomena  more  satisfactorily  tJian 


* This  proportion,  which  is  given  by  Dr.  Heniy  in  tlie  last  edition  of 
his  Elements  on  the  authority  of  Mr.  Dalton,  is  I believe  not  faJ’from  the 
truth,  and  is  certainly  more  correct  tlian  tliat  of  1 to  28. 


44; 


CALORIC. 


any  view  that  has  been  proposed  in  its  place.  It  is  entirely  consistent 
with  analogy.  For  since  caloric  is  regarded  as  a matenal  substance,  it 
would  be  altogether  anomalous  were  it  not  influenced,  like  other  kinds 
of  matter,  by  chemical  athnity;  and  if  this  be  admitted,  it  ought  certain- 
ly in  combining,  to  lose  some  of  the  properties  by  which  it  is  distin- 
guished in  its  free  state.  According  to  this  view  it  is  intelligible  how 
two  substances,  from  being  in  the  same  condition  with  respect  to  free 
caloric,  may  have  the  same  temperature;  and  yet  that  their  actual  quan- 
tities of  caloric  may  be  very  diff  erent,  in  consequence  cf  one  containing 
more  of  that  principle  in  a combined  or  latent  state  than  the  other.  Rut 
in  admitting  tlie  plausibility  of  this  explanation,  it  is  proper  to  remember 
that  it  is  at  present  entirely  hypothetical;  and  that  the  language  sugges- 
ted by  an  hypothesis  should  not  be  unnecessarily  associated  witli  the 
phenomena  to  which  it  owes  its  origin.  Accordingly,  the  word  sensible 
is  better  than  free  caloric,  and  insensible  preferable  to  combined  or  latent 
caloric;  for  by  such  terms  the  fact  is  equally  well  expressed,  and  philo- 
sopliical  propriety  sti’ictly  preserved.* 


• The  theory  of  latent  heat  of  Dr.  Black,  as  applied  to  the  explana* 
tion  of  tlie  different  specific  heats  of  bodies,  would  seem  in  some  re- 
spects to  be  unpliilosophical.  If  Pictet’s  theory  of  the  equilibrium  of 
caloric  be  admitted,  then  equality  of  temperature  in  any  two  bodies 
merely  means  that  their  caloric  has  no  tendency  to  pass  from  one  to  the 
other,  without  the  idea  having  any  necessary  connection  with  the  absolute 
quantity  of  caloric  contained  in  them.  It  may  be  admitted  as  highly 
probable  that  the  reason  why  different  bodies  assume  to  themselves  un- 
equal quantities  of  heat,  when  this  principle  has  assumed  a state  of  rest, 
is  that  their  affinities  for  caloric  are  different;  yet  it  by  no  means  follows, 
that  the  caloric  in  such  bodies  is  in  two  different  states,  sensible  or  free  ^ 
and  hisensible  or  combined.  If  we  impart  ten  degi^ees  of  heat  to  equal 
weights  of  water  and  oil,  the  water  wiU  have  received  twice  as  much  calo- 
ric as  the  oil.  Here  “the  actual  quantities  of  caloric”  received  are  “ very 
different;”  but  are  we  on  this  account  to  suppose  that  part  of  the  caloric 
received  by  the  water  is  in  an  insensible  or  combined  state  ? It  will  at 
once  be  evident  that  this  cannot  be  the  case;  for  if  the  equal  weights  of 
water  and  oil,  after  being  heated  ten  degrees,  be  allowed  to  cool  equaffy, 
tlie  water  will  lose  twice  as  much  actual  caloric  as  the  oil.  Now  all  the 
caloric  lost  during  the  cooling  becomes  free  caloric;  for  it  is  distributed 
among  surrounding  bodies. 

The  fact  is,  that  the  quantity  of  caloric  gained  or  lost  by  any  number 
of  bodies,  in  being  heated  or  cooled  through  the  same  number  of  de- 
grees, bears  a constant  proportion  to  their  sevei*al  specific  heats.  Hence 
to  maintain  an  equality  of  temperature  among  any  set  of  bodies,  the 
quantity  of  caloric  contained  by  each  must  be  directly  proportional  to 
its  specific  heat.  Whatever  subverts  tliis  relation  wiU  necessarily  change 
tlie  temperatui’C. 

It  sometimes  happens  that  the  loss  or  gain  of  caloric  by  a body  is  exact- 
ly proportional  to  the  change  it  may  undergo  in  specific  heat  or  capacity. 
TIuis,  if  a body  receive  caloric,  and  have,  at  the  same  time,  its  capacity 
])roportionably  increased,  its  temperature  remains  the  same,  though  it 
be  constantly  receiving  caloric;  and  it  is  by  such  cases  as  tliese  tliat  the 
doctrine  of  insensible  or  combined  heat  is  most  plausibly  supported. 
But,  upon  taking  a nearer  view  of  the  subject,  it  will  be  found  that  the 
tempcr.iture  remains  the  same  in  conformity  with  the  principles  laid 
down  in  tliis  note;  for  the  capacity  and  heat  being  simultaneously  and 
proportionably  increased,  the  relation  between  them,  so  tar  from  being 
sultvcrtcdf  is  maintained.  B. 


CALORIC. 


45 


It  is  of  imp  Distance  to  know  the  specific  caloric  of  bodies.  The  most 
convenient  method  of  discovering-  it,  is  by  mixing*  different  substances 
tog-ether  in  the  way  just  described,  and  observing*  the  relative  quantities 
of  caloric  requisite  for  heating*  them  by  the  same  number  of  degrees. 
Thus  the  caloric  required  to  heat  equal  quantities  of  \t7'ater,  spermaceti 
oil,  and  mercury  by  one  degi-ee,  is  in  the  ratio  of  23,  11.5,  and  1,  and  there- 
fore tlieir  capacities  for  caloric  are  expressed  by  those  numbers.  Water 
is  commonly  one  of  the  materials  employed  in  such  experiments,  as  it 
is  customary  to  compare  the  capacity  of  other  bodies  with  that  of  water. 

This  method  was  first  suggested  by  Dr.  Black,  and  was  afterwards 
practised  to  a great  extent  by  Drs.  Crawford  and  Irvine*.  But  the  same 
knowledge  may  be  obtained  by  reversing  the  process, — by  noting  the 
relative  quantities  of  caloric  which  bodies  give  out  in  cooling;  for  if  wa- 
ter requires  23  times  more  caloric  than  mercury  to  raise  its  temperature 
by  one  or  more  degrees,  it  must  also  lose  23  times  as  much  in  cooling. 
The  calorimeter,  invented  and  employed  by  Lavoisier  and  Laplace,  acts 
on  this  principle.  The  apparatus  consists  of  a wire  cage,  suspended  in 
the  centre  of  a metallic  vessel  so  much  larg-er  than  itself,  that  an  interval 
is  left  between  them,  which  is  filled  with  fragments  of  ice.  The  mode 
of  estimating  the  quantity  of  caloric  which  is  emitted  by  a hot  body 
placed  in  the  wire  cage,  depends  upon  the  fact,  that  ice  cannot  be  heat- 
ed beyond  32®  F. ; since  every  particle  of  caloric  which  is  then  supplied 
is  employed  in  liquefying  it,  without  in  the  least  affecting  its  tempera- 
tui-e.  If,  therefore,  a flask  of  boiling  water  is  put  into  the  cage,  it  will 
gradually  cool,  the  ice  will  continue  at  32®,  and  a portion  of  ice-cold 
watter  will  be  formed;  and  the  same  change  will  happen  when  heated 
mercury,  oil,  or  any  other  substance  is  substituted  for  the  hot  water. 
The  sole  difference  wiU  consist  in  the  quantity  of  ice  liquefied,  which 
will  be  propoi-tional  to  tlie  caloric  lost  by  those  bodies  wliile  they  cool; 
so  that  their  capacity  is  determined  merely  by  measuring  the  quantity  of 
water  produced  by  each  of  them.  Tliis  is  done  by  allowing  the  water, 
as  it  forms,  to  run  out  of  the  calorimeter  by  a tube  fixed  in  the  bottom 
of  it,  and  carefully  weighing  the  liquid  which  issues. 

There  is  one  obvious  soui’ce  of  fallacy  in  tliis  mode  of  operating, 
against  which  it  is  necessary  to  provide  a remedy;  namely  the  ice  not  only 
receives  caloric  from  the  substance  in  the  central  cage,  but  must  also  re- 
ceive it  from  the  air  of  the  apartment  in  which  the  experiment  is  con- 
ducted. This  inconvenience  is  avoided  by  surrounding  the  whole  ap- 
paratus by  a larger  metallic  vessel  of  the  same  form  as  the  smaller  one, 
and  of  such  a size  that  a certain  space  is  left  between  them,  which  is  to 
be  filled  with  pounded  ice  or  snow.  No  external  heat  can  now  pene- 
ti-ate  to  the  inner- vessel;  because  all  the  caloric  derived  from  the  apart- 
ment is  absorbed  by  the  outer  one,  and  is  employed,  not  in  elevating  its 
tempei-ature,  but  in  dissolving  the  pounded  ice  within  it. 

Notwithstanding  tliis  precaution,  however,  the  accuracy  of  the  calori- 
meter may  fairly  be  questioned.  For  that  the  results  obtained  by  it  may 
be  correct,  it  is  essential  that  all  the  water  which  is  produced  should 
flow  out  and  be  collected.  But  there  is  reason  to  suspect  that  some  of 
the  water  is  apt  to  freeze  again  before  it  has  had  time  to  escape;  and  if 
tliis  be  true,  as  d priori  is  very  probable,  then  the  information  given  by 
the  calorimeter  must  be  rejected  as  useless. 

The  determination  of  the  specific  heat  of  gaseous  substances  is  a prob- 
lem of  importance,  and  has  accordingly  occupied  the  attention  of  seve- 
ral experimenters  of  great  science  and  practical  skill;  but  the  inquiry  is 


* Crawford  on  Animal  Heat,  and  Irvine’s  Chemical  Easays. 


46 


CALOIUC. 


beset  with  ^ many  dlfTiculties  tliat,  in  spite  of  the  talent  which  lias  been 
devoted  to  it,  oiir  best  results  can  only  be  viewed  as  approximations  re- 
quiring- to  be  con-ected  by  future  research.  13r.  Crawford,  to  whom  we 
are  indebted  for  the  first  elaborate  investig-ation  of  the  subject,  conducted 
his  experiments* in  tlie  following-  manner.  He  obtained  two  copper  ves- 
sels made  as  lig*ht  as  possible,  and  exactly  of  the  same  form,  size,  and 
weight;  exhausted  one  of  them,  and  filled  the  other  witli  the  gas  to  be 
examined.  They  were  next  heated  to  the  same  extent  by  immersion  in 
hot  watei’,  and  tlien  plunged  into  equal  quantities  of  cold  water  of  the 
same  temperature.  Each  flask  heated  the  water;  but  while  the  exliaiist- 
ed  flask  communicated  solely  the  heat  of  the  copper,  the  other  gave  out 
an  equal  quantity  of  caloric  from  the  metal  of  which  it  was  made,  to- 
gether with  that  derived  from  the  gas  in  its  interior.  The  effects  yiro- 
duced  by  the  former  deducted  from  that  of  the  latter  gave  the  heating 
power  of  the  confined  gas,  the  precise  information  wanted.  By  repeat- 
ing the  experiment  with  air  and  different  gases,  their  comparative  heat- 
ing powers,  or  their  specific  heats,  were  ascertained.  But  correct  as  is 
file  leading  principle  on  which  these  experiments  were  founded,  the 
results  are  now  universally  admitted  to  be  very  wide  of  the  truth,  and 
therefore  it  can  answer  no  useful  purpose  to  cite  them.  The  fallacy  is 
attributable  to  the  circumstance  of  the  heat  derived  from  the  containing 
vessel  being  so  great  compared  to  that  emitted  by  the  confined  gas,  that 
the  effect  ascribed  to  the  latter  is  confounded  with,  and  materially  in- 
fluenced by,  the  unavoidable  errors  of  manipulation. 

l^he  same  subject  was  investigated  by  Lavoisier  and  Laplace  by  means 
of  their  calorimeter.  A current  of  gas  was  transmitted  in  a serpentine 
tube  through  boiling  water  in  order  to  be  heated,  and  was  then  made  to 
circulate  within  the  calorimeter  in  a similar  tube  surrounded  with  ice. 
i[ts  temperature  in  entering  and  quitting  the  calorimeter  was  ascertained 
by  thermometers,  and  the  heat  lost  by  each  gas  was  estimated  by  the 
quantity  of  ice  liquefied.  Their  experiments  are  of  course  liable  to  the 
objections  already  made  to  the  use  of  ice;  but  a similar  train  of  experiments, 
not  exposed  to  this  fallacy,  was  conducted  in  the  year  1813  with  extreme 
care  by  MM.  Delaroche  and  Berard.  (An.  de  Chimie,  lxxxv.  and  Annals 
of  Pliil.,  II. ) They  transmitted  known  quantities  of  gas,  heated  to  212^  F., 
in  a uniform  current  through  the  calorimeter;  and,  instead  of  ice,  surround- 
ed the  serpentine  tube  with  water,  the  temperature  of  wliich,  as  well  as  of 
the  gas  at  its  exit,  was  ascertained  during  the  course  of  the  process  by  deli- 
cate thermometers.  By  operating  with  a considerable  quantity  of  gas,  they 
avoided  the  error  into  which  Crawford  fell;  and  the  experiments,  though 
complicated  and  involving  various  squi-ces  of  en-or,  were  conducted  with 
such  skill  and  caution  that  they  inspired  great  confidence,  and  are  still 
admitted  to  he  more  accurate  than  any  which  have  been  made  on  this 
difficult  subject.  Their  results  are  contained  in  the  following  table;  the 
specific  heat  of  the  gases  being  referred  to  atmospheric  air  as  unity  in 
tlie  two  first  columns,  and  to  water  in  tlm  tlihd^ 


CALORIC. 


47 


Names  of  Substances. 

Under  equal 
Volumes. 

Under  equal  Weights. 

Atmospheric  air 

1.0000 

1.0000 

. 0.2669 

Hydrogen  gas 

8.9033 

12.3400  . 

. 3.2936 

Oxygen  gas 

0.9765 

0.8848 

. 0.2361 

Nitrogen  gas 

1.0000 

1.0318 

. 0.2754 

Nitrous  oxide  gas 

1.3503 

0.8878 

. 0.2369 

Olefiant  gas 

1.5530 

1.5763 

. 0.4207 

Carbonic  oxide  gas  . 

1.0340 

1.0805 

. 0.2884 

Carbonic  acid  gas 

1.2583 

0.8280 

. 0.2210 

Water 

, 

. 

. 1.0000 

Aqueous  vapour  . 

• 

. 

. 0.8470 

Some  experiments  performed  by  MM.  Clement  and  Desormes,  and 
published  in  the  year  1819  in  the  Journal  de  Physique,  lxxxix.  320, 
were  confirmatory  of  the  foreg-oing*  results;  and  Mr.  Dalton,  in  the  second 
volume  of  his  Chemical  Philosophy,  pag*e  282,  states  that  he  has  repeated 
the  experiment  of  Delaroche  and  Bei-ard  on  the  specific  heat  of  atmos- 
pheric air,  and  is  convinced  of  their  estimate  being*  very  near  the  truth. 
But  the  accui-acy  of  their  results  has  been  questioned  by  others,  and  some 
of  the  objections  are  by  no  means  deficient  in  force.  One  of  these  was 
stated  by  Mi\  Hay  craft  in  the  Edinburgh  Phil.  Trans,  for  1824,  namely, 
tliat  the  g^es  were  employed  in  a moist  instead  of  a dry  state;  a circum- 
stance wliich  would  doubtless  in  some  measure  modify  the  result : and 
others  have  been  mentioned  by  MM.  De  la  Rive  andMarcet.  {An.de  Ch, 
et  de  Ph.  xxxv.  5.  and  xli.  78. ) For  example,  the  precise  temperature 
of  the  gases  used  in  their  experiments  was  not  ascertained  in  an  unex- 
ceptionable manner;  because  a thermometer  surrounded  by  gaseous  mat- 
ter is  affected,  not  only  by  contact  with  the  gas  itself,  but  likewise  by 
the  radiant  heat  emitted  or  absorbed  by  the  containing  vessel.  It  is  also 
to  be  remarked  that  the  heated  gases,  in  passing  through  the  calorimeter, 
diminished  in  volume  in  proportion  as  they  cooled.  Now  it  is  found  in- 
variably that  whenever  the  bulk  of  a gas  is  diminished,  a certain  portion 
of  insensible  heat  becomes  sensible;  so  that  in  tlie  experiments  of  Dela- 
roche and  Berard  the  heating  influence  of  the  gases  was  a complex  phe- 
nomenon, partly  dependent  on  the  caloric  lost  in  cooling,  and  partly  on 
tliat  developed  by  the  accompanying  diminution  in  volume.  This  last 
source  of  heat  ought  to  have  been  avoided,  and  in  the  experiments  of 
Crawford  it  was  so;  for  the  heated  gases  with  which  he  operated,  being 
confined  in  a close  vessel,  underwent  no  change  of  volume  while  they 
cooled,  though  of  Course  their  elasticity  was  thereby  diminished. 

These  considerations  induced  MM.  De  la  Rive  and  Marcet  to  undertake 
this  difficult  inquiry.  In  their  experiments  the  gases  were  confined  in  a 
tliin  globe  of  glass,  and  the  temperature  was  estimated,  not  by  a ther- 
mometer, but  by  the  elastic  force  communicated  by  the  heat,  according 
to  tlie  law  of  Dalton  and  Gay-Lussac  already  mentioned.  (Page  34. ) 
The  glass  vessel  was  placed  in  the  centre  of  a very  thin  copper  globe, 
the  inner  surface  of  which  was  made  to  i*adiate  freely  by  being  blackened, 
and  the  air  between  it  and  the  glass  globe  was  withdrawn  by  an  air-pump. 
The  whole  apparatus,  being  brought  to  the  temperature  of  68^  F.,  was 
immersed  during  exactly  five  minutes  in  water  kept  steadily  at  86®;  and 
the  heat  imparted  to  the  copper  was  mdlated  from  its  inner  surface,  and 
thus  reached  tlie  g'lass  globe  in  the  centre.  By  always  operating  exactly 
in  the  same  manner,  it  was  conceived  tliat  the  same  volume  of  each  gas 
would  receive  equal  quantities  of  caloric  in  equal  times;  and  that  from 
the  temperature  thus  communicated  to  each,  its  specific  heat  inig'ht  be 


48 


CALORIC. 


infeiTcd.  In  two  sets  of  experiments  thus  conducted,  tlu  y found  dial 
each  g'as  acquired  the  same  elasticity,  or  was  heutc'd  to  the  same  degree, 
ajid  tlience  they  inferred  that  ^ses  in  general,  for  equal  volumes  and 
pressures,  have  the  same  capacity  for  caloric.  'J'hey  also  operated  with 
the  same  gas  at  difierent  densities,  and  concluded  tliat  the  s])eciric  heat 
of  each  gas,  for  equal  volumes,  diminishes  slowly  as  its  density  decreases. 

In  the  All,  de  Ch,  et  de  Ph.  xlt.  113,  M.  Dulong  has  published  some 
critical  remarks  on  these  experiments,  lie  argues,  in  the  first  place, 
that  the  quantity  of  gas  employed  was  so  small,  that  any  effect  arising 
from  a difference  in  specific  heat  could  not  be  appreciated,  lie  con- 
tends, further,  that  the  temperature  acquired  by  a gas  in  such  experi- 
ments is  not  influenced  by  its  specific  caloric  only,  but  in  pait  by  the 
relative  facility  with  which  heat  is  transmitted  through  the  gas.  It  has 
been  already  observed  that  heat  is  conducted  by  gaseous  matter  with  ex- 
treme slowness,  but  is  rapidly  diffused  thi’ough  it  in  consequence  of  tlie 
mobility  of  its  particles.  Now  gases  difier  considerably  under  this  point 
of  view.  Hydi*ogen  acquires  the  temperature  of  a hot  body  placed  in  it 
much  more  rapidly  than  carbonic  acid;  and,  therefore,  were  the  same 
volume  of  these  gases  exposed  for  an  equal  short  period  to  equal  sources 
of  caloric,  the  former  would  acquire  a higher  temperature  simply  from 
its  conveying  heat  more  readily.  The  validity  of  these  strictures  can 
scarcely,  I apprehend,  be  denied.  It  may,  therefore,  be  infeiTed  from 
the  foregoing  observations,  that  the  specific  heats  of  the  gases  are  not  yet 
accurately  known,  and  that  the  numbers  stated  by  Delaroche  and  B(irard 
are  probably  the  best  approximations  liitherto  published. 

The  general  facts  hitherto  determined  concerning  the  specific  heat  of 
bodies  may  be  aiTanged  under  the  four  following  heads: 

1.  Every  substance  has  a specific  heat  peculiar  to  itself;  whence  it 
follows,  that  a change  of  composition  will  be  attended  by  a change  of 
capacity  for  caloric. 

2.  The  specific  heat  of  a body  varies  with  its  form.  A solid  has  a less 
capacity  for  caloi'ic  than  the  same  substance  when  in  the  state  of  a liquid; 
the  specific  heat  of  water,  for  instance,  being  9 in  the  solid  state,  and  10 
in  the  liquid.  Whether  the  same  weight  of  a body  has  a gi’eater  specific 
heat  in  tlie  solid  or  liquid  form  than  in  that  of  vapour,  is  a circumstance 
not  yet  decided.  The  onl}^  experiments  in  point  are  those  of  Crawford, 
and  Delaroche  and  Berard.  The  former  estimated  the  specific  heat  of 
vapour  at  1.55,  and  the  French  philosophers  at  0.847,  compared  to  that 
of  water  as  unity;  nor  is  it  possible  to  say  which  of  these  widely  discor- 
dant results  is  nearer  the  tmth,  as  neither  can  be  relied  on  with  confi- 
dence. * 

3.  Of  the  specific  heat  of  equal  volumes  of  the  same  gas  at  different 


* The  question  here  referred  to  may  not  be  decided  experimentally 
with  rigid  accuracy,  and  yet  it  is  decided  with  much  plausibility  by  the 
admitted  doctrine  of  the  formation  of  vapours  from  liquids,  and  the  in- 
creased specific  heat  of  vapours  by  rarefaction.  Dr.  Turner  admits  that 
the  specific  heat  of  water  in  the  liquid  state  is  greater  than  in  the  state 
of  ice.  Is  it  not  ])roba])le  then  that  the  specific  heat  of  steam  is  greater 
than  that  of  an  equal  weight  of  water?  Conceding  that  the  increased 
ca[)acity.  that  takes  place  as  water  changes  into  steam,  is  not  conclusive 
.as  to  the  increased  specific  heat  of  tlie  steam  itself  after  having'  been 
formed;  yet  as  a separation  of  the  ])articles  of  steam  by  rarefaction  is  admit- 
ted to  increase  its  specific  heat,  a fortiori  the  gi'cater  separation  of  the 
aijueons  jiarticles  in  [lassing  from  water  to  steam  mig'ht  be  su])])osed  to 
be  attended  with  the  same  result.  B. 


CALORIC. 


49 


densities  nothing  certain  has  been  established;  for  the  experiments  of 
MM.  De  la  Rive  and  Marcet,  above  described,  have  led  to  no  decisive 
'conclusion.  But  all  admit  that  the  specific  heat  of  equal  weights  of  the 
same  gas  increases  as  the  density  decreases.  Thus,  to  maintain  the  tem- 
perature of  100  grains  of  atmospheric  air  at  60^,  or  any  other  tempera- 
ture, more  heat  will  be  required  when  it  occupies  the  room  of  100  cubic 
inches  than  if  it  were  contained  in  half  that  space;  and  still  more  heat  will 
be  requisite  when  its  volume  is  augmented  to  200  cubic  inches.  The 
exact  rate  of  increase  is  unknown:  but  according  to  Delaroche  and  Berard 
the  ratio  is  less  rapid  than  the  diminution  in  density;  that  is,  the  specific 
caloric  of  any  gas  being  1,  it  is  not  2,  but  between  one  and  two,  when 
its  volume  is  doubled.  This  fact  being  established  in  the  case  of  elastic 
fluids,  it  may  reasonably  be  asked,  whether  the  same  law  does  not  ex- 
tend to  liquids  and  solids?  whether  water,  for  instance,  at  32 possesses 
the  same  specific  caloric  as  when  dilated  by  a high  temperature?  Drs. 
Crawford  and  Irving  contended  that  it  is  permanent  or  nearly  so,  affirm- 
ing that  solids  and  liquids  possess  the  same  specific  caloric  at  all  tem- 
peratures, so  long  as  they  suffer  no  change  of  form  or  composition.  Mr. 
Dalton,  on  the  contrary,  (Chemical  Philosophy,  parti,  p.  50),  endeavours 
to  show  that  the  specific  caloric  of  such  bodies  is  greater  in  high  than  in 
low  temperatures;  and  Petit  and  Dulong,  in  the  essay  already  quoted, 
have  proved  it  experimentally  with  respect  to  several  of  them.  Thus 
the  mean  capacity  of  iron  between 


0^  Cent,  and 
0^ 

O'" 

0^ 


100"^  Cent.  is  0.1098 

200^  . 0.1150 

300®  . 0.1218 

350?  . 0.1255 


and  the  same  is  true  of  the  substances  contained  in  the  following  table. 

Mean  Capacity  Mean  Capacity 

between  0®  and  100?  C.  between  0®  and  300®  C. 


Mercury 

0.0330 

0.0350 

Zinc 

0.0927 

0.1015 

Antimony  . 

0.0507 

0.0549 

Silver 

0.0557 

0.0611 

Copper 

0.0949 

0.1013 

Platinum 

0.0335 

0.0355 

Glass 

0.1770 

0.1900 

It  is  difficult  to  determine  whether  the  increased  specific  caloric  ob- 
served in  solids  and  liquids  at  high  temperatoes  is  owing  to  the  accu- 
mulation of  heat  within  them,  or  to  their  dilatation.  It  is  ascribed  in 
general  to  the  latter,  and  I believe  correctly;  because  the  expansion  and 
contraction  of  gases  by  change  of  pressure,  without  the  aid  of  heat,  is 
attended  with  coire spending  changes  of  capacity  for  caloric. 

4.  Change  of  capacity  for  caloric  always  occasions  a change  of  tem- 
perature. Increase  in  the  former  is  attended  by  diminution  of  the  latter, 
and  decrease  in  the  former  by  increase  of  the  latter.  Thus  when  air, 
confined  within  a flaccid  bladder,  is  suddenly  dilated  by  means  of  the 
air-pump,  a thermometer  placed  in  it  will  indicate  the  production  of  cold. 
On  the  contrary,  when  air  is  compressed,  the  corresponding  diminution 
of  its  specific  caloric  gives  rise  to  increase  of  temperature;  nay,  so  much 
heat  is  evolved  when  the  compression  is  sudden  and  forcible,  that  tinder 
may  be  kindled  by  it.  The  explanation  of  these  facts  is  obvious.  In 
the  first  case,  a quantity  of  caloric  becomes  insensible,  which  was  pre- 
viously in  a sensible  state;  in  the  second,  caloric  is  evolved,  which  was 
previously  latent. 


5 


50 


CALORIC. 


From  some  experiments,  the  result  of  which  is  given  in  the  10th  volume 
of  the  Ann.  de  Ch.  et  de  Ph.,  MM.  Diilong  and  Petit  have  inferred  tliat 
the  atoms  of  simple  substances  have  the  same  capacity  for  caloric.  The 
following*  table  is  taken  from  their  essay.  (Page  403.) 


Specijic  Caloric. 

Relative  Weights 
of  Atoms, 

Products  of  the  Weight 
of  each  Atom  hy  the 

corresponding  Capacity. 

Bismuth 

0.0288 

13.30 

0.3830 

Lead 

0.0293 

12.95 

0.3794 

Gold 

0.0298 

12.43 

0.3704 

Platinum 

0.0335 

11.16 

0.3740 

Tin 

0.0514 

7.35 

0.3779 

Silver 

0.0557 

6.75 

0.3759 

Zinc 

0.0927 

4.03 

0.3736 

Tellurium 

0.0912 

4.03 

0.3675 

Copper 

0.0949 

3.957 

0.3755 

Nickel 

0.1035 

3.69 

0.3819 

Iron 

0.1100 

3.392 

0.3731 

Cobalt 

0.1498 

2.46 

0.3685 

Sulphur 

0.1880 

2.011 

0.3780* 

In  the  new  part  of  his  Chemical  Philosophy,  page  293,  Mr.  Dalton 
has  made  some  strictures  in  reference  to  this  table,  tending  to  show  that 
tlie  opinion  of  Dulong  and  Petit  cannot  be  correct,  and  that  it  stands  in 
opposition  to  their  own  facts.  Mr.  Dalton  argues  that  the  product  of 
the  weight  of  an  atom  by  the  corresponding  capacity  for  caloric,  is  not 
a constant  quantity;  because  the  capacity  of  the  same  substance  varies 
with  change  of  form,  or  even,  accor^ng  to  their  own  experiments,  with 
variation  of  temperature,  without  change  of  form.  To  the  latter  part  of 
the  criticism  Dulong  and  Petit  are  certainly  exposed;  but  they  have  an- 
ticipated the  former  by  remarking,  that  the  law  is  not  affected  by  change 
of  form,  provided  the  substances  compared  are  taken  in  the  same  state. 
Whether  this  position  be  correct  or  not,  remains  to  be  proved. 

On  Liquefaction. 

All  bodies,  hitherto  known,  are  either  solid,  liquid,  or  gaseous;  and  the 
form  they  assume  depends  on  the  relative  intensity  of  cohesion  and  re- 
pulsion. Should  the  repulsive  force  be  comparatively  feeble,  the  par- 
ticles will  adhei-e  so  firmly  together,  that  they  cannot  move  freely  upon 
one  another,  thus  constituting  a solid.  If  cohesion  is  so  far  counter- 
acted by  repulsion,  that  the  particles  move  on  each  other  freely,  a li- 
quid is  formed.  And  should  the  cohesive  attraction  be  entirely  over- 
come, so  that  the  particles  not  only  move  freely  on  each  otlier,  but  sepa- 
I’ate  from  one  another  to  an  almost  indefinite  extent,  unless  restrained 
by  external  pressure,  an  aeriform  substance  will  be  produced. 

Now  the  property  of  repulsion  is  manifestly  owing  to  caloric;  and  as 
it  is  easy  within  certain  limits  to  increase  or  diminish  the  quantity  of  this 
principle  in  any  substance,  it  follows  that  the  form  of  bodies  may  be 


* If  the  atomic  weiglits  contained  in  this  table  were  corrected  according 
to  the  latest  determinations,  the  coincidences  between  the  specific  heats 
of  tlie  atoms  would  be  far  less  striking.  Sec  some  interesting  stnetures 
on  tills  table  by  Professor  A.  1).  Bache  of  the  University  of  Pennsylvania, 
contained  in  the  Journal  of  the  Academy  of  Natund  Sciences  of  Philadel- 
phia, for  January  1829.  B. 


CALORIC. 


51 


made  to  vaiy  at  pleasure : that  is,  by  heat  sufficiently  intense  eveiy  solid 
may  be  converted  into  a fluid,  and  every  fluid  into  vapour.  This  infer- 
ence is  so  far  justified  by  experience,  that  it  may  safely  be  considered  as 
a g’eneral  law.  The  converse  ought  also  to  be  true;  and,  accordingly, 
several  of  the  gases  have  already  been  condensed  by  means  of  pressure 
into  hquids,  and  liquids  have  been  sohdified  by  cold.  The  temperature  at 
wliich  liquefaction  takes  place  is  called  the  melting  point,  or  point  of  fu- 
sion; and  that  at  which  liquids  sohdify,  their  point  of  congelation.  Both 
tliese  points  are  different  for  different  substances,  but  uniformly  the  same, 
under  similar  circumstances,  in  the  same  body. 

The  most  important  circumstance  relative  to  liquefaction  is  the  dis- 
covery of  Dr.  Black,  that  a large  quantity  of  caloric  disappears,  or  be- 
comes insensible  to  the  thermometer,  during  the  process.  If  a pound 
of  water  at  32®  be  mixed  with  a pound  of  water  at  172®,  the  temperature 
of  the  mixture  will  be  intermediate  between  them,  or  102®.  But  if  a 
pound  of  water  at  172®,  be  added  to  a pound  of  ice  at  32^,  the  ice  will 
quickly  dissolve,  and  on  placing  a thermometer  in  the  mixture,  it  will 
be  found  to  stand,  not  at  102®,  but  at  32®.  In  this  experiment,  the 
pound  of  hot  water,  which  was  originally  at  172®,  actually  loses  140  de- 
gi*ees  of  caloric,  all  of  which  entei^ed  into  the  ice,  and  caused  its  lique- 
faction, but  did  not  affect  its  temperature;  and  it  follows,  therefore,  that 
a quantity  of  caloric  becomes  insensible  during  the  melting  of  ice  sufficient 
to  raise  the  temperature  of  an  equal  weight  of  water  140  degrees  of  Fah- 
renheit. This  explains  the  well  known  fact,  on  which  the  graduation  of 
the  thermometer  depends, — that  the  temperature  of  melting  ice  or  snow 
never  exceeds  32?  F.  All  the  caloric  wliich  is  added  becomes  insensible, 
till  the  hquefaction  is  complete. 

The  loss  of  sensible  caloric  which  attends  liquefaction  seems  essen- 
tially necessary  to  the  change,  and  for  that  reason  is  frequently  called  the 
caloric  of  fluidity.  The  actual  quantity  of  caloric  required  for  this  pur- 
pose varies  with  the  substance,  as  is  proved  by  the  following  results  ob- 
tained by  Irvine.  The  degrees  indicate  the  extent  to  which  an  equal 
weight  of  each  material  may  be  heated  by  the  caloric  of  fluidity  which  is 
pi’oper  to  it. 


Sulphur 

Spermaceti 

Lead 

Bees-wax 

Zinc 

Tin  . 

Bismuth  . 


Caloric  of  Fluidity. 
143.68?  F. 
145® 

162^ 

175® 

493® 

500® 

550® 


As  so  much  heat  disappears  during  hquefaction,  it  follows  that  caloric 
must  be  evolved  when  a liquid  passes  into  a solid.  This  may  easily  be 
proved.  The  temperature  of  water  in  the  act  of  freezing  never  falls  be- 
low 32®  F.  though  it  be  exposed  to  an  iatmosphere  in  wliich  the  ther- 
mometer is  at  zero.  It  is  obvious  that  the  water  can  preserve  its  tem- 
perature in  a medium  so  much  colder  than  itself,  only  by  the  caloric 
which  it  loses  being  instantly  supplied;  and  it  is  no  less  clear  that  the 
only  source  of  supply  is  the  caloric  of  fluidity.  Further,  if  pure  recently 
boiled  water  be  cooled  veiy  slowly,  and  kept  very  tranquil,  its  tempera- 
ture may  be  lowered  to  21?  F.  without  any  ice  being  formed;  but  the 
least  motion  causes  it  to  congeal  suddenly,  and  in  doing  so  its  tempem- 
ture  rises  to  32®  F.  * 


Sir  Ch.  Blagden,  in  Philos.  Trans,  for  1788. 


52 


CALORIC. 


• yt 


The  explanation  which  Dr.  Black  g*ave  of  these  phenomena  constitutes 
what  is  called  his  doctrine  of  latent  lieat^  which  was  partially  explained  on 
a former  occasion.  (Pag*e  43.)  lie  conceived  that  caloric  in  causing 
fluidity  loses  its  property  of  acting  on  the  thermometer  in  consequence 
of  combining  chemically  with  the  solid  substance,  and  that  liquefaction 
results,  because  the  compound  so  formed  does  not  possess  tliat  degree  of 
cohesive  attraction  on  wliich  solidity  depends.  When  allquid  is  cooled 
to  a certain  point,  it  parts  with  its  caloric  of  fluidity,  heat  is  set  free  or 
becomes  sensible,  and  the  cohesion  natural  to  the  solid  is  restored.  The 
same  mode  of  reasoning  was  applied  by  Dr.  Black  to  the  conversion  of 
liquids  into  vapours,  a change  during  which  a large  quantity  of  caloric 
disappears. 

A different  explanation  of  these  phenomena  was  proposed  by  Dr.  Irvine. 
Observing  that  a solid  has  a less  capacity  for  caloric  than  the  same  sub- 
stance when  in  a liquid  state,  he  argued  that  this  circumstance  alone  ac- 
counts for  caloric  becoming  insensible  during  liquefaction.  . For  since 
the  capacity  of  ice  and  water  for  caloric,  or  in  other  words  the  quantity 
of  heat  required  to  raise  their  temperature  by  the  same  number  of  degrees, 
was  found  to  be  as  9 to  10,  Dr.  Bvine  inferred  that  water  must  contain 
one-ninth  more  caloric  than  ice  of  the  same  temperature;  and  that  as  this 
difference  must  be  supplied  to  the  ice  when  it  is  converted  into  water, 
tliis  change  must  necessarily  be  accompanied  with  the  disappearance  of 
caloric.  Dr.  Irvine  applied  the  same  argument  to  the  liquefaction  of  all 
solids,  and  likewise  to  account  for  the  caloric  which  is  rendered  insensi- 
ble during  the  foi'mation  of  vapour. 

Two  objections  may  properly  be  urged  against  the  opinion  of  Dr.  Irvine. 
In  the  first  place,  no  adequate  reason  is  assigned  for  the  liquefaction.  It 
accounts  for  the  disappearance  of  caloric  which  accompanies  liquefac- 
tion, but  does  not  explain  why  the  body  becomes  liquid;  whereas  the 
hypothesis  of  Dr.  Black  affords  an  explanation  both  of  the  change  itself, 
and  of  the  phenomena  that  attend  it.  But  the  second  objection  is  stiU 
more  conclusive.  Dr.  Irvine  argued  on  the  belief  that  a liquid  has  in 
every  case  a greater  capacity  for  caloric  than  when  in  the  solid  state;  and 
though  this  point  has  not  been  demonstrated  in  a manner  entirely  decisive, 
yet  from  the  experiments  hitherto  made,  it  appears  that  liquids  in  general 
have  a greater  specific  caloric  than  solids,  and  that  therefore  Dr.  Irvine’s 
assumption  is  probably  coiTect.  In  like  manner  he  believed  vapours  to 
have  a gi'eater  capacity  for  caloric  than  the  liquids  that  yield  them,  and 
his  opinion  was  supported  by  the  experiments  of  Crawford  on  the  specific 
caloric  of  water  and  watery  vapour.  But  no  reliance  whatever  can  be 
placed  on  the  researches  of  Dr.  Crawford  on  this  subject;  not  only  be- 
cause his  result  is  so  different  from  that  obtained  by  Delaroche  and 
Berard,  but  because  all  his  other  experiments  on  the  specific  caloric  of 
elastic  fluids  are  decidedly  erroneous.  (Page  48.)  Indeed  from  the  fact 
of  most  gases  leaving  a less  specific  heat  than  liquids,  it  is  probable  that 
the  capacity  of  elastic  fluids  in  general  for  caloric  is  inferior  to  that  of  the 
hquids  from  wliich  they  are  derived.*  Tlie  disappearance  of  caloric 
daring  va])()rization  is  therefore  not  explicable  on  the  views  of  Irvine:  it 
is  necessary  to  employ  the  theory  of  Dr.  Black  to  account  for  that  change, 
and  therefore  the  same  doctrine  should  be  applied  to  the  analogous  phe- 
nomenon of  liquefaction. 

In  speculating  on  the  cause  of  the  specific  caloric  of  bodies  at  page 
2,  1 had  recourse  to  the  doctrine  of  latent  or  combined  caloric.  Dr. 


See  note  page  48,  I’clating  to  tliis  point,  B. 


% 


CALORIC. 


53 


Black  restricted  tlie  use  of  tliis  hypothesis  to  explain  the  phenomena  of 
liquefaction  and  vaporization;  but  I apprehend  it  may  be  applied  without 
impropriety  to  all  cases  where  caloric  passes  from  a sensible  to  an  insen- 
sible state.  That  tliis  may  happen  when  caloric  enters  a body,  without 
change  of  form,  is  easily  demonstrated.  Thus,  in  order  to  raise  an  equal 
weight  of  water  and  mercury  by  the  same  number  of  degi’ees,  it  is  neces- 
sary to  add  23  times  as  much  heat  to  the  water  as  to  the  mercury;  a fact 
which  proves  that  a quantity  of  caloric  becomes  insensible  to  the  ther- 
mometer when  the  temperature  of  water  is  raised  by  one  degi’ee,  just  as 
happens  when  ice  is  converted  into  water,  or  water  into  vapour.*  The 
phenomena  are  in  this  point  of  view  identical;  and,  therefore,  the  same 
mode  of  reasoning  by  wliich  one  of  them  is  explained,  may  be  employed 
to  account  for  the  other. 

The  disappearance  of  sensible  caloric  in  liquefaction  is  the  basis  of 
many  artificial  processes  for  producing  cold.  All  of  them  are  conducted 
on  the  principle  of  liquefying  solid  substances  without  the  aid  of  heat. 
For  the  caloric  of  fluidity  being  then  derived  chiefly  from  that  which  had 
previously  existed  within  the  solid  itself  in  a sensible  state,  the  tempera- 
ture necessarily  falls.  The  degi’ee  of  cold  thus  pi’odiiced  depends  upon 
the  quantity  of  caloric  wliicji  disappears,  and  this  again  is  dependent  on 
the  quantity  of  solid  liquefied,  and  the  rapidity  of  liquefaction. 

The  most  common  method  of  producing  cold  is  by  mixing  together 
equal  parts  of  snow  and  salt.  The  salt  causes  the  snow  to  melt  by  rea- 
son of  its  affinity  for  water,  and  the  water  dissolves  the  salt,  so  that  both 
of  them  become  liquid.  The  cold  thus  generated  is  32  degrees  below 
the  temperature  of  freezing  water;  that  is,  a thermometer  placed  in  the 
mixture  woidd  stand  at  zero.  This  is  the  way  originally  proposed  by 
Falirenheit  for  determining  the  commencement  of  his  scale. 

Any  other  substances  which  have  a strong  affinity  for  water  ma}^  be 
substituted  for  the  salt;  and  those  have  the  gi’eatest  effect  in  producing* 
cold  whose  affinity  for  that  liquid  is  greatest,  and  which  consequently 
produce  the  most  rapid  liquefaction.  The  ciy^stallized  muriate  of  lime, 
proposed  by  Lowitz,  is  by  far  the  most  convenient  in  practice.  This  salt 
may  be  made  by  dissolving  marble  in  muriatic  acid.  The  solution  should 
be  concentrated  by  evaporation,  till  upon  letting  a drop  of  it  fall  upon 
a cold  saucer  it  becomes  a solid  mass.  It  should  then  be  withdrawn 
fi*om  the  fire,  and  when  cold  be  speedily  reduced  to  a fine  powder. 
From  its  extreme  deliquescence  it  must  be  preserved  in  welhstopped  ves- 
sels. The  following  table,  from  Mr.  Walker’s  paper  in  the  Philosophic 
cal  Transactions  for  1801,  contains  the  best  proportions  for  producing 
intense  cold. 


• See  note,  page  44,  where  this  view  of  the  subject  is  controverted.  IL 


5* 


54 


CALORIC. 


Frigorijic  Mixtures  with  Snow* 


MIXTURES.  Parts 

by  weight. 

Muriate  of  Soda  1 

Snow  2 

<1; 

rhermometer  sinks 

^ to  — 5® 

Degree  of  Cold 
produced^ 

Muriate  of  Soda 

2 

Muriate  of  Ammonia 

1 

(.1 

to  — 12° 

Snow 

5 

<u 

o. 

Muriate  of  Soda 

10 

S 

Muriate  of  Ammonia 

5 

Nitrate  of  Potassa 

5 

c 

' to  — 18° 

Snow 

24 

c3 

Muriate  of  Soda 

5 

O 

Nitrate  of  Ammonia 

5 

o 

CM 

1 

o 

Snow 

12 

Diluted  Sulphuric  Acidf 
Snow 

2 

o 

O 

from 

+ 32°  to  — 23° 

55  degrees. 

Concentrated  Muriatic  Acid  5 

Snow  8 

from  + 32°  to  — 27° 

59 

Concentrated  Nitrous  Acid  4 

Snow  7 

from  + 32°  to  — 30° 

62 

Muriate  of  Lime  5 

Snow  4 

from  + 32°  to  — 40° 

72 

Crystallized  Muriate  of  Lime  3 

Snow  2 

from  -[-  32°  to 50° 

82 

Fused  Potassa  4| 

Snow  3] 

1 from  + 32°  to  — 51°  I 

83 

But  freezing  mixtures  may  be  made  by  the  rapid  solution  of  salts, 
without  the  use  of  snow  or  ice;  and  the  following  table,  taken  from 
Walker’s  Essay  in  the  Philosophical  Transactions  for  1795,  includes 
the  most  important  of  them.  The  salts  must  be  finely  powdered  and 
dry. 


* The  snow  should  be  freshly  fallen,  dry,  and  uncompressed.  If 
snow  cannot  be  had,  finely  pounded  ice  may  be  substituted  for  it. 

f Made  of  strong  acid,  diluted  with  half  its  weight  of  snow  or  dis- 
tilled water. 


CALORIC. 


55 


MIXTURES.  Parts 

by  weight. 

Muriate  of  Ammonia  5 

Nitrate  of  Potassa  5 

Water  16 

Temperature  falls 

from  + 50°  to  + 10° 

Degree  of  Cold 
produced, 

40  degrees. 

Muriate  of  Ammonia  5 

Nitrate  of  Potassa  5 

Sulphate  of  Soda  8 

Water  16 

from  -|-  50?  to  -f-  4° 

46 

Nitrate  of  Ammonia  1 

Water  1 

from  -f-  50°  to  -[-  4° 

46 

Nitrate  of  Ammonia  1 

Carbonate  of  Soda  1 

Water  1 

from  -[-  50°  to  — 7° 

57 

Sulphate  of  Soda  3 

Diluted  Nitrous  Acl  2 

from + 50°  to— 3° 

53 

Sulphate  of  Soda  6 

Muriate  of  Ammonia  4 

Nitrate  of  Potassa  2 

Diluted  Nitrous  Acid  4 

from  -j-  50°  to  — 10° 

60 

Sulphate  of  Soda  6 

Nitrate  of  Ammonia  5 

Diluted  Nitrous  Acid  4 

from  -f-  50°  to  — 14° 

64 

Phosphate  of  Soda  9 

Diluted  Nitrous  Acid  4 

from  + 50°  to  — 12° 

62 

Phosphate  of  Soda  9 

Nitrate  of  Ammonia  6 

Diluted  Nitrous  Acid  4 

from  -f  50°  to  — 21° 

71 

Sulphate  of  Soda  8 

Muriatic  Acid  5 

from  + 50°  to  0° 

50 

Sulphate  of  Soda  5 

Diluted  Sulphuric  Acidf  4 

from  + 50°  to  4-  3° 

47 

These  artificial  processes  for  generating  cold  are  much  more  effec- 
tual when  the  materials  are  previously  cooled  by  immersion. in  other 
frigorific  mixtures.  One  would  at  first  suppose  that  an  unlimited  de- 
gree of  cold  may  be  thus  produced;  but  it  is  found  that  when  the  dif- 
ference between  the  mixture  and  the  air  becomes  very  great,  caloric  is 
so  rapidly  communicated  from  one  to  the  other,  as  to  limit  the  reduc- 
tion to  a certain  point.  The  greatest  cold  produced  by  Mr.  Walker  did 
not  exceed  100  degrees  below  the  zero  of  Fahrenheit. 

Though  it  is  unlikely  that  we  shall  ever  succeed  in  depriving  any 
substance  of  all  its  caloric,  it  is  presumed  that  bodies  do  contain  a certain 
definite  quantity  of  this  principle,  and  various  attempts  have  been  made 
to  calculate  its  amount.  The  mode  of  conducting  such  a calculation  may 
be  shown  by  the  process  of  Dr.  Irvine.  That  ingenious  chemist  pro- 
ceeded on  the  assumption,  that  the  actual  quantity  of  caloric  in  bodies 
is  proportioned  to  their  capacity,  and  that  the  capacity  remains  the  same 
at  all  temperatures,  provided  no  change  of  form  takes  place.  Thus,  as 


* Composed  of  fuming  nitrous  acid,  two  parts  in  weight,  and  one  of 
water;  the  mixture  being  allowed  to  cool  before  being  used. 

f Composed  of  equal  weights  of  strong  acid  and  water,  being  allowed 
to  cool  before  use. 


56 


CALOKTC. 


the  capacity  of  ice  is  to  that  of  water  as  9 to  10,  it  follows,  according'  to 
the  hypothesis,  tliat  water  at  3'2®  must  lose  1-lOtli  of  its  caloric  to  he 
converted  into  ice.*  Now  Dr.  Black  ascertained  that  this  tenth,  which 
is  the  caloric  of  fluidity,  is  ecpial  to  140  deg'recs;  whence  it  was  infer- 
red that  water  at  32^  contains  10  times  140,  or  1400  degrees  of  caloric. 

To  be  satisfied  that  such  calculations  cannot  be  trusted,  it  is  sufficient  to 
know,  that  the  estimates  made  by  different  chemists  respecting  the  abso- 
lute quantity  of  caloric  in  water  vary  from  900  to  nearly  8000  degrees. -(• 
Besides,  did  even  the  estimates  agree  with  each  other,  the  principle  of 
the  calculation  would  still  be  unsatisfactory;  for,  in  the  first  place,  there 
is  no  proof  that  the  quantity  of  heat  in  bodies  is  in  the  ratio  of  their 
capacities;  and,  secondly,  the  assumption  that  the  capacity  of  a body 
for  caloric  is  the  same  at  all  temperatures,  so  long  as  it  does  not  expe- 
rience a change  of  form,  has  been  proved  to  be  erroneous  by  the  expe- 
riments of  Dulong  and  Petit. 

Vaporization, 

Aeriform  substances  are  commonly  divided  into  vapours  and  gases. 
The  character  of  the  former  is,  that  they  may  be  readily  converted  into 
liquids  or  solids,  either  by  a moderate  increase  of  pressure,  the  tempe- 
rature at  which  they  were  formed  remaining  the  same,  or  by  a mode- 
rate diminution  of  that  temperature,  without  change  of  pressure.  Gases, 
on  the  contrary,  retain  their  elastic  state  more  obstinately;  they  are  al- 
ways gaseous  at  common  temperatures,  and,  with  one  or  two  excep- 
tions, cannot  be  made  to  change  their  form,  unless  by  being  subjected 
to  much  greater  pressure  than  they  are  naturally  exposed  to.  Several 
of  them,  indeed,  have  hitherto  resisted  every  effort  to  compress  them 
into  liquids.  The  only  difference  between  gases  and  vapours  is  in  the 
relative  forces  with  which  they  resist  condensation. 

Caloric  appears  to  be  the  cause  of  vaporization,  as  well  as  of  lique- 
faction, and  it  is  a general  opinion  that  a sufficiently  intense  heat  would 
convert  every  liquid  and  solid  into  vapour.  A considerable  number  of 
bodies,  however,  resist  the  strongest  heat  of  our  furnaces  without  va- 
porizing. These  are  said  to  be  fixed  in  the  fire:  those  which,  under 
the  same  circumstances,  are  converted  into  vapour,  are  called  volatile. 

The  disposition  of  various  substances  to  yield  vapour  is  very  different; 
and  the  difference  depends  doubtless  on  the  relative  power  of  cohesion 
with  which  they  are  endowed.  Fluids  are,  in  general,  more  easily  va- 
porized than  solids,  as  would  be  expected  from  the  weaker  cohesion  of 
the  former.  Some  solids,  such  as  arsenic  and  sal  ammoniac,  pass  at  once 
into  vapour  without  being  liquefied;  but  most  of  them  become  liquid 
before  assuming*  the  elastic  condition. 

Vapours  occupy  more  space  than  the  substances  from  which  they 
were  produced.  According  to  the  experiments  of  Gay-Lussac,  water, 
at  its  point  of  greatest  density,  in  passing  into  vapour,  expands  to  1696 
times  its  volume,  alcohol  to  659  times,  and  ether  to  443  times,  each  va- 
pour being  at  a temperature  of  212®  F.,  and  under  a pressure  of  29.92 
inches  of  mercury.  This  shows  that  vapours  differ  in  density.  Watery 
vapour  is  lighter  than  air  at  the  same  temperature  and  pressure,  in  the 


* A slight  inaccuracy  existed  in  the  author’s  text  in  this  place,  which 
I have  taken  the  liberty  to  coi-rect.  Another  inaccuracy  relating  to  the 
same  subject  was  corrected  in  the  account  of  Dr.  Irvine’s  views,  (page 
52)  where  in  the  original  it  was  stated  that  water  contained  ien  ihnct 
more  caloric  than  ice  of  the  same  temperature.”  B. 
f Dalton’s  New  System  of  Cliemical  Philosophy, 


CALORIC. 


57 


proportion  of  1000  to  1604;  or  the  density  of  air  being*  1000,  that  of 
watery  vapour  is  623.  The  vapour  of  alcohol,  on  the  contrary,  is  half 
as  heavy  again  as  air;  and  that  of  ether  is  more  than  twice  and  a half  as 
heavy.  As  alcohol  boils  at  a lower  temperature  than  water,  and  ether 
than  alcohol,  it  was  conceived  that  the  density  of  vapours  might  be  in 
the  direct  ratio  of  the  volatility  of  the  liquids  which  produced  them. 
But  Gay-Lussac  has  shown  that  this  law  does  not  hold  generally;  for 
the  bisulphuret  of  carbon  boils  at  a higher  temperature  than  ether,  and 
nevertheless  it  yields  a heavier  vapour. 

The  dilatation  of  vapours  by  heat  was  found  by  Gay-Lussac  to  follow 
the  same  law  as  gases;  that  is,  for  every  degree  of  Fahrenheit,  they  in- 
crease by  l-480th  of  the  volume  they  occupied  at  32^.  But  the  law 
does  not  hold  unless  the  quantity  of  vapour  continues  the  same.  If  the 
increase  of  temperature  cause  a fresh  portion  of  vapour  to  rise,  then 
the  expansion  will  be  greater  than  l-480th  for  each  degree;  because 
the  heat  not  only  dilates  the  vapour  previously  existing  to  the  same  ex- 
tent as  if  it  were  a real  gas,  but  augments  its  bulk  by  adding  a fresh 
quantity  of  vapour.  The  contraction  of  a vapour  on  cooling  will  like- 
wise deviate  from  the  above  law,  whenever  the  cold  converts  any  of  it 
into  a liquid;  an  effect  which  must  happen,  if  the  space  had  originally 
contained  its  maximum  of  vapour.  Thus  aqueous  vapour  at  32^  sup- 
ports a column  of  only  0.2  of  an  inch,  while  at  212^  its  elasticity  is  equal 
to  a pressure  of  30  inches  of  mercury.  Hence  the  elastic  force  or  ex- 
pansion of  watery  vapour  between  32®  and  212®,  supposing  the  space 
to  be  in  a state  of  saturation,  is  as  1 to  150. 

Vaporization  is  conveniently  studied  under  two  heads, — Ebullition 
and  Evaporation,  In  the  first,  the  production  of  vapour  is  so  rapid  that 
its  escape  gives  rise  to  a visible  commotion  in  the  liquid:  in  the  second, 
it  passes  off  quietly  and  insensibly. 

Ebullition. 

The  temperature  at  which  vapour  rises  with  sufficient  freedom  for 
causing  the  phenomena  of  ebullition,  is  i\iQ  boiling  point.  The 

heat  requisite  for  this  effect  varies  with  the  nature  of  the  fluid.  Thus, 
sulphuric  ether  boils  at  96®  F,,  alcohol  at  176®,  and  pure  water  at  212®; 
while  oil  of  turpentine  must  be  raised  to  316®,  and  mercury  to  680®,  be- 
fore either  exhibits  marks  of  ebullition.  The  boiling  point  of  the  same 
liquid  is  constant,  so  long  as  the  necessary  conditions  are  preserved; 
but  it  is  liable  to  be  affected  by  several  circumstances.  The  nature  of 
the  vessel  has  some  influence  upon  it.  Thus,  Gay-Lussac  observed  that 
pure  water  boils  precisely  at  212®  in  a metallic  vessel,  and  at  214®  in 
one  of  glass.  It  is  likewise  affected  by  the  presence  of  foreign  particles. 
The  same  accurate  experimenter  found,  that  when  a few  iron  filings 
are  thrown  into  water  boiling  in  a glass  vessel,  its  temperature  quickly 
falls  from  214®  to  212*?,  and  remains  stationary  at  the  latter  point.  But 
the  circumstance  which  has  the  greatest  influence  over  the  boiling  point 
of  fluids  is  variation  pf  pressure.  All  bodies  upon  the  earth jire  con- 
stantly exposed  to  considerable  pressure;  for  the  atmosphere  itself 
presses  witli  a force  equivalent  to  a weight  of  15  pounds  on  every  square 
inch  of  surface.  Liquids  are  exposed  to  this  pressure  as  well  as  solids, 
and  their  tendency  to  take  the  form  of  vapour  is  very  much  counter- 
acted by  it.  In  fact,  they  cannot  enter  into  ebullition  at  all,  till  their 
particles  have  acquired  such  elastic  force  as  enables  them  to  overcome 
the  pressure  upon  their  surfaces;  that  is,  till  they  press  against  the  at- 
mosphere with  the  same  force  as  the  atmosphere  against  them.  Now 
the  atmospheric  pressure  is  variable,  and  hence  it  follows  that  the  boiL 
ing  point  of  liquids  must  also  vary. 


58 


CALORIC. 


The  only  time  at  which  the  pressure  of  the  atmosphere  is  equal  to  a 
weight  of  15  pounds  on  every  square  incli  of  surface,  is  when  the  bar- 
ometer stands  at  30  inches,  and  then  only  does  water  boil  at  212°  F. 
If  the  pressure  be  less,  that  is,  if  the  barometer  fall  below  30  inches, 
then  the  boiling  point  of  water,  and  every  other  liquid,  will  be  lower 
than  usual 5 or  if  the  barometer  rises  above  30  inches,  the  temperature 
of  ebullition  will  be  proportionally  increased.  This  is  thb  reason  why 
water  boils  at  a lower  temperature  on  the  top  of  a hill  than  in  the  valley 
beneath  it;  for  as  the  column  of  air  diminishes  in  length  as  we  ascend, 
its  pressure  must  likewise  suffer  a proportional  diminution.  The  ratio 
between  the  depression  of  the  boiling  point  and  the  diminution  of  the 
atmospherical  pressure  is  so  exact,  that  it  has  been  proposed  as  a 
method  for  determining  the  heights  of  mountains.  An  elevation  of  530 
feet  makes  a diminution  of  one  degree  of  Fahrenheit.  (Mr.  Wollaston 
in  Phil.  Trans,  for  ISIT'.) 

The  influence  of  the  atmosphere  over  the  point  of  ebullition  is  best 
shown  by  removing  its  pressure  altogether.  The  late  Professor  Robin- 
son found  that  fluids  boil  in  vacuo  at  a temperature  140  degrees  lower 
than  in  the  open  air.  (Black’s  Lectures,  p.  151.)  Thus  water  boils  in 
vacuo  at  72°,  alcohol  at  36?,  and  ether  at  — 44°  F.  This  proves  that  a 
liquid  is  not  necessarily  hot,  because  it  boils.  The  heat  of  the  hand  is 
sufficient  to  make  water  boil  in  vacuo^  as  is  exemplified  by, the  common 
pulse-glass;  and  ether,  under  the  same  circumstances,  will  enter  into 
ebullition,  though  its  temperature  is  low  enough  for  freezing  mercury. 

Water  cannot  be  heated  under  common  circumstances  beyond  212°, 
because  it  then  acquires  such  expansive  force  as  enables  it  to  overcome 
the  atmospheric  pressure,  and  fly  off  in  the  form  of  vapour.  But  if  sub- 
jected to  sufficient  pressure,  it  may  be  heated  to  any  extent  without 
boiling.  This  is  best  done  by  heating  water  while  confined  in  a strong 
copper  vessel,  called  Papin’s  Digester.  In  this  apparatus,  on  the  ap- 
plication of  heat,  a large  quantity  of  vapour  collects  above  the  water, 
and  checks  ebullition  by  the  pressure  which  it  exerts  upon  the  surface 
of  the  liquid.  There  is  no  limit  to  the  degree  to  which  water  may  thus 
be  heated,  provided  the  vessel  is  strong  enough  to  confine  the  vapour; 
but  the  expansive  force  of  steam  under  these  circumstances  is  so  enor- 
mous as  to  overcome  the  greatest  resistance. 

In  estimating  the  power  of  steam,  it  should  be  remembered  that  va- 
pour, if  separated  from  the  liquid  which  produced  it,  does  not  possess 
a greater  elasticity  than  an  equal  quantity  of  air.  If,  for  example,  the 
digester  were  full  of  steam  at  212°,  no  water  in  the  liquid  state  being 
present,  it  might  be  heated  to  any  degree,  even  to  redness,  without 
danger  of  bursting.  But  if  water  be  present,  then  each  addition  of  ca- 
loric causes  a fresh  portion  of  steam  to  rise,  which  adds  its  own  elastic 
force  to  that  of  the  vapour  previously  existing;  and  in  consequence  an 
excessive  pressure  is  soon  exerted  against  the  inside  of  the  vessel.  Pro- 
fessor Robinson  (Brewster’s  edition  of  his  works,  p.  25)  found  that  the 
tension  pf  steam  is  equal  to  two  atmospheres  at  244°  F.,  and  to  three 
at  270°  F.  The  results  of  Mr.  Southern’s  experiments,  given  in  the 
same  volume,  fix  upon  250 ’3°  as  tlie  temperature  at  which  steam  has 
the  force  of  two  atmospheres,  on  293*4°  for  four,  and  343*6°  for  eight 
atmospheres. 

This  subject  has  been  lately  examined  by  a commission  appointed  by 
the  Parisian  Academy  of  Sciences,  and  Dulong  and  Arago  took  a lead- 
ing part  in  the  in(j[uiry.  ^Plic  results,  which  are  given  in  the  following 
table,  were  obtained  by  experiment  up  to  a pressure  of  25  atmospheres, 
and  at  higher  pressures  by  calculation.  (Braude’s  Journal,  N.  S.  vii, 
191.) 


CALORIC. 


59 


Elasticity  of  the 
vapour,  taking 
atmospheric 

Temperature  ac- 
cording to  Fah- 
renheit, 

press,  as  unity. 

1 

212° 

14 

233*96 

2 

250-52 

24 

263*84 

n 

O 

275*18 

34 

285*08 

4 

293*72 

301  *28 

5 

308*84 

54 

314*24 

6 

320*36 

64 

326*26 

7 

331-70 

74 

336-86 

8 

341-96 

9 

350*78 

10 

358*88 

11 

367*34 

12 

374*00 

Elasticity  of  the 
vapour,  taking 
atmospheric 

Temperature  ac- 
cording to  Fah- 
renheit, 

press,  as  unity. 

13 

380*66° 

14 

386*94 

15 

392*86 

16 

398*48 

17 

403*82 

18 

408*92 

19 

413*96 

20 

418*46 

21 

422*96 

22 

427*28 

23 

431-42 

24 

435*56 

25 

439-34 

30 

457*16 

35 

472*73 

40 

486*59 

45 

491-14 

50 

510-60 

The  elasticity  of  steam  is  employed  as  a moving*  power  in  the  steam- 
engine.  The  construction  of  this  machine  depends  on  two  properties 
of  steam,  namely,  the  expansive  force  communicated  to  it  by  caloric, 
and  its  ready  conversion  into  water  by  cold.  The  effect  of  both  these 
properties  is  well  shown  by  a little  instrument  devised  by  Dr.  Wollas- 
ton. It  consists  of  a cylindrical  glass  tube,  six  inches  long,  nearly  an 
inch  wide,  and  blown  out  into  a spherical  enlargement  at  one  end.  A 
piston  is  accurately  fitted  to  the  cylinder,  so  as  to  move  up  and  down 
the  tube  with  freedom.  When  the  piston  is  at  the  bottom  of  the  tube, 
it  is  forced  up  by  causing  a portion  of  water,  previously  placed  in  the 
ball,  to  boil  by  means  of  a spirit-lamp.  On  dipping  the  ball  into  cold 
water,  the  steam  which  occupies  the  cylinder  is  suddenly  condensed, 
and  the  piston  forced  down  by  the  pressure  of  the  air  above  it.  By  the 
alternate  application  of  heat  and  cold,  the  same  movements  are  repro- 
duced, and  may  be  repeated  for  any  length  of  time. 

The  moving  power  of  the  steam  engine  is  the  same  as  in  this  appai*a- 
tus.  The  only  essential  difference  between  them  is  in  the  mode  of  con- 
densing the  steam'.  In  the  steam  engine,  the  steam  is  condensed  in  a 
separate  vessel  called  the  condenser^  where  there  is  a regular  supply  of 
cold  water  for  the  purpose.  By  this  contrivance,  which  constitutes  the 
great  improvement  of  Watt,  the  temperature  of  the  cylinder  never  falls 
below  212?. 

The  formation  of  vapour  is  attended,  like  liquefaction,  with  loss  of 
sensible  caloric.  This  is  proved  by  the  well-known  fact  that  the  tem- 
perature of  steam  is  precisely  the  same  as  that  of  the  boiling  water  from 
which  it  rises;  so  that  all  the  caloric  which  enters  into  the  liquid  is  solely 
employed  in  converting  a portion  of  it  into  vapour,  without  affecting  the 
temperature  of  either  in  the  slightest  degree,  provided  the  latter  is  per- 
mitted to  escape  witli  freedom.  The  caloric  which  then  becomes  latent, 
to  use  the  language  of  Dr.  Black,  is  again  set  free  when  the  vapour  is 
condensed  into  water.  The  exact  quantity  of  caloric  rendered  insensible 
by  vaporization,  may  therefore  be  ascertained  by  condensing  the  vapour 


60 


CALORIC. 


in  cold  water,  and  observing*  the  rise  of  temperature  which  ensues.  From 
the  experiments  of  Dr.  Black  and  Mr.  Watt,  conducted  on  this  princi- 
ple, it  appears  that  steam  of  212?,  in  bcing-condensedintowater  of  212®, 
gives  out  as  much  caloric  as  would  raise  the  temperature  of  an  equal  weight 
of  water  by  950  degrees,  all  of  wliich  had  previously  existed  in  the  va- 
pour witliout  being  sensible  to  a thennometer. 

The  latent  heat  of  steam  and  several  other  vapours  has  been  examined 
by  Dr.  Ure,  wliose  results  are  contained  in  the  following  table.  (Phil. 
Trans,  for  1818.) 

Latent  Heat, 


Vapour  of  Water  at  its  boiling  point  . . 967® 

Alcohol 442 

Ether  .....  302.379 

Petroleum  ....  177.87 

Oil  of  turpentine  . . . 177.87 

Nitric  acid  . . . . 531.99 

Liquid  ammonia  . . . 837.28 

Vinegar  . . . . . 875 


The  disappearance  of  caloric  that  accompanies  vaporization  was  ex- 
plained by  Dr.  Black  and  Dr.  Irvine,  in  the  way  already  mentioned  un- 
der the  head  of  liquefaction;  and  as  the  objections  to  the  views  of  the 
latter  ingenious  chemist  were  then  stated,  it  is  unnecessary  to  mention 
them  on  the  present  occasion. 

Evaporation, 

Evaporation  as  well  as  ebulhtion  consists  in  the  formation  of  vapour, 
and  the  only  assignable  difference  between  them  is,  that  the  one  takes 
place  quietly,  the  other  with  the  appearance  of  boiling.  Evaporation 
occurs  at  common  temperatures.  This  fact  may  be  proved  by  exposing 
water  in  a shallow  vessel  to  the  air  for  a few  days,  when  it  will  gradually 
diminish,  and  at  last  disappear  entirely.  Most  fluids,  if  not  all  of  them, 
are  susceptible  of  this  gi*adual  dissipation;  and  it  may  also  be  observed 
in  some  solids,  as  for  example  in  camphor.  Evaporation  is  much  more 
rapid  in  some  fluids  than  in  others,  and  it  is  always  found  that  those 
liquids,  the  boiling  point  of  which  is  lowest,  evaporate  with  the  greatest 
rapidity.  Thus  alcohol,  which  boils  at  a lower  temperature  than  water, 
evaporates  also  more  freely;  and  ether,  whose  point  of  ebullition  is  yet 
lower  than  that  of  alcohol,  evaporates  with  still  greater  rapidity. 

The  chief  circumstances  that  influence  the  process  of  evaporation  are 
extent  of  surface,  and  the  state  of  the  air  as  to  temperature,  dryness, 
stillness,  and  density. 

1.  Extent  of  surface.  Evaporation  proceeds  only  from  the  surface  of 
fluids,  and  therefore,  cseteris  paribus,  must  depend  upon  the  extent  of 
surface  exposed. 

2.  Temperature.  The  effect  of  heat  in  promoting  evaporation  may 
easily  be  shown  by  putting  an  equal  quantity  of  water  into  two  saucers, 
one  of  which  is  placed  in  a warm,  the  other  in  a cold  situation.  The  for- 
mer will  be  quite  diy  before  the  latter  has  suffered  appi’eciable  dimi- 
nution. 

3.  State  of  the  air  as  to  diyness  or  moisture.  When  water  is  covered 
by  a stratum  of  dry  air,  the  evaporation  is  rapid  even  when  its  tempera- 
ture is  low.  Tluis  in  some  dry  cold  days  in  winter,  the  evaporation  is 
exceedingly  ra]:>id;  whereas  it  goes  on  veiy  tardily,  if  tlie  atmosphere  con- 
tains much  vapoiu*,  even  though  the  air  be  veiy  wai-m. 

4.  Evaporation  is  fiir  slower  in  still  air  than  in  a cuiTent,  and  for  an 


CALOlUC. 


61 


obvioiis  reason.  The  air  immediately  in  contact  with  the  water  soon  be- 
comes moist,  and  tlnis  a check  is  put  to  evaporation.  But  if  the  air  is 
removed  from  tlie  surface  of  the  water  as  soon  as  it  has  become  charg*ed 
with  vapour,  and  its  place  supplied  with  fresh  dry  air,  then  the  evapora- 
tion continues  without  interruption. 

5.  Pressure  on  the  surfiice  of  liquids  has  a remarkable  influence  over 
evaporation.  This  is  easily  proved  by  placing*  ether  in  the  vacuum  of 
an  air-pump,  when  vapour  rises  so  abundantly  as  to  produce  ebullition. 

As  a larg'e  quantity  of  caloric  passes  from  a sensible  to  an  insensible 
state  during*  the  formation  of  vapour,  it  follows  that  cold  should  be  g*en- 
erated  by  evaporation.  A very  simple  experiment  will  prove  it.  If  a 
few  drops  of  ether  be  allowed  to  fall  upon  the  hand,  a strong  sensation 
of  cold  will  be  excited  during  its  evaporation;  or  if  the  bulb  of  a ther- 
mometer, covered  with  lint,  be  moistened  with  ether,  the  production  of 
cold  will  be  marked  by  the  descent  of  the  mercury.  But  to  appreciate 
the  degree  of  cold  which  may  be  produced  by  evaporation,  it  is  neces- 
sary to  render  it  very  rapid  and  abundant  by  artificial  processes;  and  the 
best  means  of  doing  so,  is  by  removing  pressure  from  the  surface  of  vola- 
tile liquids.  Water  placed  under  the  exhausted  receiver  of  an  air-pump 
evaporates  with  great  rapidity,  and  so  much  cold  is  generated  as  would 
freeze  the  water,  did  the  vapour  continue  to  rise  for  some  time  with  the 
same  velocity.  But  the  vapour  itself  soon  fills  the  vacuum,  and  retards 
: the  evaporation  by  pressing  upon  the  surface  of  the  water.  This  diffi- 
culty may  be  avoided  by  putting  under  the  receiver  a substance,  such  as 
sulphuric  acid,  which  has  the  property  of  absorbing  watery  vapour,  and 
consequently  of  removing  it  as  quickly  as  it  is  formed.  Such  is  the 
principle  of  Mr.  Leslie’s  method  for  freezing  water  by  its  own  evano- 
ration.* 

The  action  of  the  cryophorus,  an  ingenious  contrivance  of  the  late  Dr. 
Wollaston,  depends  on  the  same  principle.  It  consists  of  two  glass  balls, 
perfectly  free  from  air,  and  joined  together  by  a tube  as  here  represented! 


One  of  the  balls  contains  a portion  of  distilled  water,  while  the  other 
parts  of  the  instrument,  which  appear  empty,  are  full  of  aqueous  vapour, 
which  checks  the  evaporation  from  the  water  by  the  pressure  it  exerts 
upon  its  surface.  But  when  the  empty  ball  is  plunged  into  a freezing 
mixture,  all  the  vapour  within  it  is  condensed;  evaporation  commences, 
from  the  surface  of  the  water  in  the  other  ball,  and  it  is  frozen  in  two  or 
tlu-ee  minutes  by  the  cold  thus  produced. 

Liqmds  which  evaporate  more  rapidly  than  water,  cause  a still  greater 
reduction  of  temperature.  The  cold  produced  by  the  evaporation  of 
ether  in  the  vacuum  of  the  air-pump,  is  so  intense  as  under  favourable 
circumstances  to  freeze  mercuryf. 

Scientific  men  have  differed  concerning  the  cause  of  evaporation.  It 
was  once  supposed  to  be  owing  to  chemical  attraction  between  the  air  and 
\^^ter,  and  the  idea  is  at  first  view  plausible,  since  a certain  degree  of 
affimty  does  to  all  appearance  exist  between  them.  But  it  is  nevertheless 
impossible  to  attnbute  the  effect  to  this  cause'.  For  evaporation  takes 


See  art.  Cold,  in  the  Supplement  to  the  Encyclopaedia  Britannica. 

7 See  a paper  by  the  late  Dr.  Marcet,  in  Nicholson’s  Journal,  vol.  xxxiv. 

6 


62 


CALORIC. 


place  equally  in  vacuo  as  in  the  air;  nay,  it  is  an  cslablislied  fact,  that  the 
atmospliere  positively  retards  the  process,  and  that  ojie  of  the  best  means 
of  accelerating-  it  is  ])y  removing-  the  air  altog-ether.  I'he  experiments  of 
Dalton  prove  that  caloric  is  the  tme  and  only  cause  of  the  formation 
of  vapour.  He  finds  that  the  actual  quantity  of  vapour,  which  can  exist 
in  any  ^ven  space,  is  dependent  solely  upon  the  temperature.  If,  for  in- 
stance, a little  water  be  put  into  a dry  g'lass  flask,  a quantity  of  vapour 
vdll  be  formed  proportionate  to  the  temperature.  If  a thennometer  placed 
in  it  stands  at  32*^,  the  flask  will  contain  a very  small  quantity  of  vapour. 
At  40^,  more  vapour  will  exist  in  it,  at  59®  it  will  contain  still  more;  and  at 
60®,  tlie  quantity  will  be  still  further  augmented.  If,  when  the  theimome- 
teris  at  60®,  the  temperature  of  the  flask  is  suddenly  reduced  to  40®,  then 
a cei-tain  portion  of  vapour  will  be  converted  into  water;  the  quantity 
which  retains  the  clastic  form  being-  precisely  the  same  as  when  the  tem- 
peimture  was  orig-inally  at  40®. 

It  matters  not,  witli  reg-ardto  these  changes,  whether  the  flask  is  full 
of  air,  or  altogether  empty;  for  in  either  case,  it  will  eventually  contain 
the  same  quantity  of  vapour,  when  the  thermometer  is  at  the  same 
height.  The  only  effect  of  a difference  in  this  respect,  is  in  the  rapid- 
ity of  evaporation.  The  flask,  if  previously  empty,  acquires  its  full 
complement  of  vapour,  or,  in  common  language,  becomes  saturated 
with  it,  in  an  instant;  whereas  the  presence  of  air  affords  a mechanical 
impediment  to  its  passage  from  one  part  of  the  flask  to  another,  and 
therefore  an  appreciable  time  elapses  before  the  whole  space  is  satu- 
rated. 

Mr.  Dalton  found  that  the  tension  or  elasticity  of  vapour  is  always 
the  same,  however  much  the  pressure  may  vary,  so  long  as  the  tempe- 
rature remains  constant,  and  there  is  liquid  enough  present  to  preserve 
the  state  of  saturation  proper  to  the  temperature.  If,  for  example,  in 
a vessel  containing  a liquid,  the  space  occupied  by  its  vapour  should 
suddenly  dilate,  the  vapour  it  contains  W’ill  dilate  also,  and  consequently 
suffer  a diminution  of  elastic  force;  but  its  tension  will  be  quickly  re- 
stored, because  the  liquid  yields  an  additional  quantity  of  vapour,  pro- 
portional to  the  increase  of  space.  Again,  if  the  space  be  diminished, 
the  temperature  remaining  constant,  the  tension  of  the  confined  vapour 
will  still  continue  unchanged;  because  a quantity  of  it  w'ill  be  condens- 
ed proportional  to  the  diminution  of  space,  so  that,  in  fact,  the  remain- 
ing space  contains  the  very  Svame  quantity  of  vapour  as  it  did  originally. 
The  same  law  holds  good,  whether  the  vapour  is  pure,  or  mixed  with 
any  other  gas. 

The  elasticity  of  watery  vapour  at  temperatures  belotv  212®  F. 
carefully  examined  by  Mr.  Dalton  (Manchester  Memoirs,  voh  v.);  and 
his  results,  together  with  those  since  published  by  Dr.  Ure,  in  the  Phi- 
losophical Transactions  for  1818,  are  presented  in  a tabular  form  at  the 
end  of  the  volume.  They  were  obtained  by  introducing  a portion  of 
water  into  the  vacuum  of  a common  barometer,  and  estimating  the  ten- 
sion of  its  vapour  by  the  extent  to  which  it  depressed  the  column  of 
mercury  at  different  temperatures.  But  Mr.  Dalton  did  not  confine  his 
researches  to  water;  he  extended  them  to  the  vapour  of  various  liquids, 
such  as  ether,  alcohol,  ammonia,  and  solution  of  muriate  of  lime,  and  he 
inferred  from  them  the  following  law: — That  the  force  of  vapour  from 
all  liquids  is  the  same,  at  equal  distances  above  or  below  the  several 
temperatures  at  which  they  boil  in  the  open  air.  Thus  steam  at  200® 
J' . has  the  same  elasticity  as  the  vapour  of  ether  at  84®,  the  boiling 
point  of  the  former  being  212®,  and  of  the  latter  96®.  Biot  and  Amed^ 
Beilhollct  (Biot,  Traitcj  de  ph.  i.  282.)  have  found  that  this  law  applies 
cxiictly  to  many  other  liquids;  but  some  experiments  by  Dr.  Ure,  on 


CALORIC.  63 

oil  of  turpentine  and  petroleum,  would  lead  to  the  conclusion  that  it  i« 
not  universal. 

It  is  easy,  on  this  principle,  to  account  for  the  elastic  force  of  the  va- 
pours of  liquids,  whose  boiling  point  is  very  high,  being  inappreciable 
at  moderate  temperatures.  Thus  sulphuric  acid  boils  at  620^  F.;  and 
therefore  at  212®,  that  is  408  degrees  below  its  point  of  ebullition,  tbje 
elasticity  of  its  vapour  should  be  equal  to  that  of  aqueous  vapour  at 
— 196®,  or  408  degrees  belovy  the  boiling  point  of  water.  In  like  man- 
ner mercury,  which  boils  at  680®,  yields  vapour  whose  elastic  force  at 
212®  may  be  estimated  as  equal  to  that  of  watery  vapour  at  — 256®,  or 
468  degrees  below  the  point  at  which  water  enters  into  ebullition-  Ac- 
cording to  the  same  law,  mercury  requires  a temperature  of  500®,  or  180 
degrees  below  its  boiling  point,  in  order  that  its  vapour  should  have 
the  same  tension  as  watery  vapour  at  32?.  From  these  considerations 
it  is  inferred,  that  though  in  a common  barometer  the  space  above  the 
column  may  contain  a little  mercurial  vapour,  and  consequently  may  not 
be  an  absolute  vacuum,  the  influence  of  that  vapour  in  depressing  the 
column,  even  at  considerable  temperatures,  is  altogether  inappreciable. 

It  admits  of  inquiry  whether  liquids  of  weak  volatility,  such  as  mer- 
cury and  oil  of  vitriol,  give  off  any  vapour  at  common  temperatures. 
An  opinion  has  prevailed,  that  evaporation  not  only  takes  place  from 
the  surface  of  these  and  similar  liquids  at  all  times,  but  that  vapour  of 
exceedingly  weak  tension  is  emitted  at  common  temperatures  from  all 
substances  however  fixed  in  the  fire,  even  from  the  earths  and  metals, 
when  they  are  either  placed  in  a vacuum,  or  surrounded  by  gaseous 
matter.  It  has  accordingly  been  supposed,  that  the  atmosphere  con- 
tains diffused  through  it  minute  quantities  of  the  vapours  of  all  the 
bodies  with  which  it  is  in  contact;  and  this  idea  has  been  made  the 
basis  of  a theory  of  the  origin  of  meteorites.  But  this  doctrine  has  been 
successfully  combated  by  Mr.  Faraday,  in  his  essay  On  the  Existence  of 
a Limit  to  Vaporization,  published  in  the  Philosophical  Transactions 
for  1826.  The  argument  employed  by  Mr.  Faraday  is  founded  on  the 
principle  by  which  the  late  Dr.  Wollaston  has  accounted  for  the  limited 
extent  of  the  atmosphere.  Since  the  volume  of  gaseous  substances  is 
dependent  on  the  pressure  to  which  they  are  subject,  the  air  in  the 
higher  regions  of  the  atmosphere  must  be  much  more  rare  than  in  the 
lower,  because  the  former  sustains  the  pressure  of  a shorter  atmospheric 
column  than  the  latter;  so  that  in  ascending  upwards  from  the  earth, 
each  successive  stratum  of  air,  being  less  compressed  than  the  fore- 
going, is  likewise  more  attenuated.  Now  it  is  found  experimentally 
that  the  elasticity- or  tension  of  any  gaseous  matter  diminishes  in  the 
same  ratio  as  its  volume  increases;  and,  accordingly,  whenever  the  te- 
nuity of  a portion  of  air,  owing  to  its  distance  from  the  earth’s  surface 
or  any  other  cause,  is  exceedingly  great,  its  tension  is  exceedingly  small. 
Reasoning  on  this  principle.  Dr.  Wollaston  conceives  that  at  a certain 
altitude,  probably  at  a distance  of  40  or  50  miles  from  the  surface  of 
the  earth,  the  rarefaction  and  consequent  loss  of  elastic  force  is  so  ex- 
treme, that  the  mere  gravity  of  the  particles  becomes  equal  to  their 
elasticity,  and  thus  puts  a limit  to  their  separation. 

What  Dr.  Wollaston  suggests  of  aerial  particles,  Mr.  Faraday  sup- 
poses to  occur  in  all  substances;  and  this  supposition  is  perfectly  legi- 
timate, because  gaseous  matter  in  general  is  subject  to  the  same  law  of 
expansion,  and  is  likewise  under  the  influence  of  gravity.  He  infers 
that  every  kind  of  matter  ceases  to  assume  the  elastic  form,  whenever 
the  gravitation  of  its  particles  is  stronger  than  the  elasticity  of  its  va- 
pour, The  loss  of  tension  necessary  for  eflecting  this  object  may  be 
accomplished  ih  two  ways,  either  by  extreme  dilatation,  or  by  cold. 


CALORIC. 


C4 

For  substances  of  great  volatility,  such  as  air  and  most  gases,  the  for- 
mer is  necessary;  because  the  degree  of  cold  which  we  can  command 
at  the  earth’s  surface  diminishes  their  tension  in  a degree  quite  insufH- 
cient  to  destroy  their  elasticity.  But  the  volatility  of  innumerable  bodies 
is  so  small,  that  their  vapour  at  common  temperatures  approximates  in 
rarity  to  the  air  at  the  limits  of  the  atmosphere,  and  a small  degree  of 
cold  may  suffice  for  rendering  its  elasticity  a force  inferior  to  its  oppo- 
nent, gravity.  In  that  case,  the  vapour  would  be  entirely  condensed. 
Mr.  Faraday  found  that  mercury,  at  a temperature  varying  from  60?  to 
80?,  yields  a small  quantity  of  vapour;  but  in  winter  no  trace  of  vapour 
could  be  detected.  Hence  it  is  inferred,  that  at  the  former  tempera- 
ture the  elasticity  of  mercurial  vapour  is  slightly  superior  to  the  gravity 
of  its  particles,  and  that  in  cold  weather  the  latter  power  preponderates, 
and  puts  an  entire  check  to  the  evaporation  of  mercury.  The  earths 
and  metals,  which  are  more  fixed  than  mercury,  have  vapours  of  such 
feeble  tension,  that  the  highest  natural  temperature  is  unable  to  con- 
vert them  into  vapour.  Another  force,  which  co-operates  with  gravity 
in  overcoming  elasticity,  is  the  attraction  of  aggregation,  or  the  attrac- 
tion exerted  by  a solid  or  liquid  on  the  contiguous  particles  of  the  same 
substance  in  the  gaseous  form.  This  argument  affords  very  sufficient 
grounds  for  believing  that  the  vapours  of  earthy  and  metallic  substances 
are  never  present  in  the  atmosphere. 

The  presence  of  vapour  has  a considerable  influence  over  the  bulk  of 
gases;  and  as  chemists  often  find  it  convenient  to  determine  the  quan- 
tity of  gaseous  substances  by  measure,  it  is  important  to  estimate  the 
effect  thus  produced,  in  order  to  make  allowance  for  it.  The  mode  by 
which  a vapour  acts  is  obvious.  If  a few  drops  of  water  are  added  to 
a portion  of  dry  air,  confined  in  a glass  tube  over  mercury,  the  air  will 
speedily  become  saturated  with  vapour,  and  must  in  consequence  be  ir.- 
creased  in  bulk.  For  the  elastic  power  of  the  vapour  being  added  to 
that  previously  exerted  by  the  gas  alone,  the  mixture  will  necessarily 
exert  a stronger  pressure  upon  the  mercury  that  confines  it,  and  will 
therefore  occupy  a greater  space.  It  is  equally  clear  that  the  degree 
of  augmentation  will  depend  on  the  temperature;  for  it  is  the  tempera- 
ture alone  wdiich  determines  the  tension  of  the  vapour. 

As  the  elasticity  of  vapour  is  not  at  all  affected  by  mere  admixture 
■witii  gases,  it  is  easy  to  correct  the  fallacy  to  which  its  presence  gives 
rise,  by  means  of  the  data  furnished  by  the  experiments  of  Dalton.  The 
formula  for  the  correction  is  thus  deduced.  Let  n be  the  bulk  of  dry 
air  or  other  gas  expressed  in  the  degrees  of  a graduated  tube;  jo  the  ten- 
sion of  the  dry  air,  equal  to  the  atmospheric  pressure;  n'  the  bulk  of  the 
air  when  saturated  with  watery  vapour,  and /the  tension  of  that  vapour. 
(Riot’s  Traite  de  Phys.  I.  303.) 

It  is  a well-known  law  in  pneumatics  that  the  elasticity  of  a gas  is  in- 
versely as  its  volume;  so  that,  wdien  the  dry  air  increases  in  bulk  from  n 
to  n',  its  elasticity  diminishes  in  the  ratio  of  n'  to  n.  Hence  its  elasticity 

ceases  to  be  but  is  expressed  p is  now  that  is,  the 

elasticity  of  the  dihitcd  air,  added  to  the  elasticity  of  the  yapoiu*  pre- 
sent, is  c(pial  to  the  ])rcssure  of  the  atmosphere.  From  this  last  equa- 
tion are  deduced  the  following  values:  pn-{-fn'=p7V',  p7i=pn'^fn' -y 

an<l  tlErll. 

V 

One  cxam))le  will  suffice  for  showing  the  use  of  this  formula.  Having 
100  measures  of  air  saturated  with  watery  vapour  at  60®  F.,  the  barome- 
ter standingat  30  inches,  how  many  measures  would  the  air  occupy  if 


CALORIC. 


65 


quite  dry^  ti'  = 100;  o ==:30;/=0.524,  the  tension  of  watery  vapour  at 
^ 100  X (30  — 0.524) 

60*^,  according  to  Mi%  Dalton’s  table.  Hence  n = ^ =* 

100  X 29.476 

— = 98.25,  wliich  is  the  answer  required. 

oO 

The  presence  of  watery  vapour  in  the  atmosphere  is  owing  to  evapora- 
tion. All  the  accumulations  of  water  upon  the  surface  of  the  earth  are 
subjected  by  its  means  to  a natural  distillation.  The  impmities  with 
wliich  they  are  impregnated  remain  behind,  while  the  pure  vapour  as- 
cends into  the  air,  gives  rise  to  a multitude  of  meteorological  phenomena, 
and  after  a time  descends  again  upon  the  earth.  As  evaporation  goes 
on  to  a certain  extent  even  at  low  temperatures,  it  is  probable  that  the 
atmosphere  is  never  absolutely  free  from  vapour. 

The  quantity  of  vapour  present  in  the  atmosphere  is  very  variable,  in 
consequence  of  the  continual  change  of  temperature  to  which  the  air  is 
subject.  But  even  when  the  temperature  is  the  same,  the  quantity  of  va- 
pour is  still  found  to  vary;  for  the  air  is  not  always  in  a state  of  satura- 
tion. At  one  time  it  is  excessively  diy,  at  another  it  is  fully  satui’ated; 
and  at  other  times  it  varies  between  these  extremes.  This  variable  con- 
dition of  the  atmosphere  as  to  saturation  is  ascertained  by  the  hygrometer. 

A great  many  hygrometers  have  been  invented;  but  they  may  all  be 
referred  to  three  principles.  The  construction  of  the  first  kind  of  hy- 
grometer is  founded  on  the  property  possessed  by  some  substances  of 
expanding  in  a humid  atmosphere,  owing  to  a deposition  of  moisture 
within  them;  and  of  parting  with  it  again  to  a dry  air,  and  in  consequence 
contracting.  Almost  all  bodies  have  the  power  of  attracting  moistiue 
from  the  air,  though  in  different  proportions.  A piece  of  glass  or  metal 
weighs  sensibly  less  when  carefully  dried,  than  after  exposure  to  a moist 
atmosphere;  though  neither  of  them  is  dilated,  because  the  water  cannot 
penetrate  into  their  interior.  Dilatation  from  the  absorption  of  moisture 
appears  to  depend  on  a deposition  of  it  witliin  the  texture  of  a body,  the 
particles  of  which  are  moderately  soft  and  yielding.  The  hygrometric 
property  therefore  belongs  cliiefly  to  organic  substances,  such  as  wood, 
the  beard  of  corn,  whalebone,  hair,  and  animal  membranes.  Of  these 
none  is  better  than  the  human  hair,  which  not  only  elongates  freely  from 
imbibing  moisture,  but,  by  reason  of  its  elasticity,  recovers  its  original 
length  on  diying.  The  hygrometer  of  Saussure  is  made  with  this  ma- 
teriaL 

The  second  kind  of  hygrometer  points  out  the  opposite  states  of  dry- 
ness and  moisture- by  the  rapidity  of  evaporation.  Water  does  not  evapo- 
rate at  all  when  the  atmosphere  is  completely  satui'ated  with  moisture; 
and  the  freedom  with  wliich  it  goes  on  at  other  times,  is  in  proportion 
to  the  dryness  of  the  air.  The  hygrometric  condition  of  the  air  may  be 
determined,  therefore,  by  observing  the  rapidity  of  evaporation.  The 
most  convenient  method  of  doing  this,  is  by  covering  the  bulb  of  a thep- 
luometer  with  a piece  of  silk  or  linen,  moistening  it  with  water,  and  ex- 
posing it  to  the  air.  The  descent  of  the  mercury,  or  the  cold  produced, 
will  correspond  to  the  quantity  of  vapour  formed  in  a given  time.  Mr. 
Leslie’s  hygrometer  is  of  this  kind. 

I'he  tliird  kind  of  hygimmeter  is  on  a principle  entirely  different  from 
the  foregoing.  When  the  air  is  satiuated  with  vapour,  and  any  colder 
body  is  brought  into  contact  with  it,  deposition  of  moisture  immediately 
hikes  place  on  its  surface.  This  is  often  seen  when  a glass  of  cold  spring 
• water  is  earned  into  a warm  room  in  summer;  and  the  phenomenon  is  wit- 
f nessed  during  the  formation  of  dew,  the  moisture  appearing  on  those  sub- 

6* 


66 


CALOmC. 


stances  only  wbicli  are  colder  than  the  air.  1'hc  dc;^rcc  indicated  by 
the  thermometer  when  dew  beg’ins  to  be  deposited,  is  called  the  dew- 
point. If  the  saturation  is  complete,  the  least  diminution  of  temperature 
is  attended  with  the  formation  of  dew;  but  if  the  air  is  diy,  a body  must  be 
several  degrees  colder  before  moisture  is  deposited  on  its  surface;  and  in- 
deed the  drier  the  atmosphere,  the  greater  will  be  the  dillerence  between 
its  temperature  and  the  dew-point.  Attempts  were  made  to  estimate  the 
hygrometi-ic  state  of  the  air  on  this  principle  by  the  Florentine  Academi- 
cians, but  the  lirst  accurate  method  was  introduced  by  iVI.  Ix  Hoi,  and 
since  adopted  by  Mr.  Dalton.  It  consists  simply  inputting  cold  water 
into  a glass  vessel,  the  outside  of  which  is  carefully  dried,  and  marking 
the  temperature  of  the  liquid  at  which  dew  begins  to  be  deposited  on  the 
glass.  The  water  when  necessary  is  cooled  either  by  means  of  ice  or  a 
freezing  mixt  u’e*.  ^ This  method,  when  carefully  performed,  is  suscep- 
tible of  great  precision. 

The  hygrometer  of  Mr.  Daniell,  described  in  his  Meteorological  Essays 
acts  on  the  same  principle.  It  consists  of  a cryophorus,  as  described  at 
page  61,  but  modified  somewhat  in  form,  and  containing  ether  instead  of 
water.  Within  one  of  its  balls  is  fixed  a delicate  thermometer,  the  bulb 
of  wliich  is  partially  immersed  in  the  ether  so  as  to  indicate  its  tempera- 
ture, and  the  other  ball  is  eovered  with  muslin.  When  the  instrument  is 
\ised,  the  muslin  is  moistened  with  ether,  and  the  cold  produced  by  its 
evaporation  condenses  the  vapour  within  the  cryophorus,  and  causes  the 
ether  to  evaporate  rapidly  in  the  other  ball.  The  eold  thus  generated 
chills  the  ether  itself  and  the  ball  containing  it;  and  in  a short  time  its 
temperature  descends  so  low,  that  dew  is  deposited  on  the  surface 
of  the  glass.  As  soon  as  this  tak^s  place,  the  temperature  is  observed 
by  the  thermometer. 

I'he  same  object  is  attained  in  a still  easier  way  by  means  of  a contri- 
^ ance  described  by  Mr.  Jones  of  London  in  the  Philos.  Trans,  for  1826, 
and  soon  after  in  the  Edin.  Philos.  Journal,  No.  xvii,  p.  155,  by  Dr. 
Coldstream  of  Leith.  It  consists  of  a delicate  mercurial  thermometer, 
the  bulb  of  which  is  made  of  thin  black  glass,  and,  excepting  about  a 
fourth  of  its  surface,  is  covered  with  muslin.  On  moistening  the  muslin 
with  ether,  the  temperature  of  the  bulb  and  mercury  falls,  and  the  un- 
covered portion  of  the  bulb  is  soon  rendered  dim  by  the  dxposition  of 
moisture.  The  temperature  indicated  at  that  instant  by  the  thermometer  is 
the  devv-point.  It  appears  from  some  remarks  of  Mr.  Daniell  in  the 
Quarterly  Journal  of  Science,  that  this  hygrometer  was  originally  inven- 
ted in  Germany,  so  that  Mr.  Jones  and  Dr.  Coldstream  are  second  inven- 
t'jrs.  Mr.  Daniell  considers  the  instrument  inaccurate,  believing  that, 
as  the  ether  is  applied  to  a part  only  of  the  bulb,  the  mercury  within 
will  be  cooled  unequally;  that  the  portion  corresponding  to  the  covered 
part  of  the  bulb  will  be  colder  than  the  mercury  opposite  to  the  exposed 
part,  and  conseq\iently  the  dew-point  will  appear  lower  tlian  it  ought  to 
l;e.  'riiis  objection  certainly  applies  when  the  muslin  is  rendered  very 
moist  with  ether,  and  the  temperature  of  the  bulb  rapidly  reduced;  but 


* In  this  experiment,  the  cold  water  in  the  glass  vessel  will  probably 
liave  a tempei’ature  either  above  or  below  the  dew  point.  If  its  temper- 
ature be  above  this  point,  the  author  very  properly  directs  that  it  should 
Ijc  cooled  by  means  of  ice  or  a freezing  mixture,  until  dew  begins  to  be 
de  posited.  If,  liowevcr,  the  temperature  be  below  the  dew  point,  dew 
will  be  instantly  deposited  w'itlumt  indicating  the  point  in  qticstion.  The 
f)recise  direction  to  meet  this  case  would  be  carefully  to  note  tlic  tem- 
perature at  which  tlic  dew  ceases  to  be  formed.  15. 


CALORIC. 


67 


when  the  cooling*  Is  slowly  efTectecl,  I believe  the  indications  of  this  hy- 
gi'ometer  to  be  at  least  as  correct  as  those  afforded  by  the  very  elegant, 
yet  more  costly  and  less  portable,  apparatus  of  Mr.  Daniell.  For  facts 
confirmatory  of  this  opinion  the  reader  may  consult  an  essay  in  the  Edin- 
burgh Journal  of  Science,  No.  xiii.  p.  36,  by  Mr.  Foggo,  junior,  of  Leith. 

It  is  desirable  on  some  occasions,  not  merely  to  know  the  hygrometric 
condition  of  air  or  gases,  but  also  to  deprive  them  entirely  of  their  va- 
pour. This  may  be  done  to  a great  extent  by  exposing  them  to  intense 
cold;  but  the  method  now  generally  preferred  is  by  bringing  the  moist  gas 
in  contact  with  some  substance  which  has  a powerful  chemical  attraction 
fai’  water.  Of  these  none  is  prefei*able  to  chloride  of  calcium. 

Constitution  of  Gases  with  respect  to  Caloric* 

The  experiments  of  Mr.  Faraday,  on'the  liquefaction  of  gaseous  sub- 
stances, appear  to  justify  the  opinion  that  gases  are  merely  the  vapours 
of  extremely  volatile  liquids.  Most  of  these  liquids,  however,  are  so 
volatile,  that  their  boiling  point,  under  the  atmospheric  pressure,  is  low- 
er than  any  natural  temperature;  and  hence  they  are  always  found  in 
the  gaseous  state.  By  subjecting  them  to  peat  pressure,  their  elasticity 
is  so  far  counteracted  that  they  become  liquid.  But  even  when  thus 
compressed,  a very  moderate  heat  is  sufficient  to  make  them  boil;  and 
on  the  removal  of  pressure  they  resume  the  elastic  form,  most  of  them 
with  such  violence  as  to  cause  a report  like  an  explosion,  and  others 
with  the  appearance  of  brisk  ebullition.  An  intense  degree  of  cold  is 
produced  at  the  same  time,  in  consequence  of  caloric  passing  from  a 
sensible  to  an  insensible  state. 

The  process  for  condensing  gases  (Philos.  Trans,  for  1823)  consists 
in  exposing  ti\em  to  the  pressure  of  their  own  atmospheres.  The  ma- 
terials for  producing  the  gas  are  put  into  a strong  glass  tube,  which  is 
afterwards  sealed  hermetically,  and 
bent  in  the  middle,  as  represented 
by  the  figure.  J'he  gas  is  generated, 
if  necessaiy,  by  the  application  of 
heat,  and  when  the  pressure  becomes  sufficiently  great,  the  liquid  is 
formed  and  collects  in  the  free  end  of  the  tube,  which  is  kept  cool  to 
facilitate  the  condensation.  Most  of  these  experiments  are  attended 
with  danger  from  the  bursting  of  the  tubes,  against  which  the  operator 
must  protect  himself  by  the  use  of  a mask. 

The  pressure  required  to  liquefy  gases  is  very  variable,  as  will  ap- 
pear from  the  following  table  of  the  results  obtained  by  Mr.  Faraday. 

Sulphurous  acid  gas  . 2 atmospheres  at  45°F. 


Sulphuretted  hydrogen  gas  17  . . .50 

Carbonic  acid  gas  . 36  . . 32 

Chlorine  gas  . . . 4 . . .60 

Nitrous  oxide  gas  ,50  . . 45 

Cyanogen  gas  . . 3.6  . . .45 

Ammoniacal  gas  . 6.5  . . 50 

IMuriatic  acid  gas  . . 40  . . . 50* 


* The  general  law  in  regard  to  the  elasticity  or  tension  of  gases  is 
that  this  property  increases  with  the  compressing  force.  Oersted,  hovV- 
ever,  has  shown,  that  it  does  not  always  hold;  for  he  ascertained  that 
condensable  gases,  subjected  to  a pressure  approaching  to  that  at  which 
their  condensation  would  take  place,  undergo  a greater  diminution  of 
volume  than  is  proportional  to  the  pressure.  Berzelius  accounts  for 


68 


LIGHT. 


Sources  of  Caloric, 

The  sources  of  caloric  may  be  reduced  to  six.  1.  The  sun.  2.  Com- 
bustion. 3.  Electricity.  4.  The  bodies  of  animals  during'  life.  5.  Che- 
mical action.  6.  Mechanical  action.  All  these  means  of  procuring  a 
supply  of  caloric,  except  the  last,  will  be  more  conveniently  considered 
in  other  parts  of  the  work. 

The  mechanical  method  of  exciting  caloric  is  by  friction  and  percu> 
sion.  When  parts  of  heavy  macliinery  rub  against  one  another,  tho 
heat  excited,  if  the  parts  of  contact  are  not  well  greased,  is  sufficient 
for  kindling  wood.  The  axle-tree  of  carriages  has  been  burned  from 
tliis  cause,  and  the  sides  of  ships  are  said  to  have  taken  fire  by  the  ra.- 
pid  descent  of  the  cable.  Count  Uumford  has  given  an  interesting  ac- 
count of  the  caloric  excited  in  boring  cannon,  which  was  so  abundant 
as  to  heat  a considerable  quantity  of  water  to  its  boiling  point.  It  ap- 
peared from  his  experiments  that  a body  never  ceases  to  give  out  heat, 
by  friction,  however  long  the  operation  may  be  continued;  and  he  in- 
ferred from  this  observation  that  caloric  cannot  be  a material  substance^ 
but  is  merely  a property  of  matter.  M.  Pictet  observed  that  solids 
alone  produce  heat  by  friction,  no  elevation  of  temperature  taking  place 
from  the  mere  agitation  of  fluids  with  one  another.  He  found  that  the 
heat  excited  by  friction  is  not  in  proportion  to  the  hardness  and  elas- 
ticity of  the  bodies  employed.  On  the  contrary,  a piece  of  brass  rub- 
bed with  a piece  of  cedar  wood  produced  more  heat  than  when  rubbed 
with  another  piece  of  metal;  and  the  heat  was  still  greater  when  two 
pieces  of  wood  were  employed. 


SECTION  II. 

LIGHT. 

Light  is  similar  to  caloric  in  many  of  its  properties.  They  are  both 
emitted  in  the  form  of  rays,  traverse  the  air  in  straight  lines,  and  are 
subject  to  the  same  laws  of  reflection.  The  intensity  of  each  diminishes 
as  the  square  of  the  distance  from  their  source.  They  often  accompany 
each  other;  and  on  some  occasions  seem  to  be  actually  converted  into 
one  another.  It  lias  been  supposed,  from  this  circumstance,  that  they 
are  modifications  of  tlie  same  agent;  and  though  most  persons  regard 
them  as  independent  principles,  yet  they  are  certainly  allied  in  a way 
which  is  at  present  quite  inexplicable. 

There  are  two  kinds  of  light,  natural  and  artificial;  the  former  pro- 
ceeding from  the  sun  and  stars,  the  latter  from  bodies  which  are 
strongly  heated.  The  light  derived  from  these  sources  is  so  diflerent, 
that  it  is  necessary  to  speak  of  them  separately. 


this  fact  by  supposing  that  the  close  proximity  of  the  molecules  of  a 
gas,  occasiojicd  by  great  pressure,  bring'sthe  particles  more  completely 
witliin  the  sphere  of  each  other’s  attraction,  and  thus  counteracts  the 
separating  jiowcr  of  the  caloric,  which  he  conceives  to  act  under  unla- 
vourablc  circumstances,  unless  the  ponderable  pai'ticles  are  at  a certain 
di.stancc  from  each  otlicr.  (nerzelius,  I'raitc  de  Chiniie,  i.  83,  86.) 
I'hese  views  have  u beiLring  on  the  experiments  of  xMr.  Faraday  cited 
in  tlie  text-  XI. 


LIGHT. 


69 


The  solar  rays  come  to  us  either  directly,  as  in  the  case  of  sunshine, 
or  indirectly,  in  consequence  of  being-  diffused  through  the  atmosphere, 
constituting  daylight,  Tliey  pass  freely  through  some  solid  and  liquid 
bodies,  hence  called  transparent,  such  as  glass,  rock-crystal,  water,  and 
many  others,  which,  if  clear  and  in  moderately  thin  layers,  intercept  a 
portion  of  light  that  is  quite  inappreciable  when  compared  with  the 
quantity  transmitted,  Opakc  bodies,  on  the  contrary,  intercept  the  rays 
entirely,  absorbing  some  of  them  and  reflecting  others.  In  this  respect, 
also,  there  is  a close  analogy  between  light  and  caloric;  for  every  good 
reflector  of  the  one  reflects  the  other  also. 

Though  transparent  substances  permit  light  to  pass  through  them, 
they  nevertheless  exert  considerable  influence  upon  it  in  its  passage. 
All  the  rays  which  fall  obliquely  are  refracted,  that  is,  are  made  to  de- 
viate from  their  original  direction.  It  was  this  property  of  transparent 
media  which  enabled  Sir  Isaac  Newton  to  discover  the  compound  na- 
ture of  solar  light,  and  to  resolve  it  into  its  constituent  parts.  The  sub- 
stance commonly  employed  for  this  purpose  is  a triangular  piece  of 
glass  called  the  jomm.  Its  action  depends  upon  the  different  refrangi- 
bility  of  the  seven  coloured  rays  which  compose  a colourless  one.  The 
violet  ray  suffers  the  greatest  refraction,  and  the  red  the  least:  the  other 
colours  of  the  rainbow  lie  between  them,  disposed  in  regular  succes- 
sion according  to  the  degree  of  deviation  which  they  have  individually 
experienced.  The  coloured  figure  so  produced  is  called  ihe  prismatic 
spectrum,  which  is  always  bounded  by  the  violet  ray  on  the  one  side, 
and  by  the  red  on  the  other. 

I'he  prismatic  colours,  according  to  the  experiments  of  Sir  W.  Her- 
schel,  differ  in  their  illuminating  power.  The  orange  possesses  this 
property  in  a higher  degree  than  the  red;  and  the  yellow  rays  illumi- 
nate objects  still  more  perfectly.  The  maximum  of  illumination  lies 
in  the  brightest  yellow  or  palest  green.  The  green  itself  is  almost 
equally  bright  with  the  yellow;  but  from  the  full  deep  green,  the  illu- 
minating power  decreases  very  sensibly.  That  of  the  blue  is  nearly 
equal  to  that  of  the  red;  the  indigo  has  much  less  than  the  blue;  and 
the  violet  is  very  deficient.  (Phil.  Trans.  1800.) 

The  solar  rays,  both  direct  and  diffused,  possess  the  property  of 
exciting  heat  as  well  as  light.  This  effect  takes  place  only  when  the 
rays  are  absorbed;  for  the  temperature  of  transparent  substances  through 
which  they  pass,  or  of  opake  ones  by  which  they  are  reflected,  is  not 
affected  by  them.  Hence  it  happens  that  the  burning  glass  and  con- 
cave reflector  are  themselves  nearly  or  quite  cool,  at  the  very  moment 
of  producing  intense  heat  by  collecting  the  sun’s  rays  into  a focus.  The 
extreme  coldness  that  prevails  in  the  higher  strata  of  the  air  arises  from 
the  same  cause.  The  rays  pass  unabsorbed  through  the  atmosphere; 
and  its  lower  parts  would  also  be  excessively  cold,  did  they  not  receive 
caloric  by  communication  from  the  earth. 

The  absorption  of  light  is  much  influenced  by  the  nature  of  the  sur- 
face on  which  it  falls;  and  it  is  remarkable  that  those  substances  which 
absorb  radiant  non-luminous  caloric  most  powerfully,  are  likewise  the 
best  absorbers  of  light.  But  there  is  one  property  of  surfaces,  namely, 
colour,  which  has  a great  influence  over  the  absorption  of  light,  but  ex- 
ceedingly little,  if  any,  over  that  of  pure  radiant  caloric.  That  dark- 
coloured  substances  acquire  in  sunshine  a higher  temperature  than  light 
ones,  may  be  inferred  from  the  general  preference  given  to  the  latter 
as  articles  of  dress  during  summer;  and  this  practice,  founded  on  the 
experience  of  mankind,  has  been  justified  by  direct  experiment.  Dr. 
Hooke,  and  subsequently  Dr.  Franklin,  proved  the  fact  by  placing 
pieces  of  cloth  of  the  same  texture  and  size,  but  of  different  colours, 


70 


LIGHT. 


upon  snow,  and  allowing  the  sun’s  rays  to  full  upon  them.  Tlie  durk- 
Coloured  specimens  always  absorbed  more  caloric  than  the  light  ones, 
the  snow  beneath  the  former  having  melted  to  a greater  extent  tJian 
under  the  others;  and  it  was  remarked  that  the  effect  was  nearly  in  pro- 
portion to  the  depth  of  shade.  The  late  Sir  II.  Davy  has  more  recently 
examined  the  subject,  and  arrived  at  the  same  conclusions. 

The  rays  of  the  prismatic  spectrum  differ  from  one  another  in  their 
heating  power  as  well  as  in  colour.  I’heir  difference  in  this  respect 
Was  first  noticed  by  Herschel,  who  was  induced  to  direct  his  attention 
to  the  subject  by  the  following  circumstance.  In  viewing  the  sun  by 
means  of  large  telescopes  through  differently  coloured  darkening  glass- 
es, he  sometimes  felt  a strong  sensation  of  heat  with  very  little  light, 
and  at  other  times  he  had  a strong  light  with  little  heat, — differences 
which  appeared  to  depend  on  the  colour  of  the  glasses  which  he  usecL 
This  observation  led  to  his  celebrated  researches  on  the  heating  power 
of  the  prismatic  colours,  which  were  published  in  the  Thilosophical 
Transactions  for  1800. 

The  experiments  were  made  by  transmitting  a solar  beam  through  a 
prism,  receiving  the  spectrum  on  a table,  and  placing  the  bulb  of  a very 
delicate  thermometer  successively  in  the  different  parts  of  it.  While 
engaged  in  this  inquiry,  he  observed  not  only  that  the  red  was  the  hot- 
test ray,  but  that  there  was  a point  a little  beyond  the  red,  altogether  out 
of  the  spectrum,  where  the  thermometer  stood  higher  than  in  the  red  it- 
self. By  repeating  and  varying  the  experiment,  he  discovered  that  the 
most  intense  heating  power  was  always  beyond  the  red  ray,  where 
tliere  was  no  light  at  all;  and  that  the  heat  progressively  diminished  in 
passing  from  the  red  to  the  violet,  where  it  was  least.  He  thence  in- 
ferred that  there  exists  in  the  solar  beam  a distinct  kind  of  ray,  w'hich 
causes  heat  but  not  light;  and  that  these  rays,  from  being  less  refran- 
gible than  the  luminous  ones,  deviate  in  a less  degree  from  their  original 
direction  in  passing  through  the  prism. 

All  succeeding  experiments  confirm  the  statement  of  Sir  W.  Her- 
^chel,  that  the  prismatic  colours  have  very  different  heating  powers; 
but  they  are  at  variance  with  respect  to  the  spot  at  which  the  heat  is  at 
& maximum.  Some  assert  with  Sir  W.  Herschel  that  it  is  beyond  the 
red  ray;  while  others,  and  in  particular  Professor  Leslie,  contend  that 
it  is  in  the  red  itself.  The  observations  of  M.  Seebeck  in  the  Edinburgh 
Journal  of  Science,  I.  358,  appear  decisive  of  the  question.  He  found 
that  the  point  of  greatest  heat  was  variable  according  to  the  kind  of 
prism  which  was  employed  for  refracting  the  rays.  When  he  used  a 
prism  of  fine  flint  glass,  the  greatest  heat  was  constantly  beyond  the 
red.  With  a prism  of  crown  glass,  the  greatest  heat  was  in  the  red  it- 
self. When  he  employed  a prism  externally  of  glass,  but  containing 
water  within,  the  maximum  was  neither  in  the  red,  nor  beyond  it,  but 
ill  the  yellow.  It  is  difficult  to  account  for  these  phenomena,  except 
on  the  supposition  that  the  different  kinds  of  prisms  differ  in  their  power 
of  refracting  caloric.  These  experiments  therefore  confirm  the  opinion 
of  Sir  W.  Herschel,  that  the  sunbeam  contains  calorific  rays,  distinct 
from  the  luminous  ones;  and  render  it  higlily  probable  that  the  heating 
effect  imputed  to  tlie  latter,  is  solely  owing  to  the  presence  of  tlie 
former. 

It  has  long  been  known  that  solar  light  is  capable  of  producing  pow- 
erful chemical  changes.  One  of  the  most  striking  instances  of  it  is  its 
power  of  darkening  the  white  chloride  of  silver,  an  effect  which  takes 
place  slowly  in  the  diffused  light  of  day,  but  in  the  course  of  two  or 
tliree  minutes  by  exposure  to  the  sunbeam.  This  effect  was  once  at- 
ti'ibutcd  U>thc  iuflucuce  of  the  luminous  rays;  but  it  appeal's  from  the 


LIGHT. 


71 


observations  of  Ritter  and  Wollaston,  that  it  is  owing*  to  the  presence  of 
certain  rays  that  excite  neither  heat  nor  light,  and  which,  from  their 
peculiar  agency,  are  termed  chemical  rays.  It  is  found  that  the  greatest 
chemical  action  is  exerted  just  beyond  the  violet  ray  of  the  prismatic 
spectrum;  that  the  spot  next  in  energy  is  occupied  by  the  violet  ray 
itself;  and  that  the  property  gradually  diminishes  as  we  advance  to  the 
green,  beyond  which  it  seems  wholly  wanting.  It  hence  follows  that 
the  chemical  rays  are  still  more  refrangible  than  the  luminous  ones,  in 
consequence  of  which  they  are  dispersed  in  part  over  the  blue,  indigo, 
and  violet,  but  in  the  greatest  quantity  at  a point  which  is  even  beyond 
the"latter. 

The  more  refrangible  rays  of  light  are  said  to  possess  the  property  of 
rendering  steel  or  iron  magnetic.  The  existence  of  this  property  was 
first  asserted  by  Dr.  Morichini  of  Rome.  Other  observers  subsequently 
failed  in  obtaining  the  same  results;  but  in  the  year  1826  the  fact  ap» 
peared  to  be  decisively  established  by  the  learned  and  accomplished 
Mrs.  Somerville,  in  an  essay  published  in  the  Transactions  of  the  Royal 
Society.  In  her  experiments,  sewing  needles  were  rendered  magnetic 
by  exposure  for  two  hours  to  the  violet  ray;  and  the  magnetic  virtue 
was  communicated  in  a still  shorter  time,  when  the  violet  rays  were  con- 
centrated by  means  of  a lens.  The  indigo  rays  were  found  to  possess 
a magnetizing  power  almost  to  the  same  extent  as  the  violet;  and  it  was 
also  observed,  though  in  a less  degree,  in  the  blue  and  green  rays.  It 
is  wanting  in  the  yellow,  orange,  and  red.  Needles  were  likewise  ren- 
dered magnetic  by  the  sun’s  rays,  transmitted  through  green  and  blue 
glass.  These  results  have  been  verified  by  M.  Zantedeschi  of  Pavia 
(Bibb  Univ.  for  May,  1829);  but  their  accuracy  is  denied  by  MM.  Riess 
and  Moser,  who  consider  that  the  means  employed  by  Mrs.  Somerville 
for  ascertaining  the  magnetic  state  of  the  needles  were  not  sufficiently 
exact.  They  found  the  oscillation  of  needles  to  be  wholly  unaf- 
fected by  exposure  to  the  prismatic  colours.  (Brewster’s  Journal,  II. 
225.  N.  S.)  This  must  still  be  regarded,  therefore,  as  one  of  the  dis- 
puted points  in  science. 

The  second  kind  of  light  is  that  which  is  emitted  by  substances  when 
strongly  heated.  All  bodies  begin  to  emit  light  when  caloric  is  accu- 
mulated within  them  in  great  quantity;  and  the  appearance  of  glowing  or 
shining,  wffiich  they  then  assume,  is  called  incandescence.  The  tempera- 
ture at  which  solids  in  general  begin  to  shine  in  the  dark  is  between 
600®  and  700®  F.;  but  they  do  not  appear  luminous  in  broad  daylight 
till  they  are  heated  to  about  1000®.  The  colour  of  incandescent  bodies 
varies  with  the  intensity  of  the  heat.  The  first  degree  of  luminousness 
is  an  obscure  redi  As  the  heat  augments,  the  redness  becomes  more 
and  more  vivid,  till  at  last  it  acquires  a full  red  glow.  Should  the  tem- 
perature still  continue  to  increase,  the  character  of  the  glow  changes, 
and  by  degrees  it  becomes  white,  shining  with  increasing  brilliancy  as 
the  intensity  of  the  heat  augments.  Liquids  and  gases  likewise  become 
incandescent  when  strongly  heated;  but  a very  high  temperature  is  re- 
quired to  render  a gas  luminous,  more  than  is  sufficient  for  heating  a 
solid  body  even  to  whiteness.  The  different  kinds  of  flame,  as  of  the 
fire,  candles,  and  gas  light,  are  instances  of  incandescent  gaseous  mat- 
ter. 

All  artificial  lights  are  produced  by  the  combustion  or  burning  of  in- 
flammable matter.  So  large  a quantity  of  caloric  is  evolved  during  the 
process,  that  the  body  is  made  incandescent  in  the  moment  of  bein^ 
consumed.  Those  substances  are  preferred  for  the  purposes  of  illumi- 
nation that  yield  gaseous  products  when  strongly  heated,  which,  by  be- 
coming luminous  while  they  burn,  constitute  flame.  The  light  derived 


72 


LIGHT. 


from  such  sources  differs  from  solar  light  in  being  accompanied  by  free 
radiant  caloric  similar  to  that  emitted  by  a non-luminous  heated  body. 
The  free  radiant  caloric  may  be  separated  by  a screen  of  moderately 
thick  glass;  but  the  light  so  purified  still  heats  any  body  that  absorbs  it, 
whence  it  would  appear  that  it  retains  some  calorific  rays  which,  like 
those  in  the  solar  beam,  accompany  the  luminous  ones  ir^  their  passage 
through  solid  transparent  media.*  Terrestrial  light  h^been  supposed 
to  contain  no  chemical  rays;  but  the  experiments  with  lime  strongly 
heated  by  the  method  of  Mr.  Drummond,  have  proved  that  artificial 
light  of  great  intensity  is  productive  of  chemical  changes  similar  to 
those  occasioned  by  solar  light.  (Annals  of  Philosophy,  xxvii,  451.) 

Light  is  emitted  by  some  substances  at  common  temperatures,  giving 
rise  to  an  appearance  which  is  called  phosphorescence.  This  phenome- 
non seems  owing  in  some  instances  to  a direct  absorption  of  light  which 
is  afterwards  slowly  emitted.  A composition  made  by  heating  to  red- 
ness a mixture  of  calcined  oyster  shells  and  sulphur,  known  by  the 
name  of  Canton’s  Phosphorus,  possesses  this  property  in  a very  remark- 
able degree.  It  shines  so  strongly  for  a few  minutes  after  exposure  to 
light,  that  when  removed  to  a dark  room,  the  hour  on  a watch  may  be 
distinctly  seen  by  it.  After  some  time  it  ceases  to  be  luminous,  but  re- 
gains the  property  when  exposed  during  a short  interval  to  light.  No 
chemical  change  attends  the  phenomenon. 

Another  kind  of  phosphorescence  is  observable  in  some  bodies  when 
they  are  strongly  heated.  A piece  of  marble,  for  example,  heated  to  a 
degree  which  would  only  make  other  bodies  red,  emits  a brilliant  white 
light  of  such  intensity  that  the  eye  cannot  support  its  impression. 

The  third  species  of  phosphorescence  is  observed  in  the  bodies  of  some 
animals,  either  in  the  dead  or  living  state.  Some  marine  animals,  and 
particularly ^sh,  possess  it  in  a remarkable  degree.  It  may  be  witnessed 
in  the  body  of  the  herring,  which  begins  to  phosphoresce  a day  or  two 
after  death,  and  before  any  visible  sign  of  putrefaction  has  set  in.  Sea- 
water is  capable  of  dissolving  the  luminous  matter;  and  it  is  probably  from 
this  cause  that  the  waters  of  the  ocean  sometimes  appear  luminous  at 
night  when  agitated.  This  appearance  is  also  ascribed  to  the  presence 
of  certain  animalcules,  which,  like  the  glow-worm  of  this  country,  or  the 
fire-fly  of  the  West  Indies,  are  naturally  phosphorescent. 

It  is  sometimes  of  importance  to  measure  the  comparative  intensities 
of  light,  and  the  instrument  by  which  this  is  done  is  called  2^  Photometer . 

The  only  photometer  which  is  employed  for  estimating  the  relative 
strength  of  the  sun’s  light  is  that  of  >Ii*.  Leslie.  It  consists  of  his  dif- 
ferential thermometer,  with  one  ball  made  of  black  glass.  The  clear 
ball  transmits  all  the  luminous  rays  that  fall  upon  it,  and  therefore  its 
temperature  is  not  affected  by  them;  they  are  all  absorbed,  on  the  con- 
trary, by  the  black  ball,  and  by  heating  and  expanding  the  air  within, 
cause  the  liquid  to  ascend  in  the  opposite  stem.  The  whole  instrument 
is  covered  with  a case  of  tlnn  glass,  the  object  of  which  is  to  prevent  the 
balls  from  being  affected  by  currents  of  cold  air.  The  action  of  this 
photometer  depends  on  the  lieat  produced  by  the  absorption  of  lig'ht. 
Mr.  I.eslic  conceives  tliat  light  wlicn  a]3sorbed  is  converted  into  heat;  but 
according  tr)  tlic  experiments  already  refeiTcd  to,  the  effect  must  be  at- 
tributed, not  so  much  to  the  light  itself,  as  to  the  absorption  of  the  calorific 
rays  by  which  it  is  accom])anied. 

Mr.  Leslie  recommends  his  photometer  also  for  determining  the  rela- 
tive intensities  of  artificial  light,  such  as  that  emitted  by  candles,  oil,  or 


* Mr  Powel,  in  Phil.  Trans,  for  1825. 


ELECTRICITY. 


73 


gus.  This  application  of  it  differs  from  the  foregoing*,  because  light 
proceeding  from  terrestrial  sources  contains  caloric  under  two  forms. 
One  portion  is  analogous  to  tliat  emitted  by  a hot  body  which  is  not 
luminous;  the  other  is  similar  to  that  which  accompanies  solar  light.  It 
is  presumed  that  the  first  form  of  caloric  will  not  prove  a source  of  eiTor; 
that  these  rays  are  wholly  intercepted  by  the  outer  case  of  glass;  or  that, 
should  a few  penetrate  into  the  interior,  they  will  be  absorbed  equally  by 
both  balls,  and  will  therefore  heat  them  to  the  same  extent.  It  is  proba- 
ble that  tills  reasoning  is  not  Wide  of  the  truth;  and,  consequently,  the 
photometer  will  give  correct  indications  so  far  as  regards  the  new  ele- 
ment— non-luminous  caloric-  But  it  is  not  applicable  to  lights  which  differ 
in  colour,  because  the  relation  between  the  heating  and  illuminating 
power  of  such  lights  is  exceedingly  variable.  Thus,  the  light  emitted 
by  burning  cinders  or  red-hot  iron,  even  after  passing  through  glass, 
contains  a quantity  of  calorific  rays,  which  is  out  of  all  proportion  to  the 
luminous  ones;  and,  consequently,  they  may  and  do  produce  a greater 
effect  on  the  photometer  than  some  lights  whose  illuminating  powers  are 
far  stronger. 

The  second  kind  of  photometer  is  on  a totally  different  principle.  It 
determines  the  comparative  strength  of  lights  by  a comparison  of  their 
shadows.  This  instiaiment  was  invented  by  Count  Riunford,  and  is  de- 
scribed by  him  in  his  Essays.  It  is  susceptible  of  great  accuracy  when 
employed  with  the  requisite  care;*  but,  like  the  foregoing,  its  indica- 
tions cannot  be  trusted  when  there  is  much  difference  in  the  colour  of 
the  lights.  In  this  case,  the  best  mode  of  obtaining  an  approximative  re- 
sult, is  by  observing  the  distance  from  each  light  at  which  any  given  ob- 
ject, as  a printed  page,  ceases  to  be  cfistinctly  visible.  The  illuminating 
power  of  the  Jig'hts  so  compared  is  as  the  squares  of  tlieii*  distances- 


SECTION  III. 

ELECTRICITY. 

WiiEx-  certain  substances,  such  as  amber,  glass,  sealing-wax,  or  sulphur, 
are  rubbed,  and  then  brought  near  small  fragments  of  paper,  cork,  or 
other  light  bodies,  the  latter  move  rapidly  towards  the  former,  and  adhere 
during  a longer  or  shorter  interv^al  to  their  surface.  If  the  body  which 
is  thus  excited  by  friction  is  light  and  freely  suspended,  it  will  move  to- 
wards the  substances  in  its  vicinity.  After  a while  the  excited  body  loses 
its  influence;  but  it  may  be  renewed  for  any  number  of  times  by  friction. 
The  movement  observed  in  these  instances  is  attributed  to  a peculiar 
kind  of  attraction,  and  the  unknown  cause  of  this  attraction  is  called 
Electricity,  from  the  Greek  word  amber,  because  the  electric 

property  was  first  noticed  in  tliis  substance. 

The  ancients  were  aware  tliat  amber  and  the  lyncurium,  (supposed  to 
bo  our  tourmalin, ) may  be  rendered  electric  by  friction,  but  it  was  not 
known  tliat  other  bodies  may  be  similarly  excited  until  the  commence- 
ment of  the  17th  century,  when  Dr.  Gilbert  pf  Colchester  detected  the 
same  property  in  a variety  of  other  substances.  Of  those  wliich  he  has 
enumerated  in  his  treatise  de  Magnete,  tlie  principal  are  the  diamond, 


* See  an  Essay  on  the  Construction  of  Coal  Gas  Burners,  8cc.  in  the 
Edinburgh  Philosophical  Journal  for  1825. 

7 


ELECTRICITY. 


rock-crystal  and  severrd  of  the  precious  stones,  i^lass,  sulpliiir,  mastic, 
sealing-wax,  and  resin;  and  in  making  tills  discovery  lie  laid  the  founda- 
tion of  the  science  of  electricity.  A few  additional  facts  were  noticed 
during  the  course  of  the  same  century  by  Boyle,  Otto  de  Guericke,  and 
Dr.  Wall,  and  in  1709  Mr.  Ilawkesbce  published  an  account  of  many  cu- 
rious electrical  experiments;  but  no  material  progi'css  was  made  in  tliis 
department  of  knowledge  till  between  the  years  1729  and  1733,  when 
tlie  discoveiy  of  new  and  important  facts  by  Mr.  Stephen  Grey  in  this 
country,  and  M.  Dufay  in  France,  attracted  general  attention  to  the  sub- 
ject, and  speedily  acquired  for  it  the  regular  fom  of  a science.* 

The  most  important  fact  established  by  :Mi\  Grey  was  the  fundamen- 
tal one,  that  electricity  passes  freely  along  cei’tain  substances,  and  tliatits 
progi’ess  is  more  or  less  entirely  aiTested  by  others.  M.  Dufay,  in  re- 
peating the  experiments  of  Grey,  obseiw ed  that  an  electrified  substance 
not  only  attracts  light  bodies,  but  causes  them  after  contact  to  fly  off 
from  its  siu’face  as  if  by  a principle  of  repulsion.  Tliis  singular  phenome- 
non, wliicli  is  termed  electrical  repulsion,  had  been  previously  noticed  by 
Otto  de  Guericke,  but  the  meidt  of  original  observation  seems  also  justly 
due  to  the  French  philosopher.  Dufay  li  ke wise  noticed  that  the  electiicity 
excited  on  glass  is  different  from  that  of  resin,  and  hence  inferred  the 
existence  of  two  kinds  of  electricity,  the  vitreous  and  resinous,  the  for- 
mer belonging  to  glass,  and  the  latter  to  resin.  He  established  an  ex- 
cellent mode  of  distinguishing  them,  by  finding  tliat  substances  possessed 
of  the  same  kind  of  electricity  always  I’epel  each  other;  and  that  attrac- 
tion is  as  uniformly  exerted  between  substances  which  are  in  opposite 
states  of  electrical  excitement. 

Another  fact  of  consequence,  relative  to  the  excitement  of  electricity 
by  friction,  was  discovered  in  1759  by  IMi’.  Symmer,  (Philos.  Trans,  ii. 
340. ) who  found  that  when  two  bodies  are  rubbed  together,  both  are 
excited,  and  that  one  always  possesses  vitreous  and  the  other  resinous 
electricity.  This  induced  Symmer  to  modify  the  doctrine  of  the  two 
electricities.  Dufay  conceived  viti'eous  electricity  to  be  peculiar  to  some 
substances  and  resinous  electricity  to  others.  Symmer,  on  the  contrary, 
maintained,  thstt  bodies  in  their  ordinary  unexcited  condition  contain  both 
kinds  of  electricity  in -a  state  of  combination;  and  as  they  then  neutralize 
or  counteract  each  othei'’s  effects,  no  electrical  phenomena  are  apparent; 
that  friction  produces  excitement  by  separating  the  two  principles;  and 
tliat  excitation  continues  until  that  kind  of  electricity,  wliich  has  been 
withdrawn,  is  restored. 

Dufay’s  doctrine  of  the  two  electricities,  as  modified  by  SjTnmer,  is 
consistent  with  all  the  facts  which  subsequent  observation  has  brought  to 
lig’ht,  and  is  adopted  almost  universally  in  France  and  other  parts  of  the 
continent.  It  is  found  that  all  substances  when  electrified  by  friction, 
are  thrown  into  opposite  states  of  excitement;  that  electrical  repulsion  is 
never  observed  ]>ut  between  bodies  simdarly  electrified;  and  that  electri- 
cal attraction  is  as  uniformly  owing  to  the  substances  possessing  different 
kinds  of  electricity.  For  these  phenomena,  however,  Dr.  Franklin  pro- 
posed a difierent  explanation,  founded  on  the  supposition  of  there  being 
oiJy  one  kind  of  eleciricity.  According  to  tliis  plnlosopher,  whp  bodies 
contain  tiieir  natural  f[uantity  of  electricity,  they  do  not  manifest  any 
L icetrical  prf)i)erti<.-s;  but  they  are  excited  either  by  its  increase  or  di- 
junutlon.  On  rubbing  a tube  ol’ glass  with  a woollen  cloth,  thecdectri- 
cal  couditl(»n  of  both  substanct  s is  disturbed;  the  fonner  acquhes  more 
or  is  ovcrcliarged,  the  other  less  than  its  natiual  quantity  or  is  undcr- 


' For  the  historical  detaihi,  see  Priestley’s  History  of  Electricity. 


ELECTRICITY. 


charged.  These  opposite  states  he  expressed  by  the  tc:vrc\^  positive  and 
negative,  the  first  con’esponding  to  the  vitreous,  the  second  to  the  re- 
sinous electricity  of  Dufay.  Electrical  repulsion,  according  to  Franklin, 
takes  place  between  substances  which  contain  either  more  or  less  than 
their  natiu’al  quantity;  and  electrical  attraction  is  only  exerted  between 
two  bodies,  one  of  which  contains  more  than  its  natural  quantity,  and 
the  otlier  less.  The  excess  of  electricity  has  a strong  tendency  to  pass 
from  a positively  to  a negatively  excited  surface,  so  as  to  restore  tiije 
equilibrium  in  both;  and  this  always  happens  either  by  contact,  or  from 
such  proximity  that  the  electricity  is  able  to  pass  from  one  to  the  other 
through  tlie  intervening  stratum  of  air.  The  phenomena  of  electricity 
are  explicable  by  both  these  theories;  but  as  that  of  Dr.  Franklin  is  com- 
monly adopted  in  Britain,  I shall  employ  it  in  preference  in  this  treatise. 

It  has  been  objected  to  this  hypothesis  that  it  does  not  account  satis- 
factorily for  the  repulsion  observed  between  bodies  negatively  electri- 
fied. The  separation  of  two  positively  electric  bodies  is  easily  accounted 
for  by  the  repulsive  power  supposed  to  be  exerted  among  the  particles 
of  the  electricity  accumulated  upon  them;  while  substances  which  are 
negative,  or  possess  less  than  their  natural  quantity  of  electricity,  can- 
not be  influenced  by  such  a power,  and  therefore,  it  is  argued,  ought 
not  to  diverge  or  separate.  This  mode  of  reasoning,  however,  is  en- 
tirely hypothetical.  There  is  no  proof  that  the  divergence  observed  in 
similarly  electrified  bodies  is  owing  to  actual  repulsion;  and  the  pheno- 
menon may  be  explained  equally  well  on  the  principle,  that  the 
excited  substances  are  attracted  in  opposite  directions,  in  consequence 
of  the  contiguous  strata  of  air  being  rendered  oppositely  electrical  by 
induction.  In  this  way  all  the  phenomena  of  electrical  attraction  and 
repulsion  are  referrible  to  the  attractive  power  exerted  between  bodies 
in  opposite  states  of  excitement.  The  term  repulsion,  according  to  this 
view,  is  used  merely  to  express  the  act  of  separation  or  divergence. 

Nothing  certain  is  known  concerning  the  principle  or  cause  of  the 
phenomena  of  electricity.  It  may  possibly  be  only  a property  of  mat- 
ter, called  into  action  by  particular  circumstances;  but  the  phenomena 
accord  much  better  with  the  opinion,  which  is  now  almost  universally 
received  by  philosophers,  that  it  is  a highly  subtile  elastic  fluid,  too 
light  to  affect  the  most  delicate  balances,  capable  of  moving  with  ex- 
treme velocity,  and  present  in  all  bodies.  Its  influence,  in  excited 
bodies,  is  diffused  uniformly  in  every  direction;  and  like  light  and  other 
principles  which  are  subject  to  this  law,  its  power  diminishes  as  the 
squares  of  the  distance.  It  is  one  of  the  most  energetic  principles  in 
nature.  It  is  the  cause  of  thunder  and  lightning;  the  phenomena  of 
galvanism,  and  probably  of  magnetism,  are  produced  by  it;  and  the  in- 
fluence which  it  exerts  over  chemical  changes  is  so  great,  that  some 
philosophers  regard  it  as  the  cause  of  chemical  attraction.  The  par- 
ticles of  the  electric  fluid  are  supposed  to  be  highly  repulsive  to  each 
other,  and  to  be  powerfully  attracted  by  other  material  substances. 
The  tendency  to  pass  from  overcharged  surfaces  to  those  that  are  in  a 
negative  state,  may  be  ascribed  to  one  or  other  of  these  properties,  or 
perhaps  to  their  conjoint  operation. 

Electricity  may  be  excited  in  all  solid  substances  by  friction.  This 
assertion  seems  at  first  view  contrary  to  fact.  It  is  well  known  that  a 
metallic  substance,  if  held  in  the  hand,  may  be  rubbed  for  any  length 
of  time  without  exhibiting  the  least  sign  of  electricity;  an  observation 
which  led  to  the  division  of  bodies  into  such  as  may  be  excited  by  fric- 
tion, and  into  those  that,  under  the  same  circumstances,  give  no  sign  of 
electrical  excitement.  The  former  were  called  Electrics,' latter 
Non-electrics,  But  the  distinction  is  not  founded  in  nature.  A metallic 


76 


ELECTmCITy. 


substance  does  not  indeed  exhibit  any  trace  of  electricity  w hen  rubbed 
in  the  same  way  as  a piece  of  glass;  but  if,  while  it  is  rubbed  with  the 
dry  fur  of  a cat,  it  is  supported  by  a glass  handle,  it  will  tlicn  readily 
evince  signs  of  electrical  excitement. 

The  difficulty  and  apparent  impossibility  of  exciting  metallic  bodies, 
receives  an  explanation  from  the  fact  observed  by  Grey,  that  the  elec- 
tric fluid  passes  with  great  facility  along  the  surface  of  some  substances, 
and  with  difficulty  over  that  of  others;  and  this  discovery  has  led  to  the 
division  of  bodies  into  Conductors  and  Non-conductors  of  electricity.  If 
an  excited  conductor,  such  as  a metallic  wire,  be  made  to  communicate 
at  one  of  its  extremities,  with  the  earth,  the  electricity  will  pass  to  it 
from  the  opposite  end  in  an  instant,  even  though  it  were  several  miles 
in  length;  so  tliat  when  the  equilibrium  is  disturbed,  it  will  be  at  once 
restored  along  the  whole  wire,  just  as  effectually  as  if  every  point  of  it 
communicated  with  the  ground.  But  an  excited  stick  of  glass  or  resin 
is  not  affected  in  the  same  manner;  for  as  electricity  does  not  obtain  a 
free  passage  along  them,  the  equilibrium  is  restored  in  those  parts  only, 
which  are  actually  touched.  For  this  reason  a non-conductor  of  elec- 
tricity, though  held  in  the  hand,  may  be  readily  excited;  but  a good 
conducting  body  cannot  be  brought  into  that  state,  unless  it  be  insu^ 
lated,  that  is,  cut  off  from  communication  with  the  earth  by  means  of 
some  non-conductor.  This  is  generally  effected  either  by  supporting  a 
body  with  a handle  of  glass,  or  by  placing  it  on  a stool  made  with  glass 
feet. 

To  the  class  of  conductors  belong  the  metals,  charcoal,  plumbago, 
water,  and  most  substances  which  contain  water  in  its  liquid  state,  such 
as  animals  and  plants.  The  conductive  power  of  these  substances  is 
different.  Of  the  metals,  according  to  the  experiments  of  Mr.  Harris, 
silver  and  copper  are  the  best  conductors  of  electricity;  and  then  fol- 
low gold,  zinc,  platinum,  iron,  tin,  and  lead.  (Philos.  Trans,  for  1827, 
Part  I.  21.)  To  the  list  of  non-conductors  belong  glass,  resins,  sulphur, 
the  diamond,  dried  wood,  precious, stones,  silk,  hair,  and  wool.  Atmos- 
phejic  air  is  also  a non-conductor.  If  it  were  not  so,  no  substance  could 
retain  its  electricity  when  surrounded  by  it.  Aqueous  vapour  suspend- 
ed in  the  air  injures  the  non-conducting  property  of  the  latter,  and 
hence  electrical  experiments  do  not  succeed  so  well  when  the  air  is 
charged  with  moisture  as  when  it  is  dry.  The  presence  of  a little  mois- 
ture communicates  conducting  properties  to  the  most  imperfect  con- 
doctor;  and  hence  it  is  impossible  to  excite  glass  by  rubbing  it  with  a 
moist  substance.  i 

A knowledge  of  the  different  conducting  power  of  bodies  is  required  | 
for  explaining  some  circumstances  which  appear  contradictory  to  a pre-  I 
ceding  statement.  It  is  above  mentioned  that  when  two  bodies  are  ex-  i 
cited  by  friction,  they  are  rendered  oppositely  electric;  but  if  a tube  of  j 
glass  is  rubbed  by  a person  communicating  with  the  ground,  the  glass 
will  become  positively  electrical,  while  the  hand  of  the  operator  mani- 
fests no  sign  whatever  of  excitement.  The  cause  of  this  is  obvious. 
The  operator  is  not  electrified,  because  the  earth  restores  the  electric 
fluid  as  soon  as  it  is  withdrawn  by  the  glass;  but  if  he  is  insulated,  the 
indications  of  negative  electricity  will  immediately  appear.  Hence  it 
is  a lailc  to  insulate  a conductor,  whenever  it  is  wished  to  examine  its 
electrical  condition. 

The  experiments  which  have  been  made  concerning  the  effects  of 
friction,  have  demonstrated  that  the  same  substance  is  not  always  simi- 
larly electrified.  Its  electricity  is  influenced  partly  by  the  state  of  its 
s\jrface,  and  partly  by  the  nature  of  the  body  with  which  it  is  rubbed. 
Thus  smooth  glass  is  rendered  positive  by  friction  with  woollen  cloth j 


ELECTRICITY. 


whereas  if  Its  surface  is  rough,  it  becomes  negative  from  the  same  treat- 
ment. Smooth  glass  which  is  positive  with  woollen  cloth,  is  rendered 
negatively  electrical  by  being  rubbed  with  a cat’s  fur.  The  following 
table  from  Cavallo’s  Complete  Treatise  on  Electricity,  shows  the  kind 
of  excitement  produced  by  the  friction  of  various  substances. 


The  back  of  a cat 
Smooth  glass 


Rough  glass 


Is  Tendered 
^ Positive  ^ 

^ Positive  ^ 

"I  Positive  ^ 

. c 

I Negative  < 


By  frietion  with 

Every  substance  with  which  it  has  been 
hitherto  tried. 

Every  substance  hitherto  tried  except 
the  back  of  a cat. 

Dry  oiled  silk,  sulphur,  and  metals. 

Woollen  cloth,  quills,  wood,  paper, 
sealing-wax,  white  wax,  the  human 
hand. 


Tourmalin 


Hare’s  skin 


Positive  ^ Amber,  a current  of  air. 

J Negative  ^ Diamond,  the  human  hand. 

C Metals,  silk,  loadstone,  leather,  the 
\ hand,  paper,  baked  wood. 


^ Positive 


j 


Negative  ^ Other  finer  furs. 


White  silk 


Black  silk 


Sealing-wax 


Baked  wool 


Positive 

Negative 

Positive 


I Negative 


Positive 
j Negative 

J 


Positive 

Negative 


J 

5 

J 


Black  silk,  metals,  black  cloth. 

Paper,  hand,  hair,  weasel’s  skin. 
Sealing  wax. 

The  skin  of  the  hare,  weasel,  and  fer- 
ret, loadstone,  brass,  silver,  iron,  and 
the  hand. 


^ Metals. 


The  skin  of  the  hare,  weasel,  and  fer- 
ret, the  hand,  leather,  woollen  cloth, 
paper. 


^Silk. 

^ Flannel. 


Mr.  Singer  states  that  sealing-wax  is  not  rendered  positive  by  friction 
with  all  metals: — iron,  steel,  lead,  and  bismuth,  as  also  plumbago,  leave 
it  negative,  Mr.  Cavallo’s  statement  with  respect  to  white  silk  and 
paper  does  not  agree  with  my  observation.  The  effect  of  white  paper 
is  variable;  but  in  a number  of  trials  I found  that  by  coarse  brown  pa- 
per white  silk  was  invariably  rendered  positive. 

The  foregoing  remarks  on  the  effects  of  friction  will  render  intelli- 
gible the  principle  of  the  electrical  machine.  In  the  time  of  Grey  a 
supply  of  electricity  was  obtained  for  experimental  purposes  by  rub- 
bing a glass  tube  with  the  dry  hand.  Glass  globes  made  to  revolve  by 
machinery  were  afterwards  substituted  for  the  tube,  the  friction  being 
at  first  produced  with  the  hand,  and  subsequently  by  means  of  a fixed 
rubber.  As  now  constructed,  the  electrical  machine  is  formed  either 
with  a cylinder  or  plate  of  glass,  which  is  pressed  during  its  rotation  by 

7* 


78 


ELECTRICITY. 


cushions  stuffed  with  hair.  The  cushion  is  usually  covered  with  an 
amalgam  of  tin  and  zinc,  which,  partly  by  increasing  the  friction,  and 
partly  by  the  oxidation  of  the  metals,  materially  assists  the  action  of  the 
machine.  The  electricity  developed  on  the  glass  is  conducted  away  by 
an  insulated  bar  of  brass  placed  close  to  it,  called  the  prime  conductor ^ on 
which  it  is  collected  in  considerable  quantity.  By  this  means  the  elec- 
tricity spread  over  the  whole  surface  of  the  prime  conductor  may  be 
carried  off  at  the  same  instant,  and  thus  act  with  far  greater  power 
than  if  accumulated  on  glass  or  any  other  imperfectly  conducting  sub- 
stance. 

The  electricity  which  is  so  freely  and  unceasingly  evolved  during  tlie 
action  of  a good  electrical  machine,  is  derived  from  the  great  reservoir 
of  electricity,  the  earth.  This  is  obvious  from  the  fact,  that  if  the  whole 
apparatus  is  insulated,  the  evolution  of  electricity  immediately  ceases; 
but  the  supply  is  as  instantly  restored,  when  the  requisite  communica- 
tion is  made  with  the  ground.  In  the  state  of  complete  insulation  the 
glass  and  prime  conductor  are  positive  as  usual,  and  the  rubber  is  nega- 
tively excited;  but  as  the  electricity  then  developed  is  derived  solely 
from  the  machine  itself,  its  quantity  is  exceedingly  small.  When  the 
machine  is  used,  therefore,  the  rubber  is  made  to  communicate  with 
the  earth.  As  soon  as  friction  is  begun,  the  glass  becomes  positive, 
and  the  rubber  negative;  but  as  the  latter  communicates  with  the 
ground,  it  instantly  recovers  the  electricity  which  it  had  lost,  and  thus 
continues  to  supply  the  glass  with  an  uninterrupted  current.  If  the 
rubber  is  insulated,  and  the  prime  conductor  communicates  with  the 
ground,  the  electricity  of  the  former  and  all  conductors  connected  with 
it,  is  carried  away  into  the  earth,  and  they  are  negatively  electrified. 

Friction  is  not  the  only  cause  of  electrical  excitement.  Bodies  are 
sometimes  excited  by  elevation  of  temperature,  a property  first  noticed 
in  certain  crystallized  minerals,  such  as  tourmalin  and  boracite,  which 
do  not  possess  that  symmetric  arrangement  of  parts  commonly  existing 
in  ciystals.  The  electric  equilibrium  is  disturbed  in  metallic  rods  or 
wires  by  one  extremity  having  a different  temperature  from  that  of  the 
other,  as  was  first  observed  by  Professor  Seebeck,  and  since  shown  to 
be  true  of  all  metals  by  Professor  Gumming.  (Annals  of  Phil.  v.  427. 
N.  S.)  The  experiment  i§  usually  made  by  heating  the  point  of  junc- 
tion of  two  metallic  wires,  which  are  soldered  together;  but  M.  Bee- 
querel  has  proved  that  the  contact  of  one  metal  with  another  is  not 
essential.  (An.  de  Ch.  p.  xli.  353.) 

Another  and  apparently  very  fruitful  source  of  electricity  is  chemical 
action.  This  was  strongly  denied  by  the  late  Sir  H.  Davy  in  his  Bake- 
rian  lecture  for  1826;  but  the  experiments  of  Becquerel,  De  la  Rive, 
and  Pouillet,  afford  in  my  opinion  decisive  proof  that  chemical  union 
and  decomposition  are  both  attended  with  electrical  excitement.  (An. 
de  Ch.  et  de  Ph.  T.  35,  36,  37,  38,  and  39.)  M.  Pouillet,  in  particular, 
has  demonstrated  that  the  gas  arising  from  the  surface  of  burning  char- 
coal is  positive,  while  the  charcoal  itself  is  negative;  and  he  has  proved 
that  similar  phenomena  arc  produced  by  the  combustion  of  hydrogen, 
alcohol,  oil,  and  other  inflammables  of  the  same  kind.  In  all  tliese  in- 
stances the  combustible,  in  the  act  of  burning,  renders  contiguous  par- 
ticles negative;  while  the  oxygen  imparts  electricity  to  the  products 
of  combustion,  which  thereby  become  positive.  The  fact,  with  respect 
to  charcoal,  was  originally  noticed  by  Volta,  La  Place,  and  Lavoi^r, 
but  was  subsequently  denied  by  Saussure  and  Sir  H.  Davy.  M.  Pouillet 
has  reconciled  these  conflicting  statements  by  showing  that  the  i^ilt 
depends  on  the  mode  in  which  the  experiment  is  conducted.  For  if  the 
carbonic  acid  be  completely  removed  from  tlie  burning  masa  at  the  in- 


ELECTRICITY. 


79 


stant  of  its  formation,  both  are  found  to  be  electrical?  but  if,  on  the 
contrary,  the  carbonic  acid  subsequently  flows  over  the  surface  of  the 
charcoal,  the  equilibrium  will  instantly  be  restored,  and  of  course  no 
sign  whatever  of  excitement  be  perceptible. 

The  electric  equilibrium  is  likewise  disturbed  by  the  contact  of  differ- 
ent substances,  especially  of  metals?  a fact  first  demonstrated  by  Volta, 
w’ho  founded  on  it  a theory  of  galvanism.  The  experiment  is  commonly 
made  with  well  cleaned  plates  of  zinc  and  copper,  which  are  supported 
and  insulated  by  handles  of  glass.  On  holding  the  zinc  plate  by  its 
glass  handle,  laying  it  repeatedly  on  the  copper,  which  at  the  time  need 
not  be  insulated,  and  after  each  contact  touching  with  it  the  instrument^ 
shortly  to  be  described,  called  the  Condenser,  a positive  charge  is  grad- 
ually accumulated.  On  operating  in  the  same  way  witli  the  insulated 
plate  of  copper,  it  is  found  to  communicate  a negative  charge.  From 
such  experiments  it  is  infen’ed,  that  the  contact  of  zinc  and  copper  dis- 
turbs the  electric  equilibrium  in  both  metals,  the  latter  yielding  some  of 
its  electricity  to  the  former  and  becoming  negative,  while  the  zinc  is  there- 
by rendered  positive.  But  the  inference,  though  extremely  probable, 
is  not  free  from  objection.  In  fact,  so  long  as  contact  continues,  there  is 
no  electric  appearance  whatever?  and  the  metals  are  assumed  to  be  differ- 
ently electrified  at  that  time,  in  consequence  of  the  phenomena  which 
they  exhibit  after  their  sepai-ation.  There  is,  therefore,  an  obvious  as- 
sumption. But,  on  the  other  hand,  the  absence  of  the  indications  of  ex- 
citement is  not  conclusive  against  the  received  doctrine?  because,  con- 
sistently witli  the  laws  of  electricity,  the  oppositely  electrical  state  of  the 
two  metals,  while  they  continue  together,  must  counteract  the  effect  to 
which  either  separately  would  give  rise. 

The  excitement  of  electricity  by  contact  has  been  denied  by  some  phi- 
losophers, and  of  late  this  doctrine  has  been  attacked  by  M.  de  la  ^ve 
of  Geneva.  (An.  de  Ch.  et  de  Ph.  xxxix.  297.)  He  there  contends 
that  the  phenomena  ascribed  to  metallic  contact  are  really  due  to  slight 
oxidation  produced  by  moisture  and  the  oxygen  of  the  air  acting  on  the 
plate  of  zinc.  He  has  adduced  experiments  to  prove,  tliat  if  the  oxida- 
tion of  the  zinc  be  increased  by  acid  fumes,  the  electric  charge  is  pro- 
portionably  augmented?  and  that  the  same  effects  aiise  when  a very  oxi- 
dable  metal,  such  as  potassium,  is  substituted  for  the  zinc.  He  further 
states  that  when  the  experiment  is  made  in  a vessel  of  hydi'Ogen  or  nitro- 
gen, no  electricity  whatever  is  developed.  Tliis  last  observation  how- 
ever, tiie  only  decisive  argument  adduced,  has  since  been  con’ected  by 
Professor  P faff  of  Kiel,  in  wh(j)se  experiments  the  contact  of  zinc  and 
copper  affected  the  electrometibr  as  much  when  made  in  a jar  of  hydro- 
gen or  nitrogen,  as  in  atmosplieric  air.  There  is  therefore,  no  reason 
to  doubt  tlie  fact  as  originally  stated  by  Volta?  altliough  tlie  quantity  of 
electricity,  excited  by  mere  )6ontact,  appears  to  be  very  minute- 

Change  of  fonn,  such  as  liquefaction  and  tlie  passage  of  liquids  into 
the  solid  state,  and  the  fori/iation  and  condensation  of  vapoiu*,  is  another 
reputed  soiuce  of  electricyty.  To  processes  of  this  nature,  continually 
ta]^ng  place  in  the  atmosphere,  the  electricity  of  the  clouds  is  generally 
ascribed.  But  the  essays  of  M.  Pouillet  on  the  source  of  atmospheric 
dlectricity,  tend  to  subvert  the  opinions  hitlierto  received.  He  has 
proved  the  evaporation  of  water  from  a vessel  of  platinum  to  be  unatten- 
ded woth  electrical  appearances?  whereas  if  tlie  process  is  accompanie<i 
with  chemical  decomposition,  as  in  the  evaporation  of  saline  solutions, 
or  if*  the  vessel  consists  of  iron  or  other  oxidable  material,  which  is  more 
or  less  chemically  attacked  by  tlie  evaporating  water,  then  the  develop- 
ment of  electricity  is  very  decisive.  From  experiments  of  this  kind  M. 
Pouillet  concludes  that  the  electricity,  hithea-to  refeiTed  to  changes  of 


80 


ELECTRICITY. 


form,  IS  entirely  owing*  to  the  chemical  action  by  which  they  arc  g-encmlly 
attended;  and  these  phenomena,  of  whicli  the  evaporation  of  water  from 
tJie  ocean,  from  rivers  and  the  surface  of  the  earth,  affords  an  instance,  as 
also  the  chemical  chang-es  that  attend  tlie  growth  and  nutrition  of  plants, 
he  reg’ards  as  a fertile  source  of  the  electricity  of  the  atmosphere.  (An. 
de  Ch.  et  de  Ph.  xxxv.  401,  and  xxxvi.  5. ) 

Another  cause  of  excitement  is  proximity  to  an  electrified  body;  and 
as  the  explanation  of  many  electrical  phenomena  depends  on  a know- 
ledg*e  of  tliis  fiict,  it  is  of  importance  to  understand  it  clearly.  When  a 
substance  excited  positively  is  broug'ht  near  another  in  its  natural  state 
and  insulated, the  electric  equihbrium  of  the  latter  is  instantly  disturbed ; 
tlie  parts  nearest  to  the  former  become  neg’ative,  and  tlie  clistant  parts 
positive.  If  the  body  is  not  insulated,  its  electricity  passes  into  the  eartli, 
and  it  becomes  negatively  electrical.  If,  on  the  contraiy,  the  excitint^ 
substance  is  negative,  it  causes  tlie  contiguous  parts  of  a body  in  its  vi- 
cinity to  become  positive.  Hence  it  may  be  established  as  a law,  that  an 
electi’ified  body  tends  to  produce  in  contiguous  substances  an  electric 
state  opposite  to  its  own.  The  electricity  developed  in  this  way  is  said 
to  be  induced^  or  to  be  excited  by  induction.  The  movement  of  light 
bodies  towards  an  excited  stick  of  sealing-wax,  or  glass  tube,  is  accoun- 
ted for  on  tliis  principle.  Thus  the  vicinity  of  the  negative  seahng-wax 
rendei's  tlie  suiTOtmding  objects  positive,  and  therefore  a mutual  attrac- 
tion is  exerted.  When  the  inside  of  a glass  bottle  is  rendered  positive 
by  contact  with  the  prime  conductor  of  the  electrical  machine,  the  out- 
side, if  in  communication  with  the  earth,  parts  with  electricity  and  be- 
comes negative.  Both  surfaces,  therefore,  are  electrified  and  are  in 
opposite  states;  and  if  a communication  be  established  between  them  by 
means  of  a good  conductor,  the  excess  of  electricity  instantly  passes 
along  it,  and  both  sides  of  the  glass  return  to  their  natural  condition. 
Tliat  the  experiment  may  succe^  in  the  most  perfect  manner,  it  is  ne- 
cessary to  cover  the  bottle  externally  and  internally,  except  to  within 
three  or  four  inches  of  its  summit,  with  tinfoil  or  some  other  good  con- 
ductor, in  order  that  every  point  of  both  sides  of  the  glass  may  be  brought 
into  communication  at  the  same  moment.  For  witliout  tliis  precaution 
the  electric  equilibrium  of  the  two  surfaces  of  the  bottle,  owing  to  the 
imperfect  conducting  power  of  glass,  wiU  be  restored  on  those  points  only 
w^hich  are  touched.  The  apparatus  thus  described  is  much  employed 
by  electricians,  and  has  received  the  name  of  the  Leyden  pliial,  in  con- 
sequence of  its  remarkable  effects  having  been  first  exliibited  at  the  Uni- 
i^ersity  of  Leyden.  To  render  it  more  convenient  for  use,  the  aperture 
of  the  glass  jar  or  phial  is  closed  by  some  imperfect  conductor,  such  as 
dry  wood,  tlirough  the  centre  of  which  passes  a metallic  rod  that  com-' 
municates  with  the  tinfoil  in  the  ii\side  of  the  jar.  The  phial  is  electri- 
fied or  charged  by  holding  the  outside  in  the  hand,  or  placing  it  on  the 
ground,  while  tlie  metallic  rod  is  made  to  receive  spai'ks  from  the  prime 
conductor  of  an  electrical  machine.  If  the  jar  is  insidated,  no  charge 
will  be  received,  or  at  lexst  very  slight  indications  of  excitement  will  be 
manifested.  By  aminging  a number  of  Leyden  phials  in  a box  lined 
with  tinfoil,  so  that  they  may  all  communicate  freely,  by  tlieir  outer  sur- 
faces, and  tlicn  bringing  their  inner  surfaces  into  communication  by  wires, 
tlie  wlioh;  series  may  be  charged  and  discharged  in  the  same  manner  as 
a single  phial.  I'his  arrangement  is  known  by  tlie  name  oi*  the  Ekciri- 
cal  Battcri/. 

Some  of  the  phenomena  of  lightning  arc  explained  on  tlie  principle  of 
induced  electricity.  When,  for  instance,  a negatively  electi-ificd  cloud 
appniaches  tlie  earth,  all  objects  in  its  vicinity  arc  positively  excited; 
and  wlicn  it  oomes  witliin  what  is  called  the  striking  distmee^  that  is,  so 


ELECTRICITY. 


81 


near  that  the  tendency  of  the  electricity  to  pass  from  the  positive  to  the 
neg’ative  body  overcomes  the  I'esistance  of  tlie  intermediate  stratum  of 
air,  tlie  equilibrium  is  restored  with  a report  and  flash  of  light,  exactly 
as  in  the  discharge  of  a Leyden  phial.  A similai*  effect  is  produced  by 
an  electrified  cloud  on  other  clouds  within  the  sphere  of  its  influence. 

The  principle  of  induced  electricity  was  ingeniously  applied  by  Volta 
in  tlie  constmction  of  the  condenser.  This  apparatus,  shown  in  the  an- 
nexed figure,  consists  of  two  brass  plates  A and  B,  sup- 
jiorted  on  a common  stand  D.  One  of  the  plates  B is 
attached  to  the  stand  by  means  of  a joint  C,  so  that, 
though  represented  upright,  it  may  be  placed  horizon- 
tally, and  thus  be  withdi-awn  from  the  vicinity  of  the 
plate  A,  the  support  of  which  is  made  of  glass.  On  com- 
municating electricity  to  the  insulated  plate  by  contact 
with  a positively  excited  body,  the  plate  B,  which  for 
that  pui’pose  is  placed  close  to  A,  is  rendered  negative 
by  induction,  its  electricity  passing  along  the  stem  into 
the  eai-th;  and,  as  happens  in  the  Leyden  jar,  the  ex- 
citement of  B will  be  proportional  to  that  of  A.  The  negative  charge 
of  B tends  to  preseiwe  the  positive  charge  of  A,  which  will  consequently 
receive  electricity  from  any  positive  surface  without  losing  what  it  had 
previously  acquired.  Thus  is  electricity  accumulated  or  condensed  on 
A;  so  that  a substance  too  feebly  excited  to  produce  any  appreciable 
effects  of  itself,  may  by  repeated  contact  with  the  insulated  plate  of  a 
condenser  communicate  a charge  of  considerable  intensity.  The  effect 
of  the  accumulation  is  made  apparent  by  withdrawing  B,  and  bringing  A 
into  contact  witli  a delicate  electrometer.  The  condenser  is  much  em- 
ployed in  experiments  of  delicacy,  and  the  plate  A is  often  permanently 
fixed  on  the  gold  leaf  electrometer  invented  by  Bennett. 

Tlie  passage  of  electricity  is  frequently  attended  with  the  production 
of  heat  and  light,  effects  which  invariably  ensue  when  it  meets  with  an 
impediment  to  its  progress,  as  in  passing  through  an  imperfect  conductor. 
The  most  familiar  illustration  of  tliis  is  afforded  by  its  passage  through 
the  air,  when  it  gives  rise  to  a spark  accompanied  with  a peculiar  snap- 
ping noise,  if  in  small  quantity  5 or  to  the  phenomena  of  thunder  and 
lightning,  when  it  takes  place  on  a large  scale.  On  the  contrary,  it 
passes  along  perfect  conductors,  such  as  the  metals,  without  any  per- 
ceptible waimth  or  light,  provided  the  extent  of  their  surface  is  in  pro- 
portion to  the  quantity  of  electricity  to  be  transmitted  by  them;  but  if 
the  charge  is  too  gi’eat  in  relation  to  the  extent  of  the  'conducting  sur- 
face, intense  heat  will  be  produced. 

Electi’icity  acts  with  surprising  energy  on  the  animal  system.  When 
a large  quantity  of  the  klectric  fluid  passes  through  the  body,  the  vital 
functions  cease  on  the  instant,  as  is  exemplified  b^y  the  numerous  acci- 
dents on  record  of  persons  being  killed  by  lightning.  Even  the  small 
quantity  of  electricity  contained  in  a Leyden  phial  gives  a very  powerful 
shock,  exciting  a sudden  spasm  of  the  muscles  along  wliich  it  passes,  so 
violent  as  to  produce  a disagreeable  or  even  painful  sensation.  The 
shock  from  a large  electrical  battery  is  much  more  severe,  and  smaller 
animals,  such  as  rabbits  and  fowls,  are  destroyed  by  its  action. 

It  is  very  important,  in  conducting  electrical  experiments,  to  possess 
an  easy  method  of  discovering  when  any  substance  is  electrified,  of  as- 
certaining its  intensity  or  the  degree  to  which  it  is  excited,  and  distin- 
giiishing.the  kind  of  excitement.  The  mode  of  effecting  these  objects 
is  founded  on  electrical  attraction  and  repulsion,  and  the  instruments 
employed  for  the  purpose  are  called  Electroscopes  and  Electrometers,  the 
latter  denoting  the  intenrity  of  electricity,  the  foimer  merely  indicating' 


82 


ELECTRICITY. 


excitement,  and  the  electrical  state  by  which  it  is  produced.  The  term 
clecU’omctcr,  however,  is  often  indiscriminately  applied  to  all  such  in- 
stiniments,  since  tlie  methods  of  ascertaining’ the  kind  of  excitement  give 
at  tlie  same  time  some  idea  of  its  intensity.  A body  is  known  to  be  ex- 
cited by  its  power  of  attracting  light  substiinces;  and  a small  ball  made  of 
the  pith  of  elder,  suspended  on  a silk  thread,  afi’ords  a convenient  ma- 
terial for  tJie  expenment.  Another  mode  of  acquiring  the  same  infoima- 
tion  is  by  means  of  two  pith  balls  suspended  from  the  same  point  by  silk 
threads  of  equal  length.  When  all  the  s\irrounding  objects  are  unexci- 
ted, tlie  pith  balls  remain  in  contact;  but  on  the  approach  of  any  electri- 
fied body,  the  two  balls  arc  excited  by  induction,  and,  having  the  same 
electricity,  diverge  or  retreat  from  each  other.  A more  delicate  coiitri- 
vance,  bat  of  a similar  kind,  was  invented  by  Mr.  Bennett,  and  Is  known 
by  tlie  name  of  tlie  Gold  Leaf  Electrometer,  It  consists 
essentially  of  a cylindrical  glass  bottle,  with  its  aperture 
closed  by  a brass  plate,  from  the  centre  of  which  two 
slips  of  gold  leaf  are  suspended.  The  brass  plate,  witli 
its  slips  of  gold  leaf,  are  thus  insulated,  and  the  latter  pre- 
vented from  being  moved  by  currents  of  air  by  the  glass 
with  wliich  tliey  are  surrounded.  The  approach  of  any 
electrified  body,  even  though  feebly  excited,  to  the  brass 
plate,  is  immediately  detected  by  the  divergence  of  the 
leaves.  In  the  annexed  wood-cut  this  electrometer  is  exhibited  witli  its 
leaves  in  a state  of  divergence. 

A very  simple  method  of  distinguishing  the  kind  of  excitement  is  the 
following.  If  a piece  of  white  silk  be  drawn’ a few  times  rapidly  be- 
tween the  fingers,  it  will  become  negative;  and  if  in  this  state  it  is  sus- 
pended in  the  air,  it  will  be  attracted  by  a body  positively  excited,  and 
repelled  by  one  which  is  negative.  When  rubbed  on  black  cloth  the 
silk  is  rendered  positive,  and  will  then  of  course  retreat  from  a substance 
similarly  electrified,  and  be  attracted  by  one  in  an  opposite  state.  The 
indications  of  the  gold  leaf  electrometer  are  still  more  delicate.  If  the 
leaves  are  diverging  with  positive  electricity,  the  approach  of  a posi- 
tively excited  body  to  the  brass  plate  increases  the  divergence;  because 
the  electric  equilibrium  is  immediately  disturbed,  and  while  the  plate 
becomes  negative,  the  gold  leaves  acquire  a still  greater  degree  of  elec- 
tricity. The  approach  of  a negatively  excited  body  would  of  course  be 
productive  of  a change  precisely  opposite,  and  the  divergence,  if  pro- 
duced by  positive  electricity,  would  be  diminished,  or  even  entirely 
destroyed.  To  prepare  the  electrometer  for  an  observation,  it  is,  how- 
ever, necessary  to  communicate  to  it  a known  state  of  excitement. 
This  may  be  done  by  toilching  the  electrometer  with  an  electrified 
body,  such  as  an  excited  glass  tube  or  stick  of  sealing-wax,  when  the 
whole  metallic  surface  of  the  electrometer  is  electrified  in  the  same 
manner  as  the  substance  by  which  it  was  touched.  A more  convenient 
method  is  to  communicate  electricity  permanently  by  induction.  Thus, 
on  placing  a negatively  excited  body,  as  for  example  a stick  of  sealing- 
wax  after  friction  on  woollen  clotli,  near  the  brass  plate  of  the  electro- 
meter, the  electric  equilibrium  of  its  whole  metallic  surface  is  disturbed; 
the  brass  plate  becomes  positive,  and  the  slips  of  gold  leaf  diverge  from 
being  negative.  On  witlidrawing  the  sealing-wax,  the  excess  of  elec- 
tricity accumulated  on  the  plate  returns  to  the  leaves,  and  the  equili- 
brium is  restored;  but  if,  wliilc  the  sealing-wa'x  is  near  the  top  of  the 
instrument,  the  plate  is  touched  with  the  finger,  a portion  of  electricity 
is  supplied  to  the  gold  leaves  from  the  earth,  and  the  divergence  ceases 
more  or  less  completely,  while  the  excess  of  electricity  is  preserved  on 
the  plate  by  the  vicinity  of  the  sealing-wax.  On  removing  the  fin- 


ELECTRICITY. 


83 


ger,  and  then  the  sealing  wax,  the  brass  is  left  with  an  excess  of  elec- 
tricity, which  extends  over  the  whole  metallic  surface  of  the  electrome- 
ter, and  thus  produces  a divergence  which  continues  for  a considerable 
time  if  the  glass  be  dry,  and  the  atmosphere  moderately  free  from 

moisture.  . • i.  « • - 

The  electrometer  most  frequently  used  for  estimating  the  intensity 
of  electricity  in  ordinary  experiments  is  that  shown  in  the  annexed 
wood-cut,  invented  by  Mr.  Henley,  and  known  by  the 
name  of  Quadrant  Electrometer,  It  consists  of  a smooth 
round  stem  of  wood  a b,  about  seven  inches  long,  to  the 
upper  part  of  which,  and  projecting  from  its  side,  is  at- 
tached a semicircular  piece  of  ivory.  In  the  centre  c of 
the  semicircle  is  fixed  a pin,  from  which  is  suspended, 
to  serve  as  an  index,  a slender  piece  of  wood  or  cane 
d e,  four  inches  in  length,  and  terminated  by  a small  ball. 

When  the  apparatus  is  screwed  on  the  prime  conductor 
of  the  electrical  machine,  or  placed  on  any  electrified 
body,  it  indicates  differences  of  electric  intensity  by  the 
extent  to  which  the  index  recedes  from  the  stem;  and 
in  order  to  express  the  divergence  in  numbers,  the  low- 
er half  of  the  semicircle,  which  is  traversed  by  the  index, 
is  divided  into  90  equal  parts  called  degrees.  But  this 
instrument,  though  convenient  for  experiments  of  illustration,  is  not 
suited*  to  researches  of  delicacy,  wherein  the  object  is  to  examine  the 
effects  of  substances  feebly  electrified,  and  ascertain  their  relative  forces 
with  accuracy.  For  such  purposes  the  electrometer  invented  by  Cou- 
lomb, commonly  called  the  Electrical  Balance,  should  be  employed.  It 
consists  of  a small  needle  of  gum-lac  or  other  non-conducting  substance, 
suspended  horizontally  by  a silk  thread  as  spun  by  the  silk-worm,  or  by 
a fine  silver  wire.  On  the  point  of  the  needle  is  fixed  a small  gilt  ball 
made  of  the  pith  of  elder;  and  the  whole  is  covered  with  a glass  case 
to  protect  it  from  moisture  and  currents  of  air.  The  pith  ball,  when 
the  apparatus  is  at  rest,  is  in  contact  with  the  knob  of  a metallic  con- 
ductor, which  passes  through  a hole  in  the  glass  case,  and  is  secured  in 
its  place  by  cement;  but  when  an  excited  body  is  made  to  touch  the 
conductor,  the  pith  ball  in  contact  with  it  is  similarly  excited,  and  re- 
cedes from  it  to  an  extent  ])roportional  to  the  degree  of  excitement. 
The  needle  consequently  describes  the  arc  of  a circle,  and  in  its  revo- 
lution twists  the  supporting  thread  more  or  less  according  to  the  length 
of  the  arc  described.  The  torsion  thus  occasioned  calls  into  play  the 
elasticity  of  the  -thread, — a feeble  but  constant  force,  which  opposes 
the  movement  of  the  needle,  measures  by  the  extent  to  which  it  is 
overcome  the  intensity  of  the  excited  body,  and  brings  back  the  needle 
to  its  original  position  as  soon  as  the  electric  equilibrium  is  restored. 

In  some  of  the  preceding  remarks  a term  has  been  employed  which 
requires  explanation.  By  electric  tension  or  intensity  is  meant  that  state 
of  a body  which  is  estimated  by  an  electrometer.  When  a body  acts 
feebly  on  the  electrometer  its  intensity  is  low,  and  it  differs  but  little 
from  its  natural  state;  and  on  the  contrary  if  it  affects  the  electrometer 
powerfully,  its  electric  tension  is  great.  The  higher  the  intensity  of  a 
body,  the  more  is  it  removed  from  its  natural  state,  and  the  greater  its 
tendency  to  return  to  an  equilibrium.  Intensity  is  distinct  from  quan- 
tity of  electricity.  That  intensity  is  not  dependent  on  quantity  alone, 
is  proved  by  the  fact  tliat  the  tension  of  a charged  Leyden  phial  may  be 
equal  to  that  of  a large  battery  containing  twenty  times  more  electricity. 
The  tension  appears  to  depend  on  the  quantity  of  electricity  accumu- 
lated or  deficient  in  a given  space;  so  that  the  intensity  of  those  sub- 


84 


GALVANISM. 


stances  is  ^eatest,  which  have  the  greatest  excess  or  deficiency  of  elec- 
tricity in  proportion  to  their  surface. 

This  accounts  for  the  freedom  with  which  electricity  is  conducted 
away  by  pointed  surfaces.  For  the  electricity  accumulated  on  a sharp 
point,  though  its  quantity  may  be  very  small,  is  nevertheless  large  com- 
pared with  the  surface:  the  electric  tension  of  the  point  is  therefore 
very  great;  and  hence  if  positive  it  gives  off  electricity  to  surrounding 
objects,  and  if  negative  receives  it  from  them,  with  extreme  velocity. 

Electricity  appears  to  diffuse  itself  over  the  surface  of  bodies;  and  the 
quantity  contained  on  the  same  substance,  all  other  circumstances  being 
the  same,  depends  on  the  extent  of  surface,  and  is  not  connected  with 
quantity  of  matter.  Thus  a solid  sphere  of  brass  cannot  contain  more 
electricity  than  a hollow  sphere  of  the  same  diameter. 


SECTION  IV. 

GALVANISM. 

The  science  of  galvanism  owes  its  name  and  origin  to  the  experiments 
on  animal  irritability  made  by  Galvani,  Professor  of  Anatomy  at  Bologna, 
in  the  year  1790.  In  the  course  of  the  investigation  he  discovered  the 
fact,  that  muscular  contractions  are  excited  in  the  leg  of  a frog  recently 
killed,  when  two  metals,  such  as  zinc  and  silver,  one  of  which  touches 
the  crural  nerve,  and  the  other  the  muslces  to  which  it  is  distributed,  are 
brought  into  contact  with  one  another.  Galvani  imagined  that  the  phe- 
nomena are  owing  to  electricity  present  in  the  muscles,  and  that  the 
metals  only  serve  the  purpose  of  a conductor.  He  conceived  that  the 
animal  electricity  originates  in  the  brain,  is  distributed  to  every  part  of 
the  system,  and  resides  particularly  in  the  muscles.  He  was  of  opinion 
that  the  different  parts  of  each  muscular  fibril  are  in  opposite  states  of 
electrical  excitement,  like  the  two  surfaces  of  a charged  Leyden  phial, 
and  that  contractions  take  place  whenever  the  electric  equilibrium  is 
restored.  This  he  supposed  to  be  effected  during  life  through  the  me- 
dium of  the  nerves,  and  to  have  been  produced  in  his  experiments  by 
the  intervention  of  metallic  conductors. 

The  views  of  Galvani  had  several  opponents,  one  of  whom,  the  cele- 
brated Volta,  Professor  of  Natural  Philosophy  at  Pavia,  succeeded  in 
pointing  out  their  fallacy.  Volta  maintained  that  electric  excitement 
is  due  solely  to  the  metals,  and  that  the  muscular  cpntractions  are  occa- 
sioned by  the  electricity  thus  developed,  passing  along  the  nerves  and 
muscles  of  the  animal.  To  the  experiments  instituted  by  Volta  we  are 
indebted  for  the  first  galvanic  apparatus,  which  was  described  by  him 
in  the  Philosophical  I’ransactions  iot  1800,  and  which  has  properly  re- 
ceived the  name  of  the  Voltaic  Pile:  and  to  the  same  distinguished  phi- 
losopher belongs  the  real  merit  of  laying  the  foundation  of  the  science 
of  galvanism. 

The  most  simple  kind  of  galvanic  arrangement  Is  made  by  placing  a 
disc  or  plate  of  zinc  and  copper  near  each  other  in  a vessel  of  water 
acidulated  with  sulphuric  acid,  and  soldering  on  each  a metallic  wire, 
which  wires  may  be  made  to  touch  one  another  at  the  will  of  the  ope- 
rator. The  wires  may  even  be  dispensed  with;  for  the  object  being  to 
establish  metallic  communication  between  the  phites  by  means  of  a con- 
ductor which  is  not  covered  by  the  liquid,  it  is  suflicient  to  incline  the 
upper  part  of  the  plates  towards  each  other  until  they  are  in  contact. 


GALVANISM. 


85 


The  employment  of  wires,  however,  as  shown  in 
figure  1,  is  attended  with  many  advantages  in 
conducting  galvanic  experiments,  and  they  are, 
therefore,  always  resorted  to;  but  it  must  be  re- 
membered that  they  merely  act  as  a convenient 
conducting  material,  without  contributimr  essen-^1 
tially  to  the  result.  ^ ^ 

The  simple  galvanic  arrangement,  or  circle  as  — ^ . 

It  IS  often  called,  remains  in  activity  as  Ion,:-  as  chemical  aclion  between 
the  zmc  and  the  acid  continues.  The  phenomena  which  may  be  ob- 
served m the  apparatus  vary  according  as  the  conducting  wires  do  or  do 
not  communicate  with  each  other.  In  the  former  case  tlie  circuit,  or 
course  along  which  the  electric  current  passes,  is  said  to  be  closed;  and 
in  the  latter  the  circuit  is  broken  or  interrupted.  Chemical  action  be- 
tween  the  acid  and  zinc  goes  on  in  both  cases;  but  the  hydrogen  evolved 
from  water  appears  at  the  surface  of  the  zinc  only,  if  the  circuit  is 
broken,  and  arises  from  both  metals  when  the  circuit  is  closed.  If  in 
the  interrupted  state  of  the  circuit  the  electric  condition  of  the  wires  is 
examined,  that  attached  to  the  copper  plate  will  be  found  to  be  posi- 
tive,  and  the  wire  connected  with  the  zinc  negative.  If  the  wires  are 
made  to  touch  one  another,  their  tension  immediately  ceases;  because 
as  by  the  contact  of  oppositely  electrified  bodies  in  general,  the  equi’ 
ibrium  IS  thereby  re-established.  But  since  the  condition  which  Lused 
the  excitement  in  the  first  instance  remains  the  same,  a continued  devel- 

Ondhe  • anticipated;  and,  accordingly,  the  wires 

on  the  instant  of  separation  are  again  oppositely  electrified,  and  their 
tension  as  '"stantly  disappears  when  the  circuit  is  again  closed.  Hence 
It  was  inferred,  that  in  the  closed  circuit  a continuous  curreilt  of  elec^ 
tricity  passes  from  the  copper  plate  to  the  wire  connected  with  it  is 
communicated  by  it  to  the  other  wire,  and  is  then  conducted  to  the 
zinc  pMe.-  the  happy  discovery  of  Oersted,  by  leading  to  the  invention 
f the  Galvanometer,  which  will  be  described  in  an  after-part  of  this 
section,  has  supplied  us  with  the  means  of  discovering  the  presence  of 
such  a current,  estimating  its  force,  and  even  ascertaifing  itrdiiectfoif 

t-nThrShfstate  of  P^rof  plates  is  ffsuch  lowT^ 

n ’ “ ^ t ® ^ opposite  wires  in  the  broken  circuit  can 

only  be  ascertained  by  means  of  a delicate  electrometer  aided  bv  ?b^ 
condenser;  but  when  the  tension  is  increased  by  tr  unked 
several  ent  pairs,  as  in  compound  galvanic  arrangements  the  ordi 
nary  gold  leaf  electrometer  will  readily  be  affected.  l“remplovment' 
of  such  instiuments  may  now,  however,  be  dispensed  with-  sinL  the 
galvanometer  indicates  the  positive  and  negative  wire  of  any  galvanic 
circle  with  ease  and  certainty,  even  when  the  intensity  is  too^feeble  to 
be  appreciated  by  the  most  delicate  electrometer,  ^ ^ 

electricity  accumulates  on  the  wire  attached"  to  the  copper  plate 
and  IS  deficient  on  that  connected  with  the  zinc,  it  was  suppLed  tifat’ 

ptoon,e„x„',ed  b^voTtt  K 

With  each  other;  and  the  inference  has  been  fullv  iustifipd  hv  o /!* 

nr. 

8 


36 


GALVANISM. 


solution,  from  the  solution  to  the  copper,  and  from  the  copper  along 
the  communicating  wires  back  again  to  the  zinc.  Such  at  least  is  the 
view  of  the  phenomena  founded  on  the  Franklinian  doctrine;  but  ac- 
cording to  the  theory  of  the  two  electricities,  there  are  two  distinct  cur- 
rents, one  of  positive  or  vitreous  electricity,  which  takes  the  direction 
above  described,  and  the  otlier  of  negative  or  resinous  electricity,  which, 
starting  from  the  copper,  assumes  a course  exactly  opposite. 

These  remarks  will  render  intelligible  several  terms  which  will  be 
employed  in  the  course  of  this  section.  13y  the  expression  positive  wire 
OT  pole  simple  galvanic  circles  is  always  meant  the  wire  connected 
with  the  copper  plate,  and  by  the  negative  pole  or  -wire  that  attached  to 
the  plate  of  zinc.  It  is,  likewise,  usual  to  speak  of  the  zinc  plate  being 
positive  with  respect  to  the  copper  plate,  and  of  the  latter  being  nega- 
tive with  respect  to  the  former;  and  in  all  simple  galvanic  arrangements 
that  element  which  corresponds  to  the  zinc  plate  of  the  ordinary  circle, 
and  from  which  the  current  of  electricity  appears  to  set  out,  is  said  to 
be  positive  in  relation  to  the  other  substance  with  which  it  is  associated. 
Nor  does  this  language  appear  inconsistent  with  the  laws  of  electricity: 
for  the  electric  fluid  could  scarcely  be  given  off  by  the  zinc,  unless  the 
surface  so  yielding  it  were  positive;  nor  should  it  pass  over  to  the  cop- 
per, unless  the  surface  of  that  metal  were  negative.  It  seems,  indeed, 
that  the  zinc,  where  covered  with  liquidy  becomes  positive  at  the  expense 
of  the  uncovered  portion  and  its  wire;  while  the  wet  surface  of  copper 
is  rendered  negative  by  yielding  its  own  electricity,  as  well  as  that 
which  it  derives  from  the  zinc,  to  the  conducting  wire  to  which  it  is 
attached. 

Simple  galvanic  circles  may  be  formed  in  various  ways  and  of  various 
materials;  but  the  combinations  usually  employed  consist  either  of  two 
perfect  and  one  imperfect  conductor  of  electricity,  or  of  one  perfect 
and  two  imperfect  conductors.  The  substances  included  under  the  title 
of  perfect  conductors  are  metals  and  charcoal,  and  the  imperfect  con- 
ductors are  water  and  aqueous  solutions.  It  is  essential  to  the  opera- 
ration  of  the  first  kind  of  circle,  that  the  imperfect  conductor  act  che- 
mically on  one  of  the  metals;  and  in  case  of  its  attacking  both,  the  ac- 
tion must  be  greater  on  one  metal  than  on  the  other.  It  is  likewise 
found  generally,  if  not  universally,  that  the  metal  most  attacked  is  posi- 
tive with  respect  to  the  other,  or  bears  to  it  the  same  relation  as  zinc  to 
copper  in  the  ordinary  circle.  The  late  Sir  H.  Davy,  in  his  Bakerian 
Lecture  for  1826  (Phil.  Trans.),  has  given  the  following  list  of  the 
first  kind  of  arrangements,  the  imperfect  conductor  being  either  the 
common  acids,  alkaline  solutions,  or  solutions  of  the  hydrosulphurets. 
The  metal  first  mentioned  is  positive  to  all  those  standing  after  it  in  the 
series. 

With  common  Acids, 

Potassium  and  its  amalgams,  barium  and  its  amalgams,  amalgam  of 
zinc,  zinc,  amalgam  of  ammonium?,  cadmium,  tin,  iron,  bismuth,  anti- 
mony?, lead,  copper,  silver,  palladium,  tellurium,  gold,  charcoal,  pla- 
tinum, iridium,  rhodium. 

With  Alkaline  Solutions. 

The  alkaline  metals  and  their  amalg?inis,  zinc,  tin,  lead,  copper,  iron, 
silver,  palladium,  gold,  and  platinum. 

With  Solutions  of  Hydrosulphurets. 

7iinc,  tin,  copper,  iron,  bismuth,  silver,  platinum,  palladium,  gold, 
cUarcoiiI. 


GALVANISM. 


87 


The  following'  table  of  Voltaic  arrangements  of  the  second  kind  is 
from  Sir  H.  Davy’s  Elements  of  Chemical  Philosophy. 

Table  of  some  Electrical  Arrangements , consisting  of  one  Conductor,  and 
two  imperfect  Conductors, 


Solution  of  sulphur  and  potassa, 
of  potassa, 
of  soda. 


Copper,  Nitric  acid. 

Silver,  Sulphuric  acid, 

Lead,  Muriatic  acid, 

Tin,  Any  solutions  con- 

Zinc,  taining  acid. 

Other  metals, 

Charcoal. 

The  most  energetic  of  these  combinations  is  that  in  which  the  metal 
is  chemically  attacked  on  one  side  by  hydrosulphiiret  of  potassa,  and  on 
the  other  by  an  acid.  The  experiment  may  be  made  by  pouring  dilute 
nitric  acid  into  a cup  of  copper  or  silver,  which  stands  in  another  ves- 
sel containing  hydrosulphuret  of  potassa.  The  following  arrangements 
may  also  be  employed.  Let  two  pieces  of  thick  flannel  be  moistened, 
one  with  dilute  acid,  and  the  other  with  sulphuretted  alkali,  and  then 
placed  on  opposite  sides  of  a plate  of  copper,  completing  the  circuit 
by  touching  each  piece  of  flannel  with  a conducting  wire:  or,  take  two 
discs  of  copper,  each  with  its  appropriate  wire;  immerse  one  disc  into 
a glass  filled  with  dilute  acid,  and  the  other  into  a separate  glass  with 
alkaline  solution,  and  connect  the  two  vessels  by  a few  threads  of  ami- 
anthus or  cotton  moistened  with  a solution  of  salt.  A similar  combina- 
tion may  be  disposed  in  this  order.  Let  one  disc  of  copper  be  placed 
on  a piece  of  glass  or  dry  wood;  on  its  upper  surface  lay  in  succession 
three  pieces  of  flannel,  the  first  moistened  with  dilute  acid,  the  second 
with  solution  of  salt,  and  the  third  with  sulphuretted  alkali,  and  then 
cover  the  last  with  the  other  disc  of  copper. 

The  use  of  metallic  bodies  is  not  essential  to  the  production  of  gal- 
vanic phenomena.  Combinations  have  been  made  with  layers  of  char- 
coal and  plumbago,  of  slices  of  muscle  and  brain,  and  of  beet-root  and 
wood;  but  the  force  of  these  circles,  though  accumulated  by  the  union 
of  numerous  pairs,  is  extremely  feeble,  and  they  are  very  rarely  em- 
ployed in  practice. 

Of  the  simple  galvanic  circles  just  described,  the  only  one  used  for 
ordinary  purposes  is  that  composed  of  a pair  of  zinc  and  copper  plates 
excited  by  an  acid  solution.  The  form  and  size  of  pig*.  2. 
the  apparatus  are  exceedingly  various.  Instead  of  ^ 
actually  immersing  the  plates  in  the  solution,  a piece 
of  moistened  cloth  may  be  placed  between  them. 

Sometimes  the  copper  plate  is  made  into  a cup  for 
containing  the  liquid,  and  the  zinc  is  fixed  between 
its  two  sides,  as  shown  by  the  accompanying  trans- 
verse vertical  section,  figure  2;  care  being  taken  to 
avoid  actual  contact  between  the  plates  by  interpos- 
ing pieces  of  wood,  cork,  or  other  im- 
perfect conductor  of  electricity.  An- 
other contrivance,  which  is  much  more 
convenient,  because  the  zinc  may  be 
removed  at  will  and  have  its  surface 
cleaned,  is  that  represented  by  the  an- 
nexed wood-cut,  figure  3.  C is  a cup 
made  with  two  cylinders  of  sheet  cop- 
per, of  unequal  size,  placed  one  within 
the  other,  and  soldered  together  at  bot- 
tom, so  as  to  leave  an  intermediate 
space  a a a,  for  containing  the  zinc  cy- 


88 


GALVANISM. 


linder  Z and  the  acid  solution.  The  small  copper  cups  b b are  useful 
appendag’es;  for  by  filling  them  with  mercury,  and  inserting*  the  ends 
of  a wire,  the  galvanic  circuit  may  be  completed  or  broken  with  ease 
and  expedition.  This  apparatus  is  very  serviceable  in  experiments  on 
electro-magnetism. 

Another  kind  of  circle  may  be  formed  by  coiling  a sheet  of  zinc  and 
copper  round  each  other,  so  that  each  surface  may  be  opposed  to  one 
of  copper,  and  separated  from  it  by  a small  interval.  The  London  In- 
stitution possesses  an  immense  apparatus  of  this  sort,  made  under  the 
direction  of  Mr,  Pepys,  each  plate  of  which  is  sixty  feet  long  and  two 
wide.  The  plates  are  prevented  from  coming  into  actual  contact  by 
interposed  ropes  of  horsehair;  and  the  coil,  when  used,  is  lifted  by 
ropes  and  pulleys,  and  let  down  into  a tub  containing  dilute  acid.  This 
contrivance  was  first  resorted  to  by  Dr.  Hare  of  Philadelphia;  but  his 
apparatus,  instead  of  being  one  large  coil,  consisted  of  eighty  small 
coils,  and  is,  therefore,  a compound  galvanic  circle.  From  its  remark- 
able power  of  igniting  and  deflagrating  metals.  Dr.  Hare  gave  it  the 
name  of  Calorimotor  or  Bejlagrator*  (An.  of  Phil.  i.  329.  N.  S.) 

Compound  Galvanic  Circles. 

^ This  expression  is  applied  to  those  galvanic  arrangements  which  con- 
sist of  a series  of  simple  circles.  The  first  combinations  of  the  kind 


* Dr.  Turner  has  here  confounded  two  different  instruments.  The 
Calorimotor  of  Dr.  Hare,  as  first  "constructed  by  him  in  1819,  consisted 
of  twenty  sheets  of  zinc,  alternating  with  twenty  sheets  of  copper,  each 
about  nineteen  inches  square.  All  the  sheets  of  the  same  metal  were 
soldered  to  separate  metallic  bars,  so  as  to  form,  in  effect,  of  each  me- 
tal, but  one  galvanic  plate;  and  consequently,  of  the  two  metals,  one 
galvanic  pair  of  very  large  size.  Subsequently,  Dr.  Hare  modified  this 
apparatus,  with  the  effect  of  increasing  its  power,  by  connecting  the 
sheets  of  each  metal  into  two  groups  of  ten  each,  so  as  to  form  two  gal- 
vanic pairs,  the  alternating  arrangement  of  the  metals  being  still  pre- 
served. The  name  of  the  apparatus  has  allusion  to  its  powerful  influ- 
ence in  exciting  heat,  while  its  electrical  effects  are  almost  null. 

The  term  Bejlagrator  is  applied  by  Dr.  Hare  to  a modified  apparatus 
invented  by  him  in  1821,  which  is  more  powerful,  in  producing  the  igni- 
tion of  charcoal  and  the  deflagration  of  metals,  than  any  other  instru- 
ment, possessing  the  same  extent  of  metallic  surface.  The  principles 
adopted  in  its  construction  embrace  the  advantages  of  great  compact- 
ness, economy  in  the  quantity  of  the  exciting  fluid,  the  dispensing  with 
the  insulating  cells,  and  the  quick  and  simultaneous  excitation  of  the 
wliole  of  the  plates  by  a simple  contrivance.  So  far  from  consisting, 
like  the  calorimotor,  of  one  or  two  galvanic  pairs,  it  may  consist  of  any 
number  of  them,  at  the  pleasure  of  the  operator.  The  instrument,  as 
first  constructed,  consisted  of  eighty  pairs,  aiTanged  in  coils,  and  made  to 
descend  into  glass  jars.  Afterwards,  flat  hollow  copper  cases,  open  above 
and  below,  and  containing  a plate  of  zinc,  kept  from  contact  with  the 
copper  by  grooved  pieces  of  wood,  were  substituted  for  the  coils;  and 
the  insulation  was  dispensed  with  as  not  producing  an  increase  of  ef- 
fect suflicient  to  justify  the  expense  of  its  adoption.  The  copper  cases 
thus  prepared  were  packed  together,  either  with  pasteboard  soaked  in 
shell  lac,  or  with  thin  pieces  of  veneering  w'ood  placed  between  them, 
'rlie  necessary  metallic  connexion  being  established  between  the  zinc 
of  one  case,  and  the  contiguous  copper  case,  the  instrument  w^as  com- 
pleted. For  fuller  details,  see  Sillimaii^s  Chemisiryt  vol.  ii.  651.  B. 


GALVANISM. 


89 


were  described  by  Volta,  and  are  well  known  under  the  Fig.  4. 
names  of  Voltaic  pile  and  Couronne  de  Tasses,  The  Voltaic 
pile  is  made  by  placing  pairs  of  zinc  and  copper,  or  zinc 
and  silver  plates,  one  above  the  other,  as  shown  in  figure  4, 
each  pair  being  separated  from  those  adjoining  by  pieces  of 
cloth,  rather  smaller  than  the  plates,  and  moistened  with  a 
saturated  solution  of  salt.  The  relative  position  of  the  me- 
tals in  each  pair  must  be  the  same  in  the  whole  series;  that  j 
is,  if  the  zinc  be  placed  bdow  the  copper  in  the  first  pair,/ 
the  same  order  should  be  observed  in  all  the  others.  With-1 
out  such  precaution  the  apparatus  would  give  rise  to  oppo- ' 
site  currents,  which  would  neutralize  each  other  more  or 
less  according  to  their  relative  forces.  The  pile,  which  may  consist  of 
any  convenient  number  of  combinations,  should  be  contained  in  a frame 
formed  of  glass  pillars  fixed  into  a piece  of  thick  dry  wood,  by  which  it 
is  both  supported  and  insulated.  Any  number  of  these  piles  may  be 
made  to  act  in  concert  by  establishing  metallic  communication  between 
one  pole  o.f  each  pile  with  the  opposite  pole  of  the  pile  immediately 
following. 

The  Voltaic  pile  is  now  rarely  employed,  because  we  possess  other 
modes  of  forming*  galvanic  combinations  which  are  far  more  powerful 
and  convenient.  The  galvanic  battery,  proposed  by  Mr.  Cruickshank, 
consists  of  a trough  of  baked  wood,  about  thirty  inches  long,  in  which 


Fig.  5. 


are  placed  at  equal  distances  fifty  pairs  of  zinc 
and  copper  plates  previously  soldered  together, 
and  so  arranged  that  the  same  metal  shall  always 
be  on  the  same  side.  Each  pair  is  fixed  in  a ^ 
groove  cut  in  the  sides  and  bottom  of  the  box, 
the  points  of  junction  being  made  water-tight 
by  cement.  The  apparatus  thus  constructed  is 
alwa3^s  ready  for  use,  and  is  brought  into  action 
by  filling  the  cells  left  between  the  pairs  of 
plates  with  some  convenient  solution,  which 
serves  the  same  purpose  as  the  moistened  cloth  in  the  pile  of  Volta.  By 
means  of  the  accompanying  wood-cut  the  mode  in  which  the  plates  are 
arranged  will  easily  be  understood. 

Other  modes  of  combination  are  now  in 
use,  which  facilitate  the  employment  of  the 
galvanic  apparatus  and  increase  its  energ}^ 

Most  of  these  may  be  regarded  as  modifica-  - 
tions  of  the  Couronne  de  Tasses.  In  this  ap- 
paratus the  exciting  solution  is  contained  in 
separate  cups  or  glasses,  disposed  circularly 
or  in  a line.  Each  glass  contains  a pair  of 
plates;  and  each  zinc  plate  is  attached  to  the 
copper  of  the  next  pair  by  a metallic  wire,  as  re- 
presented in  the  figure.  (Fig.  6.)  Instead  of 
glasses,  it  is  more  convenient  in  practice  to  em- 
ploy  a trough  of  baked  wood  or  glazed  earthen- 
ware,  divided  into  separate  cells  by  partitions  of 
the  same  material;  and  in  order  that  the  plates 

may  be  immersed  into  and  taken  out  of  the  liquid  

conveniently  and  at  the  same  moment,  they  are  all 


attached  to  a bar  of  dry  wood,  the  necessary  con-  llHi 
nexion  between  the  zinc  of  one  cell  and  tlie  cop-  j 
per  of  the  adjoining  one  being  accomplished,  as  ' 
shown  in  figure  7,  by  a slip  or  wire  of  copper. 

8* 


90 


GALVANISM. 


A material  improvement  in  the  foreg-oing*  apparatus  was  s\iggestcd  hj 
I)r.  Wollaston,  (Mr.  Children’s  Essay  in  Phil.  Trans,  for  1815)  who  re- 
commended that  each  cell  shoidd  contain  one  zinc  and  two  copper 
plates,  so  that  both  surfaces  of  the  former  metal  might  be  opposed  to 
one  of  the  latter.  The  plates  communicate  with  each  other,  and  the 
zinc  between  them  with  the  copper  of  the  adjoining  cell.  An  increase 
of  one-half  the  power  is  said  to  be  obtained  by  this  method. 

A variation  of  this  contrivance,  which  appears  to  me  advantageous, 
has  been  suggested  by  Mr.. Hart  of  Glasgow,  who  proposes  to  have  the 
double  copper  plates  of  the  preceding  battery  made  with  sides  and  bot- 
toms, so  that,  as  in  figure  2,  they  may  contain  the  exciting  liquid.  The 
plates  are  attached,  as  in  hgure  7,  to  a bar  of  wood,  and  supported  above 
the  ground  by  vertical  columns  of  the  same  material,  by  which  they  are 
insulated.  The  cells  are  filled  by  dipping  the  whole  battery  into  a 
trough  of  the  same  form,  full  of  the  exciting  liquid.  (Brewster’s  Jour- 
nal, iv.  19.) 

The  size  and  number  of  the  plates  may  be  varied  at  pleasure.  The 
largest  battery  ever  made  is  that  of  Mr.  Children,  described  in  the  essay 
above  refeiTed  to,  the  plates  of  which  are  six  feet  long,  and  two  feet 
eight  inches  broad.  The  common  and  most  convenient  size  for  the 
plates  is  four  or  six  inches  square;  and  when  great  power  is  required, 
a number  of  different  batteries  are  united  by  establishing  metallic  com- 
munication between  the  positive  pole  of  one  battery  and  thetiegative  pole 
of  the  adjoining  one.  The  great  battery  of  the  Royal  Institution  is  com- 
posed of  2000  pairs  of  plates,  each  plate  having  32  square  inches  of  sur- 
face. It  was  with  this  apparatus  that  Sir  H.  Davy  effected  the  decom- 
position and  determined  the  constitution  of  the  alkalies,  a discovery 
which  has  at  once*  extended  so  much  the  bounds  of  chemical  science, 
and  conferred  immortal  honour  on  the  name  of  the  discoverer. 

The  electrical  phenomena  of  compound  galvanic  arrangements  are 
similar  to  those  of  the  simple  circle.  The  poles  in  the  broken  circuit  are 
oppositely  excited;  and  in  the  closed  circuit  an  electric  current  passes 
through  the  apparatus  and  over  the  conductors  as  long  as  chemical  ac- 
tion continues.  The  direction  of  the  current  appears  at  first  view  to  be 
different  from  that  of  the  simple  circle;  for  the  extremity  which  termi- 
nates with  a copper  plate  is  negative,  the  electricity  passes  from  it 
tivrough  the  battery  itself  towards  the  last  zinc,  which  is  positive,  and 
thence  along  the  conducting  wires  to  the  last  copper  plate.  (Figs.  4,  5, 
aud  6.)  It  is  hence  customary,  in  reference  to  the  compound  circle,  to 
speak  of  the  zinc  and  positive  pole  as  identical;  whereas  the  wire  con- 
nected with  the  zinc  plate  in  the  simple  circle  is  negative.  But  the  dif- 
ference is  rather  apparent  than  real,  and  arises  from  the  compound  gal- 
vanic circle  being  terminated  by  two  superfluous  plates,  which  are  not 
essential  to  the  result.  This  will  more  fully  appeal*  in  the  course  of  the 
following  remai’ks. 

Theories  of  Galvanism. 

Df  the  theories  proposed  to  account  for  the  development  of  electricity 
in  g-alvanic  combinations,  three  in  pai’ticidar  have  attracted  the  notice  of 
philosophers.  The  first  originated  with  Volta,  who  conceived  that  elec- 
tricity is  set  in  motion,  and  the  supply  kept  up,  solely  by  contact  or  com- 
munication between  the  metals.  (Page  79.)  He  regarded  the  inter- 
posed solutions  merely  as  conductors,  by  means  of  wliich  the  electricity 
developed  by  each  pair  of  plates  is  conveyed  from  one  part  of  the  appa- 
ratus to  the  otlier.  Thus  in  the  pile  or  ordinaiy  battery,  represented  by 
tlic  following  scries. 


GALVANISM. 


91 


5 2 1 

r ^ r ^ \ r ^ ^ 

+ zinc  copper  fluid  zinc  copper  fluid  zinc  copper  — 

Volta  considered  that  contact  between  the  metals  occasions  the  zinc  in  each 
pair  to  be  positive,  and  the  corresponding  copper  plate  to  be  negative; 
that  the  positive  zinc  in  each  pair  except  the  last,  being  separated  by  an 
intervening  stratum  of  liquid  from  the  negative  copper  of  the  following 
pair,  yields  to  it  its  excess  of  electricity;  and  that  in  this  way  each  zinc 
plate  communicates,  not  only  the  electricity  developed  by  its  own  con- 
tact with  copper,  but  also  that  which  it  had  received  from  the  pair  of 
plates  immediately  before  it.  Thus,  in  the  three  pairs  of  plates  con- 
tained in  brackets,  the  second  pair  receives  electricity  from  the  first 
only,  while  the  third  pair  draws  a supply  from  the  first  and  second. 
Hence  electricity  is  most  freely  accumulated  at  one  end  of  the  battery, 
and  is  proportionally  deficient  at  the  opposite  extremity.  The  intensity 
is  therefore  greatest  in  the  extreme  pairs,  gradually  diminishes  in  ap- 
proacliing  the  centre,  and  the  central  pair  itself  is  neither  positively  nor 
negatively  excited. 

In  batteries  constructed  according  to  the  principle  of  the  Couronne  de 
Tassesy  (fig.  6.)  the  electro-motion y as  Volta  called  it,  is  ascribed  to  metal- 
lic communication  between  the  zinc  of  one  glass  and  the  copper  of  the 
adjoining  one.  Butin  single  pairs,  as  in  figures  1 and  2,  where  the  wires 
are  found  to  be  excited  without  the  plates  having  any  metallic  commu- 
nication with  each  other,  this  explanation  is  inadmissible.  It  is  then 
necessary,  reasoning  on  the  principles  of  Volta,  to  ascribe  the  electricity 
to  contact  between  the  metals  and  the  exciting  liquid;  and  a similar  ex- 
planation must  be  apphed  to  circles  composed  of  one  perfect  and  tw^o 
imperfect  conductors. 

It  may  be  objected  to  this  view,  that  though  contact,  as  nearly  aU  ad- 
mit, may  disturb  the  electric  equilibrium,  the  quantity  of  electricity  thus 
developed  is  too  small  to  account  for  the  astonishing  phenomena  of  gal- 
vanism. But  a far  more  powerful  objection,  which  appears  in  fact  un- 
answerable, is  deduced  from  the  chemical  phenomena  of  galvanic  circles, 
the  study  of  which  has  given  rise  to  the  chemical  theory  of  the  pile.  Volta 
attached  little  importance  to  the  chemical  changes,  considering  them  as 
contributing  nothing  to  the  general  result,  and,  therefore,  leaving  them 
entirely  out  of  view  in  the  formation  of  his  theory.  The  constancy  of 
their  occurrence,  however,  soon  attracted  notice.  In  the  earlier  discus- 
sions on  the  cause  of  spasmodic  movements  in  the  frog,  (page  84)  Fa- 
broni  contended,  in  opposition  to  Volta,  tliat  the  effect  was  not  owing  to 
electricity  at  all,  but  to  the  stimulus  of  the  metallic  oxide  formed,  or  of 
the  heat  evolved  during  its  production.  More  extended  researches  soon 
proved  the  fallacy  of  this  doctrine;  but  Fabroni  made  a most  ingenious 
use  of  the  facts  within  his  knowledge,  and  paved  the  way  to  tlie  chemi- 
cal theory  of  Wollaston. 

The  late  I)r.  Wollaston,  fully  admitting  electricity  as  the  galvanic 
agent,  assigned  chemical  action  as  the  cause  by  which  it  is  excited. 
The  repetition  and  extension  of  Volta’s  experiments  by  the  English 
chemists,  speedily  detected  the  eiTor  he  had  committed  in  overloofcng 
the  chemical  phenomena  which  occur  within  the  pile.  It  was  observed 
tliat  no  sensible  effects  are  produced  by  a combination  of  conductors 
which  do  not  act  chemically  on  each  other;  that  the  action  of  the  pile  is 
alw'ays  accompanied  by  the  oxidation  of  the  zinc;  and  that  the  energy  of 
the  pile  in  general  is  proportioned  to  the  activity  with  which  its  plates 
are  coiToded.  Observations  of  this  nature  induced  Dr.  W^ollaston  to 
conclude  that  the  process  begins  with  tlie  oxidation  of  the  zinc, — that 


92 


GALVANISM. 


the  oxidation  is  the  primary  cause  of  the  development  of  electricity; 
and  he  published  several  ing’enioiis  experiments  in  the  Philosoplftcal 
Transactions  for  1801  in  support  of  his  opinion. 

Recent  researches,  which  have  decisively  established  the  important 
fact  of  electricity  being*  freely  developed  by  chemical  action,  (pag*e  78) 
have  added  additional  force  to  the  arg*uments  of  Wollaston.  The  exper- 
iments of  De  la  Rive  in  particular  appear  altog*ether  irreconcileable  with 
the  theory  of  Volta.  (An.  de  Ch.  et  de  Ph.  xxxviii.  225.)  Tliis  inge- 
nious philosopher  contends  that  the  direction  of  a galvanic  current  is  not 
determined  by  metallic  contact,  nor  even  by  the  nature  of  the  metals  re- 
latively to  each  other,  but  by  their  chemical  relation  to  the  exciting  li- 
quid. As  the  general  result  of  his  inquiries,  he  states,  that  of  two  metals 
composing*  a galvanic  circle,  that  one,  which  is  most  energetically  at- 
tacked, will  be  positive  with  respect  to  the  other.  Thus  when  tin  and 
copper  are  placed  in  acid  solutions,  the  former,  which  is  most  rapidly 
coiToded,  gives  a current  towards  the  copper,  as  the  zinc  does  in  the 
common  circle;  but  if  they  are  put  into  a solution  of  ammonia,  which 
acts  most  on  the  copper,  the  direction  of  the  current  will  be  reversed. 
Copper  is  positive  to  lead  in  strong  nitric  acid,  which  oxidizes  the  former 
most  freely;  whereas  in  dilute  nitric  acid,  by  w’hich  the  lead  is  most  ra- 
pidly dissolved,  the  lead  is  positive.  Even  two  plates  of  copper  immei'S- 
ed  in  solutions  of  the  same  acid,  or  of  common  salt,  of  different  strengths, 
will  form  a galvanic  circle,  the  plate  on  which  chemical  action  is  most 
free  giving  a current  of  electricity  towards  the  other.  Nay,  it  is  possible 
to  construct  a battery  solely  with  zinc  plates  excited  by  the  same  acid  of 
the  same  strength,  provided  one  side  of  the  plates  is  polished  and  the 
other  rough;  for  the  difference  of  polish  causes  the  two  surfaces  of  each 
plate  to  be  unequally  attacked  by  the  acid,  and  an  electric  current  is 
the  result.  These  and  similar  facts  of  the  same  kind  appear  quite  in- 
consistent with  the  views  of  Volta.  They  go  far  to  establish  the  chemir 
cal  theory  of  galvanism,  and  in  my  opinion  entitle  it  to  a preference 
over  every  other  which  has  been  suggested.* 

But  though  the  development  of  electric.ty  in  galvanic  combinations 
is  chiefly  dependent  on  chemical  action,  which  also  determines  the  di- 
rection of  the  current,  it  does  not  follow  that  metallic  contact  is  alto- 
gether inefficient.  The  quantity  of  electricity  thus  excited  is,  however, 
so  small  compared  with  what  is  evolved  by  chemical  change,  that  the 
effect  of  the  former  is  in  general  lost  in  the  greater  influence  of  the 
latter.  On  some  occasions,  nevertheless,  the  agency  of  contact  is  con- 
spicuous. The  electric  column  of  De  Luc,  formed  by  successive  pairs 
of  silver  and  zinc,  or  silver  and  Dutch  gilt  leaf,  separated  by  pieces  of 
paper,  and  contained  in  a glass  tube,  owes  its  action  chiefly  to  the  metal- 
lic contact.  This  apparatus,  which  yields  electricity  in  small  quantity, 
but  of  considerable  tension,  will  continue  in  activity  for  years.  True  it 
is  that  the  more  oxidable  metal  of  the  column  is  slowly  corroded;  but 
the  chemical  changes  do  not  appear  at  all  proportionate  to  the  effects 
o))served,  and  can  scarcely  I apprehend  be  admitted  as  the  sole  cause 
of  their  production. 

The  third  theory  of  the  pile  is  Intermediate  between  the  two  others, 
and  was  proposed  by  the  late  Sir  11.  Davy.  Me  inferred  from  nume- 
rous experiments,  that  there  is  no  reason  to  question  the  fact  originally 
stated  by  Volta,  that  the  electric  equilibrium  is  disturbed  by  the  con- 


* I'lic  reader  will  find  an  able  development  of  this  theory  in  the  article 
Galvanism,  written  for  tlic  Library  of  Useful  Knowledge  by  Dr.  Roget, 
to  whose  treatise  1 am  indebted  for  several  valuable  suggestions. 


GALVANISM, 


93 


tact  of  different  substances  without  any  chemical  action  taking  place 
between  them.  He  acknowledged,  however,  with  Dr.  Wollaston,  that 
the  chemical  changes  contribute  to  the  general  result;  and  maintained 
that,  though  not  the  primary  cause  of  the  phenomenon,  they  are  so  far 
essential,  that  without  such  changes  the  galvanic  excitement  can  neither 
be  considerable  in  degree,  nor  of  long  duration.  In  his  opinion  the 
action  is  commenced  by  the  contact  of  the  metals,  and  kept  up  by  the 
chemical  phenomena. 

The  mode  in  which  Sir  H.  Davy  conceived  that  the  chemical  changes 
act,  is  by  restoring  the  electric  equilibrium  whenever  it  is  disturbed. 
By  the  contact  of  the  zinc  and  copper  plates,  the  former  is  rendered 
positive  throughout  the  whole  series,  and  the  latter  negative;  and  by 
means  of  the  conducting  fluid  with  which  the  cells  are  filled,  the  elec- 
tricity accumulates  on  one  side  of  the  battery,  and  the  other  becomes 
as  strongly  negative.  But  the  quantity  of  electricity,  thus  excited, 
would  not  be  sufficient,  as  is  maintained,  for  causing  energetic  action. 
For  this  effect  the  electric  equilibrium  of  each  pair  of  plates  must  be 
restored  as  soon  as  it  is  disturbed,  in  order  that  they  may  be  able  to  fur- 
nish an  additional  supply  of  electricity.  The  chemical  substances  of 
the  solution  are  supposed  to  effect  that  object  in  the  following  manner. 
The  negative  ingredients  of  the  liquid,  such  as  oxygen  and  the  acids, 
pass  over  to  the  zinc;  while  the  hydrogen  and  the  alkalies,  which  are 
positive,  go  to  the  copper;  in  consequence  of  which,  both  the  metals 
are ‘for  the  moment  restored  to  their  natural  condition.  But  as  the  con- 
tact between  them  continues,  the  equilibrium  is  no  sooner  restored  than 
it  is  again  disturbed;  and  when,  by  a continuance  of  the  chemical 
changes,  the  zinc  and  copper  recover  their  natural  state,  electricity  is 
again  developed  by  a continuance  of  the  same  condition  by  which  it  was 
excited  in  the  first  instance.  In  this  way  Sir  H.  Davy  explained  why 
chemical  action,  though  not  essential  to  the  first  development  of  elec- 
tricity, is  necessary  for  enabling  the  Voltaic  apparatus  to  act  with  ener- 
gy*— It  is  obvious  that  the  facts  above  adduced  in  opposition  to  the 
theory  of  Volta,  apply  also  to  that  of  Sir  H.  Davy, 

The  chemical  theory  of  galvanism  suggests  a view  of  the  essential 
elements  of  the  pile,  different  from  that  taken  by  Volta.  In  the  sub- 
joined series,  for  instance, 


2 1 

. 4-^  r — ^ N r — ^ 

zinc  copper  fluid  zinc  copper  fluid  zinc  copper  • 

) V 


-v-- 


■V“ 

1 


Volta  considered  electro-motion  to  be  caused  by  each  of  the  three  pairs 
of  plates  included  in  the  upper  brackets;  whereas  there  are  in  fact  only 
two  simple  circles,  which  are  indicated  by  the  lower  brackets.  The 
extreme  plates  are  altogether  superfluous,  and  on  removing  these  the 
combination  is  reduced  to  the  following  simpler  form; 


-}-  copper  fluid  zinc  copper  fluid  zinc  — 


In  this  arrangement  the  direction  of  the  current  is  obviously  the  same 
as  in  the  simple  circle;  and  it  only  appears  to  be  different  in  batteries 
of  the  usual  construction,  because  the  last  efficient  zinc  plate  is  attach- 
ed to  a useless  copper  plate,  and  the  last  efficient  copper  is  connected 
with  a plate  of  zinc  which  is  equally  superfluous.* 


* The  view  which  Dr.  Turner  has  here,  for  the  first  time,  presented 


94 


GALVANISM. 


Effects  of  Galvanism. 

The  more  remarkable  effects  of  galvanism  may  be  conveniently  con- 
sidered under  three  heads:  1st,  electrical  effects;  2d,  its  chemical 
agency;  and  3d,  its  action  on  the  magnet. 

I.  Under  the  first  head  are  included  all  those  effects  of  the  battery 
'which  resemble  the  usual  phenomena  produced  by  the  electrical  ma- 
chine. When  a wire  attached  to  the  positive  pole  of  a Voltaic  bat- 
tery is  made  to  communicate  with  Bennett’s  Electrometer,  the  gold 
leaves  diverge  with  positive  electricity,  and  a wire  from  the  negative 
side  produces  an  effect  precisely  opposite.  But  in  order  that  these 
phenomena  should  ensue,  the  two  wires  must  not  touch  each  other;  for 
in  that  case  an  electric  current  would  be  cstablislied  along  the  wires, 
and  the  tension  cease.  When  wires  connected  with  the  opposite  poles 
or  sides  of  an  active  galvanic  trough  are  brought  near  each  other,  a spark 
is  seen  to  pass  between  them;  and  on  establishing  the  communication 
by  means  of  the  hands  previously  moistened,  a distinct  shock  is  perceiv- 
ed. These  effects  are  rendered  more  conspicuous  by  connecting  one 
of  the  wires  with  the  inner  surface,  and  the  other  with  the  outside  of  a 
Leyden  phial  or  battery,  when  successive  charges  will  be  received,  by 
means  of  which  all  the  ordinary  electrical  experiments  may  be  exliibit- 
ed.  On  connecting  the  opposite  ends  of  a sufficiently,  powerful  bat- 
tery by  means  of  fine  metallic  wires  or  slender  pieces  of  charcoal,  these 
conductors  become  intensely  heated;  the  wires  even  of  the  most  refrac- 
tory metals  are  fused,  and  a vivid  white  light  appears  at  the  points 
of  the  charcoal,  equal  if  not  superior  in  intensity  to  that  emitted 
during  the  burning  of  phosphorus  in  oxygen  gas;  and  as  this  pheno- 
menon takes  place  in  an  atmosphere  void  of  oxygen,  or  even  under 
the  surface  of  water,  it  manifestly  cannot  be  ascribed  to  combustion. 
If  the  communication  be  established  by  metallic  leaves,  the  metals  burn 
with  vivid  scintillations.  Gold  leaf  burns  with  a white  light  tinged  with 
blue,  and  yields  a dark  brown  oxide;  and  the  light  emitted  by  silver  is 
exceedingly  brilliant,  and  of  an  emerald  green  colour.  Copper  emits  a 
bluish-white  light  attended  with  red  sparks,  lead  a beautiful  purple 
light,  and  zinc  a brilliant  white  light  inclining  to  blue,  and  fringed  with 
red.  (Singer.)  The  properties  above  enumerated  naturally  gave  rise 
to  the  belief,  that  the  agent  or  power  excited  by  the  Voltaic  apparatus 


of  the  elementary  combination  of  the  ordinary  galvanic  battery,  or  In 
other  words,  of  the  simple  galvanic  circle,  is  very  satisfactory.  Every  one 
must  perceive  that  the  elementary  galvanic  combination  cannot  be  the 
copper  and  zinc  plate  in  metallic  connexion  with  each  other;  for  it  may 
be  asked,  where  is  tlie  positive  and  negative  poles  of  such  a combina- 
tion, and  in  what  way  can  the  circuit  be  completed,  so  as  to  discharge 
it?  On  the  otlier  hand,  when  it  is  assumed  that  the  copper  and  zinc 
plate,  as  connected  by  the  exciting  fluid,  is  the  elementary  combination, 
the  difficulties  implied  in  the  above  questions  wholly  disappear.  For 
here  the  electric  fluid  passes  from  the  zinc  to  the  copper,  and  conse- 
quently the  copper  is  positive  and  the  zinc  negative;  and  the  circuit  is 
completed  and  the  electrical  equilibrium  restored,  the  moment  a 
metallic  connexion,  as  by  a wire,  is  established  between'the  two  plates. 
All  this  may  be  inferred  from  the  elementary  battery  of  Wollaston.  ^ 
I’liese  views  were  adopted  by  the  editor  of  this  work  in  an  article 
which  he  published  in  the  Fort  Folio  of  Philadelphia,  for  April,  1824, 
in  explanation  of  the  supposed  reversed  polarity  of  the  galvanic  defla- 
grator  of  Dr.  Hare.  Vort  Folio,  xvii.  323,  B. 


GALVANISM. 


95 


is  identical  with  that  which  is  called  into  activity  by  the  electrical  ma- 
chine; and  the  arguments  in  favour  of  this  opinion  are  quite  satisfac- 
tory. For  not  only  may  all  the  common  electrical  experiments  be  per- 
formed by  means  of  galvanism;  but  it  has  been  shown  by  Dr.  Wollas- 
ton, (Phil.  Trans,  for  1801)  that  the  chemical  effects  of  the  galvanic 
battery  may  be  produced  by  electricity. 

The  conditions  required  for  producing  the  electrical  effects  of  the 
Voltaic  battery  are  different.  Some  phenomena  are  dependent  alto- 
gether on  the  electric  intensity  of  the  apparatus;  for  others  both  quan- 
tity and  intensity  are  essential;  and  for  the  production  of  other  effects 
the  passage  of  a large  quantity  of  electricity  is  alone  required.  The 
electric  tension  of  a battery  depends  chiefly  on  the  number  of  the  se- 
ries, and  comparatively  little  either  on  the  size  of  the  plates,  or  the 
fluid  by  which  they  are  excited;  whereas  all  these  conditions  have  a 
material  influence  over  the  quantity  of  electricity.  When  it  is  wished 
to  procure  a high  degree  of  tension,  a great  number  of  small  plates 
should  be  employed,  and  the  cells  filled  with  water.  On  the  contrary, 
when  quantity  of  electricity  is  the  chief  object,  great  extent  of  surface 
is  necessary;  the  individual  plates  should  be  of  large  size,  and  excited 
by  an  acid,  which  promotes  the  object,  partly  by  producing  brisk  che- 
mical action,  and  partly  by  conducting  more  perfectly  than  water  or 
solutions  of  neutral  salts. 

Since  the  force  of  electrical  attraction  and  repulsion  arises  from  in- 
tensity independent  of  quantify  of  electric  fluid,  it  is  manifest  that  an 
electrometer  is  affected  solely  by  the  tension  of  a battery,  and  serves  as 
a measure  of  its  degree.  For  acting  on  the  electrometer,  therefore,  a 
battery  of  numerous  small  plates  is  peculiarly  suited;  their  size  need 
not  exceed  an  inch  or  two  inches  square.  Mr.  Singer,  in  his  Treatise 
on  Electricity  and  Galvanism,  stated,  that  common  river  water  is  the 
best  material  for  exciting  a battery  of  this  kind,  and  that  the  addition 
of  saline  or  acid  matter  even  diminishes  the  intensity.  My  own  obser- 
vations lead  me  to  doubt  the  accuracy  of  this  statement. 

For  producing  sparks,  charging  an  electrical  battery,  or  giving 
shocks,  both  tension  and  quantity  of  electricity  are  desirable;  and  the 
apparatus  designed  for  such  purposes  should  have  a numerous  series  of 
plates  about  four  inches  square,  and  be  excited  with  dilute  acid.  In 
burning  metallic  leaf,  fusing  wire,  and  igniting  charcoal,  a large  quan- 
tity of  electricity  is  the  only  requisite.  The  phenomena  seem  to  arise 
from  the  electricity  passing  along  these  substances  with  difficulty;  a 
circumstance  which,  as  perfect  conductors  are  used,  can  only  happen 
when  the  quantity  to  be  transmitted  is  out  of  proportion  to  the  extent 
of  surface  over  which  it  has  to  pass.  It  is  therefore  an  object  to  excite 
as  large  a quantity  of  electricity  in  a given  time  as  possible,  and  for  this 
purpose  a few  large  plates  answer  better  than  a great  many  small  ones. 
A strong  acid  solution  should  also  be  used;  for  an  energetic  action, 
though  of  short  duration,  is  more  important  than  a moderate  one  of 
greater  permanence.  A mixture  of  fourteen  or  sixteen  parts  of  water 
to  one  of  nitrous  acid  is  applicable;  or  for  the  sake  of  economy,  a mix- 
ture of  one  part  of  nitrous  to  two  parts  of  sulphuric  acid  may  be  sub- 
stituted for  pure  nitrous  acid.  The  large  battery  of  Mr.  Children, 
though  capable  of  fusing  several  feet  of  platinum  wire,  had  an  electric 
tension  so  feeble,  that  it  did  not  affect  the  gold  leaves  of  the  electrome- 
ter, gave  a shock  scarcely  perceptible  even  when  the  hands  were  moist, 
communicated  no  charge  to  a Leyden  phial,  and  could  not  produce 
chemical  decomposition.* 


* Dr.  Hare  has  broached  a very  ingenious  theory  to  account  for  the 
1 heat  excited  by  galvanic  action.  He  does  not  consider  it  probable  that 


96 


GALVANISM. 


IL  The  chemical  ag'ency  of  the  Voltaic  apparatus,  to  which  chemists 
are  indebted  for  their  most  powerful  instrument  of  analysis,  was  discov- 
ered by  Messrs.  Carlisle  and  Nicholson,  soon  after  the  invention  was 
made  known  in  this  country.  The  substance  first  decomposed  by  it 
was  water.  When  two  gold  or  platinum  wires  are  connected  witli  tlie 
opposite  poles  of  a battery,  and  their  free  extremities  are  plunged  into 
the  same  cup  of  water,  but  without  touching  each  other,  hydrogen  gas 
is  disengaged  at  the  negative  wire,  and  oxygen  at  the  positive  side,  lly 
collecting  the  gases  in  separate  tubes  as  they  escape,  they  are  found  to 
be  quite  pure,  and  in  the  exact  proportion  of  two  measures  of  hydro- 
gen to  one  of  oxygen.  When  wires  of  a more  oxidable  metal  are  em- 
ployed, the  result  is  somewhat  different.  The  hydrogen  gas  appears 
as  usual  at  the  negative  pole,-  but  the  oxygen,  instead  of  escaping,  com- 
bines with  the  metal,  and  converts  it  into  an  oxide. 

This  important  discovery  led  many  able  experimenters  to  make  simi- 
lar trials.  Other  compound  bodies,  such  as  acids  and  salts,  were  ex- 
posed to  the  action  of  galvanism,  and  all  of  them  were  decomposed 
without  exception,  one  of  their  elements  appearing  at  one  side  of  the 
battery,  and  the  other  at  its  opposite  extremity.  An  exact  uniformity 
in  the  circumstances  attending  the  decomposition  was  also  remarked. 
Thus,  in  decomposing  water  or  other  compounds,  the  same  kind  of  body 
was  always  disengaged  at  the  same  side  of  the  battery.  The  metals,  in- 
flammable substances  in  general,  the  alkalies,  earths,  and  the  oxides  of 
the  common  metals,  Avere  found  at  the  negative  pole;  while  oxygen, 
chlorine,  and  the  acids,  went  over  to  the  positive  surface. 

In  performing  some  of  these  experiments.  Sir  H.  Davy  observed,  that 
if  the  conducting  wires  were  plunged  into  separate  vessels  of  water, 
made  to  communicate  by  some  moist  fibres  of  cotton  or  amianthus,  the 
two  gases  were  still  disengaged  in  their  usual  order,  the  hydrogen  in 
one  vessel,  and  the  oxygen  in  the  other,  just  as  if  the  wires  had  been 
immersed  into  the  same  portion  of  that  liquid.  This  singular  fact,  and 
another  of  the  like  kind  observed  by  Hisinger  and  Berzelius,  induced 
him  to  operate  in  the  same  way  with  other  compounds,  and  thus  gave 
rise  to  his  celebrated  researches  on  the  transfer  of  chemical  substances 
from  one  vessel  to  another,  detailed  in  the  Philosophical  Transactions 
for  ISOr.  In  these  experiments  two  agate  cups,  N and  P,  were  em- 
ployed, the  first  communicating  with  the  negative,  the  second  with  the 


the  heat  extricated  by  galvanic  combinations  is  the  effect  of  the  current 
of  electricity  passing  with  difficulty  along  conductors,  in  consequence 
of  the  quantity  to  be  transmitted  being  out  of  proportion  to  the  extent 
of  the  surfaces  over  which  it  has  to  pass.  On  the  contrary,  he  believes 
that  caloric,  like  electricity,  is  an  original  product  of  galvanic  action. 
According  to  his  views,  the  relative  proportion  of  the  two  principles 
evolved  depends  upon  the  construction  of  the  apparatus;  the  caloric 
being  in  proportion  to  the  extent  of  the  generating  surface,  and  the 
electricity  to  the  number  of  the  series.  In  the  case  of  batteries,  in  which 
the  size  and  number  of  the  plates  are  very  considerable,  both  electricity 
and  caloric  are  presumed  by  him  to  be  generated  in  large  quantities. 
When  the  number  of  the  plates  is  very  great,  and  their  size  insignifi- 
cant, as  in  De  Luc’s  column,  electricity  is  the  sole  product;  and  con- 
versely, where  the  size  is  very  great  and  the  number  of  the  series  small, 
caloric  is  abundantly  produced,  and  the  electrical  effects  are  nearly 
null.  Following  up  the  latter  idea,  Dr.  Hare  constructed  the  instru- 
ment which  he  calls  Cidorimotor,  or  mover  of  heat,  described  in  the  note 
at  p.  88.  B. 


GALVANISM. 


97 

positive  pole  of  the  battery,  and  connected  together  by  moistened  ami- 
anthiis.  On  putting  a solution  of  sulphate  of  potussa  or  soda  into  N 
and  dis  died  water  into  P,  the  acid  very  soon  passed  over  to  the  latter 
wliile  the  liquid  in  the  former,  which  was  at  first  neutral,  became  dis- 
tinctly dkahne.  The  process  was  reversed  by  placing  the  saline  solu- 
tion in  P,  and  the  distilled  water  in  N,  when  the  alkali  went  over  to  the 
negative  cup,  leaving  free  acid  in  the  positive.  That  the  acid  in  the 
first  experiment  and  the  alkaline  base  in  the  second,  actually  passed 
along  the  amianthus,  was  obvious;  for  on  one  occasion,  when  nitrate  of 
silver  was  subsMuted  for  the  sulphate  of  potassa,  the  amianthus  leading 
to  N was  coated  with  a film  of  metal.  A similar  transfer  may  be  effecN 
ed  by  putting  distilled  water  into  N and  P,  and  a saline  solution  in  a 
third  cup  placed  between  the  two  others,  and  connected  with  each  bv 

Td  UieSkauTn? 

The  plvanic  action  not  only  separates  the  elements  of  compound 
bodies,  but  suspends  the  operation  of  affinity  so  entirely,  as  to  enable 
an  acid  to  pass  through  an  alkaline  solution,  or  an  alkali  through  water 
containing  a free  acid,  without  combination  taking  place  between  them. 
Ihe  three  cups  being  arranged  as  in  the  last  experiment.  Sir  H.  Davv 
put  a solution  of  sulphate  of  potassa  in  N,  pure  water  in  P,  and  a weak 
.‘ntermediate  cup,  so  that  no  sulphuric  acid 
could  find  Its  way  to  the  distilled  water  in  P without  passing  through 
the  ammoniacal  liquid  in  its  passage.  A battery  composed  of  150  pairs 
o 4-inch  plates  was  set  in  action,  and  in  five  minutes  free  acid  appeared 
atthe  positive  pole  Muriatic  and  nitric  acids  were  in  like  manner 
made  to  pass  through  strong  alkaline  solutions;  and  on  reversing  the 
experiment,  alkalies  were  transmitted  directly  through  acid  liquids 
without  entering  into  combination  with  them.  “ ^ 

The  analogy  between  the  preceding  phenomena  and  the  attractions 
and  repulsions  exerted  by  ordinary  electricity  is  too  close  to  escape  ob- 
servation.  If  an  acid  or  an  alkali  pass  from  one  vessel  to  another  in 
opposiuon  to  gravity  and  chemical  affinity,  it  is  clear  that  this  singular 
phenomenon  must  arise  from  the  substance  so  transferred  being  under 
the  influence  of  a still  stronger  attraction;  and  the  only  power  to  which 
such  an  effect  can  in  the  present  case  be  attributed,  is  electricity. 
JSow,  in  all  instances  of  common  electrical  attraction,  the  bodies  attract 
one  another  in  consequence  of  being  in  opposite  states  of  excitement; 
and  in  like  manner,  tlife  tendency  of  acids  towards  the  zinc,  and  of  alka- 
lies towards  the  copper  extremity  of  the  Voltaic  apparatus,  can  be  ex- 
plained, consistently  with  our  present  knowledge,  only  on  the  supposi- 
tion that  the  fomer  are  negatively,  and  the  latter  positively  electric,  at 
the  moment  of  being  separated  from  one  another.  To  account  for  the 
elements  of  compounds  being  in  such  a state,  a peculiar  hypothesis  was 
advanced  by  Sir  H.  Davy,  which  has  received  the  appellation  of  the 
ekctro^i^tcal  theory,  and  has  been  adopted  by  several  philosophers, 
specially  by  Berzelius.  This  theory  was  first  developed  by  its  author 
in  .«o7  in  his  essay  on  Some  Chemical  Agencies  of  Electricity,  and  he 
gave  ail  additional  explanation  of  his  views  in  the  Bakerian  Lecture  for 
Some  parts  of  the  doctrine  are  unfortunately  expressed  in  a 
manner  somewhat  obscure,  and  this  circumstance  has  given  rise  to  ac- 
cidental misrepresentation;  but  a careful  perusal  of  Sir  H.  Davy’s  es- 
says induces  me  to  hope,  that  the  following  is  a correct  statement  of 
Ills  opiiuons. 

It  was  demonstrated  by  Volta  that  the  mere  contact  of  certain  metals, 
as  lor  example  zinc  and  copper,  causes  the  development  of  electricity; 
tor  after  separation  they  are  found,  if  insulated,  to  be  oppositely  ejcc- 


GALVANISM. 


*1 

trified.  It  Is  inferred,  and  I conceive  correctly,  that  the  electric  cqui^ 
iibrium  is  disturbed  at  the  moment  of  contact,  and  that  one  metal  be- 
comes positively,  and  the  other  negatively  electric;  but  so  long  as 
contact  continues,  no  sign  of  electrical  excitement  is  evinced,  because 
the  presence  of  two  surfaces  oppositely  electrified  to  the  same  degree, 
counteracts  or  neutralizes  the  effect  which  either  separately  would  prt)- 
duce.  The  development  of  electricity  by  contact  is  by  no  means  con- 
fined to  the  metals.  Sir  H.  Davy  observed  that  a dry  alkali  or  alkaline 
earth  is  excited  positively  by  contact  with  a metal,  and  that  dry  acids 
:^fter  having  touched  a metal  are  negative;  and  he  has  further  shown 
that  acids  and  alkalies  in  their  dry  state  excite  each  other,  the  former 
after  contact  being  negative  and  the  latter  positive.  A similar  disturb- 
ance of  the  electric  equilibrium  is  conceived  to  be  produced  by  the 
contact  of  the  ultimate  particles  or  atoms  of  two  bodies,  as  is  developed 
in  the  same  substances  when  in  mass.  The  two  particles  are  thus  ren- 
dered oppositely  electric,  and  if  not  prevented  by  cohesion  to  particles 
of  their  own  kind  or  other  causes,  they  remain  permanently  attached  to 
each  other  by  the  force  of  electrical  attraction,  and  thus  give  rise  to  a 
nev/  compound.  What  chemists  term  chemical  attraction  or  affinity  is 
therefore,  under  this  point  of  view,  an  electrical  force  arising  from  par- 
ticles of  a different  kind  attracting  each  other,  in  consequence  of  being 
in  opposite  states  of  electrical  excitement.  The  particles  thus  adher-' 
ing  or  combined  retain  their  electric  state,  as  happens  with  two  discs  of 
zinc  and  copper  while  in  contact,  without  exhibiting  any  signs  of  elec- 
trical excitement  either  at  the  moment  of  combination,  or  during  its 
continuance.  The  very  existence  of  the  compound,  indeed,  depends 
on  its  elements  retaining  their  state  of  excitement;  and  were  they  both 
brought  into  the  same  electric  condition,  or  subjected  to  the  influence 
of  surfaces  of  greater  intensity  than  that  by  which  their  union  was  main- 
tained, decomposition  would  necessarily  ensue.  This  is  precisely  the 
manner  in  which  chemical  decomposition  is  thought  to  be  effected  by 
the  agency  of  galvanism.  On  immersing  the  extremities  of  wires  con- 
nected with  the  opposite  poles  of  a Voltaic  battery  into  a cup  of  water, 
the  wire  attached  to  the  zinc  being  positive  will  attract  the  oxygen^ 
and  if  its  intensity  exceed  that  by  which  the  elements  of  water  are  held 
together,  the  oxygen  will  be  drawn  towards  it  and  the  hydrogen  re- 
pelled. The  wire  connected  with  the  copper  or  negative  side  of.  the 
apparatus  exerts  an  attraction  for  the  hydrogen,  and  is  repulsive  to  the 
oxygen;  so  that  the  same  element  which  is  repelled  by  one  wire  is  at- 
tracted by  the  other.  Other  compounds  will  of  course  be  liable  to  de- 
composition on  the  same  principle.* 


" If  the  explanation  here  given  of  the  chemical  agencies  of  the  Vol- 
taic apparatus  were  well  founded,  then  it  would  follow  that  decompo- 
sition should  take  placo,  if  the  same  portion  of  water  was  placed  in 
connexion,  at  the  same  time,  with  the  positive  pole  of  one  battery  and 
the  negative  pole  of  another.  Tims  the  negative  oxygen  being  attract- 
ed more  strongly  by  tlie  positive  or  zinc  pole  than  by  the  positive  hy- 
drogen with  wiiicli  it  is  comliined,  would  have  its  union  with  the  latter 
severed,  a result  which  would  be  favoured  by  tlie  repulsion  exercised 
by  the  positive  pole  ou  tlie  hydrogen.  Again,  the  positive  hydrogen 
would  be  attracted  hy  be  negative  pole  and  tlie  oxygen  be  repelled. 
Tint  I doubt  very  miilj'  wliethcr  any  decomposition  would  take  place 
under  such  cii'cums;;u:c<"s,  and  hence  I believe  that  a current  of  the 
galvanic  fluid  tliroiigh  compounds  is  essential  to  its  decomposing  pow- 
ers D. 


GALVANISM. 


It  will  appear  on  a little  reflection,  that  the  accuracy  of  this  very  in- 
genious doctrine  has  not  yet  been  demonstrated.  There  is  no  proof 
that  the  ultimate  particles  of  bodies  do  become  electric  by  contact,  or 
that  they  retain  their  opposite  electricities  when  combined.  Even  wei’o 
these  points  established,  it  would  not  necessarily  follow  that  chemical 
aflinity  is  identical  with  electrical  attraction.  Besides,  it  has  not  been 
fully  proved,  that  the  chemical  agency  of  the  Voltaic  apparatus  de- 
pends on  electrical  attraction  and  repulsion.  The  theory  does  not  yet 
stand  on  so  firm  a basis  as  to  induce  chemists  to  abandon  the  nomencla- 
ture they  have  hitherto  employed,  and  cease  to  regard  affinity  as  a dis- 
tinct species  of  attraction.  But  at  the  same  time  it  must  be  admitted, 
tliat  the  electro-chemical  theory  is  founded,  as  all  theoretical  views 
ought  to  be,. on  extensive  observation  and  numerous  facts;  that  it  sup- 
plies chemists  with  a principle  capable  of  accounting  for  the  plieno- 
mena  ascribed  to  aflinity;  and  affords  a consistent  explanation  of  the 
chemical  agencies  of  the  Voltaic  apparatus.  Experience  lias  shown  that 
it  is  a safe  guide  in  experimental  research,  and  it  has  the  unquestionable 
merit  of  having  led  to  one  of  the  most  brilliant  discoveries  ever  made  in 
chemistry. 

Regarding  all  compounds  as  constituted  of  oppositely  electrical  ele- 
ments, Sir  H.  Davy  conceived  that  none  of  them  should  resist  decompo- 
sition, if  exposed  to  a battery  of  sufficient  intensity;  and  he  accordingly 
subjected  to  galvanic  action  substances  which  till  then  had  been  regard- 
ed as  simple,  expecting  that  if  they  were  compound,  they  woidd  be  re- 
solved into  their  elements.  The  result  exceeded  expectation.  Thfe 
alkalies  and  earths  were  decomposed;  a substance  with  the  aspect  and 
properties  of  a metal  appeared  at  the  negative  pole,  while  oxygen  gas 
was  disengaged  at  the  positive  surface.  (Pliil.  Trans,  for  1808.) 

The  same  views  have  been  applied  with  considerable  success  on  a very 
recent  occasion.  It  has  been  long  known  that  the  copper  sheathing  of 
vessels  oxidizes  very  readily  in  sea-water,  and  consequently  wastes  with, 
such  rapidity  as  to  require  frequent  renewal.  Sir  H.  Davy  pb served 
that  tlie  copper  derived  its  oxygen  from  atmospheric  air  dissolved  in  the 
water,  and  that  the  oxide  of  copper  then  took  muriatic  acid ’from  the 
soda  and  magnesia,  forming  with  it  a submuriate  of  the  oxide  of  cojj- 
per.  Now  if  the  copper  did  not  oxidize,  it  could  not  combine  with, 
muriatic  acid;  and  according  to  Sir  H.  Davy,  it  only  combines  with  oxy- 
gen, because  by  contact  with  that  body  it  is  rendered  positively  electri- 
cal. If,  therefore,  the  copper  could  by  any  means  be  made  negative, 
then  the  copper  and  oxygen  would  have  no  tendency  to  unite.  The  ob- 
ject then  was  to  render  copper  permanently  negative.  Now  this  is  done 
by  bringing  copper  in  contact  with  zinc  or  iron;  for  the  former  then  be- 
comes negative,  and  the  latter  positive. 

Acting  on  this  idea,  it  was  found  that  tlie  oxidation  of  the  copper  may 
be  completely  prevented.  A piece  of  zinc  as  large  as  a pea,  or  the  head 
of  a small  round  nail,  was  found  fully  adequate  to  preserve  forty  or  fifty 
square  inches  of  copper;  and  this  wherever  it  was  placed,  whether  at 
tiie  top,  bottom,  or  middle  of  the  sheet  of  copper,  or  under  whatever 
, form  it  was  usei  And  when  the  connexion  between  different  pieces  of 
copper  w^  completed  by  wires,  or  thin  filaments  of  the  40th  or  50th  of 
. an  inch  in  diameter,  the  effect  was  the  same;  every  side,  every  surface, 

I every  particle  of  the  copper  remained  bright,  whilst  the  iron  or  the  zinc 
[/was  slowly  corroded.  Sheets  of  copper  defended  by  l-40th  to  1-lOOOtk 
j part  of  tlieir  surface  of  zinc,  malleable  and  cast  iron,  were  exposed  dii- 
i ring  many  weeks  to  the  flow  of  tlie  tide  in  Portsmouth  harbour,  and  their 
[ weight  ascertained  before  and  after  the  experiment.  When  the  metal- 
1 fie  protector  was  from  l-40th  to  1 -150th  there  was  no  coiTosion  nor  decay 
' of  the  copper;  with  smaller  quantities,  such  as  l-200th  to  l-460tli,  the 


100 


GALVANISM. 


copper  underwent  a loss  of  weight  wliich  was  greater  in  proportion  os 
the  protecU)rwas  smaller;  and  as  a proof  of  the  universality  of  the  prin- 
ciple, it  was  found  that  even  1-lOOOth  part  of  cast  iron  saved  a cci-tain 
proportion  of  the  copper.  (Phil.  Trans,  for  1824.) 

Unhappily  for  the  application  of  tliis  principle  in  practice,  it  is  found 
that  unless  a ceidain  degi’ee  of  corrosion  takes  place  in  the  copper,  its 
surface  becomes  foul  from  the  adhesion  of  sea-weeds  and  shcll-fisli.  'I’hc 
oxide  and  submuriate  of  copper,  formed  when  tlie  sheathing  is  unpro- 
tected, is  probably  injurious  to  these  plants  and  animals,  and  thus  pre- 
serv<is  the  copper  free  from  foreign  bodies.  It  appears  also  that,  in  ves- 
sels whose  sheathing  is  protected  from  con^osion,  the  negatively  electric 
copper  attracts  the  positively  electric  bodies,  such  as  magnesia  and  lime, 
dissolved  in  sea-water;  and  that  these  earths  tlien  form  a nidus  for  the 
adhesion  of  other  matters.  It  is  hoped  that  by  duly  adjusting  the  pro- 
portion of  iron  and  copper,  a certain  degree  of  corrosion  may  be  allowed 
to  occur,  sufficient  to  prevent  the  adhesion  of  foreign  bodies,  and  yet 
materially  to  retard  the  waste  of  tlie  copper;  but  the  attempts  to  accom- 
plish so  desirable  an  object  have  not  yet  been  altogether  successful. 

Tliese  principles  may  be  usefully  applied  on  other  occasions.  One 
obvious  application  of  the  kind,  suggested  by  Mr.  Pepys,  is  to  preserve 
iron  or  steel  instmments  from  rust  by  contact  with  a piece  of  zinc.  The 
iron  or  steel  is  thereby  rendered  negative;  while  the  zinc,  being  positive, 
is  oxidized  with  increased  rapidity. 

The  electro-chemical  theory  fui'nishes  a scientific  principle,  by  which 
chemical  substances  may  be  arranged.  According  to  the  method  sug- 
gested by  this  doctrine,  bodies  are  divided  into  gi’oups  accordingly  a» 
their  natural  electric  energies  are  the  same  or  different.  By  the  term 
natmral  electric  energy  is  not  meant  that  a substance,  considered  singly, 
naturally  possesses  one  kind  of  excitement  rather  than  another;  but  that 
by  its  nature  it  is  disposed,  from  contact  with  other  bodies,  to  assume 
one  particular’  electi’ical  state  rather  tlian  another.  Thus  oxygCn  is  call- 
u'.d  a negative  electric,  because  it  is  negatively  excited  by  other  bodies ; 
whereas  the  natural  electric  energy  of  potassium  is  believed  to  be  posi-. 
tive,  because  it  acquires  an  excess  of  electricity  by  contact  with  other 
substances.  The  electric  energies  are  ascertained  by  exposing  com- 
pounds to  the  action  of  a galvanic  battery,  and  observing  the  pole  at 
which  the  elements  appear.  Those  that  collect  round  the  positive  pole 
are  s?jd  to  have  a negative  electric  energy;  and  those  are  considered 
positive  electi’ics  which  are  attracted  towards  the  negative  pole.  Of  the 
(dementary  principles  oxygen,  chlorine,  bromine,  iodine,  and  fluorine, 
are  regarded  as  negative  electrics  by  Dr.  Henry,  who  has  adopted  this 
principle  of  arrangement;  and  aU  the  others  compose  his  more  nume- 
r<Mis  list  of  positive  electrics. 

Considerable  difficulty  arises  in  the  arrangement  of  some  substances, 
in  consequence  of  their  possessing  one  kind  of  electric  energy  in  rela- 
tion to  some  bodies,  and  an  opposite  energy  witii  respect  to  others. 
Oxygen  is  negative  in  every  combination,  and  potassium  appears  to  be 
as  unifomily  positive;  but  sulphur,  though  positive  with  respect  to  oxy- 
gen, is  negative  in  relation  to  tlie  metals.  Hydrogen  is  highly  positive 
in  regard  to  oxygen,  chlorine,  and  other  analogous  principles;  but  with 
the  metals  its  electric  energy  is  negative. 

Tlie  following  columns,  shov/ing  tlie  electric  energy  of  the  different 

Icmcmtaiy  substances  iu  relation  to  each  other,  are  taken  from  Berze- 
lius’s System  of  Clicmistry.  They  arc  given  by  tlie  author  as  an  approx- 
imation to  tlieir  tnic  order,  ratlicr  than  as  rigidly  exact.  All  the  bodiea 
f numcTated  in  tJic  first  column  arc  negative  to  those  of  the  second.  In 
the  first  column  each  substance  is  negative  to  tliose  below  it;  and  in  the 


GALVANISM. 


101 


second,  each  dement  Is  positive  with  reference  to  tliose  which  occupy 
a lower  place  in  the  series. 


L 

2. 

Nf^ative  Eledtrics, 

Positive  Electnes. 

Oxygen. 

Potassium, 

Sulphur. 

Sodium. 

Nitrogen. 

Litliium. 

Chlorine. 

Barium. 

IcKiine. 

Strontium. 

Fluorine. 

Calcium. 

Phosphorus. 

^Magnesium. 

Selenium. 

Glucinium. 

Arsenic. 

Yttrium. 

Chromium. 

Aluminium. 

Molybdenum. 

Zirconium. 

Tungsten. 

Manganese. 

Boron. 

Zinc. 

Carbon. 

Cadmium. 

Antimony. 

Iron. 

Tellurium. 

Nickel. 

Columbium. 

Cobalt. 

Titanium. 

Cerium. 

Silicium. 

Lead. 

Osmium. 

Tin. 

Hydrogen. 

Bismuth, 

Uranium. 

Copper. 

Silver. 

Mercury. 

Palladium. 

Platinum. 

Rhodium, 

Iridium. 

Gold.* 

The  statements  made  in  the  text  are,  perhaps,  not  expressed  with 
sufficient  clearness  for  tlie  con;prehension  of  the  student.  The  doctrine 
laid  down  by  Br.  Turner  is,  that  substances,  considered  singly,  fa*e 
neither  positive  nor  neg'ative;  or  in  other  words,  that  they  are  in  a neuter 
state  like  the  earth.  Nevertheless,  they  are  capable  of  exciting  each 
other  by  being  first  brought  in  contact,  and  then  separated.  If  two  sub  - 
stances touch  each  other,  and  are  then  separated,  one  will  become  positive 
and  the  other  negative;  but  the  result  is  not  conclusive  as  to  the  electric 
energy  of  either,  because  the  electric  state  of  each  may  possibly  be  re- 
versed by  contact  with  some  other  substance.  These  positions  are  rigidly 
exact  with  respect  to  aU  the  simple  substances,  except  oxygen  and  pot- 
assium-; for,  as  the  former  yields  electricity  to  all  other  substances,  it 
must  always  be  negative,  and  as  the  latter  takes  electricity  from  all  other 
I substances,  it  must  be  invariably  positive.  Tlius  it  is  plain  that  the  elec- 
1 trie  energy  of  none  of  tlie  simple  bodies  is  absolute,  except  that  of  oxy  - 
, gen  and  potassium;  while  the  electric  energy  of  the  remaining  sinuple 
bodies  is  relative,  and  is  either  positive  or  negative,  according  to  cir- 
cumstances. It  is  for  these  reasons  that  I have  thought  that  the  an*angc- 
' ment  of  bodies  into  negative  and  positive  electrics,  as  Dr.  Turner  h:vs 
‘ done,  after  Berzelius,  is  objectionable,  as  leading  the  student  into  the 

9* 


102 


GALVANTSAT. 


For  exhibiting*  the  chemical  agency  of  galvanism,  a combination  of 
quantity  and  intensity  is  required.  The  larger  of  the  two  immense  bat*- 
teries  constinicted  by  Mr.  Children  had  scarcely  any  power  in  effecting 
chemical  decomposition;  and  a series  of  numerous  small  plates  charged 
witli  water,  and  capable  of  acting  powerfvdly  on  the  electrometer,  de- 
composes water  very  feebly.  The  most  appropriate  apparatus  for  cheTi> 
ical  purposes,  is  one  made  with  a considerable  number  of  plates  of  four 
or  six  inches  square.  An  acid  solution  should  be  employed  for  exciting 
the  battery,  and  its  strength  be  such  as  to  cause  a moderate,  long-coi> 
tinued  action,  rather  than  a violent  one  of  short  duration.  Any  of  the 
stronger  acids,  such  as  die  nitnc,  sulphuric,  or  m\iriatic,  may  be  used 
with  this  intention;  but  the  last,  according  to  Mr.  Singer,  produces  the 
most  permanent  effect,  and  is  therefore  preferable.  The  proportion 
should  be  1 part  of  acid  to  about  14  or  20  parts  of  water;  or  if  tlie  series 
IS  extensive,  the  acid  may  be  still  further  diluted  with  advantage.  The 
chemical  agency  of  a battery  increases  with  the  number  of  plates;  hut 
the  exact  rate  of  increase  has  not  been  satisfactorily  determined. 

In  order  that  chemical  decomposition  should  take  place  by  means  of 
galvanism,  tlie  compound  subjected  to  its  action  must  be  made  to  con- 
nect the  opposite  poles  of  the  battery.  No  effect  is  produced  if  a non- 
conductor is  used,  and  hence  potassa  is  not  decomposed  by  galvanism, 
unless  slightly  moistened;  nor  must  the  electric  fluid  pass  through  it  with 
the  same  facility  as  along  a metal,  for  the  apparatus  is  then  equally  inert 
The  substance  by  which  the  opposite  poles  are  connected,  must  be  what 
is  called  an  imperfect  conductor,  such  as  water,  and  saline  and  acid  so- 
lutions. All  such  liquids  may  be  considered  perfect  conductors  in  re- 
spect to  common  electricity;  but  to  electrified  surfaces  of  very  low  in- 
tensity, as  in  galvanic  batteries  even  in  their  state  of  highest  tension, 
they  are  imperfect  conductors.  Even  water,  when  quite  pure,  trans- 
mits the  electricity  of  a galvanic  apparatus  so  imperfectly,  tliat  a very 
powerful  battery  occasions  a slow  disengagement  of  gas,  when  its 
opposite  poles  communicate  through  distilled  water.  Its  conducting 
power  is  greatly  improved  by  adding  a little  saline  matter,  such  as  sul- 
phate of  soda  or  potassa;  and  the  same  battery  which  decomposed  water 
feebly  before  the  addition  of  the  salt,  will  then  cause  a free  disengage- 
ment of  gas. 

III.  The  power  of  lightning  in  destroying  and  reversing  the  poles  of 
a magnet,  and  in  communicating  magnetic  properties  to  pieces  of  iron 
which  did  not  previously  possess  them,  was  noticed  at  an  early  period 
of  the  science  of  electricity,  and  led  to  the  supposition  that  similar  effects 
may  be  produced  by  the  common  electrical  or  galvanic  apparatus.  At- 
tempts were  accordingly  made  to  communicate  the  magnetic  virtue  by 
means  of  electricity  or  galvanism;  but  no  results  of  importance  were 
obtained  till  the  winter  of  1819,  when  Professor  Oersted  of  Copenhagen 
made  his  famous  discovery,  which  forms  the  basis  of  a new  branch  of 
science  called  Electro-magnetism,  (Annals  of  Philosophy,  xvi.  273.) 

The  fact  observed  by  Professor  Oersted  was,  that  an  electric  current, 
mich  as  is  supposed  to  pass  from  the  positive  to  the  negative  pole  csf  a 
Voltaic  battery  along  a wire  which  connects  them,  causes  a magnetlG 
/•eedle  placed  near  it  to  deviate  from  its  natural  position,  and  assume  a 
new  one,  the  direction  of  which  depends  upon  the  relative  position  of 
the  needle  and  the  wire.  On  placing  the  wire  above  the  magnet  ajid 
parallel  to  it,  the  pole  next  the  negative  end  of  the  battery  always  moves 


error  of  supposing  that  each  group  was  in  its  own  nature  either  negative 
or  positive.  11. 


GALVANISM. 


m 


westward;  and  whpn  the  wire  Is  placed  under  the  needle,  the  same  pole 
goes  towards  the  east.  If  the  wire  is  on  the  same  horizontal  plane  with 
the  needle,  no  declination  whatever  takes  place;  but  the  magnet  shows 
a disposition  to  move  in  a vertical  direction,  the  pole  next  the  negtitive 
side  of  the  battery  being  depressed  when  the  wire  is  to  the  west  of  it, 
and  elevated  when  it  is  placed  on  the  east  side. 

The  extent  of  the  declination  occasioned  by  a battery  depends  Upbn 
its  power,  and  the  distance  of  the  connecting  wire  from  the  needle.  If 
the  apparatus  be  powerful,  and  the  distance  small,  the  declination  will 
amount  to  an  angle  of  45®.  But  this  deviation  does  not  give  an  exact 
idea  of  the  real  effect  w^hich  may  be  produced  by  galvanism;  for  the 
motion  of  the  magnetic  needle  is  counteracted  by  the  roagnetism  of  the 
earth.  When  the  influence  of  this  power  is  destroyed  by  means  of  aiv 
Other  magnet,  the  needle  will  place  itself  directly  across  the  connecting 
wire;  so  that  the  real  tendency  of  a magnet  is  to  stand  at  right  angles  to 
an  electric  current. 

The  communicating  wire  is  also  capable  of  attracting  and  repelfing 
the  poles  of  the  magnet.  This  is  easily  demonstrated  by  permitting  a 
horizontally  suspended  magnet  to  assume  the  direction  of  north  and 
south,  and  placing  near  it  the  conducting  wire  of  a closed  circuit,  held 
vertically  and  at  right  angles  to  the  needle,  with  the  positive  pole  next 
the  ground,  so  that  the  current  may  flow  from  below  upwards.  When 
the  wire  is  exactly  intermediate  between  the  magnetic  poles,  no  effect 
is  observed;  on  moving  the  wire  nearly  midway  towards  the  north  pole, 
the  needle  will  be  attracted;  and  repulsion  will  ensue  when  the  wire  is 
moved  close  to  the  north  pole  itself.  Similar  effects  occur  on  advano 
ing  the  wire  towards  the  south  pole.  Such  are  the  phenomena  if  the 
current  ascends  on  the  west  side  of  the  needle;  but  they  are  reversed 
when  the  wire  is  placed  vertically  on  the  east  side.  Attractions  and  re»- 
pulsions  likewise  take  place  in  a dipping  needle,  when  the  current 
flows  horizontally  across  it. 

The  discovery  of  Oersted  was  no  sooner  announced,  than  the  experi* 
ments  were  repeated  and  varied  by  philosophers  in  all  parts  of  Europe, 
and,  as  was  to  be  expected,  new  facts  were  speedily  brought  to  lighK 
Among  the  most  successful  labourers  in  this  field,  MM.  Ampere,  Arago, 
and  Biot  of  Paris,  and  Sir  H.  Davy  and  Mr.  Faraday  in  this  country,  do- 
serve  to  be  particularly  mentioned, 

M.  Ampere  observed  that  the  Voltaic  apparatus  itself  acts  oti  a mag- 
netic needle  placed  upon  or  near  it,  in  the  same  manner  as  the  wire 
which  unites  its  two  extremities.  But  the  declination  was  found  to  oc- 
cur only  when  the  opposite  ends  of  the  battery  are  in  communication, 
and  to  cease  entirely  as  soon  as  the  circuit  is  interrupted, — a difference 
which  was  supposed  to  arise  from  the  passage  of  an  uninterrupted  elec- 
tric current  through  the  apparatus,  as  along  the  connecting  wire,  taking 
place  in  the  first  case,  and  not  in  the  second.  M.  Ampere,  therefore, 
proposed  the  magnetic  needle  as  an  instrument  for  discovering  the  e»- 
Lstence  and  direction  of  an  electric  current,  (or  currents  according  to 
the  theory  of  the  two  electricities)  as  well  as  for  pointing  out  the  pro- 
per state  and  fitness  of  a galvanic  apparatus  for  electro-magnetic  expe- 
riments in  general.  When  the  needle  is  employed  with  this  mtentioa 
it  is  called  a Galvanometer  or  Galvanoscope, 

M.  Ampere  soon  after  discovered  that  a power  of  attraction  emd  re- 
pulsion may  be  communicated  by  an  electric  current  alone,  without  the 
use  of  a magnet.  Two  wires  of  copper,  brass,  or  any  other  metal, 
placed  parallel  to  each  other,  and  suspended  so  as  to  move  freely,  were 
connected  with  the  opposite  poles  of  a galvanic  apparatus.  If  tlio  eleo 
trie  current  passed  along  both  wires  in  the  same  Erection,  they  attract- 


104 


GALVANISM. 


ed  one  another;  if  in  an  opposite  direction,  they  repelled  each  otlief. 
The  result  of  this  experiment  g'ave  rise  to  the  supposition  that  the  mag- 
netic property  is  actually  communicated  to  the  wires  by  the  electric 
current;  and  this  supposition  was  confirmed  by  M.  Arago,  who  found 
that  iron  filings  are  attracted  by  a wire  placed  in  the  Voltaic  circuit,  and 
that  they  fall  off  when  the  communication  between  the  poles  is  inter- 
rupted. This  fact  was  also  discovered  about  the  same  time  by  Sir  H. 
Davy,  whose  experiments  were  minutely  described,  in  the  year  1821, 
in  the  Transactions  of  the  Royal  Society. 

The  communication  of  temporary  magnetic  properties  to  the  common 
metals  naturally  led  to  an  attempt  to  magnetize  steel  and  iron  perma- 
nently by  the  same  agent.  The  experiment  was  made  by  M.  Arago 
and  Sir  H.  Davy  about  the  same  time,  and  both  were  successful.  Sir 
H.  Davy  attached  steel  needles  to  the  connecting  wire;  placing  some 
parallel  to  it,  and  others  transversely.  The  former  merely  acted  as  a 
part  of  the  circuit;  they  did  not  possess  poles,  and  lost  their  power  of 
attracting  iron  filings  as  soon  as  the  electric  current  ceased  to  circulate 
tlirough  them.  But  the  latter  acquired  a north  and  south  pole,  and 
preserved  the  property  after  separation  from  the  wire.  M.  Arago  at 
first  operated  in  a similar  manner;  but,  at  the  suggestion  of  M.  Ampere, 
he  made  the  connecting  wire  into  the  form  of  a spiral  or  helix,  and 
placed  the  needle  to  be  magnetized  in  its  centre.  By  this  arrangement 
the  maximum  effect  was  obtained  in  a shorter  time  than  by  any  other 
method.  Sir  H.  Davy  also  rendered  a needle  magnetic  by  placing  it 
across  a wire,  along  wdiich  a charge  from  a common  Leyden  battery 
was  transmitted.  This  series  of  experiments  was  completed  by  M.  An> 
pere’s  discovery,  that  a connecting  wire,  suspended  so  as  to  have  per- 
fect freedom  of  motion,  is  influenced  by  the  magnetic  attraction  of  the 
earth. 

For  the  next  fact  of  importance,  science  is  indebted  to  the  researches 
of  Mr.  Faraday.  He  ascertained  that  the  influence  of  the  connecting - 
wire  on  the  direction  of  a magnet,  is  not  owing  to  any  attraction  or  I'e- 
pulsion  exerted  betw^een  them,  but  to  a tendency  they  have  to  revolve 
round  each  other.  He  contrived  an  apparatus,  (Quarterly  Journal,  voL 
xii.)  by  means  of  vrhich  either  pole  of  a magnet  was  made  to  revolve 
round  the  wire  as  a fixed  point;  and  then,  by  fixing  the  wire,  and  giv- 
ing free  motion  to  the  magnet,  both  poles  of  the  latter  were  made  to 
revolve  in  succession  round  the  former.  He  was  also  successful  in 
causing  the  wire  to  revolve  by  the  influence  of  the  magnetism  of  the 
earth. 

It  is  found  that  a magnetic  needle  is  equally  affected  by  every  pohit 
of  a conductor  along  which  an  electric  current  is  passing,  so  that  a wire 
transmitting  the  same  current  will  act  with  more  or  less  energy,  accord- 
ing as  the  number  of  its  parts  contiguous  to  the  needle  is  made  to  vary. 
On  this  principle  the  galvanoscope  of  Schweigger,  commonly  called 
the  Multiplier,  is  constructed.  A copper  wire  is  bent  into  a rectangular 
form  consisting  of  several  coils,  and  in  the  centre  of  the  rectangle  is 
placed  a delicately  suspended  needle,  as  shown  in  the  figure.  Each 
ooll  adds  its  influence  to  that  of  the  others;  and  as  the  current,  in  its 
pix)grcs3  along  the  wire,  passes  repeatedly  above  and  below  the  needle 
in  (q)])Osite  directions,  their  joint  action  is  the  same.  In  order  to  pre- 
vent the  electricity  from  passing  laterally  from  one  coil  to  another  in 
contact  with  it,  the  wire  should  be  covered 
with  silk.  The  ends  of  the  wire,  a and  h,  are 
left  free  for  tlie  jmrposc  of  communication 
with  the  opposite  poles  of  the  galvanic  circle.^ 

I'lie  multiplier  of  Schweigger,  or  some  modification  of  it,  ia  much  em- 
ployed in  rescai’chcs  on  galvanis.m. 


GALVANISM. 


105 


The  foregoing*  is  9 summary  of  the  magnetic  properties  of  the  Vol- 
taic apparatus,  which  form  the  basis  of  electro-magnetism,  and  were 
discovered  soon  after  the  original  experiments  of  Oersted  were  made 
known  to  the  public.  Other  facts  of  interest  have  since  been  observed, 
and  some  ingenious  general  views  have  been  proposed  to  account  for 
all  the  phenomena;  but  as  a full  discussion  of  electro-magnetism  would 
lead  into  details  too  minute  for  an  elementary  treatise,  I must  refer  the 
reader  who  wishes  for  more  ample  information  to  works  written  pro- 
fessedly on  the  subject.  In  addition  to  the  essay  of  Oersted  already  re- 
ferred to,  the  following  may  be  mentioned  as  convenient  for  consultation. 
The  Historical  Sketch  of  Electro-magnetism  in  the  Annals  of  Philoso- 
phy, N.  S.;  Popular  Sketch  of  Electro-magnetism  by  Mr.  Watkins;  the 
Recueil  (T Observations  Electro- dynamiques  by  M.  Ampere;  Professor 
Cumming’s  Manual  of  Electro-dynamics;  and  the  second  edition  of  Mr. 
Barlow’s  Essay  on  Magnetic  Attractions, 


PART  11. 

INORGANIC  CHEMISTRY. 


PRELIMINARY  REMARKS. 

In  teaching  a science,  the  details  of  which  are  numerous  and  compli- 
cated, it  would  be  injudicious  to  follow  the  order  of  discovery,  and  pro- 
ceed from  the  individual  facts  to  the  conclusions  which  have  been  de- 
duced from  them.  An  opposite  course  is  indispensable.  It  is  neces- 
sary to  discuss  general  principles  in  the  first  instance,  in  order  to  aid 
the  beginner  in  remembering  insulated  facts,  and  in  comprehending  the 
explanations  connected  with  them. 

This  necessity  is  in  no  case  more  sensibly  felt  than  in  the  study  of 
chemistry,  and  for  this  reason  I shall  commence  the  second  part  of  the 
work  by  explaining  the  leading  doctrines  of  the  science.-  One  incon- 
venience, indeed,  does  certainly  arise  from  this  method.  It  is  often 
necessary,  by  way  of  illustration,  to  refer  to  facts  of  which  the  begin- 
ner is  ignorant;  and,  therefore,  on  some  occasions  more  knowledge  will 
be  required  for  understanding  a subject  fully,  than  the  reader  may  have 
at  his  command-  But  these  instances  will,  it  is  hoped,  be  rarely  met 
with;  and  when  they  do  occur,  the  reader  is  advised  to  quit  the  point 
of  difficulty,  and  return  to  the  study  of  it  when  he  shall  hav«  acquired 
more  extensive  knowledge  of  the  details. 

To  the  chemical  history  of  each  substance  its  chief  physical  charac- 
ters will  be  added.  A knowledge  of  these  properties  is  not  only  ad- 
vantageous in  assisting  the  chemist  to  distinguish  one  body  from  ano- 
ther, but  in  many  instances  it  is  applied  to  uses  still  more  important. 
Specific  gravity  in  particular  is  a point  of  great  consequence,  and  as  this 
expression  will  hereafter  be  used  in  almost  every  page,  it  will  be  pro- 
per, before  proceeding  further,  to  explain  its  meaning.  Equal  bulks 
of  different  substances,  as  a cubic  inch  of  gold,  silver,  tin,  and  water, 
differ  more  or  less  in  weight:  their  densities  are  different;  or  in  other 
words,  they  contain  different  quantities  of  ponderable  matter  in  the 
same  space.  The  tin  will  weigh  eight  times  more  than  the  water,  the 
silver  about  ten  times  and  a half,  and  the  gold  upwards  of  nineteen 
times  more  than  tliat  fluid.  The  density  of  all  solids  and  liquids  may  be 
determined  in  the  same  manner;  and  if  they  are  compared  with  an  equal 
bulk  of  water  as  a standard  of  comparison,  a series  of  numbers  wdll  be 
obtained,  which  will  show  the  comparative  density,  or  specific  grc^ 
viUjy  as  it  is  called,  of  all  of  them. 

The  process  for  determining  specific  gravities  is,  therefore,  suflir 
cicntly  simple.  It  consists  in  weighing  a body  carefully,  and  then  de- 
termining the  weight  of  an  equal  bulk  of  water,  the  latter  being  regard- 
ed as  unity.  If,  for  example,  a portion  of  water  weighs  nine  grains, 
and  the  same  bulk  of  another  body  20  grains,  its  specific  gravity  is  de- 
mined by  the  formula,  as  9 : 20  : ; 1 (the  specific  gravity  of  water)  t» 
the  fourth  proportional  2.2222;  so  that  the  specific  gravity  of  any  sub- 
stance is  found  by  dividing  its  weight  by  the  weight  of  an  equal  volume 
of  water.  It  is  easy  to  discover  the  weight  of  equal  bulks  of  water  and  any 
other  liquid  by  filling  a small  bottle  of  known  weight  with  each  sue- 


PRELTMINATIY  HEMARKS. 


107 


ccssirety,  and  weighing  them* . The  method  of  obtaining  the  neces- 
sary data  in  case  of  a solid  is  somewhat  different.  The  body  isiirst 
weighed  in  air,  is  next  suspended  in  water  by  means  of  a hair  attached 
to  the  scale  of  a balance,  and  is  then  weighed  again.  The  difference 
between  the  two  weights  gives  the  weight  of  a quantity  of  water  equal 
to  the  bulk  of  the  solid.  This  rule  is  founded  on  the  hydrostatic  law 
that  a solid  body,  immersed  in  any  liquid,  not  only  weighs  less  than  it 
does  in  air,  but  that  the  difference  corresponds  exactly  to  the  weight 
of  the  liquid  which  it  displaces;  and  it  is  obvious  that  the  liquid  so 
displaced  is  exactly  of  the  same  dimensions  as  the  solid.  Another 
method  is  by  the  use  of  the  bottle  recommended  for  taking  the 
specific  gravity  of  liquids.  After  weighing  the  bottle  filled  with  water 
a known  weight  of  the  solid  is  put  into  it,  which  of  course  displaces  a 
quantity  of  water  precisely  equal  to  its  own  volume.  The  exact  weight 
of  the  displaced  water  is  found  by  weighing  the  bottle  again,  after  hav- 
ing wiped  its  outer  surface  with  a dry  cloth. 

The  determination  of  the  specific  gravity  of  gaseous  substances  is  an 
operation  of  much  greater  delicacy.  From  the  extreme  lightness  of 
gases,  it  would  be  inconvenient  to  compare  them  with  an  equal  bulk  of 
water,  and,  therefore,  atmospheric  air  is  taken  as  the  standard  of  com- 
parison. The  first  step  of  the  process  is  to  ascertain  the  weight  of  a 
given  volume  of  air.  This  is  done  by  weighing  a very  light  glass  flask,  fur- 
nished with  a good  stopcock,  while  full  of  air;  and  then  v;eighing  it  a 
second  time,  after  the  air  has  been  withdrawn  by  means  of  the  air-pump. 
The  difference  between  the  two  weights  gives  the  information  required. 
According  to  the  experiments  of  Sir  George  Shuckburgh,  100  cubic 
inches  of  pure  and  dry  atmospheric  air,  at  the  temperature  of  60^  F.  and 
when  the  barometer  stands  at  SO  inches,  weigh  precisely  30.5  grains. 
By  a similar  method  the  weight  of  any  other  gas  may  be  determined, 
and  its  specific  gravity  be  inferred  accordingly.  For  instance,  suppose 
100  cubic  inches  of  oxygen  are  found  to*  weigh  33.888  grains,  its  spe- 
cific gravity  will  be  thus  deduced,  as  30,5  : 33.888  : : 1 (the  sp.  gr.  of 
air)  : 1.1111,  the  specific  gravity  of  oxygen. 

There  are  four  circumstances  to  which  particular  attention  must  be 
paid  in  taking  the  specific  gravity  of  gases: — 

1.  The  gas  should  be  perfectly  pure,  otherwise  the  result  cannot  be 
accurate. 

2.  Due  regard  must  be  had  to  its  hygrometric  condition.  If  it  is  safti»- 
rated  with  moisture,  the  necessary  correction  may  be  made  for  that  ciiN 
cumstance  by  the  formula  which  will  be  found  at  page  64;  or  it  may 
be  dried  by  the  use  of  substances  which  have  a powerful  attraction  for 
moisture,  such  as  chloride  of  calcium,  quicklime,  or  fused  potassa. 

3.  As  the  bulk  of  gaseous  substances,  owing  to  their  elasticity  and  corr>- 
pressibility,  is  dependent  on  the  pressure  to  which  they  are  exposed, 
no  two  observations  admit  of  comparison,  unless  made  under  the  same 
elevation  of  the  barometer.  It  is  always  understood,  in  taking  the  spe- 
cific gravity  of  a gas,  that  the  barometer  must  stand  at  thirty  inches,  by 
which  means  the  operator  is  certain  that  each  gas  is  subject  to  equal  de- 
grees of  compression.  An  elevation  of  thirty  inches  is,  therefore,  called 
the  standard  height;  and  if  the  mercurial  column  be  not  of  that  length 
at  the  time  of  performing  the  experiment,  the  error  arising  from  this 
cause  must  be  corrected  by  calculatioui  It  has  been  established  by  carci- 
ful  experiment  that  the  bulk  of  gases  is  inversely  as  the  pressure  to  which 


* Bottles  are  prepared  for  this  purpose  by  the  phllbsophical  instru- 
m^ent-makers. 


108 


PRELIMINARY  REMARKS. 


they  are  subject.  Thus,  100  measures  of  air  under  tlie  prcfir^nix:  of  a 
thirty  inch  column  of  mercury,  will  dilate  to  200  measures,  if  the  pres- 
sure be  diminished  one  half;  and  will  be  compressed  to  fifty  mcLi- 
sures,  when  the  pressure  is  double,  or  equal  to  a mercurial  column  of 
sixty  inches.  The  correction  fortlie  effect  of  pressure  may,  therefore, 
be  made  by  the  rule  of  three,  as  will  appear  by  an  example.  If  a cer- 
tain portion  of  gus  occupy  the  space  of  100  measures  at  twenty-nine 
inches  of  the  barometer,  its  bulk  at  thii'ty  inches  may  be  obtained  by  the 
following  proportion;  as 

30  : 29  : : 100  : 96.66. 

4.  For  a similar  reason  the  temperature  should  always  be  the  same. 
The  standard  or  mean  temperature  is  60®  F. ; and  if  the  gas  be  admitted 
into  the  weighing-flask  when  tlie  thermometer  is  above  or  below  that 
point,  the  formula  of  page  35  should  be  employed  for  making  tiie 
necessary  correction. 

Chemistry  is  indebted  for  its  nomenclature  to  the  labours  of  four  cele- 
brated chemists,  Lavoisier,  Berthollet,  Guyton-Moiweau,  and  Fourcroy. 
The  principles  which  guided  them  in  its  construction  are  exceedingly 
simple  and  ingenious.  The  known  elementary  substances  and  the  more 
familiar  compound  ones  were  allowed  to  retain  the  appellation  which 
general  usage  had  assigned  to  them.  The  newly  discovered  elements 
were  named  from  some  striking  property.  Thus,  aS  it  was  supposed 
that  acidity  was  always  owing  to  the  presence  of  the  vital  air  discovered 
by  Priestley  and  Scheele,  they  gave  it  the  name  of  derived  from 

two  Greek  words  signifying  generator  of  acid;  and  they  called  inflam- 
mable air,  hydrogen,  from  the  circumstance  of  its  entering  into  the  com- 
position of  water. 

Compounds,  of  which  oxygen  forms  a part,  were  called  acids  or  oxides 
according  as  they  do  or  do  not  possess  acidity.  An  oxide  of  iron  or 
copper  signifies  a combination  of  those  metals  with  oxygen,  which  has 
no  acid  properties.  The  name  of  an  acid  was  derived  from  the  sub- 
stance acidified  by  the  oxygen,  to  which  was  added  the  termination  in 
ic.  Thus,  sulphuric  and  carbonze  acids  signify  acid  compounds  of  sul- 
phur and  carbon  with  oxygen  gas.  If  sulphur  or  any  other  body  should 
form  two  acids,  that  which  contains  the  least  quantity  of  oxygen  is  made 
to  terminate  in  ous,  as  sulphurows  acid.  The  termination  in  uret  was  in- 
tended to  denote  combinations  of  the  simple  non-metallic  substances 
either  with  one  anothei*,  with  a metal  or  with  a metallic  oxide.  Sul- 
phwre^  and  carbwrc^  of  iron,  for  example,  signify  compounds  of  sulphur 
and  carbon  with  iron.  The  different  oxides  or  sulphurets  of  the  same 
substance  were  distinguished  from  one  another  by  ^ome  epithet,  which 
was  commonly  derived  from  the  colour  of  the  compound,  such  as  the 
black  and  red  oxides  of  iron,  the  black  and  red  sulphurets  of  mercury. 
Though  tills  practice  is  still  continued  occasionally,  it  is  now  more  cus- 
tomary to  distinguish  degi’ecs  of  oxidation  by  the  use  of  derivatives  from 
file  Greek.  /Vo^oxide  signifies  the  first  degTee  of  oxidation,  c?eu/oxide 
the  second,  and  /n/oxide  tlie  third.  The  term  joeroxide  is  often  ap- 
plied to  the  highest  degre^e  of  oxidation.  The  sulphurets,  carbicets, 
&c.  of  the  same  substance  are  designated  in  a similar  v/ay.  Compounds 
ctmsisting  of  acids  in  combination  witli  alkalies,  earths,  or  metallic  oxides, 
are  tenned  sails,  the  names  of  which  are  so  contrived  as  to  indicate  the 
sulititance.^i  contained  in  tliem.  If  the  acidified  substance  contains  a 
miiximuni  of  oxygi'n,  the  name  of  the  salt  terminates  in  ate,-  if  a mini- 
mnin,  the  h rinination  in  //cis  employcck  I'lms,  the  sulplm/e,  phosphu/e, 
aiul  arieniu/t  ofpotassu,  are  salts  ol*  sulphuj^/c,  phosiihor/c,  and  arsenic 


AFFINITY. 


109 

acids;  while  the  terms  sulph;<e,  phosphite,  and  arseniie  of  potassa  de- 
note combinations  of  that  alkali  with  the  sulphurous,  phosphorous  and 
arseniaw5  acids.  ax-  > ^ 

The  advantage  of  a nomenclature  which  disposes  the  different  parts 
of  a science  in  so  systematic  an  order,  and  gives  such  powerful  assist 
ance  to  the  memory,  is  incalculable.  The  principle  has  been  acknow- 
ledged in  all  countries  where  chemical  science  is  cultivated  audits 
minutest  details  have  been  adopted  in  Britain.  It  must  be  admitted 
indeed,  that  in  some  respects  the  nomenclature  is  defective  The  er^ 
roneous  idea  of  oxygen  being  the  general  acidifying  principle,  has  ex' 
erased  an  injurious  influence  over  the  whole  structure.  It  would  have 
been  convenient  also  to  have  had  a different  name  for  hydrogen.  But 
It  IS  now  too  late  to  attempt  a change;  for  the  confusion  attending  such 
an  innovation  would  more  than  counterbalance  its  advantages  The 
origin^  nomenclature  has,  therefore,  been  preserved,  and  such  addi- 
tions have  been  made  to  it  as  the  progress  of  the  science  rendered  ne- 
cessaiy.  The  most  essential  improvement  was  suggested  by  the  dis- 
covery of  the  laws  of  chemical  combination.  The  different  salts  formed 
of  the  same  constituents  were  formerly  divided  into  neutral,  super,  and 
«4^-salts.  They  were  called  neutral,  if  the  acid  and  alkali  were  in  such 
proportion  that  one  neutralized  the  other;  super-salts,  if  the  acid  pre- 
vailed; and  sub-salts,  if  the  alkali  was  in  excess.  The  name  is  now 
regulated  by  the  atomic  constitution  of  the  salt.  If  it  is  a compound  of 
an  equivalent  of  the  acid  and  the  alkali,  the  generic  name  of  the  salt  is 
employed  without  any  other  addition ; but  if  two  or  more  equivalents  of 
me  acid  are  attached  to  one  of  the  base,  or  two  or  more  equivalents  of 
the  base  to  one  of  the  acid,  a numeral  is  prefixed  so  as  to  indicate  its  com- 
position. The  two  salts  of  sulphuric  acid  and  potassa  are  called  sulphate 
and  6i-sulphate;  the  first  containing  an  equivalent  of  the  acid  and  the 
alkali,  and  the  second  salt,  two  of  the  former  to  one  of  the  latter.  The 
three  salts  of  oxalic  acid  and  potassa  are  termed  the  oxalate,  Z>moxalate, 
and  quadrox2\aXe  of  potassa;  because  one  equivalent  of  the  alkali  is 
united  with  one  equivalent  of  acid  in  the  first,  with  two  in  the  second 
and  with  four  in  the  third  salt.  As  the  numerals  which  denote  the 
equivalents  of  the  acid  in  a super-salt  are  derived  from  the  Latin  lan- 
guage, Dr.  Thomson  proposes  to  employ  the  Greek  numerals,  dis,  iris, 
teirakis,  to  signify  the  equivalents  of  alkali  in  a sub-salt. 

This  method  is  in  the  true  spirit  of  the  original  framers  of  our  no- 
menclature.  Chemists  have  already  begun  to  apply  the  same  princi- 
ple  to  other  compounds  besides  salts;  and  there  can  be  no  doubt  that 
it  will  be  apphe^d  universally  whenever  our  knowledge  shaU  be  in  a 
state  to  admit  of  its  introduction. 


SECTION  I. 

AFFINITY. 

All  chemical  phenomena  are  owing  to  Affinity  or  Chemical  Attrac 
ion.  It  is  the  basis  on  which  the  science  of  chemistry  is  founded  It 
3,  as  it  were,  the  instrument  which  the  chemist  employs  in  all  his  ope- 

leading  object  of  his  study.  ^ 

f is'exerted  between  the  minutest  particles  of  different  kinds 

matter,  causing  them  to  combine  so  as  to  form  new  bodies  endowed 
nth  new  properUes.  It  acts  only  at  insensible  distances;  in  other  words 

10  ’ 


110 


AFriXlTY. 


apparent  contact,  or  tlic  closest  proximity,  is  necessary  to  its  action. 
Every  thing  which  prevents  such  contiguity  is  an  oljstaclc  to  combina- 
tion; and  any  force  which  increases  tlu*.  distance  between  particles  al- 
ready combined,  tends  to  sepai-ate  them  permanently  from  each  other. 
In  tlie  former  case,  they  do  not  come  withiii  tlie  sphere  of  their  mutual 
atti’action;  in  the  latter,  they  are  removed  out  of  it.  It  follows,  there- 
fore, that  though  affinity  is  regarded  as  a specific  power  distinct  from 
tJie  other  forces  which  act  on  matter,  its  action  may  be  promoted,  modi- 
fied, or  counteracted  by  several  circumstances;  and  consequently,  in 
studying  the  phenomena  produced  by  affinity,  it  is  necessary  to  inquire 
into  the  conditions  that  influence  its  operation. 

The  most  simple  instance  of  the  exercise  of  chemical  attraction  is  af- 
forded by  the  commixture  of  two  substances.  Water  and  sulphuric  acid, 
or  water  and  alcohol,  combine  readily.  On  the  contraiy,  water  shows 
little  disposition  to  unite  with  sulphuric  ether,  and  still  less  with  oil;  for 
however  intimately  their  particles  may  be  mixed  together,  they  are  no 
sooner  left  at  rest  than  the  ether  separates  almost  entirely  from  the  wa- 
ter, and  a total  separation  takes  place  between  that  fluid  and  the  oil. 
Sugar  dissolves  very  sparingly  in  alcohol,  but  to  any  extent  in  water ; 
wliile  camphor  is  dissolved  in  a very  small  degree  by  water,  and  abun- 
dantly by  alcohol.  It  appears,  from  these  examples,  that  chemical  at- 
traction is  exerted  between  diflerent  bodies  with  different  degrees  of 
force.  There  is  sometimes  no  proof  of  its  existence  at  all;  between 
some  substances  it  acts  very  feebly,  and  between  otliers  with  great 
energy. 

Simple  combination  of  two  particles  is  a common  occurrence.  The 
solution  of  salts  in  water,  the  combustion  of  phosphorus  in  oxygen  gas, 
and  the  neutralization  of  a pure  alkali  by  an  acid,  are  instances  of  the 
kind.  The  phenomena,  however,  are  often  more  complex.  It  fre- 
quently happens  that  the  formation  of  a new  compound  is  attended  by 
the  destruction  of  an  existing  one.  The  only  condition  necessary  for 
this  effect,  is  the  presence  of  some  third  body  which  has  a greater  affi- 
nity for  one  of  the  elements  of  a compound  than  they  have  for  each 
other.  Thus,  oil  has  an  affinity  for  the  volatile  alkali,  ammonia,  and 
will  unite  with  it,  forming  a soapy  substance  called  a liniment.  But  the 
ammonia  has  a still  greater  attraction  for  sulphuric  acid;  and  hence  if 
this  acid  be  added  to  the  liniment,  the  alkali  will  quit  the  oil,  and  unite 
by  preference  with  the  acid.  If  a solution  of  camphor  in  alcohol  be 
poured  into  water,  the  camphor  will  be  set  free,  because  the  alcohol 
combines  with  the  water.  Sulphuric  acid,  in  like  manner,  separates 
biuyta  from  muriatic  acid.  Combination  and  decomposition  occur  in 
each  of  these  cases; — combination  of  sulphuric  acid  with  ammonia,  of 
water  with  alcohol,  and  of  baryta  with  sulphuric  acid — decomposition 
of  the  compounds  formed  of  oil  and  ammonia,  of  alcohol  and  camphor, 
and  of  muriatic  acid  and  baryta.  I'hese  are  examples  of  what  Bergmann 
called  single  elective  affinity; — elective,  because  a substance  manifests,  as 
it  were,  a choice  for  one  of  two  others,  uniting  with  it  by  preference, 
and  to  tlie  exclusion  of  the  other.  Many  of  the  decompositions  tliat  oc- 
cur in  chemistry  are  instances  of  single  elective  affinity. 

Tlie  order  in  which  these  decom])ositions  take  place  has  been  ex- 
jiressed  in  tables,  of  which  the  following,  drawn  up  by  Gcoffroy,  is  an 
example: — 

Sulphuric  Acid, 

Baryta, 

ibtrontia. 


AFFINITY. 


Ill 


Potassa, 

Soda, 

Lime, 

Ammonia, 

Mag*nesia. 

This  table  signifies,  first,  that  sulphuric  acid  has  an  affinity  for  the 
substances  placed  below  the  horizontal  line,  and  may  unite  separately 
with  each;  and,  secondly,  that  the  base  of  the  salts  so  formed  will  be 
separated  from  the  acid  by  adding-  any  of  the  alkalies  or  earths  which, 
stand  above  it  in  the  column.  Ihus  ammonia  will  separate  magnesia, 
lime  ammonia,  and  potassa  lime;  but  none  can  withdraw  baryta  from 
sulphuric  acid,  nor  can  ammonia  or  magnesia  decompose  sulphate  of 
lime,  though  strontia  or  baryta  will  do  so.  Bergmann  conceived  that 
tliese  decompositions  are  solely  determined  by  chemical  attraction,  and 
tliat  consequently  the  order  of  decomposition  represents  the  compani- 
tive  forces  of  affinity;  and  this  view,  from  the  simple  and  natural  ex- 
planation it  affords  of  the  phenomenon,  was  for  a time  very  generally 
adopted.  But  Bergmann  was  in  error.  It  does  not  necessarily  follow, 
because  lime  separates  ammonia  from  sulphuric  acid,  that  the  lime  has 
a gi-eater  attraction  for  the  acid  than  the  volatile  alkali.  Other  causes 
are  in  operation  which  modify  the  action  of  affinity  to  such  a degree, 
that  it  is  impossible  to  discover  how  much  of  the  effect  is  owing  to  that 
power.  It  is  conceivable  that  ammonia  may  in  reality  have  a stronger 
attraction  for  sulphuric  acid  than  lime,  and  yet  that  the  latter,  from  the 
great  influence  of  disturbing  causes,  may  succeed  in  decomposing 
phate  of  ammonia. 

The  justness  of  the  foregoing  remark  will  be  made  obvious  by  the  fol- 
lowing example. — When  a stream  of  hydrogen  gas  is  passed  over  oxide 
of  iron  heated  to  redness,  the  oxide  is  reduced  to  the  metallic  state,  and 
water  is  generated.  On  the  contrary,  when  watery  vapour  is  brought 
into  contact  with  red-hot  metallic  iron,  the  oxygen  of  the  water  quits 
tlie  hydrogen  and  combines  with  the  iron.  It  follows  from  the  result 
of  the  first  experiment,  according  to  Bergmann,  that  hydrogen  has  a 
stronger  attraction  than  iron  for  oxygen;  and  from  that  of  the  second, 
that  iron  has  a greater  affinity  for  oxygen  than  hydrogen.  But  these  in- 
ferences are  incompatible  with  each  other.  The  affinity  of  oxygen  for 
the  two  elements,  hydrogen  and  iron,  must  either  be  equal  or  unequal. 
If  equal,  the  result  of  both  experiments  was  determined  by  modifying 
(fircumstances;  since  neither  of  these  substances  ought  on  this  supposi- 
tion to  take  oxygen  from  the  other.  But  if  the  forces  are  unequal,  the 
decomposition  in  one  of  the  experiments  must  have  been  determined  by 
extraneous  causes,  in  direct  opposition  to  the  tendency  of  affinity. 

To  Berthollet  is  due  the  honour  of  pointing  out  the  fallacy  of  Berg- 
mann’s  opinion.  He  was  the  first  to  show  that  the  relative  forces  of  che- 
mical attraction  cannot  always  be  determined  by' observing  the  order  in 
wliich  substances  separate  each  other  wlien  in  combination,  and  that  the 
tables  of  Geoffroy  are  merely  ttibles  of  decomposition,  not  of  affinity. 
He  likewise  traced  all  the  various  circumstances  that  modify  the  action 
of  affinity,  and  gave  a consistent  explanation  of  the  mode  in  which  they 
operate.  Berthollet  went  even  a step  further.  He  denied  the  existence 
of  elective  affinity  as  an  invariable  force,  capable  of  effecting  the  per- 
fect separation  of  one  body  from  another;  he  maintained  that  all  the  in- 
stances of  complete  decomposition  atti-ibuted  to  elective  affinity  ai*e  in 
reality  determined  by  one  or  more  of  the  collateral  circumstances  that 
influence  its  operation.  But  here  this  acute  philosopher  has  surely  gone 
too  far.  Bergmann  is  admitted  to  have  erred  in  supposing  the  result  of 


112 


ArriNri’Y. 


chemical  action  to  be  in  every  case  owing  to  elective  affinity;  but  Hcr- 
thollet  certainly  ran  into  the  opposite  extreme  in  declaring,  that  the 
effects  formerly  ascribed  to  that  power  are  never  produced  by  it.  Tliat 
chemical  attraction  is  exerted  between  bodies  witli  different  degrees  of 
energy  is,  I conceive,  indisputable.  Water  has  a miicli  greater  affinity 
for  muriatic  acid  and  ammoniacal  gases  than  for  carbonic  acid  and  sul- 
phuretted hydrogen,  and  for  these  tlian  for  oxygen  and  hydrogen.  I'hc 
attraction  of  lead  for  oxygen  is  gi^eater  than  that  of  silver  for  the  same 
substance.  The  disposition  of  gold  and  silver  to  combine  with  mercury, 
is  gi’eater  than  tlie  atU’action  of  platinum  and  iron  for  that  fluid.  As 
these  differences  cannot  be  accounted  for  by  the  operation  of  any  mo- 
difying causes,  we  must  admit  a difference  in  the  force  of  affinity  in  pro- 
ducing combination.  It  is  equally  clear  that  in  some  instances  the  sepa- 
ration of  bodies  from  one  another  can  only  be  explained  on  the  s'ame 
principle.  No  one,  1 conceive,  will  contend  that  the  decomposition  of 
hydriodic  acid  by  chlorine,  or  of  sulphuretted  hydrogen  by  iodine,  is 
determined  by  the  conciUTcnce  of  any  modifying  circumstances. 

Affinity  is  the  cause  of  still  more  complicated  changes  than  those 
wliicli  have  been  just  considered.  In  a case  of  single  elective  affinity, 
three  substances  only  are  present,  and  two  affinities  are  in  play.  But  it 
frequently  happens  that  two  compounds  are  mixed  together,  and  four 
different  affinities  brought  into  action.  The  changes  that  may  or  do  oc- 
ciu'  under  these  circumstances  are  most  conveniently  studied  by  aid  of  a 
diagi’am,  a method  wliich  was  first  employed,  I believe,  by  Dr.  Black, 
and  has  since  been  generally  practised.  Thus,  in  mixing  together  a 
solulioa  of  carbonate  cf  ammonia  and  muriate  of  lime,  their  mutual  ac- 
tion may  be  represented  in  tlie  following  manner: 


Carbonic  acid 


Ammonia 


Muriatic  acid  Lime 


Each  of  the  acids  has  an  attraction  for  both  bases,  and  hence  it  is 
possible  either  that  the  two  salts  should  continue  as  they  were,  or  that 
an  interchange  of  principles  should  ensue,  giving  rise  to  two  new  com- 
pounds,— carbonate  of  lime  and  muriate  of  ammonia.  According  to  the 
views  of  Bergmann  tlie  result  is  solely  dependent  on  the  comparative 
strength  of  affinities.  If  the  affinity  of  carbonic  acid  for  ammonia,  and 
of  muriatic  acid  for  lime,  exceed  that  of  carbonic  acid  for  lime,  added 
to  that  of  muriatic  acid  for  ammonia,  tlien  will  the  two  salts  experience 
no  change  whatever;  but  if  the  latter  affinities  preponderate,  then,  as 
does  actually  happen  in  the  present  example,  both  the  original  salts  will 
be  decomposed,  and  two  new  ones  g’encrated.  Two  decompositions 
and  two  combinations  take  place,  being  an  instance  of  what  is  called 
double  elective  ajjinity.  Mr.  Kirwan  applied  the  terms  quiescent  andfl^/rcA 
lent  to  denote  tlie  tendency  of  the  opposing  affinities,  tlie  action  of  the 
former  being  to  prevent  a change,  the  latter  to  produce  it. 

The  doctrine  of  double  elective  affinity  was  assailed  by  Berthollet  on 
the  same  ground  and  with  tlie  same  success  as  in  the  case  of  single  elec- 
tive attraction.  He  succeeded  in  proving  tliat  the  effect  cannot  always 
be  ascribed  to  tlie  sole  influence  or  affinity.  For,  to  take  the  example 


AFFINITY. 


113 


already  adduced,  if  carbonate  of  ammonia  decompose  muriate  of  lime 
by  tlie*  mere  force  of  a superior  attraction,  it  is  manifest  that  carbonate 
of  lime  ought  never  to  decompose  muriate  of  ammonia.  But  if  these 
two  salts  are  mixed  in  a dry  state  and  exposed  to  heat,  double  decom- 
position does  take  place,  carbonate  of  ammonia  and  muriate  of  lime  be- 
ing formed;  and,  therefore,  if  the  chang’e  in  the  first  example  was  pro- 
duced by  chemical  attraction  alone,  that  in  the  second  must  have  occur- 
red in  direct  opposition  to  that  power.  It  does  not  follow,  however, 
because  the  result  is  sometimes  determined  by  modifying  conditions,  that 
it  must  always  be  so.  I apprehend  that  the  decomposition  of  the  solid 
cyanuret  of  meremy  by  sulphuretted  hydrogen  gas,  which  takes  place 
even  at  a low  temperature,  cannot  be  ascribed  to  any  other  cause  than  a 
preponderance  of  tlie  divellent  over  the  quiescent  affinities. 

On  the  Changes  that  accompany  Chemical  Action. 

The  leading  circumstance  that  cliaracterizes  chemical  action  is  the 
loss  of  properties  experienced  by  the  combining  substances,  and  the 
acquisition  oi*  new  ones  by  the  product  of  their  combination.  The 
change  of  property  is  sometimes  inconsiderable.  In  a solution  of  sugar 
or  salt  in  water,  and  in  mixtures  of  water  with  alcohol  or  sulphuric  acid, 
the  compound  retains  so  much  of  the  character  of  its  constituents,  that 
there  is  no  difficulty  in  recognising  their  presence.  But  more  generally 
the  properties  of  one  or  both  of  the  combining  bodies  disappear  entire- 
ly. No  ingenuity  coidd  guess,  a priori,  that  water  is  a compound  body, 
much  less  that  it  is  composed  of  two  gases,  0X3^gen  and  hydrogen, 
neither  of  which  when  uncombined,  has  ever  been  compressed  into  a 
liquid.  Hydrogen  is  one  of  the  most  inflammable  substances  in  nature, 
and  yet  water  cannot  be  set  on  fii’e;  oxygen,  on  the  contrary,  enables 
bodies  to  burn  with  great  brilliancy,  and  yet  water  extinguishes  com- 
bustion. The  alkalies  and  earths  were  regarded  as  simple  till  Sir  H.’ 
Da\y  proved  them  to  be  compound,  and  certainly  they  evince  no  sign 
whatever  of  containing  oxygen  and  a metal.  Numerous  examples  of  a 
similar  kind  are  afforded  by  the  action  of  acids  and  alkalies  on  one  an- 
other. Sulphuric  acid  and  potassa,  for  example,  are  highly  caustic. 
The  former  is  intensely  sour,  reddens  the  blue  colour  of  vegetables,  and 
has  a strong  affinity  for  alkaline  substances;  the  latter  has  a pungent 
taste,  converts  the  blue  colour  of  vegetables  to  green,  and  combines 
readily  with  acids.  On  adding  these  principles  cautiously  to  each  other, 
a compound  results  called  a neutral  salt,  which  does  not  in  any  way  af- 
fect the  colouring  matter  of  plants,  and  in  which  the  other  distinguish- 
ing featimes  of  the  acid  and  alkah  can  np  longer  be  perceived.  They 
appear  to  have  destroyed  the  properties  of  each  other,  and  are  hence 
said  to  neutralize  one  another. 

The  other  phenomena  that  accompanj^  chemical  action  are  changes  of 
density,  temperature,  form,  and  colour. 

1.  It  is  observed  that  two  bodies  rarely  occupy,  after  combination, 
the  same  space  which  they  possessed  separately.  In  general  their  bulk 
is  diminished,  so  that  the  specific  gravity  of  the  new  body  is  gi'eater 
than  the  mean  of  its  components.  Thus  a mixture  of  100  measures  of 
water  and  an  equal  quantity  of  sulphuric  acid  does  not  occupy  the  space 
of  200  measures,  but  considerably  less.  A similar  contraction  frequent- 
I ly  attends  the  combination  of  solids.  Gases  often  experience  a remark- 
i able  condensation  when  they  unite.  The  elements  of  olefiant  gas,  for 
j -instance,  woidd  expand  to  four  times  the  bulk  of  that  compound,  if  they 
I were  suddenly  to  become  free,  and  assume  the  gaseous  form.  But  tii’e 
j rule  is  not  without  exception.  The  reverse  happens  in  some  metallic 

10* 


114 


AFFINITY. 


compounds;  and  there  are  examples  of  combination  between  pises  with- 
out any  chang’e  of  bulk. 

2.  A chang-e  of  temperature  g'enerally  accompanies  chemical  action. 
Caloric  is  evolved  either  when  there  is  a diminution  in  tlic  bulk  of  the 
combining'  substances  without  change  of  form,  or  when  a gas  is  con- 
densed into  a liquid,  or  when  a liquid  becomes  soHd.  Tlie  heat  caused 
by  mixing  sulphuric  acid  with  water  is  an  instance  of  tlie  former;  and 
the  common  process  of  slaking  lime,  during  which  water  loses  its  liquid 
form  in  combining  with  that  earth,  is  an  example  of  the  latter,  ’'fhe 
rise  of  temperature  in  these  cases  is  obviously  refemble  to  diminution  in 
the  capacity  of  the  new  compound  for  caloric;  but  intense  heat  some- 
times accompanies  chemical  action  under  circumstances  in  which  an  ex- 
planation founded  on  a change  of  specific  caloric  is  quite  inadmissible. 
At  present  it  is  enough  to  have  stated  the  fact;  the  theory  of  it  will  be 
discussed  under  the  subject  of  combustion.  The  production  of  cold  sel- 
dom or  never  takes  place  during  combination,  except  when  heat  is  ren- 
dered insensible  by  the  convei^ion  of  a solid  into  a liquid,  or  a liquid  into 
a gas.  All  the  frigorific  mixtures  act  in  tins  way. 

3.  The  changes  of  form  that  attend  chemical  action  are  exceedingly 
various.  The  combination  of  gases  may  give  rise  to  a liquid  or  a solid; 
solids  sometimes  become  liquid,  or  liquids  solid.  Several  familiar 
chemical  phenomena,  such  as  explosions,  effervescence,  and  precipita- 
tions, are  owing  to  these  changes.  The  sudden  evolutibn  of  a large 
quantity  of  gaseous  matter  occasions  an  explosion,  as  when  gunpowder 
detonates.  The  slower  disengagement  of  gas  causes  effervescence,  as 
occurs  when  marble  is  put  into  muriatic  acid.  A precipitate  is  owing 
to  the  formation  of  a new  body  which  happens  to  be  insoluble  in  the 
liquid  in  which  its  elements  were  dissolved. 

4.  The  colour  of  a compound  is  frequently  quite  different  from  that 
of  the  substances  by  which  it  is  formed.  There  does  not  appear  to  be 
any  uniform  relation  between  the  colour  of  a body  and  that  of  its  ele- 
ments, so  that  it  is  not  possible  to  anticipate  the  colour  of  any  particu- 
lar compound  by  knowing  the  principles  which  enter  into  its  composi- 
tion. Iodine,  whose  vapour  is  of  a violet  hue,  forms  a beautiful  red 
compound  with  mercury,  and  a yellow  one  with  lead.  The  brown 
oxide  of  copper  generally  gives  rise  to  green  and  blue  coloured  salts; 
while  the  salts  of  the  oxide  of  lead,  which  is  itself  yellow,  are  for  the 
most  part  colourless.  The  colour  of  precipitates  is  a very  important 
study,  as  it  often  enables  the  chemist  to  distinguish  bodies  fix)m  one 
another  when  in  solution. 

On  the  Circumstances  that  modify  and  influence  the 
Operation  of  *flffinity. 

Of  the  conditions  which  are  capable  of  promoting  or  countei*actlng 
the  tendency  of  chemical  attraction,  the  following  are  the  most  impor- 
tant; cohesion,  elasticity,  quantity  of  matter,  and  gravity.  To  these 
may  be  added  the  agency  of  the  imponderables. 

Cohesion. 

7'he  first  obvious  effect  of  cohesion  is  to  oppose  affinity,  by  impeding 
or  preventing  tljat  mutual  penetration  and. close  proximity  of  the  parti- 
cles of  different  bodies,  which  is  essential  to  the  successful  exercise  of 
their  attraction.  For  tliis  reason  bodies  seldom  act  chemically  in  their 
solid  state;  tlieir  molecules  do  not  come  within  the  sphere  of  attraction, 
and,  therefore,  combination  cannot  take  place,  although  their  affinity 
may  in  fact  be  considerable.  Liquidity,  on  the  contrary,  favsours  chemi- 


AFFINITY. 


115 


cal  action;  it  permits  the  closest  possible  approximation,  while  the  co- 
hesive power  is  comparatively  so  trifling  as  to  oppose  no  appreciable 
barrier  to  affinity. 

Cohesion  may  be  diminished  in  two  w^ays,  by  mechanical  division,  or 
by  the  application  of  heat.  The  former  is  useful  by  increasing  the  ex- 
tent of  surface;  but  it  is  not  of  itself  in  general  sufficient,  because  the 
particles,  however  minute,  still  retain  that  degree  of  cohesion  which  con- 
stitutes solidity.  Caloric  acts  with  greater  effect,  and  never  fails  in  pro- 
moting combination,  whenever  the  cohesive  power  is  a barrier  to  it.  Its 
intensity  should  always  be  so  regulated  as  to  produce  liquefaction.  The 
fluidity  of  one  of  the  substances  frequently  suffices  for  effecting  chemi- 
cal union,  as  is  proved  by  the  facility  with  which  water  dissolves  many 
salts  and  other  solid  bodies.  But  it  is  easy  to  perceive  that  the  cohe- 
sive power  is  still  in  operation:  for  a solid  is  commonly  dissolved  in  a 
greater  quantity  when  its  cohesion  is  diminished  by  caloric.  The  re- 
duction of  both  substances  to  the  liquid  state  is  the  best  method  for  en- 
suring chemical  action.  The  slight  degree  of  cohesion  possessed  by 
liquids  does  not  appear  to  cause  any  impediment  to  combination;  for 
tliey  commonly  act  as  energetically  on  each  other  at  low  temperatures, 
or  at  a temperature  just  sufficient  to  cause  perfect  liquefaction,  as  when 
their  cohesive  power  is  still  further  diminLshed  by  caloric.  It  seems 
fair  to  infer,  therefore,  that  very  little,  if  any,  affinity  exists  between 
two  bodies,  which  do  riot  combine  when  they  are  intimately  mixed  in  a 
liquid  state. 

The  phenomena  of  crystallization  are  owing  to  the  ascendancy  of  co- 
hesion over  affinity.  When  a large  quantity  of  salt  has  been  dissolved 
in  water  by  the  aid  of  heat,  part  of  the  saline  matter  generally  separates 
as  the  solution  cools,  because  the  cohesive  power  of  the  salt  then  be- 
comes comparatively  too  powerful  for  chemical  attraction.  Its  parti- 
cles begin  to  cohere  together,  and  are  deposited  in  crystals,  the  process 
of  crystallization  continuing  till  it  is  arrested  by  the  affinity  of  the  li- 
quid. A similar  change  happens,  when  a solution  made  in  the  cold  is 
gradually  evaporated.  The  cohesion  of  the  saline  particles  is  no  longer 
counteracted  by  the  affinity  of  the  liquid,  and  the  salt,  therefore,  as- 
sumes the  solid  form. 

Cohesion  plays  a still  more  important  part.  It  sometimes  determines 
the  result  of  chemical  action,  probably  even  in  opposition  to  affinity. 
Thus,  on  mixing  together  a solution  of  two  acids  and  one  alkali,  of 
which  two  salts  may  be  formed,  one  soluble  and  the  other  insoluble,  the 
alkali  will  unite  with  tliat  acid  with  wliich  it  forms  the  insoluble  com- 
pound, to  the  total  exclusion  of  the  other.  This  is  one  of  the  modify- 
ing circumstances  employed  by  Berthollet  to  account  for  tlie  phenomena 
of  single  elective  attraction,  and  it  certainly  is  applicable  to  many  of  the 
instances  to  be  found  in  the  tables  of  affinity.  When,  for  example,  mu- 
riatic acid,  sulphuric  acid,  and  baryta,  are  mixed  together,  sulphate  of 
baryta  is  formed  in  consequence  of  its  insolubility.  Lime,  which  yields 
an  insoluble  salt  with  carbonic  acid,  separates  that  acid  from  ammonia, 
potassa,  and  soda,  with  all  of  which  it  makes  soluble  compounds. 

A similar  explanation  ma)^  be  given  of  many  cases  of  double  elective 
attraction.  On  mixing  together  in  solution  four  substances.  A,  B,  C,  D, 
of  which  it  is  possible  to  form  four  compounds,  AB  and  CD,  or  AC  and. 
BD,  that  compound  will  certainly  be  produced,  wliich  happens  to  be 
insoluble.  Thus  sulphuric  acid,  soda,  muriatic  acid,  and  baryta,  may 
give  rise  either  to  sulpliate  of  soda  and  muriate  of  baryta,  or  to  sulphate 
of  baryta  and  muriate  of  soda;  but  tlie  first  two  salts  cannot  exist  togo- 
tlier  in  tlie  same  liquid,  because  the  insoluble  sulphate  of  bai-yta  is  in- 


116 


AFFINITY. 


stantly  generated,  and  its  formation  necessarily  causes  the  muriatic  acid 
to  combine  witli  the  soda.  In  like  manner  muriate  of  lime  is  decompo- 
sed by  carbonate  of  ammonia,  in  consequence  of  the  insolubility  of  car- 
bonate of  lime. 

To  comprehend  the  manner  in  which  cohesion  acts  in  these  irslanccs, 
it  is  necessary  to  consider  what  takes  place  when  in  the  same  liquid  two 
or  more  compounds  are  brought  togetlier,  wliich  do  not  give  rise  to  an 
insoluble  substance.  Thus  on  mixing  solutions  of  sidphate  'of  potassa 
and  muriate  of  soda,  no  precipitate  ensues;  because  the  salts  capable 
of  being  formed  by  double  decomposition,  sulphate  of  soda  and  muriate 
of  potassa,  are  likewise  solul)le.  In  this  case  it  is  possible  either  that 
each  acid  may  be  confined  to  one  base,  so  as  to  constitute  two  neu- 
tral salts;  or  that  each  acid  may  be  divided  between  both  bases,  yield- 
ing four  neutral  salts.  It  is  difiicidt  to  decide  this  point  in  an  un- 
equivocal manner;  but  judging  from  many  chemical  phenomena,  there 
can,  I apprehend,  be  no  doubt  that  the  arrangement  last  mentioned  is 
the  most  frequent,  and  is  probably  universal  whenever  the  relative  forces 
of  affinity  are  not  very  unequal.  When  two  acids  and  two  bases  meet 
together  in  neutralizing  proportion,  it  may  therefore  be  inferred,  tliat 
each  acid  unites  with  both  the  bases  in  a manner  regulated  by  their  re- 
spective forces  of  affinity,  and  that  four  salts  are  contained  in  solution. 
In  like  manner  the  presence  of  three  acids  and  three  bases  will  give 
rise  to  nine  salts;  and  when  four  of  each  are  present,  sixteen  salts 
will  be  produced.  This  view  affords  the  most  plausible  theory  of  the 
constitution  of  mineral  waters,  and  of  the  products  which  they  yield  by 
evaporation. 

The  influence  of  insolubility  in  determining  the  result  of  chemical 
action  may  be  readily  explained  on  tliis  principle.  If  muriatic  acid, 
sulphuric  acid,  and  baryta  are  mixed  together  in  solution,  the  base  may 
be  conceived  to  be  at  first  divided  between  the  two  acids,  and  muriate 
and  sulphate  of  baryta  to  be  generated.  The  latter  being  insoluble  is 
instantly  removed  beyond  the  influence  of  the  muriatic  acid,  so  tliat  for 
an  instant  muriate  of  baryta  and  free  sulphuric  acid  remain  in  the  liquid^ 
but  as  the  base  left  in  solution  is  again  divided  between  the  two  acids,  a 
fresh  quantity  of  the  insoluble  sulphate  is  generated;  and  this  process  of 
partition  continues,  until  either  the  baryta  or  the  sulphuric  acid  is  with- 
drawn from  tlm  solution.  Similar  changes  ensue  when  muriate  of  baryta 
and  sulphate  of  soda  are  mixed. 

The  separation  of  salts  by  crystallization  from  mineral  waters  or 
other  saline  mixtures  is  explicable  by  a similar  mode  of  reasoning. 
Thus  on  mixing  muriate  of  potassa  and  sulphate  of  soda,  four  salts  ac- 
cording to  this  view  are  generated,  namely^  the  sulphates  of  soda  and 
potassa,  and  the  muriates  of  those  bases;  and  if  the  solution  be  allowed 
to  evaporate  gradually,  a point  at  length  arrives  when  the  least  soluble 
of  these  salts,  the  sulpliate  of  potassa,  will  be  disposed  to  crystallize. 
As  soon  as  some  of  its  crystals  are  deposited,  and  thus  withdrawn  from 
the  inflq,ence  of  the  other  salts,  the  constituents  of  these  undergo  anew 
uiTangement,  whereby  an  additional  quantity  of  sulphate  of  potassa  is 
generated;  and  tliis  process  continues  until  the  greater  part  of  the  sul- 
phuric acid  and  potassa  has  combined,  and  the  compound  is  removed 
by  crystallization.  If  the  dilTercnce  in  solubility  is  considerable,  the 
separation  of  salts  may  be  often  rendered  very  complete  by  this  me- 
thod. 

The  efilorescence  of  a salt  is  sometimes  attended  with  a similar  re- 
sult. If  carbonate  of  soda  and  muriate  of  lime  are  mingled  together  in 
solution,  double  decomposition  takes  place,  and  the  insoluble  carbo- 


AFFINITY. 


117 


nate  of  lime  subsides.  But  if  carbonate  of  lime  and  sea-salt  are  mixed 
in  the  solid  state,  and  a certain  degree  of  moisture  is  present,  a mutual 
interchange  of  the  constituents  ensues.  Carbonate  of  soda  and  mu- 
riate of  lime  are  slowly  generated;  and  since  the  former,  as  soon  as  it 
is  formed,  separates  itself  from  the  mixture  by  efflorescence,  its  pro- 
duction continues  progressively.  The  efflorescence  of  carbonate  of 
soda,  which  is  sometimes  seen  on  old  walls,  or  which  in  some  countries 
is  found  on  the  soil,  appears  to  have  originated  in  this  manner. 

Elasticity. 

From  the  obstacle  which  cohesion  puts  in  the  way  of  affinity,  the 
gaseous  state,  in  which  the  cohesive  power  is  wholly  wanting,  might 
be  expected  to  be  peculiarly  favourable  to  chemical  action.  The 
reverse,  however,  is  the  fact.  Bodies  evince  little  disposition  to  unite 
when  presented  to  each  other  in ^ the  elastic  form.  Combination  does 
indeed  sometimes  take  place,  in  consequence  of  a very  energetic  at- 
traction; but  examples  of  an  opposite  kind  are  much  more  common. 
Oxygen  and  hydrogen  gases,  and  chlorine  and  hydrogen,  though  their 
mutual  affinity  is  very  powerful,  may  be  preserved  together  for  any 
length  of  time  without  combining.  This  want  of  action  seems  to  arise 
from  the  distance  between  the  particles  preventing  that  close  approxi- 
mation, which  is  so  necessary  to  the  successful  exercise  of  affinity. 
Hence  many  gases  cannot  be  made  to  unite  directly,  which  neverthe- 
less combine  readily  wffiile  in  their  nascent  state;  that  is,  while  in  the 
act  of  assuming  the  gaseous  form  by  the  decomposition  of  some  of  their 
solid  or  fluid  combinations. 

Elasticity  operates  likewise  as  a decomposing  agent.  If  two  gases, 
tlie  reciprocal  attraction  of  which  is  feeble,  suffer  considerable  conden- 
sation when  they  unite,,  the  compound  will  be  decomposed  by  very 
slight  causes.  Chloride  of  nitrogen,  which  is  an  oil-like  liquid,  com- 
posed of  the  two  gases  chlorine  and  nitrogen,  affords  an  apt  illustra- 
tion of  this  principle,  being  distinguished  for  its  remarkable  facility  of 
decomposition.  Slight  elevation  of  temperature,  by  increasing  the  na- 
tural elasticity  of  the  tw^o  gases,  or  contact  of  substances  which  have 
an  affinity  for  either  of  them,  produces  immediate  explosion. 

Many  familiar  phenomena  of  decomposition  are  owing  to  elasticity. 
All  compounds  that  contain  a volatile  and  a fixed  principle,  are  liable 
to  be  decomposed  by  a high  temperature.  The  expansion  occasioned 
by  caloric  removes  the  elements  of  the  compound  to  a greater  distance 
from  each  other,  and  thus,  by  diminishing  the  force  of  chemical  attrac- 
tion, favours  the  tendency  of  the  volatile  principle  to  assume  the  form 
which  is  natural  to  it.  The  evaporation  of  water  from  a solution  of  salt 
is  an  instance  of  this  kind. 

Many  solid  substances,  which  contain  water  in  a state  of  intimate 
combination,  part  with  it  in  a strong  heat,  in  consequence  of  the  vola- 
tile nature  of  that  liquid.  The  separation  of  oxygen  from  some  metals, 
by  heat  alone,  is  explicable  on  the  same  principle. 

From  these  and  some  preceding  remarks,  it  appears  that  the  influ- 
ence of  caloric  over  affinity  is  variable;  for  at  one  time  it  promotes  che- 
mical union,  and  opposes  it  at  another.  Its  action,  however,  is  always 
consistent.  Whenever  the  cohesive  power  is  an  obstacle  to  combina- 
tion, caloric  favours  affinity;  as  by  diminishing  the  cohesion  of  a solid, 
or  by  converting  a solid  into  a liquid.  As  the  cause  of  the  gaseous 
state,  on  the  contrary,  it  keeps  at  a distance  particles  which  would 
otherwise  unite;  or  by  producing  expansion,  it  tends  to  separate  sub- 
stances from  one  another,  which  are  already  combined.  There  is  one 


118 


AFFINITY. 


ejTect  of  caloric  which  seems  somewhat  anomalous;  namcl}",  the  com- 
bination which  ensues  in  gaseous  explosive  mixtures  on  the  approach 
of  flame.  The  explanation  given  by  Bertliollet  is  probably  correct, — 
tliat  the  sudden  dilatation  of  the  gases  in  the  immediate  vicinity  of  the 
flame,  acts  as  a violent  compressing  power  to  the  contiguous  portions, 
and  thus  brings  them  within  the  sphere  of  their  attraction. 

Some  of  the  decompositions,  wiiich  were  attributed  by  Bergmann  to 
the  sole  influence  of  elective  affinity,  may  be  ascribed  to  elasticity.  If 
tliree  substances  are  mixed  together,  two  of  whicli  can  form  a com- 
pound which  is  less  volatile  than  the  third  body,  the  last  will,  in  gene- 
ral, be  completely  driven  off  by  tlie  application  of  heat.  The  decom- 
position of  muriate  or  any  of  the  salts  of  ammonia,  by  the  pure  alkalies  or 
alkaline  earths,  may  be  adduced  as  an  example;  and  for  the  same  reason, 
all  the  carbonates  are  decomposed  by  muriatic  acid,  and  all  the  muriates 
by  sulphuric  acid.  This  explanation  applies  equally  well  to  some  cases  of 
double  decomposition.  It  explains,  for  instance,  why  the‘dry  carbonate 
of  lime  will  decompose  muriate  of  ammonia  by  the  aid  of  heat;  for  car- 
bonate of  ammonia  is  more  volatile  than  the  muriate  either  of  ammonia 
or  lime. 

^ The  influence  of  elasticity,  in  determining  the  result  of  chemical  ac- 
tion in  these  instances,  seems  owing  to  the  same  cause  which  enables 
insolubility  to  be  productive  of  similar  eflects.  Thus  on  mixing  muri- 
ate of  ammonia  and  lime,  the  acid  is  divided  between  the  two  bases; 
some  ammonia  becomes  free,  which,  in  consequence  of  its  elasticity,  is 
entirely  expelled  by  a gentle  heat.  The  acid  of  the  remaining  muriate 
of  ammonia  is  again  divided  between  the  two  bases;  and  if  a sufficient 
quantity  of  lime  is  present,  the  ammoniacal  salt  will  be  completely  de- 
composed. In  like  manner  the  decomposition  of  potassa  maybe  effect- 
ed by  iron,  though  the  affinity  of  this  metal  for  oxygen  seems  much  in- 
ferior to  that  of  potassium  for  oxygen.  If  potn.ssa  in  the  fused  state  be 
brought  in  contact  with  metallic  iron  at  a white  heat,  the  oxygen  is  di- 
vided between  the  two  metals,  and  a portion  of  potassium  set  at  liber- 
ty. But  as  potassium  is  volatile  at  a white  heat,  it  is  expelled  at  the  in- 
stant of  reduction;  and  thus,  by  its  influence  being  withdrawn,  an  op- 
portunity is  given  for  the  decomposition  of  an  additional  quantity  of 
potassa. 

Quantity  of  Matter, 

The  influence  of  quantity  of  matter  over  affinity  is  universally  ad- 
mitted. If  one  body  A unites  with  another  body  B in  several  propor- 
tions, that  compound  will  be  most  difficult  of  decomposition  which  con- 
tains the  smallest  quantity  ofB.  Of  the  three  oxides  of  lead,  for  in- 
stance, the  peroxide  parts  most  easily  with  its  ox3^gen  by  the  action  of 
caloric;  a higher  temperature  is  required  to  decompose  the  deutoxide; 
and  the  protoxide  will  bear  the  strongest  heat  of  our  furnaces,  without 
losing  a particle  of  its  oxygen. 

The  influence  of  quantity  over  chemical  attraction  may  be  further  il- 
lustrated by  the  phenomena  of  solution.  ^Vhen  equal  weights  of  a sol- 
uble salt  are  added  in  succession  to  a given  quantitv  of  water,  which  is 
capable  of  dissolving  almost  the  whole  of  the  salt  employed,  the  first 
portion  of  the  salt  will  disjippear  more  readily  tlian  the  second,  the  se- 
cond than  the  third,  the  third  tlian  the  fourtli,  and  so  on.  The  affinity 
of  the  water  for  the  saline  substance  diminislies  willi  each  addition,  till 
at  last  it  is  weakened  to  such  a degree  as  to  be  unable  to  overcome  the 
cohesion  of  the  salt.  The  process  then  ceases,  and  a saturated  solution 
is  obtained. 


AFFINITY. 


119 


Quantity  of  matter  is  employed  advantag’eously  in  many  chemical  opei’a- 
tions,  ,If,  for  instance,  a chemist  is  desirous  of  sepai’ating*  an  acid  from 
a metalhc  oxide  by  means  of  the  superior  alhnity  of  potassa  for  the  for- 
mer, he  frequently  uses  rather  more  of  the  alkali  than  is  sufficient  fop 
neutralizing’  the  acid,  lie  takes  the  precaution  of  employing  an  excess 
of  alkali,  in  oi’der  the  more  effectually  to  bring*  every  particle  of  the 
substance  to  be  decomposed  in  contact  with  the  decomposing  agent. 

15ut  Berthollet  has  attributed  a much  greater  influence  to  quantity  of 
matter.  It  was  the  basis  of  his  doctrine,  developed  in  the  Statique  ChU 
miquey  that  bocUes  cannot  be  wholly  separated  from  each  other  by  the 
affinity  of  a third  substance  for  one  element  of  a compound;  and  to  ex- 
plain why  a superior  chemical  attraction  does  not  produce  the  effect 
which  might  be  expected  from  it,  he  contended  that  quantity  of  matter 
compensates  for  a weaker  affinity.  From  the  co-operation  of  several 
disturbing  causes,  Berthollet  perceived  that  the  force  of  affinity  cannot 
be  estimated  with  certainty  by  observing  the  order  of  decompositioni; 
and  he,  therefore,  had  recourse  to  another  method.  He  set  out  by  suppos- 
ing that  the  affinity  of  different  acids  for  the  same  alkali,  is  in  the  in- 
verse ratio  of  the  ponderable  quantity  of  each  which  is  necessary  for 
iieutrahzing*  equal  quantities  of  the  alkali.  Thus,  if  two  parts  of  one 
acid  A,  and  one  part  of  another  acid  B,  are  required  to  neutralize  equal 
quantities  of  the  alkah  C,  it  was  inferred  that  the  affinity  of  B for  C was 
twice  as  great  as  that  of  A.  He  conceived,  fui-ther,  that  as  two  parts  of 
A produce  the  same  neutralizing  effect  as  one  part  of  B,  the  attraction 
exerted  by  any  alkali  towards  two  parts  of  A ought  to  be  precisely  the 
same  as  for  the  one  part  of  B;  and  he  hence  concluded  that  there  is  no 
reason  why  the  alkali  should  prefer  the  small  quantity  of  one  to  the  large 
quantity  of  the  other.  On  this  he  founded  the  principle  tliat  quantity 
of  matter  compensates  for  force  of  attraction. 

Berthollet  has  here  obviously  confounded  two  things,  namely,  force 
of  attraction  and  neutralizing  power,  which  are  really  different  and 
ought  to  be  held  distinct.  The  relative  weights,  of  muriatic  and  sul- 
phuric acids  required  to  neutralize  an  equal  quantity  of  any  alkali,  or,  in 
other  words,  their  capacities  of  saturation,  are  as  37  to  40,  a ratio  wliich 
remains  constant  with  respect  to  all  other  alkalies.  The  affinity  of  these 
acids,  according  to  BertholleFs  rule,  will  be  expressed  by  the  same  num- 
bers. But  in  taking  this  estimate,  we  have  to  make  three  assumptions, 
all  of  wiiich  are  disputable.  There  is  no  proof,  in  the  first  place,  that 
muriatic  acid  has  a greater  affinity  for  an  alkali,  such  as  potassa,  than 
sulphuric  acid.  Such  an  inference  would  be  directly  opposed  to  the 
general  opinion-founded  on  the  order  of  decomposition;  and  though  that 
order,  as  we  have  shown,  is  by  no  means  a satisfactory  test  of  the  strength 
of  affinity,  it  would  be  improper  to  adopt  an  opposite  conclusion  witliout 
having  good  reasons  for  so  doing.  Secondly,  were  it  established  that 
muriatic  acid  has  the  greater  affinity,  it  does  not  follow  that  the  attrac- 
tion of  those  acids  for  potassa  is  in  the  ratio  of  37  to  40.  And,  thirdly, 
supposing  this  point  settled,  it  is  very  improbable  that  the  ratio  of  their 
affinity  for  one  alkali  will  apply  to  all  others;  analogy  would  lead  us  to 
anticipate  the  reverse.  Independently  of  these  objections,  M.  Dulong 
has  found  that  the  principle  of  Berthollet  is  not  in  accord  with  tire  r-e- 
sults  of  experiment. 

But  though  this  mode  of  determining  the  relative  forces  of  affinity  can- 
not be  admitted,  it  is  possible  that  quantity  of  matter  may  somehow  or 
other  compensate  for  a weaker  affinity;  and  Berthollet  attempted  to 
prove  it  by  experiment,  (liesearches  into  the  Laws  of  Affinity.)  On 
boiling  sulphate  of  baryta  with  an  equal  weiglit  of  pure  potassa,  tlie 
alkali  is  found  to  have  deprived  the  baryta  of  a small  portion  of  its  acid; 


120 


AFFINITY. 


and  on  treating  oxalate  of  lime  with  nitric  acid,  some  nitrate  of  lime  is 
generated.  As  these  partial  decompositions  are  contrary  to  the  supposed 
order  of  elective  affinity,  it  was  conceived  that  they  were  produced  by 
quantity  of  matter  acting  in  opposition  to  force  of  attraction.  Jkit  they 
by  no  means  justify  such  a conclusion.  In  tlie  decomposition  of  sul- 
phate of  baryta  by  potassa,  no  care  was  taken  to  exclude  the  atmospheric 
air  during  the  operation:  the  alkali  must  consequently  have  absorbed 
carbonic  acid;  and  it  is  an  established  fact  tliat  carbonate  of  potassa  par- 
tially decomposes  sulphate  of  baryta.  A similar  omission  appears  to 
have  been  made  in  the  other  experiments,  where  decomposition  was  at- 
tempted by  pure  potassa  or  soda.  In  many  instances  the  result  may 
fairly  be  attributed  to  other  causes.  Acids  and  alkalies  have  often  a 
tendency  to  unite  in  more  than  one  proportion,  and  will  readily  form 
salts  with  excess  of  acid  or  of  base  wlien  circumstances  are  favourable 
to  their  production.  Thus  on  adding  nitric  acid  to  the  insoluble  phos- 
phate of  lime,  the  earth  is  divided  between  the  two  acids,  and  a nitrate 
and  biphosphate  of  lime  are  generated.  It  is  difficult,  if  not  impossible, 
to  effect  the  entire  decomposition  of  nitrate  of  potassa  by  a quantity  of 
sulphuric  acid  just  sufficient  for  neutralizing  the  alkali;  for  the  sulphuric 
acid,  instead  of  taking  the  whole  of  the  potassa,  is  apt  to  unite  with  part 
of  it,  and  form  the  hi  sulphate.  This  tendency  to  the  formation  of  an 
acid  salt  accounts  for  the  fact  quite  satisfactorily;  nor  is  there  reason  to 
infer  the  co-operation  of  any  other  cause.  Another  circumstance  that 
influences  the  result  of  such  experiments,  and  wliich  Berthollet  left 
entirely  out  of  view,  is  the  affinity  of  salts  for  one  another.  On  the 
whole,  therefore,  we  may  infer  that  Berthollet  has  given  no  satisfactory 
case  in  which  quantity  of  matter  is  proved  to  compensate  for  a weaker 
affinity.  Saline  substances,  indeed,  seem  ill  adapted  to  such  researches. 
For  it  is  impossible  in  many,  if  not  inmost  cases,  to  decide  upon  the  re- 
lative strength  of  the  attraction  of  two  acids  for  an  alkali,  or  of  two 
alkalies  for  an  acid,  a point,  nevertheless,  which  is  an  important  element 
in  the  inquiry;  and  even  did  we  possess  such  knowledge,  the  influence 
of  modifying  circumstances  is  such,  that  it  is  difficult  to  appreciate  the 
share  they  may  have  in  producing  a given  effect. 

Gravity, 

The  influence  of  gravity  is  perceptible  when  it  is  wished  to  make  two 
substances  unite,  the  densities  of  which  are  different.  In  a case  of  sim- 
ple solution,  a larger  quantity  of  saline  matter  is  found  at  the  bottom 
than  at  the  top  of  the  liquid,  unless  the  solution  shall  have  been  well 
mixed  subsequently  to  its  formation.  In  making  an  alloy  of  two  metals 
which  differ  from  one  another  in  density,  a larger  quantity  of  the  heavier 
metal  will  be  found  at  the  lower  than  in  the  upper  part  of  the  compound, 
unless  great  care  be  taken  to  counteract  the  tendency  of  gravity  by 
agitation.  This  force  obviously  acts,  like  the  cohesive  power,  in  pre- 
venting a sufficient  degree  of  approximation. 

Imponderables, 

The  influence  which  caloric  exerts  over  chemical  phenomena,  and 
the  modes  in  which  it  operates,  have  been  already  discussed.  The 
chemical  agency  of  galvanism  has  also  been  described.  The  effects  of 
light  will  be  most  conveniently  stated  in  other  parts  of  the  work.  Elec- 
tricity is  frequently  employed  to  produce  the  combination- of  gases  with 
one  another,  and  in  some  instances  to  separate  them.  It  appears  to  act 
by  the  heat  which  it  occasions,  and,  therefore,  on  the  same  principle  as 
flame,  ' . 


ON  THE  LAWS  OF  COMBINATION. 


121 


On  the  Measure  of  Affinity. 

As  the  foregoing  observations  prove  that  the  order  of  decomposition 
is  not  always  a satisfactory  measure  of  affinity,  it  becomes  a question 
whether  there  are  any  means  of  determining*  tlie  comparative  forces  of 
cliemical  attraction.  When  no  disturbing  causes  operate,  the  phenomena 
of  decomposition  afford  a sure  criterion;  but  when  the  conclusions  ob- 
tained in  this  v/ay  are  doubtful,  assistance  may  be  frequently  derived 
from  other  sources.  The  surest  indications  are  procured  by  observing 
the  tendency  of  different  substances  to  unite  with  the  same  principle, 
under  the  same  circumstances,  and  subsequently  by  marking  the  com- 
parative facility  of  decomposition,  when  the  compounds  so  formed  are 
exposed  to  the  same  decomposing  agent.  Thus  on  exposing  gold,  lead, 
and  iron  to  air  and  moisture,  the  iron  rusts  with  great  rapidity,  the  lead 
is  ordy  tarnished,  and  the  gold  retains  its  lustre.  It  is  hence  inferred 
that  iron  has  the  greatest  affinity  for  oxygen,  lead  next,  and  gold  least. 
This  conclusion  is  supported  by  concurring  observations  of  a like  na- 
ture, and  confirmed  by  the  circumstances  under  which  the  oxides  of  those 
metals  part  with  their  oxygen.  Oxide  of  gold  is  reduced  by  heat  only; 
and  oxide  of  lead  Is  decomposed  by  charcoal  at  a lower  temperature 
than  oxide  of  iron. 

It  is  inferred  from  the  action  of  caloric  on  the  carbonate  of  potassa, 
baryta,  lime,  and  oxide  of  lead,  that  potassa  has  a stronger  attraction  for 
carbonic  acid  than  baryta,  baryta  than  lime,  and  lime  than  oxide  of  lead. 
The  affinity  of  different  substances  for  water  may  be  determined  in  a 
similar  manner. 

Of  all  chemical  substances,  our  knowledge  of  the  relative  degrees  of 
attmction  of  acids  and  alkalies  for  each  other  is  the  most  uncertain. 
Their  action  on  one  another  is  affected  by  so  many  circumstances,  that  it 
is  in  most  cases  impossible,  with  certainty,  to  refer  any  effect  to  its  real 
cause.  The  only  methods  that  have  been  hitherto  devised  for  remedy- 
ing this  defect  are  those  of  Berthollet  and  Kirwan.  Both  of  them  are 
founded  on  the  capacities  of  saturation,  and  the  objections  which  have 
been  urged  to  the  rule  suggested  by  the  former  philosopher,  apply 
equally  to  that  proposed  by  the  latter.  But  this  uncertainty  is  of  no 
great  consequence  in  practice.  We  know  perfectly  the  order  of 
decomposition,  whatever  may  be  the  actual  forces  by  which  it  is  ef- 
fected. 


SECTION  1 1. 

ON  THE  PROPORTIONS  IN  WHICH  BODIES  UNITE,  AND  ON 
THE  LAWS  OF  COMBINATION. 

The  study  of  the  proportions  in  which  bodies  unite  naturally  re- 
solves itself  into  two  parts.  The  first  includes  compounds  whose  ele- 
ments appear  to  unite  in  a great  many  proportions;  the  second  com- 
prehends those  the  elements  of  which  combine  in  a few  proportions 
only. 

I,  The  compounds  contained  in  the  first  division  are  of  two  kinds. 
In  one,^  combination  takes  place  unlimitedly  in  all  proportions;  in  tlic 
other,  it  occurs  in  every  proportion  within  a certain  limit,  llie  union  of 
water  v/ith  alcohol  and  the  liquid  acids,  such  as  the  sulphuric,  mui-iatic. 


ox  THE  LAV>  S or  COMEIXATIOX. 


ar,<:.  latric  acids,  afTords  instances  of  tlic  first  mode  of  combirratjon^  the 
fy^iutiai'iS  of  salts  in  water  are  examples  of  the  second.  One  drop  of 
si^lpliunc  acid  may  be  diffused  throug-h  a gndlon  of  water,  or  a drop  of 
water  tlii’ougli  a gallon  of  the  acid;  or  ibcy  may  be  mixed  togctJicr  in 
an  V LjtennecUate  proportions,  and  in  each  case  tbc  }'  appear  to  unite  per- 
fectly witli  one  another.  A hundred  grains  of  water,  on  tlic  contrar>', 
w'lll  dissolve  any  quantity  of  sea-salt  which  does  not  exceed  forty  grains. 
Hr,  dissolving  power  then  ceases,  because  the  cohesion  of  the  solid  be- 
comes comparatively  too  povterful  for  the  force  of  affinity.  The  limit 
to  combination  is  in  such  instances  owdng  to  the  cohesive  power;  and 
bi;t  for  tlie  obstacle  wliich  it  occasions,  the  salt  would  most  probably 
linite  with  water  in  every  proportion. 

Au  the  substances  that  unite  in  many  proportions,  g;lve  rise  to  coip- 
pounds  which  have  this  common  character,  tliat  their  elements  are 
united  by  a feeble  affinity,  and  presciwe,  when  combined,  more  or  less 
(xf  the  properties  which  they  possess  in  a separate  state.  In  a scientific 
] ointof  view,  these  combinations  are  of  minor  importance;  but  they 
ai’e  exceedingly  useful  as  instruments  of  research.  They  enable  the 
f'diemist  to  present  bodies  to  each  other,  under  circumstances  the  most 
favourable  possible  for  acting  with  effect:  the  liquid  form  is  thus  com- 
municated to  them;  while  the  affinity  of  the  solvent  or  menstruum, 
which  holds  them  in  solution,  is  not  sufficiently  powerful  to  interfere 

Witii  their  mutual  attraction.  • i i u i 

If.  The  most  interesting  series  of  compounds  is  produced  by  suu- 
sfcinces  which  unite  in  a fc^v  proportions  only;  and  which,  in  combin- 
ing, lose  more  or  less  completely  the  properties  that  distinguished  tnem 
when  separate.  Of  these  bodies,  some  form  but  one  cornbinati^ 
Thus  there  is  only  ope  compound  of  zinc  and  oxygen,  or  of  chlorine 
and  hydrogen.  Others  combine  in  two  proportions.  Tor  example,  two 
compounds  are  formed  by  copper  and  oxygen,  or  by  hydrogen  and  oxy- 
cen.  Other  bodies  again  unite  in  three,  four,  five,  or  even  six  pro - 
iiortions,  which  is  the  greatest  number  of  compounds  that  any  two  sub- 
Rtarxes  are  known  to  produce,  excepting  those  wliich  belong  to  the 

first  division.  . . « ..  -u,  • 

The  combination  of  substances  that  unite  in  a few  proportions  oniy,  rs 
resniiated  by  three  remarkable  laws.  The^  first  of  these  laws  is,  that 
tUe  composition  of  bodies  is  fixed  and  invariable;  that  a compound  sub- 
stance, so  long  as  it  retains  its  characteristic  properties,  must  alwa},3 
consist  of  the  same  elements  united  together  in  the  same  propoi’tion- 
Sii-niroric  acid,  for  example,  is  always  composed  of  sulphur  and  oxy^n 
in  the  ratio  of  16  parts*  of  the  former  to  24  of  the  latter:  no  otto 
ch  'nents  can  form  it,  nor  can  it  be  produced  by  its  oi\ti  elements  in  anj 
othe--'  proportion.  Water,  in  like  manner,  is  formed  of  1 part  of  hyaro- 
iTCn  and  8 of  oxygen;  and  were  these  two  elements  to  umte  m any  otto 
pronr.Aion,  some  new  compound,  different  from  water,  would  be  tlie 
r/i'  »duct.  The  same  oljscrvation  applies  to  all  other  substances,  how- 
ever complicated,  and  at  wliatever  period  they  were  produced.  Thus, 
sui'  iate  of  baryta,  whether  formed  ages  ago  by  the  hand  ot  nature,  or 
cuite  rcccntlv  by  the  operations  of  tlie  chemist,  is  alwa}  s composed  o 
4'''  pirls  of  sulphuric  acid  and  78  of  baryta,  lliis  law,  in  fact,  is  uni- 
versal and  permanent.  Its  importance  is  equally  manifest  It  is  the 
(^sscr.iial  basis  of  clicmistry,  without  which  the  science  itself  could  have 

"O  existence.  . « u*  i 

Tv/n  views  have  been  proposed  by  way  of  accounting  for  this  law. 


^ By  the  c.qu'cs.sion  ‘parts’  I always  mean  parts  by  weight.^ 


ON  TIIP  LAWS  OF  COMBINATION, 


'Uo 

The  explanation  now  universally  g-iven  is  confined  to  a mere  statement, 
that  substances  are  disposed  to  combine  in  those  proportions  to  which 
they  are  so  strictly  limited,  in  preference  to  any  others;  it  is  regarded 
an  ultimate  fact,  because  the  phenomena  arc  explicable  on  no  other 
known  principle.  A diflTerent  doctrine  was  advanced  by  Berthollet  in 
his  Staiique  Chimique,  published  in  1803.  Having  observed  the  infiuence 
of  cohesion  and  elasticity  in  modifying  the  action  of  affinity  as  already 
described,  he  thought  he  could  trace  the  operations  of  the  same  causes 
in  producing  the  effect  at  present  under  consideration.  Finding  that 
tlie  solubility  of  a salt  and  of  a gas  in  water  is  limited,  in  the  former  by 
cohesion,  and  in  the  latter  by  elasticity,  he  conceived  that  the  same 
forces  would  acepunt  for  the  unchangeable  composition  of  certain  con> 
pounds.  He  maintained,  therefore,  that  within  certain  limits  bodies  have 
a tendency  to  unite  in  every  proportion;  and  that  combination  Is  never 
definite  and  invariable,  except  when  rendered  so  by  the  operation  cf 
modifying  causes,  such  as  cohesion,  insolubility,  elasticity,  quantity  of 
matter,  and  the  like.  Thus,  according  to  Berthollet,  sulphate  of  baryta 
is  composed  of  49  parts  of  sulphuric  acid  and  78  of  baryta,  not  because 
tliose  substances  are  disposed  to  unite  in  that  ratio  rather  tlian  in  another, 
but  because  the  compound  so  constituted  happens  to  have  great  cohe- 
sive power. 

These  opinions,  which,  if  true,  would  shake  the  whole  seience  of  che- 
mistiy  to  its  foundation,  were  founded  on  observation  and  experiment, 
supported  by  all  the  ingenuity  of  that  highly  gifted  philosopher.  They 
were  ably  and  successfully  combated  by  Proust,  in  several  papers  pub- 
lished m the  Journal  de  Physiquey  wherein  he  proved  that  the  metais 
are  disposed  to  combine  with  oxygen  and  with  sulphur,  only  in  oiiQ  or 
two  pr'  portions,  which  are  definite  and  invariable.  The  controversy 
which  ensued  between  these  eminent  chemists  on  that  occasion.  Is  re- 
markable for  the  moderation  with  which  it  is  conducted  on  both  skies, 
and  has  been  properly  quoted  by  Berzelius  as  a model  for  all  future  con- 
troversialists, How  much  soever  opinion  may  have  been  divided  upon 
tills  important  question  at  that  period,  the  dispute  is  now  at  an  end. 
The  infinite  variety  of  new  facts,  similar  to  those  observed  by  Proust, 
which  have  since  been  established,  has  proved  beyond  a doubt  that  tiie 
leading  principle  of  Berthollet  is  quite  erroneous.  The  tendency  of  bo- 
dies to  unite  in  definite  proportions  only,  is  indeed  so  great  as  to  excite 
a suspicion  that  all  substances  combine  in  this  way;  and  that  the  excep* 
fions  tliought  to  be  afforded  by  the  phenomena  of  solution,  are  ratlier 
apparent  tlian  real;  for  it  is  conceivable  that  the  apparent  variety  of  pro- 
portion, noticed  in  such  cases,  may  arise  from  the  mixture  of  a few  de- 
finite compounds  with  each  other. 

The  second  law  of  combination  is  still  more  remarkable  than  the  first. 
It  has  given  plausibility  to  an  ingenious  hypothesis  concerning  the  ulti- 
mate particles  of  matter,  called  the  atomic  theory.  The  law  itself,  how- 
ever, contains  nothing  hypotlietical,  being  the  mere  expression  of  a 
fact,  first  noticed  by  Mr.  Dalton,  and  subsequently  confirmed  by  many 
Other  chemists.  Its  nature  wUl  be  at  once  understood  by  perusing  the 
foEowing  table : — « 


Water  is  composed  of  . 

Ilvdrogen  1 . 

Oxyger 

i 8 

Deutoxide  of  hydrogen 

Do. 

1 . 

Do. 

16 

Carbonic  oxide  . . , 

Carbon 

6 . 

Do. 

8 

Carbonic  acid  , . . 

Do. 

6 . 

Do. 

16 

Nitrous  oxide  . . . 

Nitrogen  14  . 

Do. 

8 

Nitric  oxide  .... 

Do. 

14  . 

Do. 

16 

1-Iyponitrous  acid  . . . 

Do. 

14  . 

Do. 

24 

Nitrous  acid  .... 

Do. 

14  . 

Do. 

33 

Nitric  acid  .... 

Do. 

14  . 

Do. 

49 

124 


ON  THE  LAWS  OF  COMBINAIION. 


Xt  will  be  perceived  that  in  all  these  compounds,  the  numbers  express- 
ingthe  quantities  of  oxygen,  which  unite  with  a given  weight  of  the 
same  substance,  bear  a very  simple  ratio  to  one  another.  Deutoxide  of 
hydrogen  contains  just  twice  as  much  oxygen  as  water.  I'he  oxygen 
in  carbonic  acid  is  double  that  of  carbonic  oxide.  I'he  oxygen  in  the 
compounds  of  nitrogen  and  oxygen  is  in  the  ratio  of  1,  2,  3,  4,  and  5. 
So  obvious  indeed  is  this  law,  that  it  is  observed  at  once  on  comparing 
together  the  results  of  a few  accurate  analyses^  and  the  only  subject  of 
surprise  is,  that  it  was  not  discovered  before.  It  is  by  no  means  con- 
fined to  the  compounds  of  combustibles  with  oxygen.  I'hus,  the  ratio 
of  the  sulphur  in  the  two  sulphurets  of  mercury,  and  of  chlorine  in  the 
two  chlorides  of  mercury,  is  as  1 to  2.  It  extends  also  to  the  salts.  Bi- 
carbonate of  potassa,  for  example,  contains  twice  as  much  carbonic  acid 
as  the  carbonate;  and  the  oxalic  acid  of  the  three  oxalates  of  potassa  is 
in  the  ratio  of  1,  2,  and  4-.  We  must  regard  it,  therefore,  as  a law  which 
regulates  the  union  of  bodies;  and  its  enunciation  may  be  stated  in  the 
following  terms.  When  two  substances,  A and  B,  unite  chemically  in 
two  or  more  proportions,  the  numbers  representing  the  quantities  of  B 
combined  with  the  same  quantity  of  A are  in  the  ratio  of  1,  2,  3,  4,  £cc.; 
that  is,  tliey  are  multiples  by  some  whole  number  of  the  smallest  quan- 
tity of  B with  which  A can  unite.  Thus,  if  A + B is  the  first  compound, 
the  others  will  be  A + 2B,  or  A -I-3B,  or  A with  some  similar  multiple 
of  B.  This  law  is  often  called  the  law  of  multiples,  or  of  combination  in 
multiple  proporiions, 

Tliatthe  elements  of  compounds  are  often  arranged  according  to  the 
law  of  multiples,  as  thus  expressed,  is  a fact  which  does  not  admit  of 
the  least  question;  but  in  the  present  state  of  chemical  science,  we  are 
not  prepared  to  maintain  that  it  is  universal.  Instances  are  n^:^^  unfre- 
quently  met  w-itb,  where  a slight  deviation  from  the  law  occurs^  The 
three  c^xides  of  lead,  for  instance,  are  thus  constituted; — 

Lead*  Oxygen* 

Protoxide  « 104  * . 8 

Deutoxide  . 104  • . 12 

Peroxide  . 104  . . 16 

In  these  compounds  the  oxygen  is  as  1 ; 1^?  2;  and  the  oxides  of  manga- 
nese afford  a similar  example.  The  oxides  of  iron  are  composed  as  fol- 
lows : — 

Iron*  Oxygen* 

Protoxide  . 28  • . 8 

Peroxide  • 28  , .12 

in  which  the  ratio  of  the  oxygen  is  as  1 to  1^,  or  as  2 to  3.  ^ The  oxygen 
in  ai-senious  and  arsenic  acids,  according  to  Berzelius,  is  as  3 to  5. 
These  deviations  from  the  law  of  multiples  may  perhaps  be  rather  ap- 
parent tlian  real.  It  is  possible,  for  example,  tliat  deutoxide  of  lead 
may  be  a comjKiund  of  the  protoxide  and  peroxide  with  each  other, 
and,  tJicrcfore,  tliat  it  ought  not  to  be  enumerated  among  the  oxides  of 
tJiat  metal.  It  is  also  possible  that  the  anomaly  is  frequently  owing  to 
our  ignorance  of  compounds  which  may  hereafter  be  discovered.  Thus 
the  discovery  of  an  oxide  of  lead  consisting  of  104  paKs  of  metal  to  4 
paiis  of  oxygen,  would  render  this  series  of  compounds  conformable 
to  tlie. usual  law  of  comliination.  But  leaving  these  points  to  be  decid- 
ed by  future  observation,  and  taking  facts  as  they  are,  we  may  state 
that  bodies  combine  cither  strictly  according  to  the  law’  of  multiple  pro- 
portion as  first  slated,  or  according  to  the  slight  deviation  from  that  law 


ON  THE  LAWS  OF  COMBINATION- 


125 


?LS  illustrated  in  the  preceding  examples.  In  either  case  this  law  of 
combination  is  exceeding-Iy  simple.* 

The  tliird  lavv^  of  combination  is  intimately  connected  with  tlie  pre- 
t’eding,  and  is  not  less  remarkable.  Its  existence  and  natiire  will  at 
Once  appear,  on  a comparison  of  the  relative  quantities  of  different  bo- 
dies which  combine  togetlier.  Tims  8 parts  of  oxygen  unite  with  1 
part  of  hydrogen,  16  of  sulphur,  36  of  chlorine,  40  of  selenium,  and 
110  parts  of  silver.  Such  are  the  quantities  of  these  five  bodies  which 
are  disposed  to  unite  with  8 parts  of  oxygen;  and  it  is  found  that  when 
they  combine  with  one  another,  they  unite  either  in  the  proportions  ex- 
pressed by  those  numbers,  or  in  multiples  of  them  according  to  the 
law  already  explained.  Thus  sulphuretted  hydrogen  is  composed  of  1 
part  of  hydrogen  and  16  of  sulphur,  and  bi sulphuretted  hydrogen,  of  1 
part  of  hydrogen  to  32  of  sulphur;  36  of  chlorine  unite  with  1 of  hy- 
drogen, 16  of  sulphur,  and  110  of  silver;  and  40  parts  of  selenium, 
with  1 of  liydrogen  and  16  of  sulphur. 

It  is  manifest,  from  these  examples,  that  bodies  unite  according  to 
proportional  numbers;  and  hence  has  arisen  the  use  of  certain  terms, 
such  as  Proportion,  Combining  Proportion,  Proportional,  or  Equiva- 
lent, to  express  them.  Thus  the  combining  proportions  of  tlie  sub- 
stances just  alluded  to  are 

Hydrogen  -----  1 

Oxygen  - - - - - 8 

Sulphur  - - - - - 16 

Chlorine  - - - - 3-6 

Selenium  -----  40 

Silver  -----  110 


* The  law  of  multiples,  as  stated  by  Dr.  Turner,  certainly  does  not 
embrace  all  the  cases  of  progressive  proportion,  as  he  very  properly 
admits;  but  when  stated  in  its  most  general  terms,  it  includes  all  tlie 
instances  hitherto  observed,  V/hen  thus  expressed,  its  enunciation  may 
be  given  in  the  following  terms;  when  one  body  B combines  in 
two  or  more  proportions  with  another  body  A,  the  numbers  represent- 
ing the  quantities  of  B combined  v/ith  the  same  quantity  of  A are 
multiples  by  a whole  number  of  some  particular  number;  that  is,  con- 
tain some  number  an  even  number  of  times  without  a remainder.  The 
number  so  contained  may  be  the  same  as  the  number  representing  the 
lowest  proportion,  or  it  may  be  different.  In  the  case  of  the  five  oom- 
]X)unds  of  nitrogen  and  oxygen,  these  two  numbers  coincide;  for  here 
8 is  both  the  number  contained  an  even  number  of  times,  and  the  num- 
ber denoting  the  lowest  proportion.  Thus  8 is  contained  by  8 once,  by 
16  twice,  by  24  three  times,  and  so  on.  In  the  instance  of  the  oxides 
of  leacl,  4 is  the  particular  number  which  is  contained  an  even  number 
of  times.  Thus  8 contains  it  twice,  12,  three  times,  and  16,  four  times. 
In  the  case  of  tlie  compounds  of  arsenic  and  oxygen,  if  we  adopt  the 
results  of  Berzelius,  4 also  is  the  particular  number  of  which  the  others 
are  teven  multiples.  Thus  12  is  three  times  4,  and  20,  five  times  4. 
(See  composition  of  arsenious  and  arsenic  acids,  under  the  head  of 
ai^enic.) 

By  biking  tlie  above  view  of  progressh  e proportion,  we  avoid  the 
unsatisfactory  course  of  Dr.  Turner,  of  stating  the  law  of  multiples  in 
terms  not  sufficiently  general,  and  of  afterwards  being  compelled  to 
admit  that  deviations  from  the  law  occur.  AVhen  stateddn  the  general 
terms  adopted  in  this  note,  tlicrc  are  no  deviations  from  the  law;  and 
reasoning  upon  it  as  a general  fact,  the  atomic  mode  of  combination 
1 is  fully  suppoited.  B.  11* 


ON  THE  LAWS  OF  COMniNATION. 


The  niost  common  kind  of  com])mation  is  one  proportional  of  one 
body,  either  with  one  or  witli  two  proportionals  of  another.  Combina- 
tions of  one  to  three,  or  one  to  foui*,  are  very  uncommon,  unless  the  more 
simple  compounds  likewise  exist.  Ammonia,  however,  is  a singidar  in- 
stance of  the  reverse.  It  is  composed  of  14  pails  of  nitrog'en,  and  3 of 
hydrogen.  Now  14  being  the  precise  quantity  of  niti-ogcn  tiiat  unites 
with  8 of  oxygen,  is  considered  as  one  jiropoilional  of  nitrogen,  and 
this  quantity  is  combined  in  ammonia  with  three  proportionals  of  hydro- 
gen.  No  compound  of  nitrogen  and  hydrogen  in  any  other  proportion 
has  as  yet  been  discovered.  In  some  cases  it  appears  tliat  bodies  unite 
in  tlie  i*atio  of  two  equivalents  of  one  body  to  three  or  five  equivalents 
of  the  other.  There  is  good  reason  to  believe  that  hyposulphuric  acid 
is  constituted  in  this  manner;  and  llerzelius  is  of  opinion  tJiat  tliis  kind 
of  arrangement  is  by  no  means  unfrequent. 

But  this  law  does  not  apply  to  elementary  substances  only,  since  cotn- 
•{yound  bodies  have  tlieir  combining  proportions,  wliich  may  likewise  be 
expressed  in  numbers.  Thus,  since  water  is  composed  of  one  propor- 
tional or  8 parts  of  oxygen,  and  one  proportional  or  1 of  hydrogen,  its 
combining  proportion  or  equivalent  is  9.  The  proportional  of  sulpliuric 
acid  is  40,  because  it  is  a compound  of  one  proportional  or  16  of  mU 
phur,  and  three  proportionals  or  24  of  oxygen;  and  in  like  manner,  tlie 
combining  propoilion  of  muriatic  acid  is  37,  because  it  is  a compound 
of  one  propoilional  or  36  of  cldorlne,  and  one  proportional  or  1 of  hy- 
drogen. The  equivalent  number  of  potassium  is  40,  and  as  tiiat  quan- 
dty  combines  with  8 of  oxygen  to  form  potassa,  the  combining  propor- 
tion of  potassa  is  4,8.  Now  when  these  compounds  unite,  one  propor- 
tional of  the  one  combines  wdth  one,  two,  tlmee,  or  more  propoilionals 
of  the  other,  precisely  as  the  simple  substances  do.  Hydrate  of  po 
tassa,  for  example,  is  constituted  of  48  parts  of  potassa  and  9 of  w^ater, 
and  its  combining  proportion  is  consequently  48  9,  or  57.  Sulphate 

of  potassa  is  composed  of  40  sulphuric  acid -f- 48  potassa;  and  muriate 
of  tlie  same  alkali,  of  37  muriatic  acid -|- 48  pota-ssa.  The  combining 
proportion  of  the  former  salt  is  therefore  88,  and  of  the  latter  85. 

The  composition  of  the  salts  affords  a very  neat  illustration  of  Uiis 
subject;  and  to  exemplify  it  still  further,  I subjoin  a list  of  the  propor- 
donal  numbers  of  a few  acids  and  alkaline  bases. 


Hydi’ofluoric  acid 

19.86 

Lithia 

18 

Phosphoric  acid 

35.71 

ilagnesia 

20 

Muriatic  acid 

37 

Lime 

28 

Sulphuric  acid 

40 

Soda 

32 

Nitric  acid 

54 

Potassa 

43 

Arsenic  acid 

53 

Strontia 

52 

Seienic  acid 

64 

Baryta 

73 

X will  be  seen  at  a glance,  tiiat  the  neutralizing  power  of  flic  dilfcr- 
eut  alkalies  is  very  difierent;  for  the  proportional  of  each  base  expi-esscs 
the  precise  quantity  required  to  neutralize  a proportional  of  each  of  the 
-cids.  Thus  18  of  lithia,  32  of  soda,  and  78  of  baryta,  combine  with 
'9.86  of  hydrofluoric  acid,  forming  the  neutral  hydrofluates  of  lithia, 
ixia,  and  baryta.  Tbe  same  fact  is  obvious  with  respect  to  tlie  oci^; 
< fir  35.71  of  ]))i()splK)ric,  40  of  sidphuric,  and  58  of  arsenic  acid  unite 
•ivilh  28  of  lime,  forming  a neuli-al  phosphate,  sulphate,  and  arsejjiole: 
T lime. 

'i  hesc  circumstances  afibrd  a ready  explanation  of  a curiouB  fact,  first 
oticerl  ])y  tlic  Saxon  clicrnist  'Wenzel;  viz.,  tiiat  wdien  two  neutral  salts 
nutiially  dccomi)03C  each  other,  the  resulting  compouneb  ai’e  likfii^yiBe 


ON  THE  LAWS  OF  COMBINATION. 


127 


neutral.  The  cause  of  this  fact  is  now  obvious.  If  72  parts  of  dry  sul- 
phate of  soda  are  mixed  with  132  of  nitrate  of  baiyta,  the  78  parts  of 
bar>'ta  unite  with  the  40  of  sulphuric  acid,  and  the  54  parts  of  nitric 
acid  of  the  nitrate  combine  with  the  32  of  soda,  not  a particle  of  acid 
Or  alkali  remaining  in  an  uncombined  condition. 


Sulphate  of  Soda, 
Sulphuric  odd 
Soda 


Nitrate  of  Baryta, 

40 

54  Nitric  acid. 

32 

78  Baryta. 

72 

132 

It  inatters  hot  whether  more  or  less  than  72  parts  of  sulphate  of  soda 
are  added?  for  if  more,  a small  quantity  of  sulphate  of  soda  wiU  remain 
in  solution;  if  less,  nitrate  of  baryta  wiU  be  in  excess;  but  in  either  case 
the  neutrality  will  be  unaffected. 

The  utility  of  being  acquainted  witli  these  important  laws  is  almo§l 
too  manifest  to  require  mention.  Through  their  aid,  and  by  remembep* 
ing  the  proportional  numbers  of  a few  elementary  substances,  the  corr> 
position  of  an  extensive  range  of  compound  bodies  may  be  calculated 
with  facility.  By  knowing  that  6 is  the  combining  proportion  of  carbon 
Sind  8 of  oxygen,  it  is  easy  to  recollect  the  composition  of  carbonic  ox>  . 
ide  and  carbonic  acid;  the  first  consisting  of  6 parts  of  carbon  + 8 of 
Oxygen,  and  the  second,  of  6 carbon  + 16  of  oxygen.  40  is  the  equiv- 
alent of  potassium;  and  potassa  being  its  protoxide,  is  composed  of  40 
potassium  -f-  8 of  oxygen.  From  these  few  data,  we  know  at  once  the 
composition  of  carbonate  and  bicarbonate  of  potassa.  The  former  is 
composed  of  22  carbonic  acid-}- 48  potassa;  the  latter  of  44  carbonic 
acid  + 48  potassa.  This  knowledge  is  retained  witli  very  little  effort  of 
the  memory;  and  the  assistance  derived  from  the  method  will  be  manh 
fest  on  comparing  it  with  tlie  common  practice  of  stating  tlie  composi- 
tion in  100  parts. 


Carbonic  Oxide^ 
Carbon  42.86 

Oxygen  57. 14 

Carbonate  of  Potassa^ 
Carbonic  acid  31.43 
Potassa  68.57 


Carbonic  Acid, 

27.27 

72.73 

Bicarbonaie  of  Potassa, 
47.83 
52,17 


From  the  same  data,  calcidations,  which  would  otlierwisc  be  difficult 
or  tedious,  may  be  made  rapidly  and  with  ease,  without  reference  f6 
books,  and  frequentl}^  by  a simple  mental  process.  The  exact  quanti- 
ties of  substances  required  to  produce  a given  effect  maybe  determined 
with  certainty,  thus  affording  information  wliich  is  often  necessary  to 
the  success  of  chemical  processes,  and  of  great  consequence  both 
in  the  practice  of  the  chemical  ai-ts,  and  in  the  operations  of  phar- 
macy, 

Tim  same  knowledge  affords  a good  test  to  tlie  analyst  by  which  Im 
Ciay  judge  of  the  accuracy  of  his  result,  and  even  sometimes  correct  an 
analysis  which  he  has  not  the  means  of  perfoi-ming  with  ri^d  precision. 
Thus  a powerful  argument  for  the  accuracy  of  an  analysis  is  derived 
from  the  correspondence  of  its  result  with  the  laws  of  diemical  uniom 
On  tlie  contrary,  if  it  form  an  exception  to  tliem,  we  are  authorized  to 
regard  it  as  doubtful;  and  may  hence  be  led  to  detect  an  error,  the  ex- 
istence of  which  might  not  otherwise  have  been  suspected.  If  an  ox- 
idized body  is  found  to  contain  one  proportional  of  tlie  combustible  with 


123 


ON  THE  LAWS  OF  COMBINATION. 


7.99  of  bxygen,  it  is  fair  to  infer  that  8,  or  one  proportional  of  ox}*gx^n 
would  have  been  the  result,  had  the  analysis  been  perfect. 

The  composition  of  a substance  may  sometimes  be  determined  by  a 
calculation,  founded  on  tlie  laws  of  chemical  union,  before  an  analysis 
of  it  has  been  accomplished.  When  the  new  alkali  litliia  was  first  dis- 
covered, chemists  did  not  possess  it  in  sufficient  quantity  for  deteur 
liiining’  its  constitution  analytically.  But  the  neutral  sulphates  of  the 
alkalies  and  earths  are  known  to  be  composed  of  one  proportional  of 
each  constituent,  and  the  oxides  to  conbiin  one  proportional  of  oxygeiv 
If  it  be  found,  therefore,  by  analysis,  that  neutral  sulphate  of  lithia  is 
Composed  of  40  parts  of  sulphuric  acid  and  18  of  hthia,  it  may  bo 
inferred,  since  40  is  one  proportional  of  the  acid,  that  18  is  the  cquiw- 
alent  for  lithia;  and  that  this  oxide  is  formed  of  8 parts  of  oxygen  and 
10  of  lithium. 

The  method  of  determining  the  proportional  numbers  will  be  anfici^ 
pated  from  what  has  already  been  said.  The  commencement  is  mado 
by  carefully  analyzing  a definite  compound  of  two  simple  substances 
which  possess  an  extensive  range  of  affinity.  No  two  bodies  are  bettc'i 
adapted  for  this  purpose  than  ox3'gen  and  hydrogen,  and  that  compound 
Is  selected  which  contains  the  smallest  quantity  of  oxygen.  Water  is 
such  a substance,  and  it  is,  therefore,  regarded  as  a compound  of  one 
proportional  of  oxygen  with  one  proportional  of  hydrogen.  But  analy- 
sis proves  that  it  is  composed  of  8 parts  of  the  former  to  1 of  the  latter, 
and,  therefore,  the  equivalent  of  oxygen  is  eight  times  as  heavy  as  that 
of  hydrogen. 

Some  compounds  are  next  examined,  which  contain  the  smallest  pi’o- 
portion  of  oxygen  or  hydrogen  in  combination  with  some  other  sub- 
stance. Carbonic  oxide  with  respect  to  carbon,  and  sulphuretted  h}'- 
drogen  with  respect  to  sulphur,  answer  this  description  perfectly.  The 
former  consists  of  8 parts  of  oxygen  and  6 of  carbon;  the  latter,  of  1 pail 
of  hydrogen  and  16  of  sulphur.  The  proportional  number  of  carbon  is 
consequently  6,  and  that  of  sulphur  16.  The  proportionals  of  all  othci 
bodies  may  be  determined  in  a similar  manner. 

Since  the  proportional  numbers  merely  express  the  relative  quantifies 
df  different  substances  which  combine  together,  it  is  in  itself  immate- 
rial what  figures  are  employed  to  express  them.  The  only  essential 
point  is,  that  the  relation  should  be  strictly  observed.  Thus,  we  may 
make  the  combining  proportion  of  hydrogen  10  if  we  please;  but  then 
oxygen  must  be  80,  carbon  60,  and  sulphur  160.  We  may  call  hydn> 
gen^lOO  or  1000;  or,  if  it  were  desirable  to  perplex  the  subject  as  much 
as  possible,  some  high  uneven  number  might  be  selected,  provided  the 
due  relation  between  the  different  numbers  were  faithfully  preserved. 
But  such  a practice  would  effectually  do  away  with  the  advantage  above 
ascribed  to  the  use  of  the  proportional  numbers;  and  it  is  tlie  object  of 
every  one  to  employ  such  as  are  simple,  that  their  relation  may  be  pejs- 
ceived  by  mere  inspection.  The  opinions  of  different  chemists  concertb- 
ing  tlie  simplicity  of  numbers  being  somewhat  at  variance,  wc  possess 
Sfcveral  series  of  them.  Dr.  Thomson,  for  example,  makes  oxygen  1,  so 
that  hydrogen  is  eight  times  less  than  unit}',  or  0.125,  carbon  0.75,  and 
sulphiu-  2.  Dr.  Wollaston,  in  his  scale  of  chemical  equivalents,  estimat- 
ed oxygen  at  10;  and  hence  hydrogen  is  1.25,  carbon  7.5,  and  so  oa. 
According  to  Bcrzcfuis,  oxygen  is  100.  And  lastly,  several  otlier  che- 
mists, such  as  Dalton,  Davy,  Henry,  and  others,  have  selected  hydrogen 
us  their  unit;  and,  therefore,  the  equivalent  of  oxygen  is  a One  of 
tlicse  series  may  easily  be  reduced  to  cither  of  the  otliers  by  an  obvious 
and  simple  calculation,  and  it  is  not  very  material  to  which  of  tliem  tho 
preference  is  given;  but  i have  myself  adopted  the  last,  because,  os  it 


ON  THE  LAWS  OF  COMDINATION.  129 

rarely  contains  fractional  parts,  it  appears  best  adapted  to  the  purpose 
of  teaching. 

On  the  Atomic  Theory  of  Mr.  Dalton. 

The  brief  sketch  which  has  been  given  of  the  laws  of  combination 
will,  I tmst,  serve  to  set  the  importance  of  this  department  of  chemical 
science  in  its  true  light.  It  is  founded,  as  will  have  been  seen,  on  ex^ 
periment  alone;  and  the  lavvs  which  have  been  stated  are  the  mere  ex- 
pression of  fact.  It  is  not  necessarily  connected  witlr  any  speculation, 
and  may  be  kept  wholly  free  from  it. 

It  is  not  uncommon  for  persons,  commencing  the  study  of  chemistry, 
to  entertain  a vague  notion  that  this  department  of  the  science  compre- 
hends something  uncertain  and  hypothetical  in  its  nature,  and  to  be  thus 
led  to  form  an  erroneous  idea  of  its  importance.  This  misapprehension 
may  easily  be  traced  to  its  source.  It  was  impossible  to  reflect  on  the 
regularity  and  constancy  with  which  bodies  obey  the  laws  of  combina^ 
tion,  without  speculating  about  the  cause  of  that  regularity;  and,  con- 
sequently, the  facts  themselves  were  no  sooner  noticed,  than  an  attempt 
was  made  to  explain  them.  Accordingly,  when  Mr.  Dalton  published 
his  discovery  of  those  laws,  he  at  once  incorporated  the  description  of 
them  with  his  notion  of  their  physical  cause;  and  even  expressed  the 
former  in  language  suggested  by  the  latter.  Since  that  period,  though 
several  British  chemists  of  eminence,  and  in  particular  Dr.  Wollaston 
and  Sir  H.  Da\^,  recommended  and  practised  an  opposite  course,  both 
subjects  have  been  but  too  commonly  comprised  under  the  name  of  atomic 
theory;  and  hence  it  has  often  happened  that  beginners  have  reject* 
ed  tlie  whole  as  hypothetical,  because  they  could  not  satisfactorily  dia* 
tinguish  those  parts  which  are  founded  on  fact,  from  those  which  are 
conjectural.  All  such  perplexity  would  have  been  avoided,  and  this 
department  of  the  science  have  been  far  better  understood,  and  its  value 
more  justly  appreciated,  had  the  discussion  concerning  the  atomic  con- 
stitution of  bodies  been  always  kept  distinct  from  that  of  the  phenomena 
which  it  is  intended  to  explain.  When  employed  in  this  limited  sense, 
Che  atomic  theory  may  be  discussed  in  a few  words. 

Two  opposite  opinions  have  long  existed  concerning  the  ultimate  ele- 
ments of  matter.  It  is  supposed,  according  to  one  party,  that  every 
particle  of  matter,  however  small,  may  be  divided  into  smaller  portions, 
provided  our  instruments  and  organs  were  adapted  to  the  operation 
Their  opponents  contend,  on  the  other  hand,  that  matter  is  composed 
of  certain  atoms  which  are  of  such  a nature  as  not  to  admit  of  division* 
U’hese  opposite  opinions  have  from  time  to  time  been  keenly  contested, 
dnd  with  variable  success,  according  to  the  acuteness  and  ingenuity  of 
their  respective  champions.  But  it  was  at  last  perceived  that  no  positive 
data  existed  capable  of  deciding  the  question,  and  its  interest,  therefore, 
gradually  declined.  The  progress  of  modern  chemistry  has  revived  the 
general  attention  to  this  controversy,  by  affording  a far  stronger  argu- 
ment in  favour  of  the  atomic  constitution  of  bodies  than  was  ever  ad- 
vanced before,  and  one  which  I conceive  is  almost  irresistible.  We 
have  only  in  fact  to  assume  with  Mr.  Dalton,  that  all  bodies  are  con> 
posed  of  ultimate  atoms,  the  weight  of  which  is  different  in  different 
kinds  of  matter,  and  we  explain  at  once  the  foregoing  laws  of  chemical 
union.  Nor  do  the  phenomena  appear  explicable  on  any  other  suppo- 
sition. 

According  to  the  atomic  theory,  every  compound  is  formed  of  the 
atoms  of  its  constituents.  An  atom  of  A may  unite  with  one,  two,  tliree, 
or  more  atoms  of  B.  Thus,  supposing  water  to  be  composed  of  one 


130 


ON  THE  LAWS  OF  COMBINATION. 


at<)Tn  of  hydrogen  and  one  atom  of  oxygen,  rfeufoxlde  of  hydrogen  will 
dbnsist  of  one  atom  of  hydrogen  and  two  atoms  of  oxygen.  If  carbonic 
(5xide  is  formed  of  one  atom  of  carbon  and  one  atom  of  oxygen,  car- 
bonic acid  will  consist  of  one  atom  of  carbon  and  two  atoms  of  oxygen* 
If  in  the  compounds  of  nitrogen  and  oxygen  enumerated  at  page  123, 
€ho  first  or  protoxide  is  constituted  of  one  atom  of  nitrogen  and  one 
fitom  of  ox}"gen,  the  foui*  others  will  be  regarded  as  compounds  of  one 
atom  of  nitrogen  with  two,  three,  four,  and  five  atoms  of  oxygen.  From 
Uiese  instances  it  will  appear,  that  the  law  of  multiple  proportion  is  a 
rlecessary  consequence  of  the  atomic  tlieory.  There  is  also  no  apparent 
reason  why  two  or  more  atoms  of  one  substance  may  not  combine  with 
two,  tlirce,  four,  five,  or  more  atoms  of  another.  Such  combinations 
will  account  for  tlic  complicated  proportion  noticed  in  some  compounds, 
especially  in  many  of  those  belonging  to  the  animal  and  vegetable  king"- 
doms. 

In  consequence  of  the  satisfactory  explanation  which  the  laws  of  clio 
thical  union  receive  by  means  of  the  atomic  theory,  it  has  become  cus- 
tomary to  employ  the  term  atom  in  the  same  sense  as  combining  propor- 
tion or  equivalent.  For  example,  instead  of  describing  water  as  a com- 
pound of  one  equivalent  of  oxygen  and  one  equivalent  of  hydrogen,  it 
IS  Said  to  consist  of  one  atom  of  each  element.  In  like  manner  sulphate 
6f  potassa  is  said  to  be  formed  of  one  atom  of  sulphuric  acid  and  ono' 
^tom  of  potassa,  the  word  in  this  case  denoting,  as  it  were,  a compound 
Sitom,  that  is,  the  smallest  integral  particle  of  the  acid  or  alkali;  a par- 
ticle wliich  does  not  admit  of  being  divided,  except  by  the  separation  of 
its  elementary  or  constituent  atoms.  The  numbers  expressing  the  pro- 
portions in  which  bodies  unite,  must  likewise  indicate,  consistently  wdth 
this  view,  the  relative  weights  of  atoms;  and,  accordingly,  these  num- 
bers are  often  called  atomic  weights.  Thus  as  water  is  composed  of  8 
parts  of  oxygen  and  1 of  hydrogen,  it  follows,  on  the  supposition  of 
water  consisting  of  one  atom  of  each  element,  that  an  atom  of  oxygen 
must  be  eight  times  as  heavy  as  an  atom  of  hydrogen.  If  csj'bonic  oxide 
is  formed  of  an  atom  of  carbon  and  an  atom  of  oxygen,  the  relative 
weight  of  their  atoms  is  as  6 to  8;  and  in  short  £he  relative  weights  of 
(he  atoms  of  all  other  bodies  are  expressed  by  the  numbers  which  d^ 
note  tlieir  combining  proportions. 

Though  the  phenomena  of  chemical  combination  leave  little  doubt  of 
the  atomic  constitution  of  matter,  other  powerful  arguments  may  now 
be  adduced  in  favour  of  this  theory.  Dr.  Wollaston,  in  his  Essay  on 
Che  Finite  Extent  of  the  Atmosphere,  (Philos.  Trans,  for  1822,)  has  sup- 
ported this  doctrine  on  a new  and  independent  principle,  the  particulars 
of  which  will  be  stated  in  the  section  on  nitrogen.  Another  argument, 
of  much  greater  force,  is  deducible  from  the  peculiar  connexion  noticed 
by  Pi’ofessor  Mitcherlich  between  the  form  and  composition  of  certain 
substances,  a subject  which  will  be  discussed  under  the  head  of  crystal 
lization. 

But  in  adopting  the  notion  that  matter  is  composed  of  ultimate  indi- 
visible particles,  I am  by  no  means  satisfied  of  the  propriety  of  expres- 
sing the  facts  of  the  science  in  language  founded  on  this  theory;  bo 
causc,  though  the  elements  of  bodies  be  arranged  atomically,  we  ha\'B 
no  certain  method  of  ascertaining,  in  the  present  state  of  chemistiy,  how 
many  atoms  are  contained  in  any  compound.  This  difficulty  is  particu- 
larly felt  witli  respect  to  those  series  of  compounds  in  which  half  a pro- 
portional occurs;  for  as  llic  idea  of  half  an  atom  is  inconsistent  witli  tlie 
atomic  theory,  such  an  arrangement  of  the  atoms  must  be  imagined,  as 
shall  avoid  tlic  occurrence  of  a fraction.  The  mode  of  accomplishing 
tlib  object  may  be  cxcmpUlicd  in  reference  to  the  oxides  of  lead  and 


ON  THE  LAWS  OP  COMBINATION* 


131 


Iix>n,  the  constituents  of  which  were  mentioned  on  a forme?  occasion^ 
(Page  124.)  Tlie  oxides  of  lead  may  either  be  regarded  as  composed^ 
the  protoxide  of  one  atom  of  lead  and  one  atom  of  oxygen,  the  deutoxide 
of  two  atoms  of  lead  and  three  atoms  of  oxygen,  and  the  peroxide  of  one 
atom  of  lead  and  two  atoms  of  oxygen;  or  they  may  be  viewed  as  com- 
pounds, the  protoxide  of  one  atom  of  lead  and  two  atoms  of  oxygen,  tlio 
deutoxidc  of  one  atom  of  lead  and  three  atoms  of  oxygen,  and  the  per- 
oxide of  one  atom  of  lead  and  four  atoms  of  oxygen.  In  like  manner 
the  oxides  of  iron  are  either  composed,  the  protoxide  of  one  atom  of  iron 
and  one  atom  of  oxygen,  and  the  peroxide  of  two  atoms  of  iron  and 
tliree  atoms  of  oxygen;  or  the  protoxide  of  one  atom  of  iron  and  twp 
atoms  of  oxygen,  and  the  peroxide  of  one  atom  of  iron  and  three  atoms 
of  oxygen.  The  uncertainty  attending  these  atomic  speculations  can- 
not be  more  forcibly  evinced  than  by  the  fact,  that  Berzelius  two  or 
tliree  years  ago  regarded  all  the  stronger  bases,  such  as  the  alkalies, 
alkaline  earths,  and  the  protoxides  of  several  of  the  common  metals, 
as  composed  of  one  atom  of  metal  and  two  atoms  of  oxygen;  but  that  he 
has  subsequently  abandoned  this  view,  and  now  believes  the  very  same 
substances  to  contain  one  atom  of  metal  and  one  atom  of  oxygen.  Such 
sudden  changes  cannot  take  place  without  producing  material  confu- 
sion; and  they  tend  to  show  that  the  science  is  not  yet  so  far  advanced 
as  to  admit  of  the  atomic  constitution  of  bodies  being  settled  on  perma- 
nent principles.  Until  the  period  when  this  desirable  object  may  be 
accomplished,  it  is  to  be  hoped  that  chemists  will  persevere  in  the  prac- 
tice, which  is  now  universal  in  Britain  and  adopted  by  several  distin- 
guished philosophers  on  the  continent,  of  stating  the  combining  pro- 
portions of  bodies  as  nearly  as  possible  in  the  w^ay  supplied  by  analysis, 
instead  of  doubling  some  numbers  and  halving  others  to  make  th^m 
conformable  to  some  favourite  hypothesis  of  the  moment. 

Mr,  Dalton  supposes  that  the  atoms  of  bodies  are  sphencal;  and  he 
has  invented  certain  symbols  to  represent  the  mode  in  which  he  con- 
ceives they  may  combine  together,  as  illustrated  by  the  following  figures* 


O Hydrogen. 
© Nitrogen. 


o Oxygen. 
® Carbon, 


Binary  Cmipounds, 

O G Water. 

O ® Carbonic  oxide* 

Ternary  CompouncU^ 

O O O Deutoxide  of  hydrogen* 
0^0  Carbonic  acid. 


&c.  &c.  Sec. 


Ail  substances,  containing  only  two  atoms,  he  called  bmary  com- 
pounds, those  composed  of  three  atoms  ternary  compounds,  .of  four., 
quaternary,  and  so  on. 

There  are  several  questions  relative  to  the  nature  of  atoms,  most  of 
which  will  perhaps  never  be  decided.  Of  this  nature  are  the  questions 
which  relate  to  the  actual  form,  size,  and  weight  of  atoms,  and  to  the 
circumstances  in  which  they  mutually  differ.  All  that  we  know  with 
any  certainty  is,  that  their  weights  do  differ,  and  by  exact  analysis  the 
relations  between  them  may  be  determined. 

It  is  but  justice  to  the  memory  of  the  late  Mr.  Higgins  of  Dublin,  to 
state  that  he  first  made  use  of  the  atomic  hypothesis  in  chemical  rea- 


132 


ON  THE  LAWS  OP  COMBINAl’IOK. 


aonin^.  In  his  “ Comparative  View  of  the  Phlogistic  and  Antiphlogistic 
Theories,*’  published  in  the  year  1789,  he  observes  (pages  56  and  37) 
that  “ in  volatile  vitriolic  acid,  a single  ultimate  particle  of  sulphur  is 
intimately  united  only  to  a single  particle  of  dephlogisticated  air;  and 
that,  in  perfect  vitriolic  acid,  every  single  particle  of  sulphur  is  united 
to  two  of  dephlogisticated  air,  being  the  quantity  necessary  to  satura- 
tion;” and  he  reasons  in  the  same  way  concerning  the  constitution  of 
water  and  the  compounds  of  nitrogen  and  oxygen.  These  remarks  of 
Mr.  Higgins  do  not  appear  to  have  had  the  slightest  connexion  with  the 
subsequent  views  of  Mr.  Dalton.  Indeed,  from  facts  which  have  come 
to  my  knowledge  relating  to  the  history  of  Mr.  Dalton’s  discovery,  I 
am  satisfied  that  this  philosopher  had  not  seen  the  work  of  Mr.  Higgins 
Vill  after  he  had  given  an  account  of  his  own  doctrine.  The  observar 
tions  of  Mr.  Higgins,  therefore,  though  highly  creditable  to  his  sagacity, . 
(Jo  not  affect  Mr.  Dalton’s  merit  as  an  original  observer.  They  were 
made,  moreover,  in  so  casual  a manner,  as  not  only  not  to  have  attracted 
the  notice  of  his  contemporaries,  but  to  prove  that  Mr.  Higgins  himself 
attached  no  particular  interest  to  them.  Mr.  Dalton’s  chief  merit  lies 
in  the  discovery  of  the  laws  of  combination,  a discovery  which  is  solely 
and  indisputably  his;  but  in  which  he  would  have  been  anticipated  by . 
Mr.  Higgins,  had  that  chemist  perceived  the  importance  of  his  own 
opinions. 

On  the  Theory  of  Volumes, 

Soon  after  the  publication  of  the  New  System  of  Chemical  Philosophy 
in  1808,  in  which  work  Mr.  Dalton  explained  his  views  of  the  atomic 
constitution  of  bodies,  a paper  appeared  in  the  second  volume  of  the 
Mdmoires  d^Jircueily  by  M.  Gay-Lussac,  on  the  “ Combination  of  Gaseous 
Substances  with  one  another.”  He  there  proved  that  gases  unite  to- 
gether by  volume  in  very  simple  and  definite  proportions.  In  the  com»- 
bined  researches  of  himself  and  M.  HumboMt,  those  gentlemen  found 
that  water  is  composed  precisely  of  100  measures  of  oxygen  and  200 
measures  of  hydrogen;  and  M.  Gay-Lussac,  being  struck  by  this  pecur 
liarly  simple  proportion,  was  induced  to  examine  the  combinations  of 
other  gases  with  the  view  of  ascertaining  if  any  thing  similar  occurred 
in  other  instances. 

The  first  compounds  which  he  examined  were  those  of  ammoniacal 
gas  with  muriatic,  carbonic,  and  fluoboric  acid  gases.  100  volumes  of 
the  alkali  were  found  to  combine  with  precisely  100  volumes  of  muriatic 
acid  gas,  and  they  could  be  made  to  unite  in  no  other  ratio.  With  both 
the  other  acids,  on  the  contrary,  two  distinct  combinations  were  pos- 
sible. These  are 

100  fluoboric  acid  gas,  with  100  ammoniacal  gas. 

100  do.  200  do. 

100  carbonic  acid  gas  100  do. 

100  do.  200  do. 

Various  other  examples  were  quoted,  both  from  liis  own  experiments 
and  from  those  of  otliers,  all  demonstrating  the  same  fact.  Thus  am- 
monia was  found  by  A.  Berthollct  to  consist  of  100  volumes  of  nitrogen 
and  300  volumes  of  hydrogen;  sulphuric  acid  contains  100  volumes  of 
sulphurous  acid  and  50  volumes  of  oxygen;  and  carbonic  acid  is  formed 
by  burning  a mixture  of  50  volumes  of  oxygen  and  100  volumes  of  car- 
bonic oxide. 

From  these  and  other  instances  M.  Gay-Lussac  established  the  fact, 
that  gaseous  substances  unite  in  the  simple  ratio  of  1 to  1, 1 to  2,  1 to 
3,  &c.;  and  this  original  observation  has  been  confirmed  by  such  a mul- 


ON  THE  LAWS  OF  COMBINATION. 


133 


tiplicity  of  experiments,  that  it  may  be  regarded  as  one  of  the  best 
established  laws  in  chemistry.  Nor  does  it  apply  to  the  true  gases 
merely,  but  to  vapours  likewise.  For  example,  sulphuretted  hydrogen, 
sulphurous  acid,  and  hydriodic  acid  gases  are  composed  of 

100  vol.  hydrogen  and  100  vol.  vapour  of  sulphur. 

100  oxygen  100  . . sulphur. 

100  hydrogen  100  . . iodine. 

There  are  very  good  grounds  to  suppose,  also,  that  solid  bodies 
which  are  fixed  in  the  fire  would,  if  in  the  form  of  vapour,  be  subject 
to  the  same  law.  By  a method  wliich  will  shortly  be  explained,  it  may 
be  calculated  that  the  specific  gravity  of  the  vapour  of  carbon  is  0.4166, 
atmospheric  air  being  unity.  Now,  if  we  assume  that  carbonic  acid  is 
formed  of  100  volumes  of  oxygen,  and  100  volumes  of  the  vapour  of 
carbon,  condensed  into  the  space  of  100  volumes,  the  specific  gravity 
of  carbonic  acid  will  be'1‘1111  (the  sp.  gr.  of  oxygen)  +0'4166=3 
1*5277,  which  is  the  precise  number  determined  by  experiment. 
Again,  it  follows  from  oiU'  assumption,  that  carbonic  acid  is  composed 
by  weight  of 

Oxygen  ITlll  . 16,  or  ttvo  proportionals. 

Carbon  0 4166  . 6,  or  one  proportional, 

and  this  deduction  is  confirmed  by  analysis. 

If  we  assume  that  carbonic  oxide  is  composed  of  50  volumes  of  oxy- 
gen and  100  volumes  of  the  vapour  of  carbon,  condensed  into  the 
space  of  100  volumes,  then  its  specific  gravity  will  be  0*5555  (half  the 
sp.  gr.  of  oxygen)  0-4166  = 0*9721;  and  its  composition  will  be 

Oxygen  0*5555  . 8,  or  one  proportional. 

Carbon  0*4166  . 6,  or  one  proportional, 

both  of  which  results  have  been  determined  by  other  methods. 

The  compounds  of  carbon  and  hydrogen  are  equally  illustrative  of 
the  same  point.  If  light  carburetted  hydrogen  is  formed  of  200  vol- 
umes of  hydrogen  and  100  volumes  of  the  vapour  of  carbon,  conden- 
sed into  100  volumes,  its  specific  gravity  should  be  0*1388  (twice  the 
sp.  gi*.  of  hydrogen)  0-4166=;0*5554;  audits  composition  by  weight 
will  be 

Hydrogen  0-1388  . 2,  or  two  proportionals. 

Carbon  0 4166  . 6,  or  one  proportional. 

If  100  volumes  of  ok:fiarit  gas  are  composed  of  200  volumes  of  hydro- 
gen and  200  volumes  of  the  vapour  of  carbon,  its  specific  gravity  will 
be  0*1388  0 •8332=0-9720;  and  its  composition  by  weight  must  be 

Hydrogen  0 1388  . 2,  or  two  proportionals. 

Carbon  0*8332  . 12,  or  two  proportionals. 

Both  of  these  results  have  been  ascertained  by  analysis. 

Another  remarkable  fact  established  by  M.  Gay-Lussac  in  the  same 
paper  is,  that  the  diminution  of  bulk  which  gases  frequently  suffer  in 
combining,  is  also  in  a very  simple  ratio.  Thus,  the  4 volumes  of 
which  ammonia  is  constituted,  (3  volumes  of  hydrogen  and  1 of  nitro- 
gen) contract  to  one-half  or  2 volumes  when  they  unite.  There  is  a 
contraction  to  two-thirds  in  the  formation  of  nitrous  oxide  gas.  The 
same  ‘applies  to  the  combination  of  gases  and  vapours.  There  is  a con- 
traction to  a half  in  the  formation  of  sulphuretted  hydrogen;  and  to  a 
half  in  tliat  of  sulphurous  acid.  The  instances  just  quoted  relative  to 
tile  vapour  of  carbon  confirm  the  same  remark.  There  is  a contraction 

12 


134 


ON  THE  LAWS  OF  COMBINATION. 


to  two-thirds  in  carbonic  oxide;  to  a half  in  carbonic  acid;  to  a tliird  in 
lig-ht  carburetted  hydrogen;  and  to  a fourth  in  olefiant  gas. 

The  rapid  progress  which  chemistry  has  made  within  the  last  fe\r 
years  is  in  great  measure  attributable  to  the  ardour  with  which  pneuma- 
tic chemistry  has  been  cultivated.  That  very  department,  which  at 
first  sight  appears  so  obscure  and  difficult,  has  afforded  a greater  num- 
ber of  leading  facts  than  any  other;  and  the  law  of  Gay-Lussac,  by  giv- 
ing an  additional  degree  of  precision  to  such*  researches^  as  well  as  from 
its  own  intrinsic  value,  is  one  of  the  brightest  discoveries  that  adorn  the 
annals  of  the  science.  The  practice  of  estimating  the  quantity  in 
weight  of  any  gas,  by  measuring  its  bulk  or  volume,  of  itself  suscepti- 
ble of  much  accuracy,  is  rendered  still  more  precise  and  satisfactory  by 
tire  operation  of  this  law.  It  will  not  perhaps  be  superfluous,  there- 
fore, to  exemplify  the  method  of  reasoning  employed  in  these  investi- 
g'ations  by  a few  exam.ples;  which  will  serve,  moreover,  as  a useful 
specimen  to  the  beginner  of  the  nature  of  chemical  proof. 

One  essential  element  in  every  inquiry  of  this  kind,  which  is  indeed 
the  keystone  of  the  whole,  is  a knowledge  of  the  specific  gravity  of 
the  gases.  But  it  is  exceedingly  difficult  to  determine  the  specific  gra- 
vity of  gases  with  perfect  accuracy;  for  not  only  do  slight  alterations  of 
temperature  and  pressure  during  the  experiment  aifect  the  result,  but 
the  presence  of  a little  watery  vapour,  atmospheric  air,  or  other  impu- 
rity, may  cause  material  error,  especially  when  the  gas  to’  be  weighed 
is  either  very  light  or  very  heavy.  The  specific  gravity  of  important  gases 
has,  accordingly,  been  stated  diflerently  by  diflerent  chemists,  and 
there  is  none  in  regard  to  which  more  discordant  statements  have  been 
made  than  that  of  hydrogen  gas.  Fortunately  we  possess  the  power  of 
correcting  the  results,  and  of  testing  their  accuracy,  by  other  means 
which  are  less  liable  to  error.  The  specific  gravity  of  oxygen,  hydro- 
gen, and  nitrogen  gases,  air  being  1,  may  be  thus  estimated: 

Oxygen  - - - 3.1111 

Hydrogen  - - - 0.0G94 

Nitrogen  - - - 0.9722 

It  has  been  proved  by  analysis  that  200  volumes  of  ammoniacal  gas 
are  composed  of  300  volumes  of  hydrogen  and  100  volumes  of  ni- 
trogen, a fact  from  which  the  specific  gravity  of  that  alkali  may  be  cal- 
culated. 

Thus,  0.9722  -f  (0.0694  X 3)  = 1.1804 

1.1804 

= 0.2951,  the  specific  gi’avity  which  ammoniacal  gas  should 

have,  if  its  constituent  gases  suffered  no  contraction;  but  as  they  con- 
tract to  one-half,  the  real  specific  gravity  is  double  what  it  otherwise 
would  be,  that  is  0.5902.  Now,  if  by  weighing  a certain  quantity  of 
ammoniacal  gas,  the  same  number  is  procured  for  its  specific  gravity, 
there  is  a very  strong  presumption  that  the  elements  of  the  calculation 
are  correct. 

Nitric  oxide  is  composed  of  100  volumes  of  nitrogen  and  100  volumes 
of  oxygen,  united  without  any  contraction;  and  forming,  consequently, 
200  voiumc.s  of  the  compound.  Its  specific  gravity  nuist,  therefore,  be 

. 1.1111  4-0.9722 

the  mean  of  its  components,  or  ^ =1.0416.  The  cor- 

respondence of  this  number  with  that  found  by  w'^eighing  the  gas  itself, 
affords  powerful  testimony  that  the  density  of  oxygen  and  nitrogen 
gases  has  been  correctly  determined.  It  is  obvious,  indeed,  that  the 
♦ulculatcd  results,  us  being  free  from  the  unavoidable  errors  of  manipu- 


ON  THE  LAWS  OF  COMBINATION. 


135 


latlon,  must  be  the  more  accurate,  provided  the  elements  of  the  calcu- 
lation may  be  tmsted. 

Dr.  Henry  has  proved  by  careful  analysis  that  100  volumes  of  light 
carburetted  hydrogen  gas,  a compound  of  carbon  and  hydrogen,  re- 
quire 200  volumes  of  oxygen  for  complete  combustion^  that  water  and 
carbonic  acid  are  the  sole  products ^ and  that  the  latter  amounts  pre- 
cisely to  100  volumes.  From  these  data,  the  proportions  of  its  consti- 
tuents and  its  specific  gravity  may  be  determined.  For  100  volumes  of 
carbonic  acid  contain  100  volumes  of  the  vapour  of  carbon,  which  must 
have  been  present  in  the  carburetted  hydrogen,  and  100  volumes  of 
oxygen.  One-half  of  the  oxygen  originally  employed  is  thus  accounted 
foi’;  and  the  remainder  must  have  combined  with  hydrogen.  But  100 
volumes  of  oxygen  require  200  volumes  of  hydrogen  for  combination, 
all  of  which  must  likewise  have  been  contained  in  the  carburetted  hy- 
drogen. Hence  it  is  inferred,  that  100  volumes  of  light  carburetted 
hydrogen  are  composed  of  100  volumes  of  the  vapour  of  carbon  and 
200  volumes  of  hydrogen.  Its  specific  gravity  must,  therefore,  be 
0.5554;  that  is,  0.4165  (the  sp.  gr.  of  carbon  vapour)  -j-  0.1388  or  twice 
the  sp.  gr.  of  hydrogen  gas. 

Having  ascertained  that  light  carburetted  hydrogen  gas  is  composed 
of  two  measures  of  hydrogen  and  one  of  the  vapour  of  carbon,  it  is 
easy  to  calculate  the  proportion  of  its  constituents  by  weight.  For  this 
purpose  we  need  only  multiply  the  bulk  of  the  gases  by  their  re- 
spective specific  gravities.  Thus  200  x 0-0^94  = 13.88,  and  100  X 
0.4166  = 41.66.  Hence  light  carburetted  hydrogen  is  composed  by 
weight  of 


Carbon 

Hydrogen 


41.66 

13.88 


6 

2 


The  theory  of  volumes  has  very  considerable  resemblance  to  the  laws 
of  combination  by  weight  developed  by  Mr.  Dalton;  for  the  multiple 
proportions  are  as  apparent  in  the  former  as  in  the  latter.  But  there  is 
one  remarkable  difference  between  them.  The  weight  of  either  ele- 
ment of  a compound  has  no  apparent  dependence  on  that  of  the  other. 
Thus  6 parts  of  carbon  and  8 of  oxygen  constitute  carbonic  oxide,  and 
8 parts  of  oxygen  and  14  of  nitrogen  are  contained  in  nitrous  oxide; 
but  8 is  not  a multiple  by  any  whole  number  of  6,  nor  14  of  8.  On  the 
other  hand,  the  elements  of  a compound  are  always  united  by  volume 
in  the  ratio  of  1 to  1,  1 to  2,  1 to  3,  and  so  on.  This  simple  ratio  is 
peculiarly  interesting,  because  it  appears  to  indicate  a close  correspond- 
ence in  the  size  of  the  atoms  of  gaseous  bodies.  It  naturally  suggests 
the  idea  that  this  peculiarity  may  arise  from  the  atoms  of  elementary' 
principles  possessing  the  same  magnitude.  On  this  supposition,  equal 
measures  of  such  substances  in  the  gaseous  form,  at  the  same  tempera- 
ture and  pressure,  would  probably  contain  an  equal  number  of  atoms; 
and  the  specific  gravity  of  these  gases  would  depend  on  the  relative 
weight  of  their  atoms.  The  same  numbers  which  indicate  the  specific 
gravity  of  elementary  principles  in  the  gaseous  state,  would  then  ex- 
press the  relative  weights  of  their  atoms;  so  that  the  latter  would  be  as- 
certained by  means  of  the  former,  or  the  atomic  weight  of  a solid  or 
liquid  represent  the  specific  gravity  of  its  vapour.  The  proportional 
numbers  adopted  by  Sir  11.  Davy  in  his  Elements  of  Chemical  Philoso- 
phy, and  the  atomic  weights  employed  by  Berzelius  in  his  System  of 
Chemistry,  were  selected  in  accordance  with  this  view.  Thus  water 
being  formed  of  2 measures  of  hydrogen  and  1 measui'e  of  oxygen,  is 


136 


ON  THE  LAWS  OF  COMRINATION. 


believed  by  Berzelius  to  consist  of  2 atoms  of  the  former  and  1 atom  of 
the  latter;  and  for  a similar  reason,  he  regards  protoxide  of  nitrogen  as 
a compound  of  2 atoms  ob- nitrogen  and  1 atom  of  oxygen.  ’^Fhc-  atoms 
and  volumes  of  the  four  elementary  gases,  oxygen,  chlorine,  hydrogen, 
and  nitrogen,  are  tluis  made  to  coincide  with  each  other.  This  me- 
thod, though  perliaps  preferable  to  any  other,  has  not  hitherto  bee  n 
generally  followed.  Most  chemists  consider  water,  protoxide  of  cldo- 
rine,  and  protoxide  of  nitrogen,  as  containing  one  atom  of  each  of 
their  elements;  and  consequently,  as  these  compounds  consist  of  1 mea- 
sure of  oxygen  united  with  2 measures  of  the  other  constituent,  the 
atom  of  hydrogen,  chlorine,  and  nitrogen  is  supposed  to  occupy  twice 
as  much  space  as  an  atom  of  oxygen.  An  atom  of  oxygen  is,  there- 
fore, represented  by  half  a volume,  and  an  atom  of  the  other  three 
gases  by  a whole  volume. 

^ Dr.  Prout,  in  an  ingenious  essay  ‘‘On  the  delation  between  the  Spe- 
cific Gravities  of  Bodies  in  their  Gaseous  State  and  the  Weights  of 
their  Atoms,’’  published  in  the  6th  volume  of  the  Annals  of  Philosophy, 
(Old  Series,  p.  321,)  considers  it  probable  that  the  same  relation,  which 
is  thoug'ht  to  exist  between  the  atoms  and  volumes  of  the  four  elemen- 
tary gases,  may  hold  equally  of  the  vapours  of  the  other  elements. 
Thus  in  representing  the  atom  of  oxygen  by  half  a volume,  he  believes 
the  atoms  of  the  other  elementary  principles,  such  as  iodine,  carbon, 
and  sulphur,  correspond  to  a whole  volume  of  their  vapour.  From  tliis 
he  has  deduced  a mode  of  calculating  the  specific  gravity, of  any  vapour 
from  the  atomic  weig’ht  of  the  body  which  yields  it.  The  rule  consists 
in  multiplying  0.5555,  or  half  the  specific  gravity  of  oxygen  gas,  by 
the  atomic  weight  of  any  element,  and  dividing  the  product  by  the 
atomic  weight  of  oxygen;  the  quotient  is  the.  specific  gravity  of  the  va- 
pour. For  example,  the  specific  gravity  of  the  vapour  of  carbon  i« 
thus  found:  As 

8:6::  0.5555  : 0.4166 

in  which  8 is  the  atomic  weight  of  oxygen,  6 that  of  carbon,  and  0.4166 
the  specific  gravity  of  the  vapour  of  carbon.  I'he  same  relation  which 
exists  between  the  atomic  weight  of  oxygen  and  half  its  specific  gravi- 
ty, subsists  between  the  atomic  weight  of  any  other  element,  and  the 
specific  gravity  of  its  vapour.  Though  the  accuracy  of  Dr.  Prout’s 
views  has  not  yet  been  established  by  experiment,  his  formula  may 
often  be  employed  with  advantag'e. 

In  the  essay  above  quoted.  Dr.  Prout  has  advanced  several  instances, 
in  which  the  equivalents  or  atomic  weights  of  bodies  appear  to  be  mul- 
tiples by  a v/hole  number  of  the  atomic  weight  of  hydrogen  gas;  and 
he  threw  out  a conjecture  that  the  same  relation  may  perhaps  exist  in 
other  cases,  his  subject  has  since  been  experimentally  investigated 
by  Dr.  Thomson,  who  has  declared  after  a most  elaborate  Inquiry,  the 
fruits  of  which  are  contained  in  liis  “First  Principles  of  Chemi.stry, ” 
that  the  law  is  of  universal  ajiplication;  that  the  atomic  weights  of  all 
the  simple  sub.stances  winch  lie  has  examined,  are  not  only  multiple.9 
by  a whole  number  of  the  atomic  weight  of  hydrogen,  Imt  with  a few 
exceptions  of  two  atoms  of  liydrogcn.  But  in  opposition  to  this  .state- 
ment, Berzelius  in.sists  that  the  law  is  inconsistent  with  the  results  of 
his  analysc.s,  and  that  the  cxi>criments  of  Dr.  'I  homson  arc  inaccurate. 
My  own  observations  have  sati.sfied  me,  that  some  of  the  fundamental 
experiments  of  Dr.  'I’liomson  are  fauKy;  and  1 cannot  hesitate  in  con- 
cluding that  the  question  i.s  just  as  far  from  being  decided  us  ever. 


ON  THE  LAWS  Oi?  COMBINATION. 


137 


On  the  Theory  of  Berzelius. 

It  is  well  known  that  the  celebrated  Professor  of  Stockholm  has  for 
many  years  devoted  himself  to  the  study  of  the  laws  of  definite  pro- 
portions^ and  that  he  has  been  led  to  form  a peculiar  hypothesis,  by 
way  of  generalizing’  the  facts  which  his  industry  had  collected.  To 
give  a detailed  account  of  his  system  does  not  fall  v/ithin  the  plan  of 
this  work;  but  considering  the  extraordinary  number  of  facts  with 
which  this  indefatigable  chemist  has  enriched  the  science,  and  espe- 
cially this  department,  I think  it  proper  to  give  a short  account  of  his 
doctrines,  offering  at  the  same  time  a few  comments  upon  them. 

Berzelius  mentions  in  the  historical  introduction  to  his  treatise  on  the 
“ Theory  of  Definite  Proportions,^’  that  he  commenced  his  researches 
on  the  subject  in  the  year  1807;  and  that  the)"  originated  in  the  study  of 
tlie  works  of  Richter.  From  Richter’s  explanation  of  the  fact,  that 
w"hen  two  neutral  salts  decompose  one  another,  the  resulting  compounds 
are  likewise  neutral,  he  perceived  that  one  good  analysis  of  a few  salts 
would  furnish  the  means  of  calculating  the  composition  of  all  others. 
He  accordingly  entered  upon  an  inquiry,  which  waf3  at  first  limited  in 
its  object;  but  as  he  proceeded,  his  views  enlarged,  and  advancing 
from  one  step  to  another,  he  at  length  set  about  determining  the  laws 
of  combination  in  general.  In  perusing  his  account  of  the  inv^estiga- 
tion,  we  are  at  a loss  whether  most  to  admire  the  number  of  exact  ana- 
lyses which  he  performed,  the  variety  of  new  facts  he  determined,  his 
acuteness  in  detecting  sources  of  error,  his  ingenuity  in  devising  new 
analytical  processes,  or  the  persevering  industry  which  he  displayed  in 
every  part  of  the  inquiry.  But  it  is  at  the  same  time  impossible  to 
suppress  regret,  that,  instead  of  forming  a complex  system  of  his  own, 
he  did  not  adopt  the  more  simple  views  of  Mr.  Dalton.  This  he  might 
have  done  with  very  great  propriety;  since  the  fundamental  laws  which 
he  discovered  are,  with  very  little  exception,  either  identical  with  those 
previously  pointed  out  by  the  British  pliilosopher,  or  the  direct  result 
of  their  operation. 

Berzelius  assumes,  with  Mr.  Dalton,  the  existence  of  ultimate  indi- 
visible atoms,  to  the  combination  of  which  with  one  another  the  laws 
of  chemical  proportion  are  owing. 

The  first  law  of  Berzelius  is  the  following.  “One  atom  of  one  ele- 
ment unites  with  one,  two,  three,  or  more  atoms  of  another  element.” 
This  coincides  vyith  the  law  of  Mr.  Dalton,  and  requires  no  comment, 
further  than  that  ithas  been  amply  confirmed  by  the  labours  of  Berzelius. 
The  second  is,  that  “two  atoms  of  one  element  combine  with  three 
and  five  atoms  of  another.”  These  are  the  two  laws  which  regulate 
the  union  of  simple  or  elementary  atoms. 

The  combination  of  compound  atoms  with  each  other  obeys  another 
law,  and  is  confined  within  still  narrower  limits.  “ I’vvo  compounds 
which  contain  the  same  electro-neg’ative  body,  always  combine  in  such 
a manner  that  the  electro-negative  element  of  the  one  is  a multiple  by 
a whole  number  of  the  same  element  of  the  other.”  Thus,  for  in- 
stance, if  two  oxidized  bodies  unite,  the  oxyg'en  of  one  is  a multijde 
by  a whole  number  of  the  oxygen  in  the  other.  Of  this  various  exam- 
ples may  be  given.  Hydrate  of  potassa  is  composed  of 

Fotassa  48,  the  oxygen  of  which  is  8. 

Water  9,  do.  8.  * 

In  like  manner,  if  two  acids  or  two  oxides  combine,  the  same  will  be 
observed. 


12* 


158 


ON  THE  LAWS  OF  COMBINATION. 


In  the  earthy  minerals,  which  often  contain  several  oxide?,  the  Mine 
law  is  found  to  prevail  with  great  uniformity. 

1 he  composition  of  salts  is  likewise  under  its  influence.  Carbonate 
of  potassa,  for  example,  is  composed  of 

Carbonic  acid  22,  the  oxygen  of  which  is  16. 

Potassa  48,  do.  8. 

and  sulphate  of  potassa  of 

Sulphuric  acid  40,  the  oxygen  of  which  is  24. 

Potassa  48,  do.  8. 

Berzelius  has  remarked  that  the  nitrates,  phosphates,  and  arscniatc% 
may  in  some  instances  prove  exceptions  to  the  law.  There  is  also  a 
similar  relation,  in  salts  which  contain  water  of  crystallization,  between 
the  oxygen  of  the  base  of  the  salt  and  that  of  the  water.  For  instance, 
crystallized  sulphate  of  soda  is  composed  of 

Sulphuric  acid  40. 

Soda  - 32,  the  oxygen  of  which  is  8. 

Water,  - 90,  do.  80. 

Double  salts  are  also  influenced  by  the  same  law.  In  tartrate  of  po- 
tassa and  soda,  for  example,  tlie  oxygen  of  the  potassa  is  exactly  equal 
to  the  oxygen  in  the  soda;  and  the  oxygen  in  the  tartaric  .acid,  which 
neutralizes  the  potassa,  is  equal  to  that  of  the  soda. 

But  this  is  not  all  that  Berzelius  has  remarked  with  respect  to  the 
constitution  of  the  salts.  He  observes  that  in  each  series  of  salts,  the 
same  relation  always  exists  between  the  oxygen  of  the  acid  and  that  of 
the  base.  In  all  the  neutral  sulphates  this  ratio  is  as  three  to  one,  as 
may  be  seen  in  the  sulphates  of  soda  and  potassa.  In  the  carbonates, 
the  oxygen  of  the  acid  is  double,  and  in  the  bicaibonates  Quadruple  the 
ox3''gen  of  the  base. 

The  existence  of  these  remarkable  laws  was  discovered  by  Berzelius 
at  a very  early  period  of  his  researches;  ami  he  mentions,  that  as  sub- 
sequent observation,  during  the  course  of  several  years,  has  not  aL 
forded  a single  exception  to  them,  he  now  regards  them  as  univer- 
sal. He,  accordingly,  places  unlimited  confidence  in  their  accuracy, 
and  is  in  the  habit  of  calculating  the  composition  of  bodies  on  this  prin- 
ciple. 

It  will  of  coui’se  be  interesting  to  inquire  into  the  cause  of  these  phe- 
nomena; to  ascertain  if  there  is  any  property  peculiar  to  oxygen,  or 
other  negative  electrics,  which  may  give  rise  to  them.  Berzelius  him- 
self says  that  “the  cause  is  involved  in  such  deep  obscurity,  that  it  is 
impossible  at  the  present  moment  to  give  a probable  guess  at  it.”  I 
have  the  misfortune  to  differ  entirely  from  Berzelius  on  this  question. 
So  far  from  being  obscure,  it  is  perfectly  intelligible,  and  is  |)recisely 
what  may  be  anticipated  from  the  present  state  of  clieraical  know- 
ledge. Most  of  the  salts  called  neutral  sulphates  are  composed  of 
one  proportional  or  one  atom  of  sulphuric  acid,  and  one  proportional 
of  some  protoxide.  This  is  the  case  with  all  the  alkaline  and  earthy 
sulphates,  and  with  those  of  several  of  the  common  metals,  such  us 
lead,  zinc,  and  iron.  Now,  one  proportional  of  sulphuric  acid  is  com- 
posed of 

Sulplmr  16,  or  one  proportional. 

Oxygen  24,  or  three  proportionals. 

and  every  protoxide  of 

\ Metal  — , or  one  proportional. 

Oxygen  8,  or  one  proportional. 


ON  THE  LAWS  OF  COMBINATION. 


139 


Hence  a number  of  laws  may  be  deduced  which  must  hold  in  every 
sulpliate  of  a protoxide. 

1.  The  oxyg'en  of  the  acid  is  a multiple  of  that  of  the  base. 

2.  The  acid  contains  three  times  as  much  oxygen  as  the  base. 

3.  The  sulphur  of  the  acid  is  just  double  the  oxygen  of  the  base. 

4.  The  acid  itself  is  five  times  as  much  as  the  oxygen  of  the  base. 

Metallic  sulphurets  are  frequently  composed  of  one  proportional  of 

each  element;  and  should  qxidation  ensue,  so  that  the  sulphur  is  con- 
verted into  sulphuric  acid,  and  the  metal  into  a protoxide,’  they  will  be 
in  the  exact  proportion  for  forming  a neutral  sulphate.  Berzelius  has 
proved  by  analysis  that  this  happens  frequently,  and  he  is  disposed  to 
convert  it  into  a general  law. 

Again,  the  carbonates  are  composed  of  one  proportional  of  carbonic , 
acid,  and  one  proportional  of  some  protoxide.  But  one  proportional 
of  carbonic  acid  is  composed  of 

Carbon  6,  or  one  proportional. 

Oxygen  16,  or  two  proportionals; 

and  every  protoxide  of 

Metal  — , or  one  proportional. 

Oxygen  8,  or  one  proportional. 

It  is  inferred,  therefore,  that  in  all  the  carbonates,  the  oxyg’en  of  the 
acid  is  exactly  double  that  of  the  base;  and  the  same  mode  of  reason- 
ing is  applicable  to  the  various  genera  of  salts.  These  few  examples 
will  suffice  to  show,  that  the  phenomena  which  seemed  so  obscure  to 
Berzelius,  are  rendered  quite  obvious  by  the  Daltonian  method.  We 
perceive,  moreover,  that  no  constant  ratio  can  exist  between  the  quan- 
tity of  oxide  and  that  of  the  acid  or  oxygen  of  the  acid;  and  the  rea- 
son is,  because  the  atomic  weights  of  the  metals  in  general  are  differ- 
ent. But  this  view  of  the  subject  answers  another  useful  purpose;  it 
enables  us  to  see  whe'ther  the  law  of  Berzelius  is  or  is  not  universal. 
This  subject  has  been  ably  discussed  in  his  “ First  Principles’’  by  Dr. 
Thomson,  who  has  adduced  several  instances,  where,  from  the  consti- 
tution of  the  combining  substances,  the  Law  of  Berzelius  does  not  and 
cannot  apply. 

An  attempt  has  been  made  within  these  few  years  to  determine  the 
atomic  constitution  of  minerals,  an  inquiry  in  which  Berzelius  has  high- 
ly distinguished  himself.  The  composition  of  minerals  must  of  course 
be  influenced  by  the  usual  laws  of  combination,  though  there  are 
sometimes  obstacles  in  the  way  of  discovering  it.  In  the  compounds 
made  artificially,  chemists  possess  the  power  of  having  each  constituent 
perfectly  pure;  but,  unfortunately,  w'e  cannot  always  command  the 
same  condition  with  respect  to  natural  productions,  'fhe  materials  of 
wdiich  a mineral  is  composed,  once  formed  part  of  some  heterogeneous 
fluid  or  semifluid  mass;  and  in  assuming  ^the  solid  form  they  are  very 
likely  to  have  enclosed  within  them  some  substance  which  is  not,  che- 
mically considered,  an  essential  ingredient  of  the  mineral.  The  result 
of  chemical  analysis,  accordingly,  does  not  always  give  us  a view  of 
the  actual  constitution  of  a mineral  species;  some  substances  are  often 
detected  which  are  foreign  to  it,  and  the  chemist  must  exercise  his 
judgment  in  determining  what  is  and  what  is  not  essential.  Now  no- 
thing is  so  well  calculated  to  direct  him  as  a knowledge  of  tlie  laws  of 
combination;  but  as  a great  discretionary  power  is  in  his  hands,  it  is 
important  that  his  mode  of  investigation  should  be  the  simplest  possi- 
ble, and-that  his  rules  should  be  founded  on  well-established  principles, 
Wiiicli  involve  nothing  hypothetical.  It  is  but  very  lately  that  due  care 


140 


OXYGEN. 


has  been  bestowed  in  selecting*  sufficiently  pure  specimens  for  examina- 
tion, or  in  perfoiTning'the  analyses  themselves  with  the  precision  neces- 
sary for  determining*  the  chemical  constitution  of  minerals.  It  were 
much  to  be  wished,  that  the  first  essays  in  this  difficult  field  should  be 
confined  as  much  as  possible  to  such  minerals  as  contain  but  few  sub- 
stances, and  which  occur  in  distinct  transparent  crystals. 

We  are  indebted  to  Berzelius  for  this  mode  of  studying*  the  compo- 
sition of  minerals;  and  certainly  if  skill  in  analytical  investigation  could 
encourage  any  one  to  make  the  attempt,  none  could  undertake  it  with 
greater  chance  of  success  than  the  indefatigable  Professor  of  Stock- 
holm. In  the  analytic  part  of  the  inquiiy,  the  province  in  which  thi.s 
celebrated  chemist  shines  pre-eminent,  his  labours  have  been  greatly 
conducive  to  the  interests  of  science;  but  it  is  to  be  regretted  that  his 
facts,  themselves  simple  and  unchangeable,  are  too  often  complicated 
by  calculations  founded  on  theoretical  views  which  are  liable  to  change. 
These  views  it  is  foreign  to  the  purpose  of  this  work  to  develop;  but 
the  reader  will  find  an  able  account  of  them,  and  of  the  symbols  which 
Berzelius  has  devised  for  expressing  the  atomic  constitution  of  mi- 
nerals, in  the  ninth  volume  of  the  Annals  of  Philosophy,  N.  S.,  by  Mi*. 
Children. 


SECTION  III. 


OXYGEN. 

Oxygen  gas  was  discovered  by  Priestley  in  1774,  and  by  Scheele  a 
year  or  two  after,  without  previous  knowledge  of  Priestley's  discoveiy. 
Several  appellations  have  been  given  to  it.  Priestley  named  it  depldo^ 
gisticated  air;  it  was  called  empyreal  air  by  Scheele,  and  vital  air  by 
Condorcet.  The  name  it  now  bears,  derived  from  the  Greek  words 
0^0 <;  acid  2iT\di  y swot M \ generate,  was  proposed  by  Lavoisier,  from  the 
supposition  that  it  is  the  sole  cause  of  acidity. 

Oxygen  gas  may  be  obtained  from  several  sources.  The  peroxide  of 
manganese,  lead,  and  mercury,  nitre,  and  chlorate  of  potassa,  yield  it 
in  large  quantity  when  they  are  exposed  to  a red  heat.  The  substances 
commonly  employed  for  the  purpose  are  peroxide  of  mangane.se  and 
Chlorate  of  potassa.  It  may  be  procured  from  the  former  in  two  ways; 
either  by  heating  it  to  redness  in  a gun-barrel,  or  in  a retort  of  iron  or 
earthen-ware;  or  by  putting  it,  in  the  state  of  fine  powder,  into  a flask 
with  about  an  equal  weight  of  concentrated  sulphuric  acid,  and  heating 
the  mixture  by  means  of  a lamp.  I'o  understand  the  theory  of  these 
])roce.sses,  it  is  neces.sary  to  bear  in  mind  the  composition  of  the  three 
following  oxides  of  manganese: 

Manganese.  Oxygen. 

Protoxide  - 28,  or  one  prop,  -f.  8 = 36 

Deutoxide  - 28  - + = 40 

Peroxide  - 28  - -j-  16  = 44 

On  applying  a red  heat  to  the  last,  it  ]^arts  with  half  a proportional 
of  oxygen,  and  is  converted  into  the  deutoxide.  Every  44  grains  of 
the  peroxide  will,  therefore,  lose,  if  quite  pure,  4 grains  of  ox}gen, 
or  nearly  12  cubic  inches;  and  one  ounce  will  yield  about  128  cubic 
inches  of  gas.  The  action  of  sulphuric  acid  is  different.  The  peroxide 


OXYGEN. 


141 


loses  a whole  proportional  of  oxygen,  and  is  converted  into  the  pro- 
toxide, which  unites  with  the  acid,  forming  a sulphate  of  the  protoxide 
of  manganese.  Every  44  grains  of  peroxide  must  consequently  yield  8 
grains  of  oxygen  and  36  of  protoxide,  which  by  uniting  with  one  pro- 
portional (40)  of  the  acid,  forms  76  of  the  sulphate.  The  first  of  these 
processes  is'the  most  convenient  in  practice. 

The  gas  obtained  from  peroxide  of  manganese,  though  hardly  ever 
quite  pure,  owing  to  the  presence  of  iron,  carbonate  of  lime,  and  other 
earthy  substances,  is  sufficiently  good  for  ordinary  purposes.  It  yields 
a gas  of  better  quality,  if  previously  freed  from  carbonate  of  lime  by 
dilute  muriatic  or  nitric  acid;  but  when  oxygen  of  great  purity  is  re- 
quired, it  is  better  to  obtain  it  from  chlorate  of  potassa.  For  this  pur- 
pose, the  salt  should  be  put  into  a retort  of  green  glass,  or  of  white 
glass  made  without  lead,  and  be  heated  nearly  to  redness.  It  first  be- 
comes liquid,  though  quite  free  from  water,  and  then,  on  increase  of 
heat,  is  wholly  resolved  into  pure  oxygen  gas,  which  escapes  with  ef- 
fervescence, and  into  a white  compound,  called  chloride  of  potassium, 
which  is  left  in  the  retort.  The  theory  of  the  decomposition  is  as  fol- 
lows. Chlorate  of  potassa  is  composed  of 

Chloric  acid  76,  or  one  proportional. 

Potassa  48,  or  one  proportional. 

124 

These  compounds  are  thus  constituted: — 

Chlorine  - 36,  or  one  prop.  Potassium  40,  or  one  prop. 

Oxygen  - 40,  or  five  prop.  Oxygen  8,  or  one  prop. 

Chloric  acid  76,  or  one  prop.  Potassa  48,  or  one  prop. 

The  chlorine  and  potassium  are  both  separated  from  oxygen,  and  then 
unite  together.  So  that  124  gi'ains  of  the  salt  are  resolved  into  76  grains 
of  chloride  of  potassium,  and  48  grains,  or  141  cubic  inches,  of  pure 
oxygen. 

Oxygen  gas  is  colourless,  has  neither  taste  nor  smell,  is  not  chemical- 
ly affected  by  the  imponderables,  refracts  light  very  feebly,  and  is  a 
non-conductor  of  electricity.  It  is  the  most  perfect  negative  electric 
that  we  possess,  always  appearing  at  the  positive  pole  when  any  com- 
pound which  contains  it  is  exposed  to  the  action  of  galvanism.  It  emits 
light,  as  well  as  heat,  when  suddenly  and  forcibly  compressed.  When 
not  united  with, other  ponderable  matter,  it  is  always  in  the  form  of 
gas;  but  even  in  tliis  its  purest  state  it  is  probably  combined,  as  is 
most  likely  true  of  all  the  elementary  principles,  with  heat,  light,  and 
electricity. 

Oxygen  gas  is  heavier  than  atmospheric  air.  Chemists  differ  as  to  its 
precise  weight;  but  according  to  the  experiments  of  Dr.  Thomson, 
whose  estimate  is  generally  adopted  in  Britain,  100  cubic  inches  of  oxy- 
gen, when  the  thermometer  is  at  60®  F,  and  the  barometer  stands  at 
30  inches,  weig'h  33.888  grains.  Its  specific  gravity  is  hence  regarded 
as  1.1111. 

Oxygen  gas  is  very  sparingly  absorbed  by  water,  100  cubic  inches  of 
that  liquid  dissolving  only  3 or  4 of  the  gas.  It  has  neither  acid  nor  al- 
kaline properties;  for  it  does  not  change  the  colour  of  blue  flowers,  nor 
does  it  evince  a disposition  to  unite  directly  either  with  acids  or  alkalies. 
U has  a very  powerful  attraction  for  most  simple  substances;  and  there 
is  not  one  of  them  with  which  it  may  not  he  made  to  combine.  The  act 
of  combining  with  oxygen  is  called  oxidatiorii  and  bodies  which  have 


142 


OXYGEN. 


united  with  it  are  said  to  be  oxidized.  The  compounds  so  formed  arc 
divided  by  chemists  into  acids  and  oxides.  The  former  division  includes 
those  compounds  which  possess  the  general  properties  of  acids;  and  the 
latter  comprehends  those  which  not  only  want  that  cliaractcr,  but  of 
which  many  are  highly  alkaline,  and  yield  salts  by  uniting  with  acids. 
The  phenomena  of  oxidation  are  variable.  It  is  sometimes  produced 
with  great  rapidity,  and  with  evolution  of  heat  and  light.  Ordinary 
combustion,  for  instance,  is  nothing  more  than  rapid  oxidation;  and  all 
inflammable  or  combustible  substances  derive  their  power  of  burning  in 
the  open  air  from  their  affinity  for  oxygen.  On  other  occasions  it  takes 
place  slowly,  and  without  any  appearance  either  of  heat  or  light,  as  is 
exemplified  by  the  rusting  of  iron  when  exposed  to  a moist  atmosphere. 
Different  as  these  processes  may  appear,  oxidation  is  the  result  of  both; 
and  both  depend  on  the  same  circumstance,  namely,  the  presence  of 
oxyg'en  in  the  atmosphere. 

All  substances  that  are  capable  of  burning  in  the  open  air,  burn  with 
far  greater  brilliancy  in  oxygen  gas.  A piece  of  wood,  on  which  the 
least  spark  of  light  is  visible,  bursts  into  flame  the  moment  it  is  put  into  a 
jar  of  oxygen;  lighted  charcoal  emits  beautiful  scintillations;  and  phos- 
phorus burns  with  so  powerful  and  dazzling  a light  that  the  eye  can- 
not bear  its  impression.  Even  iron  and  steel,  which  are  not  com- 
monly ranked  among  the  inflammables,  undergo  rapid  combustion  in 
oxygen  gas. 

The  changes  tliat  accompany  these  phenomena  are  no  less  remarkable 
than  the  phenomena  themselves.  W hen  a lighted  taper  is  put  into  a 
vessel  of  oxygen  gas,  it  burns  for  a while  with  increased  splendour; 
but  the  size  of  the  flame  soon  begins  to  diminish,  and  if  the  mouth  of 
the  jar  be  properly  secured  by  a cork,  the  light  will  in  a short  time  dis- 
appear entirely.  The  gas  has  now  lost  its  characteristic  property;  for  a 
second  lighted  taper,  immersed  in  it,  is  instantly  extinguished.  This 
result  is  general.  The  burning  of  one  body  in  a given  portion  of  oxy- 
gen unfits  it  more  or  less  completely  for  supporting  the  combustion  of 
another;  and  the  reason  is  manifest.  Combustion  is  produced  by  the 
combination  of  inflammable  matter  with  oxygen  gas.  The  quantity  of^ 
free  oxygen,  therefore,  diminishes  during  the  process,  and  is  at  lengthm 
nearly  or  quite  exhausted.  The  burning  of  all  bodies,  however  inflam-^ 
mable,  must  then  cease,  because  the  presence  of  oxygen  is  necessary 
to  its  continuance.  For  this  reason  oxygen  gas  is  called  a supporter  of 
combustion.  The  oxygen  often  loses  its  gaseous  form  as  well  as  its  other 
properties.  If  phosphorus  or  iron  be  burned  in  a jar  of  pure  oxygen 
over  water  or  mercury,  the  disappearance  of  ihQ  g^s^^becomes  obvious 
by  the  ascent  of  the  liquid,  which  is  forced  up  by  the"  pi-essure  of  the 
atmosphere,  and  fills  the  vessel.  Sometimes,  on  the  contrary,  the  oxy-  , 
gen  suffers  only  diminution  of  volume,  or  it  may  even  undergo  no 
change  of  bulk  at  all,  as  is  exemplified  by  the  combustion  of  the  dia- 
mond. 7 

'rhe  changes  experienced  by  the  burning  body  "are  equally  striking.  ! 
Mfliile  tlie  oxygen  loses  its  power  of  supporting  combustion,  the  inflam- 
mable substance  lays  aside  its  combustibility.  It  is  then  an  oxidized 
body,  and  cannot  be  made  to  burn  even  by  aid  of  the  purest  oxygen. 

It  has  also  increased  in  weight.  It  is  an  error  to  suppose  that  bodies 
lose  any  thing  while  they  burn.  The  materials  of  our  fires  and  candles 
do  indeed  disappear,  but  they  are  not  destroyed.  Although  they  fly  off 
in  the  gaseous  form,  and  are  commonly  lost  to  us,  it  is  not  difficult  to 
collect  and  preserve  all  the  products  of  combustion.  When  this  is 
done  with  recpiisite  care,  it  is  constantly  found  that  the  combustible  mat- 
ter weighs  more  after  than  before  combustion;  and  that  the  increase  in 


OXYGEN. 


143 


'Weight  is  exactly  equal  to  the  quantity  of  oxygen  which  has  disappeared 
during  the  process. 

Oxygen  gas  is  necessary  to  respiration.  No  animal  can  live  in  an  at- 
mosphere which  does  not  contain  a certain  portion  of  uncombined  oxy- 
gen; for  an  animal  soon  dies  if  put  into  a portion  of  air  from  which  the 
oxygen  has  been  previously  removed  by  a burning  body.  It  may, 
therefore,  be  anticipated  that  oxygen  is  consumed  during  respira- 
tion. If  a bird  be  confined  in  a limited  quantity  of  atmospheric  air,  it 
will  at  first  feel  no  inconvenience;  but  as  a portion  of  oxygen  is  with- 
drawn at  each  inspiration,  its  quantity  diminishes  rapidly,  so  that  respi- 
ration soon  becomes  laborious,  and  in  a short  time  ceases  altogether. 
Should  another  bird  be  then  introduced  into  the  same  air,  it  will  die  in 
the  course  of  a few  seconds;  or  if  a lighted  candle  be  immersed  in  it, 
its  flame  will  be  extinguished.  Respiration  and  combustion  have,  there- 
fore, the  same  eflect.  An  animal  cannot  live  in  an  atmosphere  which 
is  unable  to  support  combustion,  nor,  in  general,  can  a candle  burn  in 
air  which  contains  too  little  oxygen  for  respiration. 

It  is  singular  that,  though  oxygen  is  necessary  to  respiration,  in  a 
state  of  purity  it  is  deleterious.  When  an  animal,  as  a rabbit  for  exam- 
ple, is  supplied  with  an  atmosphere  of  pure  oxygen  gas,  no  inconveni- 
j.ence  is  at  first  perceived;  but  after  the  interval  of  an  hour  or  more  the 
circulation  and  respiration  become  very  rapid,  and  the  system  in  gene- 
ral is  highly  excited.  Symptoms  of  debility  subsequently  ensue,  which 
continue  to  increase  till  death  supervenes. 

On  the  Theory  of  Combustion* 

The  only  phenomena  of  combustion  noticed  by  an  ordinary  observer, 
are  the  destruction  of  the  burning  body,  and  the  development  of  heat 
and  light;  but  it  has  been  demonstrated  that,  in  addition  to  these  cir- 
cumstances, oxygen  gas  invariably  disappears,  and  a new  compound 
consisting  of  oxygen  and  the  combustible  is  generated.  The  term 
combustion,  therefore,  in  its  common  signification,  implies  the  rapid 
union  of  oxygen  gas  and  combustible  matter,  accompanied  with  heat 
and  light.  As  the  evolution  of  heat  and  light  is  dependent  on  chemi- 
^cal  action,  the  same  phenomena  may  be  expected  in  other  chemical 
'processes;  and  accordingly  heat  and  light  are  frequently  emitted  quite 
independently  of  oxygen.  Thus  phosphorus  takes  fire,  and  a taper 
burns  for  a short  time,  in  a vessel  of  chlorine;  and  several  of  the  com- 
mon metals,  such  as  copper,  antimony,  and  arsenic,  in  a state  of  fine 
division,  become  red-hot  when  introduced  into  ajar  of  that  gas.  Pot- 
assium takes  fire  in  cyanogen  gas,  and  copper  leaf  or  iron  wire,  if  mo- 
derately heated,  undergoes  the  same  change  in  the  vapour  of  sulphur, 
A mixture  of  iron  filings  and  sulphur,  when  heated  so  as  t <3)bring  the 
latter  into  perfect  fusion,  emits  intense  heat  and  light  at  the  instant  of 
combination;  and  a like  effect,  though  in  a far  less  degree,  is  produced 
by  the  action  of  concentrated  sulphuric  acid  on  pure  magnesia.  Most 
of  these  and  similar  examples,  especially  when  one  of  the  combining 
substances  is  gaseous,  are  frequently  included  under  the  idea  of  com- 
' bustion;  and  they  certainly  belong  to  the  same  class  of  phenomena.  In 
the  subsequent  observations,  however,  I shall  employ  the  term  in  its 
ordinary  sense;  but  the  remarks  concerning  increase  of  temperature, 
whether  with  or  witliout  light,  apply  equally  to  all  cases  where  heat  is 
developed  as  a result  of  chemical  action. 

For  many  years  prior  to  the  discovery  of  oxygen  gas,  the  pheno- 
mena-of  combustion  were  explained  on  the  Stahlian  or  phlogistic  hypo- 
thesis. All  combustible  bodies,  according  to  Stahl,  contain  a certain 
principle  wliich  he  called  phlogislon,  to  the  presence  of  which  he  as- 


144 


OXYGEN. 


cribed  their  combustibility.  He  supposed  that  when  a body  burns, 
phlogiston  escapes  from  it;  and  that  when  the  body  lias  lost  plilogiston, 
it  ceases  lobe  combustible,  and  is  then  a dephlogisticatcd  or  incombus- 
tible substance.  A metallic  oxide  was  consequently  regarded  as  a sim- 
ple substance,  and  the  metal  itself  was  a compound  of  its  oxide  with 
phlogiston.  The  heat  and  light  which  accompany  combustion  were  at- 
tributed to  the  rapidity  w'itli  which  phlogiston  is  evolved  during  the 
process. 

The  discovery  of  oxygen  proved  fatal  to  the  Stahlian  doctrine.  I^a- 
voisier  had  the  honour  of  overthrowing  it,  and  of  substituting  in  its  place 
the  antiphlogistic  theoiy.  The  basis  of  his  doctrine  has  already  been 
stated; — that  combustion  and  oxidation  in  general  consist  in  the  conibi- 
nation  of  combustible  matter  with  oxygen.  I'his  fact  he  established  be- 
yond a doubt.  On  burning  phosphorus  in  a jar  of  oxygen,  he  observed 
that  a considerable  quantity  of  the  gas  disappeared,  that  the  phosphorus 
gained  materially  in  weight,  and  that  the  increase  of  the  latter  exactly 
coiTesponded  to  the  loss  of  the  former.  An  iron  wire  was  burnt  in  a si- 
milar manner,  and  the  weight  of  the  oxidized  iron  was  found  equal  to 
that  of  the  wire  originally  employed,  added  to  the  quantity  of  oxygen 
which  had  disappeared.  That  the  oxygen  is  really  present  in  the  oxi- 
dized body  he  proved  by  a very  decisive  experiment.  Some  liquid  mer- 
cury was  confined  in  a vessel  of  oxygen  gas,  and  exposed  to  a tempem- 
ture  sufficient  for  causing  its  oxidation.  The  oxide  of  mercury,  so  pro- 
duced, was  put  into  a small  retort  and  heated  to  redness,  when  it  was  re- 
converted into  oxygen  and  fluid  mercury,  the  quantity  of  the  oxygen 
being  exactly  equal  to  that  which  had  combined  with  the  mercury  in  the 
first  part  of  the  operation. 

To  account  for  the  production  of  heat  and  light  during  combustion, 
Lavoisier  had  recourse  to  Dr.  Black’s  theory  of  latent  caloric.  Heat  is 
always  evolved,  whenever  a substance,  without  change  of  form,  passes 
from  a rarer  into  a denser  state,  and  also  when  a gas  becomes  liquid  or 
solid,  or  a liquid  solidifies;  because  a quantity  of  caloric  previously  com- 
bined, or  latent  within  it,  is  then  set  free.  Now  this  is  precisely . what 
happens  in  many  instances  of  combustion.  Thus  water  is  formed  by  the 
burning  of  hydrogen,  in  which  case  two  gases  give  rise  to  a liquid;  and  in 
forming  phosphoric  acid  with  phosphorus,  or  in  oxidizing  metals,  oxygen 
is  condensed  into  a solid.  When  the  product  of  combustion  is  gaseous, 
as  in  the  burning  of  charcoal,  the  evolution  of  heat  is  ascribed  to  the  cir- 
cumstance that  the  oxidized  body  contains  a less  quantity  of  combined 
caloric,  or  has  a less  specific  caloric,  than  the  substances  by  which  it  is 
produced. 

This  is  the  weak  point  of  Lavoisier’s  theory.  Chemical  action  is  very 
often  accompanied  by  increase  of  temperature,  and  the  caloric  evolved 
during  combustion  is  only  apai-ticular  instance  of  it.  Any  theory,  there- 
fore, by  which  it  is  proposed  to  account  for  the  production  of  heat  in 
flome  cases,  ought  to  be  applicable  to  all.  When  combustion,  or  any  other 
chemical  action  is  followed  by  considerable  condensation,  in  consequence 
of  which  the  new  body  contains  less  insensible  caloric  than  its  elements 
did  before  combination,  it  is  obvious  that  heat  will,  in  that  case,  be  dis- 
engaged. But  if  this  is  the  sole  cause  of  the  phenomenon,  it  follow’s  that 
a rise  of  temperature  ought  always  to  be  preceded  by  a corresponding 
diminution  of  ca])acity  for  caloric,  and  tliat  the  extent  of  the  former 
ought  to  be  in  a constant  ratio  witli  the  degree  of  the  latter.  Now  Petit 
and  Dulong  infer  from  their  researches  on  this  subject,  ( Annales  de  Chim. 
ct  dc  Phys.  vol.  x.)  tliat  the  degree  of  heat  developed  during  combina- 
tion, bears  no  relation  to  the  specific  caloric  of  the  combining  substances; 
and  tliat  in  the  majority  of  cases,  the  evolution  of  heat  is  not  attended  by 


OXYGEN. 


145 


any  diminution  in  the  capacity  of  the  compound.  It  is  a well  known  fact, 
that  increase  of  temperature  frequently  attends  chemical  action,  though 
the  products  contain  much  more  insensible  caloric  than  the  substances 
from  which  they  are  formed.  This  happens  remarkably  in  the  explo- 
sion of  gunpowder,  which  is  attended  by  intense  heat;  and  yet  its  mate 
rials,  in  passing  from  the  solid  to  the  gaseous  state,  expand  to  at  least 
250  times  their  volume,  and  consequently  render  latent  a large  quantity 
of  caloric. 

These  circumstances  leave  no  doubt  that  the  evolution  of  caloric  during 
chemical  action  is  owing  to  some  cause  quite  unconnected  with  that  as- 
signed by  Lavoisier;  and  if  this  cause  operates  so  powerfully  in  some 
cases,  it  is  fair  to  infer  that  part  of  the  effect  must  be  owing  to  it  on  those 
occasions,  when  the  phenomena  appear  to  depend  on  change  of  capacity 
alone.  A new  theory  is,  therefore,  required  to  account  for  the  chemical 
production  of  heat.  But  it  is  easier  to  perceive  the  fallacies  of  one  doc- 
trine, than  to  substitute  another  which  shall  be  faultless;  and  it  appears 
to  me  that  chemists  must,  for  the  present,  be  satisfied  with  the  simple 
statement,  that  energetic  chemical  action  does  of  itself  give  rise  to  in- 
crease of  temperature.  Berzelius,  in  adopting  the  electro-chemical  the- 
ory, regards  ^he  heat  of  combination  as  an  electrical  phenomenon;  and 
he  believes  it  to  arise  from  the  oppositely  electrical  substances  neutral- 
izing one  another,  in  the  same  manner  as  the  electric  equilibrium  is  re- 
stored during  the  discharge  of  a Leyden  phial.  But  such  an  opinion  can 
only  be  held  by  those  who  adopt  the  electro-chemical  theory;  and  even 
admitting  the  accuracy  of  this  doctrine,  the  reasoning  founded  on  it  by 
Berzelius  appears  to  me  inadmissible.  For,  according  to  the  theory,  the 
two  elements  of  a compound  retain  their  peculiar  state  of  excitement. 
This  condition  is  essential  to  the  continuance  of  the  union;  and  there- 
fore the  act  of  combination  is  not  analogous  to  the  discharge  of  a-^ey- 
den  phial.  The  equilibrium  is  restored  in  one  case,  but  not  in  the  other. 

The  caloric  emitted  during  combustion  varies  with  the  nature  of  the 
material.  The  effect  of  the  combustible  gases  in  raising  the  temperature 
of  water,  according  to  the  experiments  of  Mr.  Dalton,  is  shown  in  the 
following  table. — (Chemical  Philosophy,  ii.  309.) 

Hydrogen,  in  burning,  raises  an  equal  volume  of  water  5^  F. 

Carbonic  oxide 

Light  carburetted  hydrogen  - - - - - 18 

Olefiant  gas  - - - - - . -27 

Coal  gas  varies  with  the  quality  of  the  gas  from  10  to  16 

Oil  gas  varies  also  with  the  quality  of  the  gas  from  12  to  20 

Mr.  Dalton  further  states  that  generally  the  combustible  gases  give 
out  heat  nearly  in  proportion  to  the  oxygen  which  they  consume. 

In  the  thirty-seventh  volume  of  the  An.  de  Ch.  et  de  Ph.  page  180, 
M.  Despretz  has  given  a notice  of  some  experiments  on  the  heat  devel- 
oped in  combustion.  The  substances  burned  were  hydrogen,  carbon, 
phosphorus,  and  several  metals;  and  so  much  of  each  was  employed,  as 
to  require  the  same  quantity  of  oxygen.  When  the  combustion  of  hydro- 
gen gas  produced  2578  degrees  of  heat,  carbon  gave  out  2967,  andiron 
5325.  Phosphorus,  zinc,  and  tin,  emit  quantities  of  caloric  very  nearly 
the  same  as  iron.  Hence  it  follows  that,  for  equal  quantities  of  oxygen, 
hydrogen  in  burning  evolves  less  heat  than  most  other  substances.  Thes« 
results  do  not  accord  with  those  of  Mr.  Dalton. 


13 


146 


HYDROGEN. 


SECTION  IV. 

HYDROGEN. 

This  g*as  was  formerly  ter mecU*??y7ammo&/(e  air  from  its  combustibility, 
and  phlogiston  from  the  supposition  that  it  was  the  matter  of  heat;  but 
the  name  hydrogen^  derived  from  watery  has  now  become  general. 
Its  nature  and  leading  properties  were  first  pointed  out  in  the  year  1766 
by  Mr.  Cavendish.  (Philos.  I’rans.  Ivi.  144.) 

Hydrogen  gas  may  be  easily  procured  in  two  ways.  The  first  consists 
in  passing  the  vapour  of  water  over  metallic  iron  heated  to  redness. 
This  is  done  by  putting  iron  wire  into  a gun-barrel  open  at  both  ends,  to 
one  of  which  is  attached  a retort  containing  pure  water,  and  to  the  other 
a bent  tube.  The  gun-barrel  is  placed  in  a furnace,  and  when  it  has  ac- 
quired a full  red  heat,  the  water  in  the  retort  is  made  to  boil  briskly. 
The  gas,  which  is  copiously  disengaged  as  soon  as  the  steam  comes  in 
contact  with  the  glowing  iron,  passes  along  the  bent  tube,  and  may  be 
collected  in  convenient  vessels,  by  dipping  the  free  extremity  of  the  tube 
into  the  water  of  a pneumatic  trough.  The  second  and  most  convenient 
method  consists  in  putting  pieces  of  iron  or  zinc  into  dilute  sulphuric 
acid,  formed  of  one  part  of  strong  acid  and  four  or  five  of  water.  Zinc  is 
genei’ully  preferred.  The  hydrogen  obtained  in  these  processes  is  not 
absolutely  pure.  The  gas  evolved  during  the  solution  of  iron  has  an  of- 
fensi^  odour,  ascribed  by  Berzelius  to  the  presence  of  a volatile  oil, 
whioji  may  be  almost  entirely  removed  by  transmitting  the  gas  through 
alcohol.  The  oil  appears  to  arise  from  some  compound  being  formed  be- 
tween hydrogen  and  the  carbon  which  is  always  contained  even  in  the 
purest  kinds  of  common  iron;  and  it  is  probable  that  a little  carburetted 
hydrogen  gas  is  generated  at  the  same  time.  The  zinc  of  commerce  con- 
tains sulphur,  and  almost  always  traces  of  charcoal,  in  consequence  of 
which  it  is  contaminated  with  sulphuretted  hydrogen,  and  probably  with 
the  same  impurities,  though  in  a less  degree,  wliich  are  derived  from  iron. 
A little  metallic  zinc  is  also  contained  in  it,  apparently  in  combination 
with  hydrogen.  All  these  impurities,  carburetted  hydrogen  excepted, 
may  be  removed  by  passing  the  hydrogen  through  a solution  of  pure  po- 
tassa.  To  obtain  hydrogen  of  great  purity,  distilled  zinc  should  be  em- 
ployed. 

Hydrogen  is  a colourless  gas,  and  has  neither  odour  nor  taste  when 
perfectly  pure.  It  is  a powerful  refractor  of  light.  Like  oxygen,  it 
cannot  be  resolved  into  more  simple  parts,  and,  like  that  gas,  has  hither- 
to resisted  all  attempts  to  compress  it  into  a liquid.  It  is  the  lightest 
body  in  nature,  and  is  consequently  the  best  material  for  filling  balloons. 
From  its  extreme  lightness  it  is  difficult  to  ascertain  its  precise  density 
by  weigliing,  because  the  presence  of  minute  quantities  of  common  air 
or  watery  vapour  occasions  considerable  error.  From  the  composition 
of  water,  liydrogen  gas  is  inferred  to  be  sixteen  times  as  light  as  oxygen^ 
and  the  weight  of  100  cubic  indies  at  60®,  and  30  inches  of  the  barome- 
ter, sliould  therefore  be  33.888—16,  or  2.118  grains.  Its  specific  gravi- 
ty is  consequently  0.0694,  as  stated  some  years  ago  by  Dr.  Front. 

Hydrogen  does  not  change  tlie  blue  colour  of  vegetables.  It  is  spar- 
ingly ai)sorl>cd  by  water,  100  cubic  indies  of  that  liquid  dissolving  about 
one  and  a lialf  of  the  gas.  It  cannot  support  respiration;  for  an  animal 
soon  perishes  when  confined  in  it.  Death  ensues  from  deprivation  of 


HYDROGEN. 


147 


oxygen  rather  than  from  any  noxious  quality  of  the  hydrogen;  since  an 
atmosphere  composed  of  a due  proportion  of  oxygen  and  hydrogen  gases 
may  be  respired  without  inconvenience.  Nor  is  it  a supporter  of  com- 
bustion; for  when  alighted  candle  fixed  on  wire  is  passed  up  into  an  in- 
verted jar  full  of  hydrogen,  the  light  disappears  on  the  instant. 

Hydrogen  gas  is  inflammable  in  an  eminent  degree,  though,  like  other 
combustibles,  it  requires  the  aid  of  a supporter  for  enabling  its  combus- 
tion to  take  place.  This  is  exemplified  by  the  experiment  above  alluded 
to,  in  which  the  gas  is  kindled  by  the  flame  of  the  candle,  but  burns 
only  where  it  is  in  contact  with  the  air.  Its  combustion,  when  conduct- 
ed in  this  manner,  goes  on  tranquilly,  and  is  attended  with  a yellowish 
blue  flame  and  very  feeble  light.  The  phenomena  are  different  when 
the  hydrogen  is  previously  mixed  with  a due  quantity  of  atmospheric  air. 
The  approach  of  flame  not  only  sets  fire  to  the  gas  near  it,  but  the  whole 
is  kindled  at  the  same  instant;  and  a flash  of  light  passes  through  the 
mixture,  followed  by  a violent  explosion.  The  best  proportion  for  tlie 
experiment  is  two  measures  of  hydrogen  to  five  or  six  of  air.  The  ex- 
plosion is  far  more  violent  when  pure  oxygen  is  used  instead  of  atmos- 
pheric air,  particularly  when  the  gases  are  mixed  together  in  the  ratio 
of  oiie  measure  of  oxygen  to  two  of  hydrogen. 

Oxygen  and  hydrogen  gases  cannot  combine  at  ordinary  temperatures, 
and  may,  therefore,  be  kept  in  a state  of  mixture  without  even  gradual 
combination  taking  place  between  them.  Hydrogen  may  beset  on  fire, 
when  in  contact  with  air  or  oxygen  gas,  by  flame,  by  a solid  body  heat- 
ed to  bright  redness,  and  by  the  electric  spark.  If  a jet  of  hydrogen  be 
thrown  upon  recently  prepared  spongy  platinum,  this  metal  almost  in- 
stantly becomes  red-hot,  and  then  sets  fire  to  the  gas,  a discovery  which 
was  made  in  the  year  1824  by  Professor  Doebereiner  of  Jena.  The 
power  of  flame  and  electricity  in  causing  a mixture  of  hydrogen  with  air 
or  oxygen  gas  to  explode,  is  limited.  Mr.  Cavendish  found  that  flame 
occasions  a very  feeble  explosion  when  the  hydrogen  is  mixed  with 
nine  times  its  bulk  of  air;  and  that  a mixture  of  four  measures  of  hydro- 
gen w'ith  one  of  air  does  not  explode  at  all.  An  explosive  mixture  lorm- 
ed  of  two  measures  of  hydrogen  and  one  of  oxygen,  explodes  from  all 
the  causes  above  enumerated.  M.  Biot  found  that  sudden  and  violent 
compression  likewise  causes  an  explosion,  apparently  from  the  heat 
emitted  during  the  operation  ; for  an  equal  degree  of  condensation, 
slowly  produced,  has  not  the  same  effect.  The  electric  spark  ceases  to 
cause  detonation  when  the  explosive  mixture  is  diluted  with  twelve 
flrnes  its  volume  of  air,  fourteen  of  oxygen,  online  of  hydrogen;  or  when 
it  is  expanded  to  sixteen  times  its  bidk  by  diminished  pressure.  I find 
tliat  spongy  platinum  acts  just  as  rapidly  as  flame  or  the  electric  spark  in 
producing  exf)losion,  provided  the  gases  are  quite  pure  and  mixed  in  the 
exact  ratio  of  two  to  one..  * 

When  the  action  of  heat,  the  electric  spark,  and  spongy  platinum  no 
longer  cause  explosion,  a silent  and  gradual  combination  between  the 
gases  may  still  be  occasioned  by  them.  Sir  H.  Davy  observed  that  oxy- 
gen and  hydrogen  gases  unite  slowly  with  one  another,  when  they  are 
exposed  to  a temperature  above  the  boiling  point  of  mercury,  and  below 


* For  a variety  of  facts  respecting  the  causes  which  prevent  the  ac- 
tion of  flame,  electricity,  and  platinum  in  producing  detonation,  the 
reader  may  consult  the  essay  of  M.  Grotthus  in  the  Ann.  de  Chiiuic,  vol. 
Ixxxii. ; Sir  H.  Davy’s  work  on  Flame;  Dr.  Henry’s  Essay  in  the  Philo- 
sophical Transactions  for  1824;  and  a paper  by  myself  in  the  Edinburgii 
philosophical  Journal  for  the  same  year. 


148 


HYDROGEN. 


that  at  which  glass  begins  to  appear  luminous  in  the  dark.  An  explo- 
sive mixture  diluted  witli  air  to  too  great  a degree  to  explode  by  electri- 
city, is  made  to  unite  silently  by  a succession  of  electric  sparks.  Spongy 
platinum  causes  them  to  unite  slowly,  though  mixed  with  one  hundred 
times  their  bulk  of  oxygen  gas. 

A large  quantity  of  ealoric  is  evolved  during  the  combustion  of  hydro- 
gen gas.  Lavoisier  concludes  from  experiments  made  with  his  calori- 
meter (Elements,  vol.  i.),  that  one  pound  of  hydrogen  occasions  as  much 
heat  in  burning  as  is  sufficient  to  melt  295.6  pounds  of  ice.  Mr.  Dalton 
fixes  the  quantity  of  iee  at  320  pounds,  and  Dr.  Crawford  at  480.  The 
most  intense  heat  that  can  be  produced,  is  eaused  by  the  combustion  of 
hydrogen  in  oxygen  gas.  Dr.  Hare  of  Philadelphia,  who  first  burned 
hydrogen  for  this  purpose,  colleeted  the  gases  in  separate  gas-holders, 
fix)m  which  a stream  was  made  to  issue  through  tubes  communicating 
with  each  other,  just  before  their  termination.  At  this  point  the  jet  of 
the  mixed  gases  was  inflamed.  T he  effect  of  the  combustion,  though 
very  great,  is  materially  increased  by  forcing  the  two  gases  in  due  pro- 
portion into  a strong  metallic  vessel  by  means  of  a condensing  syringe, 
and  setting  fire  to  a jet  of  the  mixture  as  it  issues.  An  apparatus  of  this 
kind,  now  known  by  the  name  of  the  oxy-hydrogen  blowpipe,  was  con- 
trived by  Mr.  Newman,  and  employed  by  the  late  Professor  Clarke  in 
his  experiments  on  the  fusion  of  refractory  substances.  On  opening  a 
stop  cock  which  confines  the  compressed  gases,  a jet  of  the  explosive 
mixture  issues  with  force  through  a small  blowpipe  tube,  at  the  extremi- 
ty of  which  it  is  kindled.  In  this  state,  however,  the  apparatus  should 
never  be  used;  for  as  the  reservoir  is  itself  full  of  an  explosive  mixture, 
there  is  great  danger  of  the  flame  running  back  along  the  tube,  and 
setting  fire  to  the  whole  gas  at  once.  To  prevent  the  occurrence  of 
such  an  accident,  which  would  most  probably  prove  fatal  to  the  operator, 
Professor  Cumming  proposed  that  the  gas,  as  it  issues  from  the  reservoir, 
should  be  made  to  pass  through  a cylinder  full  of  oil  or  water  before 
reaching  the  point  at  which  it  is  to  burn;  and  Dr.  Wollaston  suggested 
the  additional  precaution  of  fixing  successive  layers  of  fine  wire  gauze 
within  the  exit  tube,  each  of  which  would  be  capable  of  intercepting  the 
communication  of  flame.  But  this  apparatus  is  rarely  necessary  in 
chemical  researches.  A very  intense  heat,  quite  sufficient  for  most  pur- 
poses, may  be  safely  and  easily  procured  by  passing  a jet  of  oxygen 
g'as  through  the  flame  of  a spirit  lamp,  as  proposed  by  the  late  Dr. 
Marcet. 

Water  is  the  sole  product  of  the  combustion  of  hydrogen  gas.  For 
this  important  fact  we  are  indebted  to  Mr.  Cavendish.  He  demonstrated 
it  by  burning  oxygen  and  hydrogen  gases  in  a dry  glass  vessel,  when  a 
quantity  of  pure  water  was  generated,  exactly  equal  in  weight  to  that  of 
the  gases  which  had  disappeared.  This  experiment,  which  is  the  syn- 
thetic proof  of  the  composition  of  water,  was  afterwards  made  on  a 
much  larger  scale  in  Paris  by  Vauquelin,  Fourcroy,  and  Seguin.  La- 
voisier first  demonstrated  its  nature  analytically,  by  passing  a known 
(juantity  of  watery  vapour  over  metallic  iron  heated  to  redness  in  a glass 
tube.  Hydrogen  gas  was  disengaged,  the  metal  in  the  tube  was  oxidiz- 
ed, and  the  weight  of  the  foi-iner,  added  to  the  increase  which  the  iron 
had  cx[)ericnc('d  from  comliining  with  oxygen,  exactly  corresponded  to 
the  (juantity  of  water  decomposed. 

It  will  soon  a])j)ear  that  a knowledge  of  the  exact  proportions  in  which 
oxygen  and  Ijydrogen  gases  unite  to  form  water,  is  a necessary  element 
in  many  chemical  reasonings.  Its  composition  by  volume  was  demon- 
strated very  satisfactorily  by  Messrs.  Nicholson  and  Carlisle,  in  their  re- 
searches on  tJic  chemical  agency  of  galvanism.  On  resolving  water  into 


HYDROGEN. 


149 


its  elements  by  this  agent,  and  collecting  them  in  separate  vessels,  they 
obtained  precisely  two  measures  of  hydrogen  and  one  of  oxygen, — a re- 
sult which  has  been  fully  confirmed  by  subsequent  experimenters.  The 
same  fact  was  proved  synthetically  by  Gay-Lussac  and  Humboldt,  in 
their  Essay  on  Eudiometry,  published  in  the  Journal  de  Physique  for 
1805.  They  found  that  when  a mixture  of  oxygen  and  hydrogen  is  in- 
flamed by  the  electric  spark,  those  gases  always  unite  in  the  exact  ratio 
of  one  to  two,  whatever  may  be  their  relative  quantity  in  the  mixture. 
When  one  measure  of  oxygen  is  mixed  with  three  of  hydrogen,  one 
measure  of  hydrogen  remains  after  the  explosion;  and  a mixture  of  two 
measures  of  oxygen  and  two  of  hydrogen  leaves  one  measure  of  oxygen. 
When  one  volume  of  oxygen  is  mixed  with  two  of  hydrogen,  both  gases, 
if  quite  pure,  disappear  entirely  on  the  electric  spark  being  passed 
through  them.  The  composition  of  water  by  weight  was  determined 
with  great  care  by  Berzelius  and  Dulong;  and  we  cannot  hesitate,  consi- 
dering* the  known  dexterity  of  the  operators,  and  the  principle  on  which 
their  method  of  analysis  was  founded,  to  regard  their  result  as  a nearer 
approximation  to  the  truth  than  that  of  any  of  their  predecessors.  They 
state,  as  a mean  of  thr^e  careful  experiments,  (Ann.  de.  Ch.  et  de  Pb. 
vol.  XV.)  that  100  parts  bf  pure  water  consist  of  88.9  of  oxygen  and  11. 1 
of  hydrogen.  Now, 

11.1  : 88.9  : ; 1 : 8.009. 


which  is  so  near  the  proportion  of  1 to  8 as  to  justify  the  adoption  of 
that  ratio.  Hence,  the  constitution  of  water  by  weight  and  measure, 
niay  be  thus  stated: 

By  weight.  By  volume. 

Oxygen  .8.1 

Hydrogen  . 1 , 2 

These  are  the  data  from  which  it  was  inferred  that  oxygen  gas  is  just 
16  times  as  heavy  as  hydrogen.  The  atomic  weights  of  oxygen  and  hy- 
drogen are  deduced  from  the  same  analysis.  As  no  compound  of  these 
substances  is  known  which  has  a less  proportion  of  oxygen  than  water, 
it  is  supposed  to  contain  one  atom  of  each  of  its  constituents.  This 
view  of  the  atomic  constitution  of  water  appears  to  be  justified  by  tlie 
strong  affinity  which  its  elements  evince  for  each  other,  as  well  as  from 
the  proportions  with  which  they  respectively  combine  with  other  bodies. 
Consequently,  regarding  the  atom  of  hydrogen  as  unity,  8 will  be  the 
relative  weight  of  an  atom  of  oxygen. 

The  processes  for  procuring  a supply  of  hydrogen  gas  will  now  be  in- 
telligible. The  first  is  the  method  by  which  Lavoisier  made  the  analy- 
sis of  water.  It  is  founded  on  the  fact  that  iron  at  a red  heat  decom- 
poses water,  the  oxygen  of  that  liquid  uniting  with  the  metal,  and  the 
hydrogen  gas  being  set  free.  That  the  hydrogen  which  is  evolved  when 
zinc  or  iron  is  put  into  dilute  sulphuric  acid  must  be  derived  from  the 
same  source,  is  obvious  from  the  consideration  that  of  the  three  sub- 
stances, iron,  sulphuric  acid,  and  water,  the  last  is  the  only  one  which 
contains  hydrogen.  The  product  of  the  operation,  besides  hydrogen, 
is  sulphate  of  the  protoxide  of  iron,  if  iron  is  used,  or  of  the  oxide  of 
zinc,  when  zinc  is  employed.  The  knowledge  of  the  combining  propor- 
tions of  these  substances  will  readily  give  the  exact  quantity  of  each 
product.  These  numbers  are, 


Water  (8  oxy.  -f-  1 hyd. ) . . 9 

Sulphuric  acid  . . . 40 

Iron  . . , . . 28 

Protoxide  of  iron  (28  iron  -f-  8 oxygen)  36 

Sulphate  of  the  protoxide  of  iron  (40  4-  36)  f 6 

13* 


150 


HYDROGEN. 


Hence  for  every  9 g'rains  of  water  wlilch  arc  decomposed,  1 grain  of 
liydrog*(‘n  will  be  set  free;  8 grains  of  oxygen  will  unite  with  28  grains 
of  iron,  forming  vS6  of  the  protoxide  of  iron;  and  the  36  grains  of  pro- 
toxide will  combine  with  40  gi’ains  of  .sulphuric  acid,  yielding  76  of  sul- 
phate of  the  protoxide  of  iron.  A similar  calculation  maybe  employed 
when  zinc  is  used,  merely  by  sub.stituting  the  atomic  weight  of  zinc 
(34)  for  that  of  iron.  According  to  Mr.  Cavendish,  an  ounce  of  zinc 
yields  676  cubic  inches,  and  an  equal  quantity  of  iron  782  cubic  inches 
of  hydrogen  gas. 

I he  action  of  dilute  sulphuric  acid  on  metallic  zinc  affords  an  instance 
of  what  was  once  called  Disposing  Affinity.  Zinc  decomposes  pure 
water  at  common  temperatures  with  extreme  slowness;  but  as  soon  a.s 
sulphuric  acid  is  added,  decomposition  of  the  water  takes  place  rapidly, 
though  the  acid  merely  unites  with  oxide  of  zinc.  The  former  expla- 
nation was,  that  the  affinity  of  the  acid  for  oxide  of  zinc  disposed  the 
metal  to  unite  with  oxygen,  and  thus  enabled  it  to  decompose  water; 
tliat  is,  the  oxide  of  zinc  was  supposed  to  produce  an  effect  previous  to 
its  existence.  The  obscurity  of  this  explanation  arises  from  regarding 
changes  as  consecutive,  which  are  in  reality  simultaneous.  'Iliere  is  no 
appearance  of  succession  in  the  process;  the  oxide  of  zinc  is  not  fonned 
previously  to  its  combination  with  the  acid,  but  at  the  same  instant. 
There  is,  as  it  were,  only  one  chemical  change,  which  consists  in  the 
combination,  at  one  and  the  same  moment,  of  zinc  with  oxygen,  and  of 
oxide  of  zinc  with  the  acid;  and  this  change  occurs  because  these  two 
affinities,  acting  together,  overcome  the  attraction  of  oxygen  and  hydro- 
gen for  one  another. 

Water  is  a transparent  colourless  liquid,  which  has  neither  smell  nor 
taste.  It  is  a powerful  refractor  of  light,  conducts  heat  very  slowly, 
and  is  an  imperfect  conductor  of  electricity.  The  experiments  of  Oer- 
sted, and  Culladon  and  Sturm  have  proved  that  water  is  compressible 
by  great  pressure;  and  according  to  the  latter  observers,  its  absolute 
diminution  for  each  atmosphere  is  51.3  millionths  of  its  volume.  (An. 
de  Ch.  et  de  Ph.  xxxvi.  140.)  The  relations  of  water,  with  respect  to 
caloric,  are  higldy  important;  but  they  have  already  been  discussed  in 
the  first  part  of  the  work.  The  specific  gravity  of  water  is  1,  the  den- 
sity of  all  solid  and  liquid  bodies  being  referred  to  it  as  a term  of  com- 
parison. One  cubic  inch,  at  62°  F.  and  30  inches  of  the  barometer, 
weighs  252.458  grains;  so  that  it  is  831  times  as  heavy  as  atmospheric 
air. 

Water  is  one  of  the  most  powerful  chemical  agents  which  we  possess. 
Its  agency  is  owing  partly  to  the  extensive  range  of  its  own  affinity,  and 
partly  to  the  nature  of  its  elements.  The  efi ect  of  the  last  circumstance 
has  already  appeared  in  the  process  for  procuring  hydrogen  gas;  and 
indeed  there  are  few  complex  chemical  changes  which  do  not  give  rise 
either  to  the  production  or  decomposition  of  water.  But,  independent- 
ly of  the  elements  of  which  it  is  composed,  it  combines  directly  with 
many  bodies.  Sometimes  it  is  contained  in  a variable  ratio,  as  in  ordi- 
nary solution;  in  other  compounds  it  is  present  in  a fixed  definite  pro- 
portion, as  is  exemplified  by  its  union  with  several  of  the  acids,  the  alka- 
lies, and  all  salts  that  contain  water  of  crystallization.  These  combina- 
tions are  termed  hych'atcs.  Thus,  concentrated  sulphuric'acid  is  a com- 
pound of  one  ecpiivalent  of  the  real  dry  acid  and  one  equivalent  of 
water;  and  its  proper  name  is  hydrous  sulphuric  acid  or  hydrate  of  sul- 
phuric acid.  'I  he  adjunct  hydro  has  been  sometimes  used  to  signify  the 
])rc3ence  of  water  in  definite  ])roporlion;  but  it  is  advisable,  to  prevent 
mi.stakcs,  to  limit  its  employment  to  the  compounds  of  hydrogen.^ 

'flic  j)urc.st  water  which  can  be  found,  as  a natural  product,  is  pro- 


HYDROGEN. 


151 


cured  by  meltinj^  freshly  fallen  snow,  or  by  receiving*  rain  in  clean  ves- 
sels at  a distance  from  houses.  But  this  water  is  not  absolutely  pure; 
for  if  placed  under  the  exliausted  receiver  of  an  air  pump,  or  boiled 
briskly  for  a few  minutes,  bubbles  of  g-as  escape  from  it.  The  air  ob- 
tained in  this  way  from  snow  water  is  much  richer  in  oxyg'en  gas  tlian 
atmospheric  air.  According  to  the  experiments  of  Gay-Lussac  and 
Humboldt,  it  contains  34.8  per  cent  of  oxygen,  and  the  air  separated  by 
ebullition  from  rain  water  contains  32  per  cent  of  that  gas.  All  water 
which  has  once  fallen  on  the  ground  becomes  impregnated  with  more 
or  less  earthy  or  saline  matters,  and  it  can  be  separated  from  them  only 
by  distillation.  The  distilled  water,  thus  obtained,  and  preserved  in 
clean  well-stopped  bottles,  is  absolutely  pure.  Recently  boiled  water 
has  the  property  of  absorbing  a portion  of  all  gases,  when  its  surface  is 
in  contact  with  them;  and  the  absorption  is  promoted  by  brisk  agitation. 
The  following  table,  from  Dr.  Henry’s  Chemistry,  shows  the  absorba- 
bility of  different  gases  by  water,  deprived  of  all  its  air  by  ebullition. 

100  cubic  inches  of  such  water,  at  the  mean  temperature  and  pres- 
sure, absorb  of 


Sulphuretted  hydrogen 
Carbonic  acid 
Nitrous  oxide 
Olefiant  gas 
Oxygen 
Carbonic  oxide 
Nitrogen 
Hydrogen 


Dalton  and  Henry. 

Saussure, 

. 100  cub.  in. 

253  cub.  in. 

100 

106 

100 

76 

12.5 

15.3 

. 3.7 

6.5 

1.56 

6.2 

1.56 

4.1 

1.56 

4.6 

The  estimate  of  Saussure  is  in  general  too  high.  That  of  Mr.  Dalton 
and  Dr.  Henry  for  nitrous  oxide,  according  to  the  experiments  of  Sir 
H.  Davy,  is  considerably  beyond  the  truth. 


Deut oxide  of  Hydrogen. 

The  deutoxide  or  peroxide  of  hydrogen  was  discovered  by  M.  The- 
nard,  in  the  year  1818.  Before  describing  the  mode  of  preparing  this 
compound,  it  must  be  observed  that  there  are  two  oxides  of  barium;  and 
that  when  the  peroxide  of  that  metal  is  put  into  w^ater  containing  free 
muriatic  acid,  oxygen  gas  is  set  at  liberty,  and  the  peroxide  is  converted 
into  protoxide  of  barium  or  baryta,  which  combines  with  the  acid.  When 
this  process  is  conducted  with  the  necessary  precautions,  the  oxygen 
which  is  set  free,  instead  of  escaping  in  the  form  of  gas,  unites  with  the 
hydrogen  of  the  water,  and  brings  it  to  a maximum  of  oxidation.  For 
a full  detail  of  all  the  minutiae  of  the  process,  the  reader  may  consult 
the  original  memoir  of  M.  Thenard;*  the  general  directions  are  the  fol- 
lowing:— To  six  or  seven  ounces  of  water  add  so  much  pure  concen- 
trated muriatic  acid  as  is  sufficient  to  dissolve  230  grains  of  baryta;  and 
after  having  placed  the  mixed  fluids  in  a glass  vessel  surrounded  with 
ice,  add  in  successive  portions  185  grains  of  deutoxide  of  barium  re- 
duced to  powder,  and  stir  with  a glass  rod  after  each  addition.  When, 
the  solution,  which  takes  place  without  effervescence,  is  complete,  sul- 
phuric acid  is  added  in  sufficient  quantity  for  precipitating  the  whole  of 
the  baryta  in  the  form  of  an  insoluble  sulphate;  in  order  that  the  muri- 
atic acid,  which  had  been  combined  with  that  earth,  may  be  completely 


• In  the  An.  de  Chim.  et  de  Phys.  vol.  viii.  ix.  and  x.;  Annals  of  Phi- 
losophy, vol.  xiii.  and  xiv. ; and  M.  '1  henard’s  Traits  de  Chimie. 


152 


HYDROGEN. 


separated  from  it.  Another  portion  of  deutoxide  of  barium,  amounting’ 
to  185  grains,  is  then  put  into  the  liquid;  the  free  muriatic  acid  instantly 
acts  upon  it,  and  as  soon  as  it  is  dissolved,  the  ])aryta  is  again  converted 
into  sulphate  by  the  addition  of  sulphuric  acid.  The  solution  is  then 
filtered,  in  order  to  separate  the  insoluble  sulphate  of  baryta;  and  fresh 
quantities  of  peroxide  of  barium  are  added  in  succession,  till  about  three 
ounces  have  been  employed.  The  liquid  then  contains  from  25  to  30 
times  its  volume  of  oxygen  gas.  The  muriatic  acid  which  has  served  to 
decompose  the  peroxide  of  barium  during  the  wliole  process,  is  now 
removed  by  the  cautious  addition  of  sulphate  of  silver,  and  the  sulphuric 
acid  afterwards  separated  by  solid  baryta. 

Peroxide  of  hydrogen,  as  thus  prepared,  is  still  diluted  with  a consid- 
erable quantity  of  water.  To  separate  the  latter,  the  mixed  liquids  are 
placed,  with  a vessel  of  strong  sulphuric  acid,  under  the  exhausted  re- 
ceiver of  an  air-pump.  As  the  water  evaporates,  the  density  of  the 
residue  increases,  till  at  last  it  acquires  the  specific  gravity  of  1.452. 
The  concentration  cannot  be  pushed  further;  for  if  kept  under  the  re- 
ceiver after  reaching  this  point,  the  peroxide  itself  gradually  but  slowly 
volatilizes  without  change. 

Peroxide  of  hydrogen,  of  specific  gravity  1.452,  is  a colourless  trans- 
parent liquid  without  odour.  It  whitens  the  surface  of  the  skin  when 
applied  to  it,  causes  a prickling  sensation,  and  even  destroys  its  texture 
if  the  application  is  long  continued.  It  acts  in  a similar  manner  on  the 
tongue;  in  addition  to  which  it  thickens  the  saliva,  and  tastes  like  cer- 
tain metallic  solutions.  Brought  into  contact  with  litmus  and  turmeric 
paper,  it  gradually  destroys  their  colour  and  makes  them  white.  It  is 
slowly  volatilized  in  vacuo,  a fact  which  shows  that  its  vapour  is  much 
less  elastic  than  that  of  water.  It  preserves  its  liquid  form  at  all  degrees 
of  cold  to  which  it  has  hitherto  been  exposed.  At  the  temperature  of 
59°  F.  it  is  decomposed,  being  converted  into  water  and  oxygen  gas. 
For  this  reason  it  ought  to  be  preserved  in  glass  tubes  surrounded  with 
ice. 

The  most  remarkable  property  of  peroxide  of  hydrogen  is  its  facility 
of  decomposition.  Diffused  daylight  does  not  seem  to  exert  any  influ- 
ence over  it,  and  even  the  direct  solar  rays  act  upon  it  tardily.  It  effer- 
vesces from  escape  of  oxygen  at  59°  F.,  and  the  sudden  application  of  a 
higher  temperature,  as  of  212°  F.,  gives  rise  to  such  rapid  evolution  of 
gas  as  to  cause  an  explosion.  Water,  apparently  by  combining  with  the 
peroxide,  renders  it  more  permanent;  but  no  degree  of  dilution  can 
enable  it  to  bear  the  heat  of  boiling  water,  at  which  temperature  it  is 
entirely  decomposed.  All  the  metals,  except  iron,  tin,  antimony,  and 
tellurium,  have  a tendency  to  decompose  the  peroxide  of  hydrogen,  con- 
verting it  into  oxygen  and  water.  A state  of  minute  mechanical  divi- 
sion is  essential  for  producing  rapid  decomposition.  If  the  metal  is  in 
mass,  and  the  peroxide  diluted  with  water,  the  action  is  slow.  The  me- 
tals which  have  a strong  affinity  for  oxyg'en  are  oxidized  at  the  same 
time,  such  as  potassium,  sodium,  arsenic,  molybdenum,  manganese,  zinc, 
tungsten,  and  chromium;  while  others,  such  as  g'old,  silver,  platinum, 
iridium,  osmium,  rhodium,  palladium,  and  mercury,  retain  the  metallic 
state. 

Peroxide  of  hydrogen  is  decomposed  at  common  temperatures  by 
many  of  the  metallic  oxides.  That  some  protoxides  should  have  this 
effect,  would  be  anticipated  in  consequence  of  their  tendency  to  pass 
into  a higher  state  of  oxidation.  The  protoxide  of  iron,  manganese, 
tin,  cobalt,  and  others,  act  on  this  princi])le,  and  are  really  converted 
into  peroxides,  "rhe  peroxide  of  barium,  strontium,  and  calcium  may 
likewise  be  formed  by  tlie  action  of  peroxide  of  hydrogen  on  baryta, 


HYDROGEN. 


153 


strontia,  and  lime.  But  it  is  a singular  fact,  and  I am  not  aware  that 
any  satisfactory  explanation  of  it  has  been  given,  that  some  oxides  de- 
compose peroxide  of  hydrogen  without  passing  into  a higher  degree  of 
oxidation.  The  peroxide  of  silver,  lead,  mercury,  gold,  platinum, 
manganese,  and  cobalt,  possess  this  property  in  the  greatest  perfection, 
acting  on  peroxide  of  hydrogen,  when  concentrated,  with  surprising 
energy.  The  decomposition  is  complete  and  instantaneous;  oxygen  gas 
is  evolved  so  rapidly  as  to  produce  a kind  of  explosion,  and  such  in- 
tense temperature  is  excited,  that  the  glass  tube  in  which  the  experi- 
ment is  conducted  becomes  red-hot.  The  reaction  is  very  great  even 
when  the  peroxide  of  hydrogen  is  diluted  with  water.  Oxide  of  silver 
occasions  very  perceptible  eflervescence,  when  put  into  water  which 
contains  only  l-50th  of  its  bulk  of  oxygen.  All  the  metallic  oxides, 
which  are  decomposed  by  a red  heat,  such  as  those  of  gold,  platinum, 
silver,  and  mercury,  are  reduced  to  the  metallic  state  when  they  act 
upon  peroxide  of  hydrogen.  This  effect  cannot  be  altogether  ascribed 
to  caloric  disengaged  during  the  action;  for  oxide  of  silver  suffers 
reduction  when  put  into  a very  dilute  solution  of  the  peroxide,  although 
the  decomposition  is  not  then  attended  by  an  appreciable  rise  of  tempe- 
rature. 

While  the  tendency  of  metals  and  metallic  oxides  is  to  decompose 
the  peroxide  of  hydrogen,  acids  have  the  ])ropcrty  of  rendering  it  more 
stable.  In  proof  of  this,  let  a portion  of  that  liquid,  somewhat  diluted 
with  water,  be  heated  till  it  begins  to  effervesce  from  the  escape  of  oxy- 
gen gas;  let  some  strong  acid,  as  the  nitric,  sulphuric,  or  muriatic,  be  then 
dropped  into  it,  and  the  effervescence  will  cease  on  the  instant.  When  a 
little  finely  divided  gold  is  put  into  a weak  solution  of  peroxide  of  hy- 
drogen, containing  only  10,  20,  or  30  times  its  bulk  of  oxygen,  brisk 
effervescence  ensues;  but  on  letting  one  drop  of  sulphuric  acid  fall  into 
it,  effervescence  ceases  instantly;  it  is  reproduced  by  the  addition  of 
potassa,  and  is  again  arrested  by  adding  a second  portion  of  acid.  The 
only  acids  that  do  not  possess  this  property  are  those  that  have  a low  de- 
gree of  acidity,  as  carbonic  and  boracic  acids;  or  those  which  suffer  a 
chemical  change  when  mixed  with  peroxide  of  hydrogen,  such  as  hy- 
driodic  and  sulphurous  acids,  and  sulphuretted  hydrogen.  Acids  ap- 
pear to  increase  the  stability  of  the  peroxide  in  the  same  way  as  water 
does,  namely,  by  combining  chemically  with  it.  Several  compounds 
of  this  kind  were  formed  by  Thenard,  before  he  was  aware  of  the  ex- 
istence of  the  peroxide  of  hydrogen.  They  were  made  by  dissolving 
peroxide  of  barium  in  some  dilute  acid,  such  as  the  nitric,  and  then 
precipitating  the  baryta  by  sulphuric  acid.  As  nitric  acid  was  supposed 
under  these  circumstances  to  combine  with  an  additional  quantity  of 
oxygen,  Thenard  applied  the  teim  oxygenized  nitric  acid  to^  the  re- 
sulting compound,  and  described  several  other  new  acids  under  a simi- 
lar title.  But  the  subsequent  discovery  of  peroxide  of  hydrogen  put 
the  nature  of  the  oxygenized  acids  in  a clearer  light;  for  their  proper- 
ties are  easily  explicable  on  the  supposition  that  they  are  composed, 
not  of  acids  and  oxygen  gas,  but  of  acids  united  with  peroxide  of  hy- 
drogen. 

Peroxide  of  hydrogen  was  analysed  by  diluting  a known  weight  of  it 
with  water,  and  then  decomposing  it  by  boiling  the  solution.  Accord- 
ing to  two  careful  analyses,  conducted  on  this  principle,  864  parts  of 
the  peroxide  are  composed  of  466  of  water,  and  398  of  oxygen  gas. 
The  466  of  water  contain  414  of  oxygen,  whence  it  may  be  inferred 
that  peroxide  of  hydrogen  contains  twice  as  much  oxygen  as  water.  A 
small  deficiency  of  oxygen  in  this  experiment  was  to  be  expected,  ow- 


154 


NITROGEN. 


ing  to  the  difficulty  of  obtaining  peroxide  of  hydrogen  perfectly  free 
from  water.  The  peroxide  consists,  therefore,  of 

Hydrogen  1 or  one  proportional. 

Oxygen  16  or  two  proportionals. 


SECTION  V. 

NITROGEN. 

The  existence  of  nitrogen  gas,  as  distinct  from  every  other  gaseous 
substance,  appears  to  liave  been  first  noticed  in  the  year  1772  by  the 
late  Dr.  Rutherford  of  Edinburgh.  Lavoisier  discovered  in  1775  that 
it  is  a constituent  part  of  the  atmosphere;  and  the  same  discovery  was 
made  soon  after,  or  about  the  same  time,  by  Scheele.  Lavoisier  called 
it  azote,  from  oi.  privative  and  life,  because  it  is  unable  to  support 
the  respiration  of  animals;  but  as  it  possesses  this  negative  property  in 
common  with  most  other  gases,  the  more  appropriate  tavm  nitrogen  has 
been  since  applied  to  it,  from  the  circumstance  of  its  being  an  essential 
ingredient  of  nitric  acid. 

Nitrogen  is  most  conveniently  prepared  by  burning  a piece  of  phos- 
phorus in  ajar  full  of  air  inverted  over  water.  The  strong  affinity  of 
phosphorus  for  oxygen  enables  it  to  burn  till  the  whole  of  that  gas  is 
consumed.  The  product  of  the  combustion,  phosphoric  acid,  is  at  first 
diffused  through  the  residue  in  the  form  of  a white  cloud;  but  as  this 
substance  is  rapidly  absorbed  by  water,  it  disappears  entirely  in  the 
course  of  half  an  hour.  The  residual  gas  is  nitrogen,  containing  a 
small  quantity  of  carbonic  acid  and  vapour  of  phosphorus,  both  of 
which  may  be  removed  by  agitating  it  briskly  with  a solution  of  pure 
potassa.  Several  other  substances  may  be  employed  for  withdrawing 
oxygen  from  atmospheric  air.  A solution  of  protosulphate  of  iron, 
charged  with  deutoxide  of  nitrogen,  absorbs  the  oxygen  in  the  space  of 
a few  minutes.  A stick  of  phosphorus  produces  the  same  effect  in  24 
hours,  if  exposed  to  a temperature  of  60?  F.  A solution  of  sulphuret 
of  potassa  or  lime  acts  in  a similar  manner;  and  a mixture  of  equal  parts 
of  iron  filings  and  sulphur,  made  into  a paste  with  water,  may  be  em- 
ployed with  the  same  intention.  Both  these  processes,  however,  are 
inconvenient  from  their  slowness.  Nitrogen  gas  may  likewise  be  obtain- 
ed by  exposing  a mixture  of  fresh  muscle  and  nitric  acid  of  specific 
gravity  1.20  to  a moderate  temperature.  Effervescence  then  takes 
place,  and  a large  quantity  of  gaseous  matter  is  evolved,  which  is  ni- 
trogen mixed  with  a little  carbonic  acid.  The  latter  must  be  removed 
by  agitation  with  lime-water;  but  tlie  residue  still  retains  a peculiar 
odour,  indicative  of  the  presence  of  some  volatile  principle  which  can- 
not ])e  wliolly  separated  from  it.  I'he  theory  of  this  process  is  some- 
what complex,  and  will  be  considered  more  conveniently  in  a subse- 
quent part  of  the  work. 

Pure  nitrogen  is  a colourless  gas,  wholly  devoid  of  smell  and  taste. 
It  does  not  change  the  blue  colour  of  vegetables,  and  is  distinguished 
from  other  gases  more  by  negative  cluiracters  than  by  any  striking  qua- 
lity. It  is  not  a supporter  of  combustion;  but,  on  the  contrary,  extin- 
guishes all  burning  bodies  that  are  immersed  in  it.  No  animal  can  live 
in  it;  but  yet  it  exerts  no  injurious  action  either  on  the  lungs  or  on  th^ 


nitrogM. 


155 

system  at  large,  the  privation  of  oxygen  gas  being  the  sole  cause  of 
death.  It  is  not  inflammable  like  hydrogen;  though,  under  favourable 
circumstances,  it  may  be  made  to  unite  with  oxygen.  Water,  when 
deprived  of  air  by  ebullition,  takes  up  about  one  and  a half  per  cent, 
of  it.  Its  specific  gravity  is  0.9722;*  and,  therefore,  100  cubic  inches, 
at  the  mean  temperature  and  pressure,  will  weigh  29.652  grains. 

Considerable  doubt  exists  as  to  the  nature  of  nitrogen.  Though 
ranked  among  the  simple  non-metallic  bodies,  some  circumstances  have 
led  to  the  suspicion  that  it  is  compound;  and  this  opinion  has  been 
warmly  advocated  by  Sir  H.  Davy  and  Berzelius.  The  chief  argument 
in  favour  of  this  view  is  drawn  from  the  phenomena  that  attend  the  form- 
ation of  what  is  called  the  ammoniacal  amalgam.  From  the  metallic 
appearance  of  this  substance,  it  was  supposed  to  be  a compound  of 
mercury  and  a metal;  and  as  the  only  method  of  forming  it  is  by  the  ac- 
tion of  galvanism  on  a salt  of  ammonia,  in  contact  with  a globule  of 
mercury,  it  follows  that  the  metal,  if  present  at  all,  must  have  been 
supplied  by  the  ammonia.  Now  ammonia  is  composed  of  hydrogen  and 
nitrogen;  and  as  the  former,  from  its  levity,  can  hardly  be  supposed  to 
contain  a metal,  it  was  inferred  that  it  must  be  present  in  the  latter. 
Unfortunately  for  this  argument,  the  supposed  metal  cannot  be  obtained 
in  a separate  state.  The  amalgam  no  sooner  ceases  to  be  under  galva- 
nic influence  than  its  elements  begin  to  separate  spontaneously,  and  in 
a few  minutes  decomposition  is  completCj  the  sole  products  being  am- 
monia, hydrogen,  and  pure  mercury.  Sir  H.  Davy  accounts  for  this 
change  on  the  supposition  that  water  is  decomposed;  that  its  oxygen  re- 
produces nitrogen  by  uniting  with  the  supposed  metal;  and  that  one 
pai't  of  its  hydrogen  forms  ammonia  by  uniting  with  the  nitrogen,  while 
the  remainder  escapes  in  the  form  of  gas.  But  Gay-Lussac  and  Thenard 
(Recherches  Physico-chimiques,  vol.  i.)  declare  that  the  amalgam  re- 
solves itself  into  mercury,  ammonia,  and  hydrogen,  even  though  per- 
fectly free  from  moisture;  and  they  infer  from  their  experiments  that  it 
is  composed  of  those  three  substances  combined  directly  with  each 
other.  It  hence  appears  that  the  examination  of  the  ammoniacal  amal- 
gam affords  no  proof  of  the  compound  nature  of  nitrogen;  nor  was  Sir 
H.  Davy’s  attempt  to  decompose  that  gas  by  aid  of  potassium,  intensely 
heated  by  a galvanic  current,  attended  by  better  success.  Berzelius 
has  defended  the  idea  that  nitrogen  is  a compound  body  on  other  prin- 
ciples; but  as  his  arguments,  though  very  ingenious,  are  merely  specu- 
lative, they  cannot  be  admitted  as  decisive  of  the  question* 

On  the  Atmosphere. 

The  earth  is  every  where  surrounded  by  a mass  of  gaseous  matter 
called  the  atmosphere,  which  is  preserved  at  its  surface  by  the  force  of 
gravity,  and  revolves  together  with  it  around  the  sun.  It  is  colourless 
and  invisible,  excites  neither  taste  nor  smell  when  pure,  and  is  not  sen- 
sible to  the  touch  unless  when  it  is  in  motion.  It  possesses  the  physical 
properties  of  elastic  fluids  in  a high  degree.  Its  specific  gravity  is  uni- 
ty, being  the  standard  with  which  the  density  of  all  gaseous  substances 
is  compared.  It  is  831  times  lighter  than  water,  and  nearly  11.260  times 
lighter  than  mercury.  The  knowledge  of  its  exact  weight  is  an  essen- 
tial element  in  many  physical  and  chemical  researches.  According  to 
the  experiments  of  Sir  G.  Shuckburgh  Evelyn,  100  cubic  inches  of 


* This  number  is  calculated  on  the  assumption  that  air  consists  of  one 
measure  of  oxygen  and  four  of  nitrogen,  and  that  1.1111  is  the  specific 
gravity  of  oxygen  gas.  See  Thomson’s  First  Principles,  vol.  i.  p.  99. 


156 


NITROGEN. 


pure  and  dry  atmospheric  air,  at  60®  F.  and  30  inches,  bar.,  weij^h  exact- 
ly 30.5  grains;  and  this  estimate,  since  supported  by  Mr.  Rice,  (An.  of 
Ph.  xiii.  339.)  has  of  late  years  been  adopted  generally  by  British  phi- 
losophers. But  it  is  probably  short  of  the  truth.  The  observations  of 
Dr.  Henry  and  Mr.  Dalton  induce  them  to  consider  31  grains  as  more  ac- 
curate; and  the  elaborate,  but  as  yet  unfinished,  inquiry  of  Dr.  Front 
has  led  him  to  the  same  conclusion.  The  estimate  of  30.5,  wliicli  is  still 
adopted  in  this  work,  is,  therefore,  only  retained  provisionally,  until  all 
doubts  on  this  important  subject  shall  be  finally  removed. 

The  pressure  of  the  atmosphere  was  first  noticed  early  in  the  seven- 
teenth century  by  Galileo,  and  was  afterwards  demonstrated  by  his  pu- 
pil Torricelli,  to  whom  science  is  indebted  for  the  invention  of  the  baro- 
meter. Its  pressure  at  the  level  of  the  sea  is  equal  to  a weight  of  about 
15  pounds  on  every  square  inch  of  surface,  and  is  capable  of  support- 
ing a column  of  water  34  feet  high,  and  one  of  mercury  of  30  inches; 
that  is,  a column  of  mercury  one  inch  square  and  30  inches  long  has  the 
same  weight  (nearly  15  pounds)  as  a column  of  water  of  the  same  size 
and  34  feet  long,  and  as  a column  of  air  of  the  same  size  reaching  from 
the  level  of  the  sea  to  the  extreme  limit  of  the  atmosphere.  By  the 
use  of  the  barometer  it  was  di.scovered  that  the  atmospheric  pressure  is 
variable.  It  varies  according  to  the  elevation  above  the  level  of  the  sea, 
and  on  this  principle  the  height  of  mountains  is  estimated.  Supposing 
the  density  of  the  atmosphere  to  be  uniform,  a fall  of  one  inch  in  the 
barometer  would  correspond  to  11.260  inches  or  938  feet  of  air;  but  in 
order  to  make  the  calculation  with  accuracy,  allowance  must  be  made 
for  the  increasing  rarity  of  the  air,  and  for  various  other  circumstances 
which  are  detailed  in  works  on  meteorology.  (Daniell’s  Meteorological 
Essays,  2d  edit.  376.)  From  ca\ises  at  present  not  understood,  the  pres- 
sure varies  likewise  at  the  same  place.  On  this  depends  the  indications 
of  the  barometer  as  a weather-glass;  for  observation  has  fully  proved, 
that  the  weather  is  commonly  fair  and  calm  when  the  barometer  is  high, 
and  usually  wet  and  stormy  when  the  mercury  falls. 

Atmospheric  air  is  highly  compressible  and  elastic;  so  that  its  parti- 
cles admit  of  being  approximated  to  a great  extent  by  compression,  and 
expand  to  an  extreme  degree  of  rarity,  when  the  tendency  of  its  parti- 
cles to  separate  is  not  restrained  by  external  force.  It  has  been  found 
experimentally  that  the  volume  of  air  and  all  other  gaseous  fluids,  so 
long  as  they  retain  the  elastic  state,  is  inversely  as  the  pressure  to  which 
tliey  are  exposed.  Thus  a portion  of  air  which  occupies  100  measures 
when  compressed  by  a force  of  one, pound,  will  be  diminished  to  50 
measures  when  the  pressure  is  doubled,  and  will  expand  to  200  mea- 
sures when  the  compression  is  equal  to  half  a pound.  I’his  law  was  first 
demonstrated  in  1662  by  the  celebrated  Boyle,  and  a second  demonstra- 
tion of  it  was  given  some  years  afterwards  by  the  French  philosopher  M. 
Mariotte,  apparently  without  being  aware  tliat  the  discovery  had  been 
previously  made  in  FiUgland.  It  is  hence  frequently  called  the  law  of 
Mariotte.  I'ill  lately  it  had  not  been  verified  for  very  great  pressures; 
but  from  the  expeiimcnts  of  Oersted  in  1825,  who  extended  his  observa- 
tions to  air  compressed  by  a force  equal  to  110  atmospheres,  it  may  be 
inferred  to  be  quite  general,  exce])t  when  the  g-aseous  matter  assumes 
the  rKpiid  form,  (falinb.  .loui’nal  of  Science,  iv.  224.)  It  has,  indeed, 
been  recently  stated  l>y  M.  Despretz  that  the  easily  condensible  gases 
vary  from  this  law,  diminishing  under  increase  of  ])ressure  much  more 
rapidly  than  atmospheric  air;  but  the  detail  of  his  experiments  has  not, 
I believe,  been  jjublished,*  (An.de  Ch.  ct  de  Ph.  xxxiv.335  and  443.) 


See  note,  page  67.  B. 


NITROGEN.  157 

At  what  pressure  air  becomes  liquid  is  uncertain,  since  all  attempts  to 
condense  it  have  hitherto  been  unsuccessful. 

The  extreme  compressibility  and  elasticity  of  the  air  accounts  for  the 
facility  with  which  it  is  set  in  motion,  and  the  velocity  with  which  it  is 
capable  of  moving.  It  is  subject  to  the  la  ws  which  characterize  elastic 
fluids  in  general.  It  presses,  therefore,  equ;:f  y on  every  side;  and  when 
some  parts  of  it  become  lighter  than  the  sin  rounding  portions,  the  denser 
particles  rush  rapidly  into  their  place  and  force  the  more  rarefied  ones  to 
ascend.  The  motion  of  air  gives  rise  to  various  familiar  phenomena.  A 
stream  or  current  of  air  is  wind,  and  an  undukitlng  vibration  excites  the 
sensation  of  sound. 

The  atmosphere  is  not  of  equal  density  at  all  its  parts.  This  is  obvi- 
ous from  the  consideration,  that  those  portions  which  are  next  the  earth 
sustain  the  whole  pressure  of  the  atmosphere,  while  the  higher  strata 
bear  only  a part.  The  atmospheric  column  diminishes  in  length  as  the 
distance  from  the  earth’s  surface  increases;  and,  consequently,  the 
greater  the  elevation,  the  lighter  must  be  the  air.  It  is  not  known  to 
what  height  the  atmosphere  extends.  From  calculations  founded  on 
the  phenomena  of  refraction,  its  height  is  supposed  to  be  about  45  miles; 
and  Dr.  Wollaston  estimated,  from  the  law  of  expansion  of  gases,  that 
it  must  extend  to  at  least  40  miles  with  properties  unimpaired  by  rare- 
faction. In  speculating  on  its  extent  beyond  that  distance,  it  becomes 
a question  whether  the  atmosphere  is  or  is  not  liniited  to  the  earth.  This 
subject  was  discussed  with  his  usual  sagacity  by  the  late  Dr.  Wollaston 
in  an  Essay  on  the  Finite  Extent  of  the  Atmosphere,  published  in  the 
Philosophical  Transactions  for  1822.  On  tlie  supposition  that  the  atmos- 
phere is  unlimited,  it  would  pervade  all  space,  and  accumulate  about 
the  sun,  moon,  and  planets,  forming  around  each  an  atmosphere,  the 
density  of  which  would  depend  on  their  respective  forces  of  attraction. 
Now  Dr.  Wollaston  inferred  from  astronomical  observations  made  by 
himself  and  Captain  Kater,  that  there  is  no  solar  atmosphere;  and  the 
obseiwations  of  other  astronomers  appear  to  jiistify  the  same  inference 
with  respect  to  the  planet  Jupiter.  If  the  accuracy  of  these  conclusions 
be  admitted,  it  follows  that  our  atmosphere  is  confined  to  the  earth;  and 
it  may  next  be  asked,  by  what  means  is  its  extc  nt  limited?  Dr.  Wollas- 
ton accounted  for  it  by  supposing  the  air,  after  attaining  a certain  de- 
gree of  rarefaction,  to  possess  such  feeble  elasticity,  that  the  tendency 
of  its  particles  to  separate  farther  from  each  other  is  counteracted  by 
gravity.  The  unknown  height  at  which  this  e([uilibrium  between  the 
two  forces  of  elasticity  and  gravitation  takes  place,  is  the  extreme  limit 
of  the  atmosphere.  It  is  further  argued,  th^it  this  mode  of  reasoning  is 
inapplicable  unless  the  air  be  supposed  to  consist  of  ultimate  atoms. 
Then  only  can  each  particle  be  separated  from  contiguous  ones,  to  a 
degree  sufficient  for  producing  that  diminiiticn  of  elasticity  required  by 
the  argument;  for  if  the  material  substance  of  air  is  divisible  without 
limit,  each  particle  will  in  itself  contain  an  infinite  number  of  other  par- 
ticles, the  tension  of  which,  in  consequence  of  their  proximity,  should 
lead  to  their  mutual  separation.  The  production  of  fresh  poi'tions  of 
air  would  on  this  principle  be  endless. 

In  order  to  account  for  the  limited  nature  ( f the  atmosphere,  accord- 
ingto  this  principle,  the  air  is  inferred  to  coiihst  of  atoms;  and  if  the  in- 
ference be  granted,  it  is  fair  to  presume  that  matter  in  general  has  a simi 
lar  constitution.  The  tendency  of  Dr.  Wo)la4ori’s  reasoning,  therefore?, 
is  to  demonstrate  the  truth  of  the  atomic  ilu  oiy.  But  even  admitting 
astronomical  observations  as  conclusive  again  t the  existence  of  a sola^ 
atmosphere,  and  as  proving  by  inference  tlic  extent  of  ours  to  be  limited, 
it  scarcely  follows,  I apprehend,  that  much  weight  can  be  attached  tg 

14 


158 


NITROGEN. 


the  argument.  The  tension  or  elasticity  of  gaseous  matter  is  lessened 
by  two  causes,  diminution  of  pressure,  and  reduction  of  temperature. 
The  former  alone  was  taken  into  account  by  Ur,  Wollaston;  but  as  the 
tendency  of  the  latter  to  deprive  gases  of  their  elastic  form  is  now  fully 
established,  it  appears  to  me  that  the  extreme  cold  which  is  admitted  to 
prevail  in  the  higher  regions  of  the  air,  may  of  itself  be  a condition  suffi- 
cient to  put  a limit  to  the  extent  of  the  atmosphere.  Some  very  inge- 
nious remarks  have  been  made  on  this  subject  by  Mr.  Graham.  (Philos, 
Mag.  and  Annals,  i.  107.) 

The  temperature  of  the  atmosphere  varies  with  its  elevation.  Gaseous 
fluids  permit  radiant  matter  to  pass  freely  through  them  without  any 
absorption,  and,  therefore,  without  their  temperature  being  influenced 
by  its  passage.  The  atmosphere  is  not  heated  by  transmitting  the  rays 
of  the  sun.  The  air  receives  its  caloric  solely  from  the  earth,  and  chiefly 
by  actual  contact;  so  that  its  temperature  becomes  progi'essively  lower, 
as  the  distance  from  the  general  mass  of  the  earth  increases.  Another 
circumstance  which  contributes  to  the  same  effect,  is  the  increasing  ten- 
uity of  the  atmosphere;  for  the  temperature  of  rarefied  air  is  less  raised 
by  a given  quantity  of  heat,  than  that  of  the  same  portion  of  air  when 
compressed,  owing  to  its  specific  caloric  being  greater  in  the  former 
state  than  in  the  latter.  From  the  joint  influence  of  both  these  causes 
it  is  found  that,  in  ascending  into  the  atmosphere,  the  temperature  di- 
minishes at  the  rate  of  one  degree  for  about  every  300  feet.  The  rate 
of  decrease  is  probably  much  slower  at  considerable  distances  from  the 
earth;  but  still  there  is  no  reason  to  doubt  that  the  temperature  con- 
tinues to  decrease  with  the  increasing  elevation.  There  must  conse- 
quently in  every  latitude  be  a point,  where  the  thermometer  never  rises 
above  32®,  and  where  ice  is  never  liquefied.  This  point  varies  with  the 
latitude,  being  highest  within  the  tropics,  and  descending  gradually  as 
w'e  advance  towards  the  poles.  The  following  table,  from  the  Supple- 
ment to  the  Encyclopedia  Britannica,  page  190,  article  Climate,  shows 
the  point  of  perpetual  ice  corresponding  to  different  latitudes. 


Latitude. 

English  feet 
in  height. 

Latitude. 

English  feet 
in  height. 

0® 

15,207 

45® 

7,671 

5® 

15,095 

50® 

6,334 

10® 

14,764 

55® 

5,034 

15® 

14,220 

60® 

3,818 

203 

13,478 

65® 

2,722 

25® 

12,557 

70® 

1,778 

30® 

11,484 

75® 

1,016 

35° 

10,287 

80® 

457 

403 

9,001 

85® 

117 

Air  was  one  of  the  four  elements  of  the  ancient  philosophers,  and 
their  opinion  of  its  nature  prevailed  generally,  till  its  accuracy  was  ren- 
dered questionable  by  the  experiments  of  Boyle,  Hooke,  and  Mayow. 
The  discovery  of  oxygen  gas  in  1774  paved  the  way  to  the  knowledge 
of  its  real  composition,  which  was  discovered  about  the  same  time  by 
Scheele  and  Lavoisier.  The  former  exposed  some  atmospheric  air  to  a 
solution  of  sulphuret  of  potassa,  which  gradually  absorbed-the  whole  of 
tlie  oxygen.  Lavoisier  effected  the  same  object  by  the  combustion  of 
iron  wire  and  phosphorus. 

The  earlier  analyses  of  the  air  did  not  agree  very  well  with  each  other. 
According  to  the  researches  of  Lavoisier,  it  is  composed  of  twenty-seven 
measure*  of  oxygen  and  seventy-three  of  nitrogen.  The  analysis  of 


NITROGEN. 


159 


Scheele  gave  a somewhat  higher  proportion  of  oxygen.  Priestley  found 
that  the  quantity  of  oxygen  varies  from  twenty  to  twenty-five  per  cent; 
and  Cavendish  estimated  it  only  at  twenty.  Tliese  discrepancies  must 
have  arisen  from  imperfections  in  the  mode  of  analysis;  for  the  propor- 
tion of  oxygen  has  been  found  by  subsequent  experiments  to  be  almost, 
if  not  exactly,  that  which  was  stated  by  Mr.  Cavendish.  The  results  of 
Scheele  and  Priestley  are  clearly  referrible  to  this  cause.  It  is  now 
known  that  the  processes  t)iey  employed  cannot  be  relied  on,  unless  cer- 
tain precautions  are  taken  of  which  those  chemists  were  ignorant.  Re- 
cently boiled  water  absorbs  nitrogen;  and,  consequently,  if  sulphuretof 
potassa  be  dissolved  in  that  liquid  by  the  aid  of  heat,  the  solution,  when 
agitated  with  air,  takes  up  a portion  of  nitrogen,  and  thereby  renders 
the  apparent  absorption  of  oxygen  too  great.  This  inconvenience  may 
be  avoided  by  dissolving  the  alkaline  sulphuret  in  cold  unboiled  water. 
The  deutoxide  of  nitrogen,  employed  by  Priestley,  removes  all  the  oxygen 
in  the  course  of  a few  seconds;  but  for  reasons  which  will  soon  be  men- 
tioned, its  indications  are  very  apt  to  be  fallacious.  The  combustion  of 
phosphorus,  as  well  as  the  gradual  oxidation  of  that  substance,  acts  in  a 
very  uniform  manner,  and  removes  the  whole  of  the  oxygen  completely. 
The  residual  nitrogen  contains  a little  of  the  vapour  of  phosphorus, 
which  increases  the  bulk  of  that  gas  by  l-40th,  for  which  an  allowance 
must  be  made  in  estimating  the  real  quantity  of  nitrogen. 

Since  chemists  have  learned  the  precautions  to  be  taken  in  the  analy- 
sis of  the  air,  a close  correspondence  has  been  observed  in  the  results  of 
their  experiments  upon  it.  The  researches  of  Davy,  Dalton,  Gay-Lus- 
sac, Thomson,  and  others,  leave  no  doubt  that  100  measures  of  pure  at- 
mospheric air  consist  of  twenty  or  twenty-one  volumes  of  oxygen,  and 
eighty  or  seventy-nine  of  nitrogen.  Dr.  Thomson,  whose  analysis  is  the 
most  recent,  fixes  the  quantity  of  oxygen  at  twenty  per  cent;  and  the 
reasons  he  has  assigned  for  regarding  this  estimate  as  more  accurate  than 
the  other,  appear  satisfactory.  The  oxygen  was  determined  (First 
Principles  of  Chemistry,  vol.  1.  p.  Of,)  by  mixing  with  the  air  a quanti- 
ty of  hy  drogen,  sufficient  to  convert  all  the  oxygen  present  into  water, 
and  kindling  the  mixture  by  the  electric  spark.  Water  is  formed  and 
is  condensed;  and  since  that  liquid  is  composed  of  one  volume  of  oxygen 
and  two  of  hydrogen,  one-third  of  the  diminution  must  give  the  exact 
quantity  of  oxygen.  This  process  is  so  easy  of  execution,  and  so  uni- 
form in  its  indications,  that  it  is  now  employed  nearly  to  tlie  total  exclu- 
sion of  all  others.* 


* The  best  analyses  of  atmospheric  air  correspond  so  nearly  with  the 
proportions  of  two  volumes  of  nitrogen  to  half  a volume  of  oxygen,  that 
it  seems  probable  that  these  proportions  (which  correspond  at  the  same 
time  with  the  theory  of  volumes)  would  be  obtained  exactly,  if  our  ex- 
periments could  be  performed  with  rigid  accuracy.  On  the  assumption 
that  these  are  the  true  proportions,  the  specific  gravity  of  oxygen  would 
be  1.1111,  and  that  of  nitrogen  0.9722.  The  reader  may  judge  how 
far  these  calculated  numbers  may  be  depended  on,  by  observing  how 
nearly  they  coincide  with  the  experimental  numbers  of  Berzelius,  the 
most  accui-ate  chemist  of  the  present  day.  This  philosopher,  in  con- 
junction with  M.  Dulong,  determined  the  specific  gravity  of  oxygen  to 
be  1.1026,  and  that  of  nitrogen  0.976.  The  composition  of  atmospheric 
air,  wdien  stated  in  volumes,  gives  the  oxygen  at  20  per  cent,  as  men- 
tioned by  Dr.  Turner;  and  yet  the  usual  analyses  make  it  21  per  cent. 
This  discrepancy  will  probably  disappear  when  the  analysis  is  perform- 
ed with  more  accuracy.  Dr.  Hare  found  that  the  average  of  a great 


160 


NITROGEN. 


Such  is  the  constltiilion  nf  pure  atmospheric  air.  Rut  the  atmosphere 
is  never  absolutely  pure;  for  it  always  contains  a certain  variable  quan- 
tity of  carbonic  acid  and  watery  ' apour,  besides  tlie  odoriferous  matter 
of  flowers  and  other  volatile  substances,  which  are  also  frequently  pre- 
sent. Saussure  found  carbon’c  acid  in  air  collected  at  the  top  of  Mont- 
Blanc;  and  it  exists  at  all  altitudt-s  which  have  been  hitherto  attained. 
Theodore  Saussure,  in  a recent  essay,  states  the  proportion  of  this  g'as 
to  vary  at  the  same  place  witliin  short  intervals  of  time.  It  is  greater  in 
summer  than  in  winter;  and  fi  oni  observations  made  during  spring, 
summer,  and  autumn,  in  t!ie  open  fields  and  in  calm  weather,  its  propor- 
tion is  inferred  to  be  always  greater  at  night  than  in  the  day.  He  found 
that  10,000  parts  of  air  contain  4.9  of  carbonic  acid  as  a mean,  6.2  as  a 
maximum,  and  3.7  as  a ncniinu'u.  (An.  de  Ch.  et  de  Ph.  xxxviii.  411.) 

The  chief  chemical  propei-ties  of  the  atmosphere  are  owing  to  the 
presence  of  oxygen  gas.  A ir  from  which  this  principle  has  been  with- 
drawn is  nearly  inert.  It  can  no  longer  support  respiration  and  combus- 
tion, and  metals  are  not  oxidized  by  being  heated  in  it.  Most  of  the 
spontaneous  changes  whieli  mineral  and  dead  organized  matters  undergo, 
are  owing  to  the  powerful  aflinities  of  oxygen.  The  uses  of  nitrogen 
are  in  a great  measure  unknown.  It  was  supposed  to  act  as  a mere  di- 
luent to  the  oxygen;  but  it  most  probably  serves  some  useful  purpose  in 
the  economy  of  animals,  tiie  exact  nature  of  which  has  not  -been  disco- 
vered. 

The  knowledge  of  the  (;;omposit;on  of  the  air,  and  of  the  importance 
of  oxygen  to  the  life  of  animals,  naturally  gave  rise  to  the  notion  that 
the  healthiness  of  the  air,  at  dificrent  times,  and  in  different  places,  de- 
pends on  the  relative  quantity  of  this  gas.  It  was,  therefore,  supposed 
that  the  purity  of  the  atmosphere,  or  iis  fitness  for  communicating  health 
and  vigour,  might  be  discovered  by  determining  the  proportion  of  oxy- 
gen; and  hence  the  origin  of  the  term  EmVometer^  which  was  applied 
to  the  apparatus  for  analyzing  the  air.  But  this  opinion,  though  at  first 
supported  by  the  discordant  results  of  the  earlier  anah^sts,  was  soon 
proved  to  be  fallacious.  It  appear.s,  on  the  contrary,  that  the  composi- 
tion of  the  air  is  not  only  constant  in  the  same  place,  but  is  the  same  in 
all  regions  of  the  earth,  and  at  all  altitudes.  Air  collected  at  the  summit 
of  the  highest  mountains,  such  as  Mont-Blanc  and  Chimborazo,  contains 
the  same  proportion  of  oxygen  as  that  of  the  lowest  valleys.  The  air  of 
Egypt  was  found  by  Berthollet  to  be  similar  to  that  of  France.  7’he 
air  which  Gay-Lussac  broug'lit  from  an  altitude  of  21,735  feet  above  the 
earth,  had  the  same  composition  as  that  collected  at  a short  distance 
from  its  surface.  Even  the  miasmata  of  marshes,  and  the  effluvia  of  in- 
fected places,  owe  their  noxious  qualities  to  some  principle  of  too  sub- 
tile a nature  to  be  detected  by  chemical  means,  and  not  to  a' deficiency 
of  oxygen.  Seguin  examined  the  infectious  atmosphere  of  an  hospital, 
the  odour  of  which  was  almost  intolerable,  and  could  discover  no  ap- 
preciable deficiency  of  oxygen,  or  other  peculiarity  of  composition. 

The  question  has  been  mucli  discussed  whether  the  oxygen  and  nitro- 
gen gases  of  the  atmosi)herc  are  simply  intermixed,  or  chemically  com- 
i)ined  with  each  other.  Appearances  are  at  first  view  greatly  in  favour 
of  the  latter  opinion.  Oxygen  and  nitrogen  gases  differ  in  density,  and, 
therefore,  it  might  be  exj^ected,  were  they  merely  mixed  together. 


number  of  analyses  of  atmospheric  air  performed  by  explosion  with  hy- 
drogen, by  means  of  liis  vei  y accurate  eudiometers,  gave  the  proportion 
of  oxygen  at  20.66  per  cent,  which  approaches  very  nearly^  to  the  quan- 
tity indicated  by  the  theory  of  volume.s.  B. 


NITROGEN. 


161 


that  the  oxygen  as  the  heavier  gas  ought,  in  obedience  to  the  force  of 
gravity,  to  collect  in  the  lower  regions  of  the  air;  while  the  nitrogen 
should  have  a tendency  to  occupy  the  higher.  But  this  has  nowhere 
been  observed.  If  air  be  confined  in  a long  tube,  preserved  at  perfect 
rest.  Us  upper  part  will  contain  just  as  much  oxygen  as  the  lower,  even 
after  an  interval  of  many  months;  nay,  if  the  lower  part  of  it  be  filled 
with  oxygen,  and  the  upper  with  nitrogen,  these  gases  will  be  found  in 
the  course  of  a few  hours  to  have  mixed  intimately  with  one  another. 
The  constituents  of  the  air  are,  also,  in  the  exact  proportion  for  com- 
bining. By  measure  they  are  in  the  simple  ratio  of  one  to  four,  which 
agrees  perfectly  with  the  law  of  combination  by  volume;  and  by  weight 
they  are  as  8 to  28,  which  corresponds  to  one  proportional  of  oxygen 
and  two  of  nitrogen. 

Strong  as  are  these  arguments  in  favour  of  the  chemical  theory,  it  is 
nevertheless  liable  to  objections  which  appear  insuperable.  The  at- 
mosphere possesses  all  the  characters  that  should  arise  from  a mechani- 
cal mixture.  There  is  not,  as  in  all  other  cases  of  chemical  union,  any 
change  in  the  bulk,  form,  or  other  qualities  of  its  elements.  The  nitro- 
gen manifests  no  attraction  for  the  oxygen.  All  bodies  which  have  an 
affinity  for  oxygen  abstract  it  from  the  atmosphere  with  as  much  facili- 
ty as  if  the  nitrogen  were  absent  altogether.  Even  water  effects  this 
separation;  for  the  air  which  is  expelled  from  rain  water  by  ebullition, 
contains  more  than  twenty  per  cent  of  oxygen.  When  oxygen  and  ni- 
trogen gases  are  mixed  together  in  the  ratio  of  one  to  four,  the  mix- 
ture occupies  precisely  five  volumes,  and  has  every  property  of  pure 
atmospheric  air.  The  refractive  power  of  the  atmosphere  is  precisely 
such  as  a mixture  of  oxygen  and  nitrogen  gases  ought  to  possess;  and 
different  from  what  would  be  expected  were  its  elements  chemically 
united.  (Edinburgh  Journal  of  Science,  iv.  211.) 

Since  the  elements  of  the  air  cannot  be  regarded  as  in  a state  of  ac- 
tual combination,  it  is  necessary  to  account  for  the  steadiness  of  their 
proportion  on  some  other  principle.  Chemists  are  divided  on  this  sub- 
ject between  two  opinions.  It  is  conceived,  according  to  one  view, 
that  the  affinity  of  oxygen  and  nitrogen  for  one  another,  though  insuf- 
ficient to  cause  their  combination  when  mixed  together  at  ordinary  tem- 
peratures, may  still  operate  in  such  a m,anner  as  to  prevent  their  sepa- 
ration; that  a certain  degree  of  attraction  is  even  then  exerted  between 
them,  which  is  able  to  counteract  the  tendency  of  gravity.  An  opinion 
of  this  kind  was  advanced  by  Berthollet,  in  his  Statique  Chimique^  and 
defended  by  the  late  Dr.  Murray.  This  doctrine,  however,  is  not  satis- 
factory. It  is,  indeed,  quite  conceivable  that  oxygen  and  nitrogen  may 
attract  each  other  in  the  way  supposed;  and  it  may  be  admitted  that 
this  supposition  explains  why  these  two  gases  continue  in  a state  of  per- 
fect mixture.  But  still  the  explanation  is  unsatisfactory;  and  for  the 
following  reason: — Mr.  Dalton  took  two  cylindrical  vessels,  one  of  which 
wks  filled  with  carbonic  acid,  the  other  with  hydrogen  gas;  the  latter 
was  placed  perpendicularly  over  the  other,  and  a communication  was 
established  between  them.  In  the  course  of  a few  hours  hydrogen  was 
detected  in  the  lower  vessel,  and  carbonic  acid  in  the  upper.  If  the 
upper  vessel  be  filled  with  oxygen,  nitrogen,  or  any  other  gas,  the  same 
phenomena  will  ensue;  the  gases  will  be  found,  after  a short  interval,  to 
be  in  a state  of  mixture,  and  will  at  last  be  distributed  equally  through 
both  vessels.  Now  this  result  cannot,  with  any  shadow  of  reason,  be 
ascribed  to  the  action  of  affinity.  It  is  well  known  that  carbonic  acid 
cannot  be  made  to  unite  either  with  hydrogen,  oxygen,  or  nitrogen; 
and,  therefore,  it  is  quite  gratuitous  to  assert  that  it  has  an  affinity  for 
them.  Some  other  power  must  be  in  opei-ation,  capable  of  producing 

14* 


162 


NITROGEN. 


the  mixture  of  gases  with  each  other,  independently  of  chemical  attrac- 
tion; and  if  this  power  can  cause  carbonic  acid  to  ascend  through  a gas 
which  is  twenty-two  times  lighter  tlian  itself,  it  will  surely  explain  why 
oxygen  and  nitrogen  gases,  the  densities  of  which  differ  so  little,  should 
be  intermingled  in  the  atmosplicre. 

The  explanation  whicli  Mr.  Dalton  has  given  of  these  phenomena  is 
founded  on  the  assumption,  that  the  particles  of  one  gas,  though  high- 
ly repulsive  to  each  other,  do  not  repel  those  of  a different  kind.  It  fol- 
lows, from  this  supposition,  tliat  one  gas  acts  as  a vacuum  with  respect 
to  another;  and,  therefore,  if  a vessel  full  of  carbonic  acid  be  made  to 
communicate  with  another  of  hydrogen,  the  particles  of  each  gas  insin- 
uate themselves  between  the  particles  of  the  other,  till  they  are  equal- 
ly diffused  through  both  vessels.  The  particles  of  the  carbonic  acid  do 
not  indeed  fill  the  space  occupied  by  the  hydi-ogen  with  the  same  velo- 
city as  if  it  were  a real  vacuum,  because  the  particles  of  the  hydrogen 
afford  a mechanical  impediment  to  their  progress.  The  ultimate  effect, 
however,  is  the  same  as  if  tlie  vessel  of  hydrogen  had  been  a vacuum, 
(Manchester  Memoirs,  Vol.  v.) 

Though  it  would  not  he  difficult  to  find  objections  to  this  hypothe- 
sis, it  has  the  merit  of  being  applicable  to  every  possible  case;  which 
cannot,  I conceive,  be  admitted  of  the  other.  It  accounts  not  only  for 
the  mixture  of  gases,  but  for  the  equable  diffusion  of  vapours  through 
gases,  and  through  each  other.  This  view  receives  considerable  sup- 
port from  some  experiments,  recently  described  in  the  Quarterly  Jour- 
nal of  Science,  N.  S.  vi.  74.  by  Mr.  Graham  of  Glasgow.  He  finds  that 
the  tendency  of  gases  to  be  diffused  varies  with  their  density.  When 
a gas  is  contained  in  a bottle  which  communicates  with  the  air  or  any 
gaseous  substance  by  means  of  a narrow  tube,  the  rapidity  of  diffusion 
will  depend  on  its  density,  being  rapid  if  the  gas  is  light,  and  less  so  if 
heavy.  In  fact,  the  diffusiveness  of  gases  is  inversely  as  some  func- 
tion, probably  the  square  root,  of  their  densities.  This  subject  is  still 
under  investigation;  but  the  explanation  manifestly  depends  rather  on 
the  mechanical  constitution  of  gases,  than  on  any  chemical  principle.* 

There  is  still  one  circumstance  for  consideration  respecting  the  at- 
mosphere. Since  ox3^gen  is  necessary  to  combustion,  to  the  respiration 
of  animals,  and  to  various  other  natural  operations,  by  all  of  which  that 
gas  is  withdrawn  from  the  air,  it  is  obvious  that  its  quantity  would  grad- 
ually diminish,  unless  the  tendency  of  those  causes  were  counteracted 
by  some  compensating  process.  To  all  appearance  there  does  exist 
some  source  of  compensation;  for  chemists  have  not  hitherto  noticed 
any  change  in  the  constitution  of  the  atmosphere.  The  only  source 
by  which  oxygen  is  known  to  be  supplied,  is  by  the  action  of  growing 
vegetables.  A healthy  plant  absorbs  carbonic  acid  during  the  day,  ap- 
propriates the  carbonaceous  part  of  that  gas  to  its  own  wants,  and 
evolves  the  oxygen  with  which  it  was  combined.  During  the  night,  in- 
deed, an  opposite  effect  is  produced.  Oxygen  gas  then  disappears,  and 
carbonic  acid  is  eliminated;  but  it  follows  from  the  experiments  of 
Priestley  and  Davy,  that  plants  during  24  hours  yield  more  oxygen  than 
they  consume.  Whether  living  vegetables  make  a full  compensation 
for  the  oxygen  removed  from  the  air  by  the  processes  above  mentioned 
I.S  uncertain.  From  the  great  extent  of  the  atmosphere,  and  the  con- 


* As  connected  with  this  subject,  the  reader  is  referred  to  an  inte- 
reKtiiig  paper  on  the  “ Penetrativeness  of  Fluids, by  Dr.  J.  K.  Mitchell, 
of  Philadelphia,  published  in  the  American  Journal  of  Medical  Sciences, 
vol.  vii.  p.  36.  15. 


NITROGEN. 


163 


tinual  agitation  to  which  its  diflTerent  parts  are  subject  by  the  action  of 
winds,  the  effects  of  any  deteriorating  process  would  be  very  gradual, 
and  a change  in  the  proportion  of  its  elements  could  be  perceived  only 
by  observations  made  at  very  distant  intervals. 

Compounds  of  Nitrogen  and  Oxygen. 


Chemists  are  acquainted  with  five  compounds  of  nitrogen  and  oxygen, 
the  composition  of  which,  as  deduced  from  the  researches  of  Gay-Lus- 
sac, Dr.  Henry,  and  Sir  H.  Davy,  is  as  follows: 


By  volume. 

By  weigh  t. 

Nitrogen. 

Oxygen. 

Nitrogen. 

Oxygen. 

Nitrous  oxide 

100 

50 

14 

8 

Nitric  oxide 

100 

100 

14 

16 

Hyponitrous  acid 

100 

150 

14 

24 

Nitrous  acid 

100 

200 

14 

32 

Nitric  acid 

100 

250 

14 

40 

The  first  of  these,  as  containing  the  smallest  quantity  of  oxygen.  Is 
regarded  as  a compound  of  one  proportional,  or  according  to  the  atomic 
theory  of  one  atom,  of  each  element.  The  atomic  weight  of  nitrogen, 
that  of  oxygen  being  8,  will,  therefore,  be  14.  The  other  four  com- 
pounds must  consequently  be  composed  of  one  atom  of  nitrogen,  united 
in  the  second  with  two,  in  the  third  with  three,  in  the  fourth  with  four, 
and  in  the  fifth  with  five,  atoms  of  oxygen. 

Protoxide  of  Nitrogen, 

This  gas  was  discovered  by  Priestley,  who  gave  it  the  name  of  dephlo- 
gisticated  nitrous  air.  Sir  H.  Davy  called  it  nitrous  oxide.  According 
to  the  principles  of  chemical  nomenclature  its  proper  appellation  is 
protoxide  of  nitrogen.  It  may  be  formed  by  exposing  nitric  oxide  for 
some  days  to  the  action  of  iron  filings,  or  otlier  substances  which  have 
a strong  affinity  for  oxygen.  The  nitric  oxide  loses  one-half  of  its  oxy- 
gen, and  is  converted  into  the  protoxide.  But  the  most  convenient 
method  of  procuring  it  is  by  means  of  nitrate  of  ammonia.  When  this 
salt  is  exposed  to  a temperature  of  400®  or  500®  F.  it  liquefies,  bubbles 
of  gas  begin  to  rise  from  it,  and  in  a short  time  brisk  effervescence  en- 
sues, which  continues  till  all  the  salt  disappears.  The  nitrate  of  ammo- 
nia should  be  contained  in  a glass . retort,  and  the  heat  be  applied  by 
means  of  a lamp,  placed  at  such  a distance  below  it  as  to  maintain  a 
moderately  rapid  evolution  of  gas. 

The  sole  products  of  this  operation,  when  carefully  conducted,  are 
water  and  protoxide  of  nitrogen.  The  theory  of  the  process  admits  of 
an  easy  explanation. 

Nitrate  of  ammonia  is  composed  of 

Nitric  acid  54  parts,  or  one  proportional. 

Ammonia  17  parts,  or  one  proportional. 

71 

These  compounds  are  thus  constituted: — 

Nitrogen  14  or  one  prop.  Nitrogen  14  or  one  prop. 

Oxygen  40  or  five  prop.  Hydrogen  3 or  three  prop. 

Nitric  acid  54  or  one  prop.  Ammonia  17  or  one  prop. 

By  the  action  of  heat  these  elements  arrange  themselves  in  a new  or- 
der. The  hydrogen  takes  so  much  oxygen  as  is  sufficient  for  forming 
water,  and  the  residual  oxygen  converts  the  nitrogen  both  of  the  nitric 


164 


NITROGEN. 


acid  and  of  the  ammonia  into  protoxide  of  nitrog-en.  The 
tion  of  71  grains  of  the  salt  will  therefore  yield 


The  decompose 


71 


Protoxide  of  nitrogen  is  a colourless  gas,  which  does  not  affect  the 
blue  vegetable  colours,  even  when  mixed  with  atmospheric  air.  Re- 
cently boiled  water,  which  has  cooled  without  exposure  to  the  air,  ab- 
sorbs nearly  its  own  bulk  of  it  at  60®  F.,  and  gives  it  out  again  unchang- 
ed by  boiling.  The  solution,  like  the  gas  itself,  has  a faint  agreeable 
odour  and  sweet  taste.  The  action  of  water  upon  it  affords  a ready 
means  of  testing  its  purity;  removing  it  readily  from  all  other  gases, 
such  as  oxygen  and  nitrogen,  which  are  sparingly  absorbed  by  that  li- 
quid. For  the  same  reason  it  cannot  be  preserved  over  cold  water;  but 
should  be  collected  either  over  hot  water  or  mercury. 

Protoxide  of  nitrogen  is  a supporter  of  combustion.  Most  substances 
burn  in  it  with  far  greater  energy  than  in  the  atmosphere.  When  a re- 
cently extinguished  candle  with  a very  red  wick  is  introduced  into  it, 
the  flame  is  instantly  restored.  Phosphorus,  if  previously  kindled, 
burns  in  it  with  great  brilliancy.  Sulphur,  when  burning  feebly,  is 
extinguished  by  it;  but  if  it  is  immersed  while  the  combustion  is  lively, 
the  size  of  the  flame  is  increased  considerably.  With  an  equal  bulk  of 
hydrogen  it  forms  a mixture  which  explodes  violently  by  the  electric 
spark  or  by  flame.  In  all  these  cases  the  product  of  combustion  is  the 
same  as  when  oxygen  gas  or  atmospheric  air  is  used.  The  protoxide  is 
decomposed;  the  combustible  matter  unites  with  its  oxygen,  and  the 
nitrogen  is  set  free.  The  protoxide  of  nitrogen  suffers  decomposition 
when  a succession  of  electric  sparks  is  passed  through  it.  A similar 
effect  is  caused  by  conducting  it  through  a porcelain  tube  heated  to  in- 
candescence. It  is  resolved,  in  both  instances,  into  nitrogen,  oxygen, 
and  nitrous  acid. 

Sir  H.  Davy  discovered  that  protoxide  of  nitrogen  may  be  taken  into 
the  lungs  with  safety,  and  that  it  supports  respiration  for  a few  minutes. 
He  breathed  nine  quarts  of  it,  contained  in  a silk  bag,  for  three  mi- 
nutes, and  twelve  quarts  for  rather  more  than  four;  but  no  quantity 
could  enable  him  to  bear  the  privation  of  atmospheric  air  for  a longer 
period.  Its  action  on  the  system,  when  inspired,  is  very  remarkable. 
A few  deep  inspirations  are  followed  by  most  agreeable  feelings  of  ex- 
citement, similar  to  the  earlier  stages  of  intoxication.  This  is  shown 
by  a strong  propensity  to  laughter,  by  a rapid  flow  of  vivid  ideas,  and 
an  unusual  disposition  to  muscular  exertion.  These  feelings,  however, 
soon  subside;  and  the  person  returns  to  his  usual  state,  without  experi- 
encing the  languor  or  depression  which  so  universally  follows  intoxica- 
tion from  spirituous  liquors.  Its  efl’ects,  however,  on  different  persons, 
are  various;  and  in  individuals  of  a plethoric  habit  it  sometimes  produces 
giddines;^,  headach,  and  other  disagreeable  symptoms.  (Researches  on 
the  Niti’ous  Oxide.) 

The  protoxide  of  niti’ogen  was  analyzed  by  Sir  II.  Davy  by  means  of 
hydrogen  gas.  He  mixed  39  measures  of  the  former  with  40  measures 
of  hydrogen,  and  fired  the  mixture  by  the  electric  spark.  Water  was 
formed;  and  the  residual  gas,  which  amounted  to  41  measures,  had  the 
properties  of  pure  nitrogen.  As  40  measures  of  hydrogen  require  20 
of  oxygen  for  combustion,  it  follows  that  39  volumes  of  the  protoxide 


NITROGEN. 


165 


of  nitrogen  contain  41  of  qitrog:in  and  20  of  oxygen.  But  since  no 
exception  has  hitherto  been  found  to  Gay-Lussac’s  law  of  gaseous  com- 
bination, it  may  be  inferred  tliat  protoxide  of  nitrogen  contains  its  own 
bulk  of  nitrogen  and  half  its  volume  of  oxygen.  The  analysis  of  this 
compound  by  Dr.  Henry,  (Annals  of  Phil.  viii.  299,  N.  S.)  performed 
by  means  of  carbonic  oxide  gas,  has  proved  beyond  a doubt  that  this  is 
the  exact  proportion.  Now, 

100  cubic  inches  of  nitrogen  weigh  29.652  grains, 
and  50  oxygen  16.944 


These  numbers  added  together  amount  to  46.596;  which  must  be  the 
weight  of  ICO  cubic  inches  of  the  protoxide;  and  its  specific  gravity  is, 
therefore,  1.5277.  Its  composition  by  weight  is  determined  by  the 
same  data,  being  16.944  of  oxygen  to  29.652  of  nitrogen,  or  as  8 to  14. 
Its  atomic  weight  or  equivalent  is,  of  course,  8 -j-  14  or  22.' 

Deiitoxide  of  Nitrogen. 

This  compound  is  best  obtained  by  the  action  of  nitric  acid,  of  spe- 
cific gravity  1.2,  on  metallic  copper.  Brisk  effervescence  takes  place 
without  the  aid  of  heat,  and  tlie  gas  may  be  collected  over  water  or 
mercury.  The  copper  gradually  disappears  during  the  process;  the 
liquid  acquires  a beautiful  blue  colour,  and  yields  on  evaporation  a salt 
which  is  composed  of  nitric  acid  and  peroxide  of  copper.  The  chemi- 
cal changes  that  occur  are  the  following. — One  portion  of  nitric  acid 
suffers  decomposition:  part  of  its  oxygen  unites  with  the  copper  and 
converts  it  into  peroxide;  while  another  part  is  retained  by  the  nitrogen 
of  the  nitric  acid,  forming  deutoxide  of  nitrogen.  The  peroxide  of 
copper  attaches  itself  to  some  undecomposed  nitric  acid,  and  forms  the 
blue  nitrate  of  copper.  Many  other  metals  are  oxidized  by  nitric  acid, 
with  disengagement  of  a similar  compound;  but  none,  mercury  except- 
ed, yields  so  pure  a gas  as  copper. 

The  gas  derived  from  this  source  was  discovered  by  Dr.  Hales.  It 
was  first  carefully  studied  by  Priestley,  who  called  it  nitrous  air.  The 
terms  nitrous  gas^  and  nitric  oxide,  are  frequently  applied  to  it;  but 
deutoxide  of  nitrogen,  as  indicative  of  its  nature,  is  the  most  suitable  ap- 
pellation. 

Deutoxide  of  nitrogen  is  a colourless  gas.  When  mixed  with  atmos- 
pheric air,  or  any  gaseous  mixture  that  contains  oxygen  in  an  uncom- 
bined state,  dense,  suffocating,  acid  vapours,  of  a red  or  orange  colour, 
are  produced,  C2i\\e(S.  nitrous  acid  vapours,  which  are  copiously  absorbed 
by  water,  and  communicate  acidity  to  it.  'I'his  character  serves  to  distin- 
guish the  deutoxide  from  every  other  substance;  and  affords  a conveni- 
ent test  of  the  presence  of  free  oxygen.  Though  it  gives  rise  to  an  acid 
by  combining  with  oxygen,  deutoxide  of  nitrogen  itself  does  not  redden 
the  blue  colour  of  vegetables;  but  for  this  experiment,  the  gas  must  be 
previously  well  washed  with  water  to  separate  all  traces  of  nitrous  acid. 
Water  absorbs  the  deutoxide  sparingl}^; — 100  measures  of  that  liquid, 
cold  and  recently  boiled,  take  up  about  11  of  the  gas. 

Very  few  inflammable  substances  burn  in  deutoxide  of  nitrogen. 
Burning  sulphur  and  a lighted  candle  are  instantly  extinguished  by  it. 
Charcoal  and  phosphorus,  however,  if  in  a state  of  vivid  combustion  at 
the  moment  of  being  immersed  in  it,  burn  with  increased  brilliancy.  The 
product  of  the  combustion  is  carbonic  acid  in  the  former  case,  and  phos- 
phoric acid  in  the  latter,  nitrogen  being  separated  in  both  instances. 
Witli  an  equal  bulk  of  hydrogen,  it  forms  a mixture  which  cannot  be 
made  to  explode,  but  which  is  kindled  by  contact  with  a lighted  candle, 


166 


NITROGEN. 


and  bums  rapidly  with  a greenish-white  flame.  Water  and  pure  nitro- 
gen  are  the  products. 

Deutoxide  of  nitrogen  is  quite  irrcspirable,  exciting  strong  spasm  of 
the  glottis,  as  soon  as  an  attempt  is  made  to  inhale  it.  The  experiment, 
however,  is  a dangerous  one;  for  if  the  gas  did  reacli  the  lungs,  it  would 
there  mix  with  atmospheric  air,  and  be  converted  into  nitrous  acid  va- 
pours, which  are  highly  irritating  and  corrosive. 

Deutoxide  of  nitrogen  is  partially  resolved  Into  Its  elements  by  being 
passed  through  red-hot  tubes.  A succession  of  electric  sparks  has  a si- 
milar effect.  It  is  converted  into  protoxide  of  nitrog'en  by  substances 
which  have  a strong  affinity  for  oxygen,  such  as  iron  filings  and  alkaline 
sulphurets.  Sir  H.  Davy  ascertained  Its  composition  by  the  combustion 
of  charcoal.  (Elements  of  Chemical  Philosophy,  p.  200.)  Two  volumes 
of  the  deutoxide  yielded  one  volume  of  nitrogen,  and  about  one  of  car- 
bonic acid;  whence  it  was  inferred  to  consist  of  equal  measures  of  oxy- 
gen and  Aitrogen  gases  united  without  any  condensation.  Gay-Lussac,  in 
his  essay  in  the  Memoires  d' Jlrcueil^  proved  that  this  proportion  is  rigid- 
ly exact.  He  decomposed  100  measures  of  the  gas,  by  heating  potassium 
in  it;  50  measures  of  pure  nitrogen  were  left,  and  the  loss  of  weight  cor- 
responded to  50  measures  of  oxygen.  The  same  fact  has  been  lately 
proved  by  Dr.  Henry  in  the  paper  already  referred  to.  From  these  data, 
its  composition  by  weight,  and  its  specific  gravity,  may  be  determined 
by  a simple  calculation: — 

50  cubic  inches  of  oxygen  weigh  16.944  grains. 

50  . . nitrogen  14.826 


31.770 

Hence  100  cubic  inches  of  deutoxide  of  nitrogen,  at  the  mean  temper- 
ature and  pressure,  weigh  31.77  grains;  audits  specific  gi’avity  is,  there- 
fore, 1.0416.  This  is  nearly  the  mean  density  of  the  deutoxide,  as  deter- 
mined directly  by  Davy,  Thomson,  and  Berard,  which  confirms  the  ac- 
curacy of  the  data  on  which  the  calculation  is  founded.  The  elements  of 
the  deutoxide  are  obviously  in  the  ratio,  by  weight,  of  14  of  nitrogen  to 
16  of  oxygen;  that  is,  one  proportional  of  the  former  to  two  of  the  latter. 
An  equivalent  of  the  compound  is,  therefore,  14  -f-  16  = 30, 

From  the  invariable  formation  of  red  coloured  acid  vapours,  whenever 
deutoxide  of  nitrogen  and  oxygen  are  mixed  together,  these  gases  detect 
the  presence  of  each  other  with  great  certainty;  and  since  the  product  is 
wholly  absorbed  by  water,  either  of  them  may  be  entirely  removed  from 
any  gaseous  mixture,  by  adding  a sufficient  quantity  of  the  other.  Priest- 
ley, who  first  observed  this  fact,  supposed  that  combination  takes  place 
between  them  in  one  proportion  only;  and  inferring  on  this  supposition, 
that  a given  absorption  must  always  indicate  the  same  quantity  of  oxygen, 
he  was  led  to  employ  deutoxide  of  nitrogen  in  eudiometry.  But  in  this 
opinion  he  was  mistaken.  The  discordant  results  that  were  obtained  by 
his  method,  soon  excited  suspicion  of  its  accuracy;  and  the  source 
of  error  has  since  been  discovered  by  the  researches  of  Dalton  and  Gay- 
Lussac.  It  appears  from  the  experiments  of  Gay-Lussac,  and  his  results 
do  not  differ  materially  from  those  of  Mr.  Dalton,  that  for  100  measures 
of  oxygen,  400  of  the  deutoxide  may  be  absorbed  as  a maximum,  and 
133  as  a minimum;  and  that  between  these  extremes,  the  quantity  of  the 
deutoxide  corresponding  to  100  of  oxygen,  is  exceedingly  variable.  It 
does  not  follow  from  this,  that  oxygen  and  deutoxide  of  nitrogen  unite 
in  every  proportion  within  these  limits.  I'he  true  explanation  is,  that 
tlie  mixture  of  these  gases  may  give  rise  to  three  compounds,  hyponi- 


NITROGEN. 


167 


trous,  nitrous,  and  nitric  acids 5 and  that  either  may  be  formed  almost,  if 
not  entirely,  to  the  exclusion  of  the  others,  if  certain  precautions  are 
adopted.  But  in  the  usual  mode  of  operating*,  two  if  not  all  are  generated 
at  the  same  time,  and  in  a proportion  to  each  other  which  is  by  no  means 
uniform.  The  circumstances  that  influence  the  degree  of  absorption, 
when  a mixture  of  oxygen  and  deutoxide  of  nitrogen  is  made  over  water, 
are  the  following; — 1,  The  diameter  of  the  tube;  2,  The  rapidity  with 
which  the  mixture  is  made;  3,  The  relative  proportion  of  the  two  gases; 
4,  The  time  allowed  to  elapse  after  mixing  them;  5,  Agitation  of  the 
tube;  and  lastly.  The  opposite  conditions  of  adding  the  oxygen  to  the 
deutoxide,  or  the  deutoxide  to  the  oxygen. 

Notwithstanding  these  many  sources  of  error,  Dalton  and  Gay-Lussac 
maintain  that  deutoxide  of  nitrogen  may  nevertheless  be  employed  in 
eudiometry;  and  they  have  described  the  precautions  which  are  required 
to  ensure  accuracy.  Mr.  Dalton  has  given  his  process  in  the  lOth  volume 
of  the  Annals  of  Philosophy,  page  38;  and  further  directions  have  been 
published  by  Dr.  Henry  in  his  Elements.  The  method  of  Gay-Lussac, 
to  which  my  own  observation  would  lead  me  to  give  the  preference, 
may  be  found  in  the  2d  volume,  page  247,  of  the  Memoir es  d^ArcueiU 
Instead  of  employing  a narrow  tube,  such  as  is  commonly  used  for  mea- 
suring gases,  Gay-Lussac  advises  that  100  measures  of  air  should  be  in- 
troduced into  a very  wide  tube  or  jar,  and  that  an  equal  volume  of  deut- 
oxide of  nitrogen  should  then  be  added.  The  red  vapours,  which  are 
instantly  produced,  disappear  very  quickly;  and  the  absorption  after 
half  a minute,  or  a minute  at  the  most,  may  be  regarded  as  complete. 
The  residue  is  then  transferred  into  a graduated  tube  and  measured. 
The  diminution  almost  always,  according  to  Gay-Lussac,  amounts  to  84 
measures,  one-fourth  of  which  is  oxygen.*  Gay-Lussac  has  applied  this 
process  to  the  analysis  of  various  mixed  gases,  in  which  the  oxygen  was 
sometimes  in  a greater,  at  others  in  a less  proportion  than  in  the  atmos- 
phere, and  the  indications  were  always  correct.  When  the  proportion 
of  oxygen  is  great,  a proportionally  large  quantity  of  the  deutoxide 
must  of  course  be  employed,  in  order  that  an  excess  of  it  may  be  pre- 
sent. 


• On  the  supposition  that  the  oxygen  and  deutoxide  of  nitrogen  unite 
in  the  proportions  to  form  nitrous  acid,  one-third,  and  not  one-fourth,  of 
the  diminution  ought  to  be  due  to  oxygen;  for  nitrous  acid  is  composed  of 
one  volume  of  oxygen  and  two  volumes  of  deutoxide  of  nitrogen.  It  may 
be  asked,  therefore,  what  are  the  real  products  of  the  experiment;  as  in 
point  of  fact,  one-fourth  of  the  gaseous  matter  which  disappears  is  due 
to  oxygen?  The  late  Dr.  Dana  ingeniously  reconciled  this  result  with 
the  theory  of  volumes,  by  supposing  that  two-thirds  of  the  deutoxide  of 
nitrogen  become  hyponitrousacid,  and  one-third,  nitrous  acid.  Thus  sup- 
posing six  volumes  of  the  deutoxide  to  be  mixed  with  a sufficient  quan- 
tity of  oxygen,  four  volumes  are  assumed  to  be  converted  into  hyponi- 
trous  acid,  by  combining  with  one  volume  of  oxygen,  and  the  remaining 
two,  into  nitrous  acid,  by  uniting  with  the  same  quantity  of  oxygen.  In 
this  manner  six  volumes  of  deutoxide  and  two  volumes  of  oxygen,  in  all 
eight  volumes,  will  disappear,  being  condensed,  as  above  explained,  in- 
to hyponitrous  and  nitrous  acids.  Now  of  these  eight  volumes,  it  is  appa- 
rent that  one-fourth  is  oxygen. 

When  the  experiment  is  performed  with  certain  precautions,  nitrous 
acid  is  the  sole  product,  and  the  formula  for  calculating  the  quantity  of 
oxygen  is  of  course  to  divide  the  deficit  by  three.  I had  the  pleasure  of 
seeing  this  proved  experimentally,  on  several  occasions,  by  Dr.  Hare  of 
the  University  of  Pennsylvania.  B, 


168 


NITROGKN. 


There  is  another  mode  of  absorbing*  oxygen  by  means  of  deutoxide  of 
nitrogen.  If  a current  of  the  deutoxide  be  conducted  into  a solution  of 
protosulphate  of  iron,  the  gas  is  absorbed  in  large  quantity,  and  the  so- 
lution acquires  a deep  olive-brown  colour,  whlcli  appears  almost  black 
when  fully  saturated.  This  solution  absorbs  oxygen  with  facility.  But 
it  cannot  be  safely  employed  in  eiidioinetry;  because  the  absorption  of 
oxygen  is  accompanied,  or  at  least  very  soon  followed,  by  evolution  of 
gas  from  the  liquid  itself. 

Sir  H.  Davy  ascertained  that  deutoxide  of  nitrogen  is  dissolved,  with- 
out decomposition,  by  a cold  solution  of  protosulphate  of  iron;  and  that 
when  the  solution  is  heated,  the  greater  part  of  the  gas  is  disengaged, 
and  the  remainder  decomposed.  The  decomposition  is  determined 
chiefly  by  the  affinity  of  protoxide  of  iron  for  oxygen  gas.  The  protoxide 
of  iron  decomposes  a portion  of  water  and  deutoxide  of  nitrogen  at  the 
same  time,  and  unites  with  the  oxygen  of  both;  while  the  hydrogen  of 
the  water  and  nitrogen  of  the  deutoxide  combine  together,  and  gene- 
rate ammonia.  Nitric  acid  is  formed  when  the  solution  is  exposed  to 
the  air  or  oxygen  gas,  but  not  otherwise. 

It  is  singular  that  both  deutoxide  and  protoxide  of  nitrogen,  notwith- 
standing the  absence  of  acidity,  are  capable  of  forming’  compounds  of 
considerable  permanence  with  the  pure  alkalies.  Tlie  circumstances 
which  give  rise  to  the  formation  of  these  compounds  will  be  stated  in 
the  description  of  nitre. 

Hyponitrous  Acid, 

On  adding  deutoxide  of  nitrogen  in  excess  to  oxygen  gas,  confined 
in  a glass  tube  over  mercury,  Gay-Lussac  observed  that  the  absorption 
is  always  uniform,  provided  a strong  solution  of  pure  potassa  is  put  into 
the  tube  before  mixing  the  two  gases.  He  found  that  100  measures  of 
oxygen  gas  combined,  under  these  circumstances,  with  400  of  the  deut- 
oxide, forming  an  acid  which  unites  with  the  potassa.  The  compound 
so  formed  is  hyponitrous  acid,  the  composition  of  which  may  be  easily 
inferred  from  the  proportions  just  mentioned.  For  as  deutoxide  of  ni- 
trogen contains  half  its  volume  of  oxygen  gas,  the  new  acid  must  be 
composed  of  200  measures  of  nitrogen  and  300  of  oxygen,  or  of  100  and 
^^“0.  It  contains,  therefore,  three  times  as  much  oxygen  as  protoxide 
oa  nitrogen;  so  that,  by  weight,  it  is  formed  of 

Nitrogen  14  one  proportional. 

Oxygen  24  three  proportionals; 

and  its  proportional  number  is  38. 

Another  method  of  forming  hyponitrous  acid  is  by  keeping  deutoxide 
of  nitrogen  for  three  months  in  a glass  tube  over  inercun^,  in  contact 
with  a concentrated  solution  of  pure  potassa.  The  deutoxide  is  resolv- 
ed into  hyponitrous  acid,  which  unites  with  the  potassa,  and  into  pro- 
toxide of  nitrogen  which  remains  in  the  tube.^ 

Hyponitrous  acid  has  not  hitherto  been  obtained  in  a free  state.  When 
an  acid  is  added  to  hyponitritc  of  potassa,  hyponitrous  acid,  instead  of 
being  dissolved  by  the  water  of  the  solution,  suffers  decomposition,  and 
is  converted,  according  to  Gay-Iaissac,  into  nitrous  acid  and  deutoxide 
of  nitrogen. 

Nitrous  Acid, 

To  form  pure  nitrous  acid  by  the  mixture  of  oxygen  gas  with  deutox- 
ide of  nitrogen,  the  operation  should  not  be  conducted  over  water  or 
mercury.  Tlie  presence  of  the  former  determines  the  production  of 
nitric  acid;  the  latter  is  oxidized  by  the  nitrous  acid,  and,  therefore. 


NITROGEN. 


169 


decomposes  it.  Sir  11.  Davy  made  this  compound  by  mixing-  two  mea- 
sures of  deutoxide  of  nitrog-en  and  one  of  oxygen,  free  from  moisture, 
in  a dry  glass  vessel,  previously  exhausted  by  the  air-pump.  (Elements, 
p.  261.)  Nitrous  acid  vapours  were  produced,  and  a contraction  en- 
sued, amounting  to  about  one-half  the  volume  of  the  mixed  gases.  The 
experiments  of  Gay-Lussac  (An.  de  Ch.  etdePh.  i.)  were  similar  in 
principle.  He  agrees  with  Sir  H.  Davy  as  to  the  proportion  of  the  two 
gases,  but  is  of  opinion  that  they  condense,  in  uniting,  to  l-3d  of  their 
original  volume.  The  conclusions  of  those  chemists  respecting  the  com- 
position of  nitrous  acid  have  been  confirmed  by  the  researches  of  Du- 
long.  (An.  de  Ch.  et  de  Ph.  ii.)  It  is  composed,  therefore,  of 

By  volume.  By  weight. 

Nitrogen  100  14  or  one  equivalent, 

Oxygen  200  32  or  four  equivalents; 

and  its  combining  proportion  is  32  14  = 46. 

Nitrous  acid  vapour  is  characterized  by  its  orange-red  colour.  It  is 
quite  irrespirable,  exciting  gi-eat  irritation  and  spasm  of  the  glottis,  even 
when  moderately  diluted  with  air.  A taper  burns  in  it  with  considerable 
brilliancy.  It  extinguishes  burning  sulphur;  but  the  combustion  of 
phosphorus  continues  in  it  with  great  vividness. 

Niti-ous  acid  may  exist  in  the  liquid  as  well  as  in  the  gaseous  form.  The 
liquid  acid  is  most  conveniently  prepared  by  exposing  crystallized  ni- 
trate of  lead,  carefully  dried,  to  a low  red  heat.  The  nitric  acid  of  the 
salt  is  by  this  means  resolved  into  nitrous  acid  and  oxygen;  and  if  the 
products  are  received  in  vessels  kept  moderately  cool,  the  greater  part 
of  the  former  is  condensed  into  a liquid.  This  substance  was  first  ob- 
tained by  Gay-Lussac,  who  regarded  it  as  hyponitrous  acid,  and  describ- 
ed it  as  such  in  the  essay  above  referred  to;  but  M.  Dulong  has  proved 
by  a careful  analysis,  that  it  is  in  reality  anhydrous  nitrous  acid.  Du- 
long procured  it  by  mixing  deutoxide  of  nitrogen  and  oxygen  gases  in 
the  ratio  of  2 to  1,  and  exposing  the  nitrous  acid  vapours  to  a low  tem- 
perature. 

The  liquid  anhydrous  acid  has  the  following  properties. — It  is  power- 
fully corrosive,  has  a strong  acid  taste  and  pungent  odour,  and  is  of  a 
yellowish-orange  colour.  Its  density  is  1.451.  It  preserves  the  liquid 
form  at  the  ordinary  temperature  and  pressure,  and  boils  at  82^  F. 
Exposed  to  the  atmosphere,  it  evaporates  with  great  rapidity,  forming 
the  common  nitrous  acid  vapours,  which,  when  once  mixed  with  air  or 
other  gases,  require  intense  cold  for  condensation. 

The  action  of  water  on  anhydrous  nitrous  acid  is  very  remarkable. 
On  mixing  it  with  a large  quantity  of  water,  it  is  instantly  resolved  into 
nitric  acid  and  deutoxide  of  nitrogen;  the  former  unites  with  the  water, 
making  a colourless  solution,  while  the  greater  part  of  the  latter  escapes 
in  the  form  of  gas.  When  nitrous  acid  is  added  to  a very  small  quanti- 
ty of  water,  none  of  the  deutoxide  is  disengaged;  and  a green  coloured 
liquid  is  produced.  If,  instead  of  employing  a very  large  or  a very 
small  proportion  of  water,  the  anhydrous  acid  be  dropped  into  a moder- 
ate quantity  of  that  fluid,  the  disengagement  of  deutoxide  of  nitrogen, 
at  first  considerable,  becomes  less  and  less  at  each  addition  of  the  acid, 
till  at  last  the  evolution  of  gas  ceases  altogether.  The  colour  of  the  so- 
lution varies  considerably  during  the  experiment.  From  being  quite 
colourless,  the  liquid  acquires  a greenish-blue  tinge,  thence  passes  into 
green  of  various  depths  of  shade,  and  at  length  becomes  of  a yellowish- 
orange, — the  colour  of  nitrous  acid  itself. 

These  changes  are  of  a complicated  nature,  and  may  be  accounted 
for  in  different  ways.  The  following  explanation  appears  to  me  moat 

15 


170 


NITROGEN. 


consistent  with  the  phenomenfx,  thoiij^h  I by  no  means  Insist  on  Its  ac- 
curacy, It  is  founded  on  the  supposition,  or  ratlier,  as  I conceive,  upon 
the  fact,  that  nitrous  and  hyponitrous  acids  cannot  exist  alone  in  water, 
but  are  always  decomposed  by  that  fluid  in  consequence  of  its  affinity 
for  nitric  acid.  When  a drop  of  nitrous  acid  is  added  to  a very  small 
quantity  of  water,  it  is  resolved  into  nitric  and  hyponitrous  acids,  the 
latter  being*  protected  from  decomposition  by  the  former  having*  com- 
bined  with  the  water.  The  hyponitrous  acid  is  therefore  mixed  with 
the  solution  of  nitric  acid,  or  is  perhaps  chemically  united  with  it.  On 
adding  a second  portion  of  nitrous  acid,  that  acid  is  protected- from  de- 
composition by  the  same  circumstance  which  preserves  the  hyponitrous; 
and,  consequently,  it  remains  in  a state  of  mixture  or  combination  with 
the  two  other  acids.  If  the  anhydrous  nitrous  acid  be  mixed  with  a 
large  quantity  of  water,  it  is  converted  into  nitric  acid  and  deutoxide 
of  nitrogen;  and  every  successive  addition  experiences  a similar  change, 
till  the  water  has  become  sufficiently  charged  with  nitric  acid  to  enable 
the  hyponitrous  to  exist  in  it.  The  subsequent  additions  of  nitrous  acid 
will  then  be  converted  into  nitric  and  hyponitrous  acids,  until  the  affini- 
ty of  the  water  for  nitric  acid  is  so  far  satisfied  that  it  can  no  longer  de- 
compose nitrous  acid. 

The  changes  which  are  produced  in  anhydrous  nitrous  acid  by  adding 
successive  portions  of  water,  may  be  anticipated  from  the  preceding 
remarks.  It  is  resolved  into  nitric  and  hyponitrous  acids,  and  into  nitric 
acid  and  deutoxide  of  nitrogen;  and  when  the  dilution  is  considerable, 
the  greater  part,  if  not  tlie  whole,  of  the  hyponitrous  acid  will  like- 
wise be  decomposed.  The  colour  of  the  fluid  at  different  periods  of 
the  process  is  attributed  to  the  quantity  of  nitrous  acid  which  is  dissolv- 
ed, and  to  the  degree  of  its  dilution.  It  is  difficult,  however,  to  per- 
ceive how  an  orange-coloured  liquid  should  give  different  shades  of 
green  and  blue  merely  by  being  diluted.  May  not  the  blue  be  caused 
by  hyponitrous  acid,  the  different  shades  of  green  by  mixtures  of  hy- 
ponitrous and  nitrous  acids,  and  the  yellow  and  orange  by  the  prepon- 
derance of  the  latter?  Some  observations  of  M.  Dulong  seem  to  justify 
this  idea;  and  it  is  supported  by  the  action  of  deutoxide  of  nitrogen  on 
nitric  acid. 

Nitrous  acid  is  a powerful  oxidizing  agent,  readily  giving  oxygen  to 
the  more  oxidable  metals,  and  to  most  substances  which  have  a strong 
affinity  for  it.  Nitrous  acid  is  of  course  decomposed  at  the  same  time; 
pure  nitrogen  and  protoxide  of  nitrogen  are  sometimes  evolved,  but 
most  commonly  it  is  converted  into  the  deutoxide.  When  transmitted 
through  red-hot  porcelain  tubes,  it  suffers  decomposition,  and  a mixture 
of  oxygen  and  nitrogen  gases  is  obtained. 

Nitric  Jlcid. 

If  a succession  of  electric  sparks  be  passed  through  a mixture  of 
oxygen  and  nitrogen  gases  confined  in  a glass  tube  over  mercury,  a little 
water  being  present,  tlie  volume  of  the  gases  will  gradually  diminish, 
and  tlie  water  after  a time  will  be  found  to  have  acquired  acid  proper- 
ties. Oji  neutralizing  the  solution  with  potassa,  or  what  is  better,  by 
putting  a solution  of  pure  potassa  instead  of  water  into  the  tube  at  the 
beginning  of  the  experiment,  a salt  is  obtained  which  possesses  all  the 
properties  of  nitrate  of  potassa.  I’his  experiment  was  performed  in 
1785  by  Mr.  Cavcndisli,  who  inferred  from  it  that  nitric  acid  is  compo- 
sed of  oxygen  and  nitrogen.  The  best  proportion  of  the  gases  was 
found  to  be  seven  of  oxygen  to  three  of  nitrogen;  but  as  some  nitrous 
acid  is  always  formed  during  the  process,  the  exact  composition  of  ni- 
tric acid  cannot  in  this  way  be  accurately  determined. 


NITROGEN. 


in 


Nitric  acid  may  be  formed  much  more  conveniently  by  adding  dent- 
oxide  of  nitrog’en  slowly  over  water  to  an  excess  of  oxygen  gas.  Gay- 
Lussac  proved  that  nitric  acid  may  in  this  manner  be  obtained  quite 
free  from  nitrous  or  hyponitrous  acid,  and  that  it  is  composed  of  100 
measures  of  nitrogen  and  250  of  oxygen.  This  result  agrees  with  the 
proportion  which  Sir  H.  Davy  has  deduced  from  his  observations;  and  it 
is  confirmed  by  an  analysis  of  nitrate  of  baryta  recently  made  by  Dr. 
Henry.  Nitric  acid  is,  therefore,  composed  of 

By  volume.  By  voeiglit. 

Nitrogen  - 100  : 14  : one  equivalent, 

Oxygen  - 250  : 40  : five  equivalents; 

and  its  combining  proportion  or  Equivalent  is  54. 

Nitric  acid  cannot  exist  in  an  insulated  state.  Deutoxide  of  nitrogen 
and  oxygen  gases  never  form  nitric  acid,  if  mixed  together  when  quite 
dry;  and  nitrous  acid  vapour  may  be  kept  in  contact  with  oxygen  gas 
without  change,  provided  no  water  is  present.  Tlie  most  simple  form 
under  which  chemists  have  hitherto  procured  nitric  acid  is  in  solution 
W’ith  water;  a liquid  whicli,  in  its  concentrated  state,  is  the  nitric  acid 
of  the  Pharmacopeia.  By  manufacturers  it  is  better  known  by  the 
name  of  aqua  fortis. 

The  nitric  acid  of  commerce  is  procured  by  decomposing  some  salt 
of  nitric  acid  by  means  of  concentrated  sulphuric  acid;  and  common 
nitre,  as  the  cheapest  of  the  nitrates,  is  always  employed  for  the  pur- 
pose. This  salt,  previously  well  dried,  is  put  into  a glass  retort,  and  a 
quantity  of  the  strongest  sulphuric  acid  is  poured  upon  it.  On  apply- 
ing heat,  ebullition  ensues,  owing  to  the  escape  of  nitric  acid  vapours, 
which  must  be  collected  in  a receiver  kept  cold  by  moist  cloths.  The 
heat  should  be  steadily  increased  during  the  operation,  and  continued 
as  long  as  any  acid  vapours  come  over. 

Chemists  differ  as  to  the  best  proportions  for  forming  nitric  acid.  The 
London  College  recommends  equal  weights  of  nitre  and  sulphuric  acid; 
and  the  Edinburgh  and  Dublin  Colleges  employ  three  parts  of  nitre  to 
two  of  the  acid.  The  proportion  of  the  London  College  is  so  calculated, 
that  the  potassa  of  the  nitre  shall  be  entirely  converted  into  a bisul- 
phate; for  one  proportional  of  nitre  (54  nitric  acid  -(-  48  potassa)  is  102, 
and  98  corresponds  to  two  proportionals  of  concentrated  sulphuric  acid. 
To  comprehend  the  nature  of  this  process,  it  is  necessary  to  observe, 
that  the  strong  sulphuric  acid  of  commerce  consists  of  one  equivalent 
of  dry  acid  and  one  of  water,  and  that  the  strongest  nitric  acid  contains 
nearly  one  equivalent  of  dry  or  real  acid  and  two  equivalents  of  water. 
Unless  supplied  with  this  proportion  of  water,  the  nitric  acid  is  re- 
solved, at  the  moment  of  quitting  the  potassa,  into  ox3^gen  and  nitrous 
acid.  Now  in  the  process  of  the  London  College,  the  water  in  the  oil 
of  vitriol  is  precisely  sufficient  for  uniting  with  the  nitric  acid,  and, 
therefore,  the  latter  passes  over  almost  entirely  as  such  into  the  receiver. 
If  the  mixture  be  introduced  into  the  retort  without  soiling  its  neck,  and 
the  heat  be  cautiously  raised,  the  product  will  be  quite  free  from  sul- 
phuric acid;  and,  therefore,  the  second  distillation  from  nitre,  recom- 
mended in  the  Pharmacopoeia,  is  superfluous. 

The  proportions  of  the  Edinburgh  and  Dublin  Colleges  are  such,  that 
the  residual  salt  is  a mixture  of  sulphate  and  bisulphate  of  potassa.  The 
acid  of  the  nitre  does  not  receive  from  the  oil  of  vitriol  the  requisite 
quantity  of  water,  and  hence  part  of  it  is  decomposed,  yielding  to- 
wards the  close  of  the  operation  an  abundant  supply  of  nitrous  acid 
fumes.  If  the  receiver  be  kept  cool,  nearly  all  these  vapours  are  con- 
densed; and  the  product  is  a mixture  of  nitric  and  nitrous  acids,  of  ^ 


172 


NITROGEN. 


deep  orang'e-rccl  colour,  very  strong*  and  fuming*,  and  of  a greater  spe- 
cific gravity,  thougli  proportionally  less  in  quantity,  than  that  obtained 
by  the  foregoing  process.  The  specific  gravity  of  the  pale  acid  is  1.500; 
while  thatof  the  red  acid  is  1.520,  or  by  previously  drying  the  nitre  and 
boiling  the  sulphuric  acid.  Dr.  Hope  states  that  it  may  be  made  so  high 
as  1.54. 

Some  manufacturers  decompose  nitre  with  half  its  weight  of  sulphu- 
ric acid,  thus  employing  the  ingredients  in  the  proportion  of  one  equi- 
valent of  each.  In  this  case  about  half  of  the  nitric  acid  is  decomposed, 
and  considerable  loss  sustained,  unless  the  requisite  quantity  of  water 
is  previously  mixed  with  the  sulphuric  acid,  or  water  be  placed  in  the 
receiver  to  condense  the  nitrous  acid.  Some  of  the  nitre  is  likewise  apt 
to  escape  decomposition;  and  the  residue  consisting  of  neutral  sulphate, 
which  is  much  less  soluble  than  the  bisiilphatc,  is  removed  from  the  re- 
tort with  difficulty. 

In  none  of  the  preceding  processes,  not  even  in  the  first,  is  the  pro- 
duct quite  colourless;  for  at  the  commencement  and  close  of  the  ope- 
ration, nitrous  acid  fumes  are  disengaged,  which  communicate  a straw- 
yellow  or  an  orange-red  tint,  according  to  their  quantity.  If  a very 
pale  acid  is  required,  two  receivers  should  be  used;  one  for  condensing 
the  colourless  vapours  of  nitric  acid,  and  another  for  the  coloured  pro- 
ducts. The  coloured  acid  is  called  nitrous  acid  by  the  college;  but  it  is 
in  reality  a mixture  or  compound  of  nitric  and  nitrous  acids,  similar  to 
what  may  be  obtained  by  mixing  anhydrous  nitrous  with  colourless  ni- 
tric acid.  It  is  easy  to  convert  the  common  mixed  acid  of  the  college 
into  colourless  nitric  acid,  by  exposing  the  former  to  a gentle  heat  for 
some  time,  when  all  the  nitrous  acid  will  be  expelled.  But  this  pro- 
cess is  rarely  necessary,  as  the  coloured  acid  may  be  substituted  in  al- 
most every  case  for  that  which  is  colourless.  Where  an  acid  of  great 
strength  is  required,  the  former  is  even  preferable. 

Nitric  acid  frequently  contains  portions  of  sulphuric  and  muriatic 
acid.  The  former  is  derived  from  the  acid  which  is  used  in  the  process; 
and  the  latter  from  sea-salt,  which  is  frequently  mixed  with  nitre.  These 
impurities  may  be  detected  by  adding  a few  drops  of  a solution  of  mu- 
riate of  baryta  and  nitrate  of  silver  to  separate  portions  of  nitric  acid, 
diluted  with  three  or  four  parts  of  distilled  water,  if  muriate  of  baryta 
cause  a cloudiness  or  j^recipitate,  sulphuric  acid  must  be  present;  if  a 
similar  effect  be  produced  by  nitrate  of  silver,  the  presence  of  muriatic 
acid  may  be  inferred.  Nitric  acid  is  purified  from  sulphuric  acid  by  re- 
distilling it  from  a small  quantity  of  nitrate  of  potassa,  with  the  alkali 
of  which  the  sulphuric  acid  unites,  and  remains  in  the  retort.  To  se- 
parate muriatic  acid,  it  is  necessary  to  drop  a solution  of  nitrate  of  sil- 
ver into  the  nitric  acid  as  long  as  a precipitate  is  formed,  and  draw  off 
tlie  pure  acid  by  distillation. 

Nitric  acid  possesses  acid  properties  in  an  eminent  degree.  A few 
drops  of  it  diluted  with  a considerable  quantity  of  water  form  an  acid 
solution,  which  reddens  litmus  paper  permanently.  It  unites  with  and 
neutralizes  alkaline  substances,  forming  with  them  salts  which  are  called 
nitrates.  In  its  purest  and  most  concentrated  state  it  is  colourless,  and 
has  a specific  gravity  of  1.50  or  1.510.  It  still  contains  a considerable 
quantity  of  water,  from  wlfich  it  cannot  be  separated  without  decom- 
position, or  by  uniting  with  some  other  body.  An  acid  of  density  1.50 
contains  25  ])(t  cent,  of  water,  according  to  the  experiments  of  Mr. 
i^hillips;  and  20.3  per  cent,  according*  to  those  of  Dr.  Ure.*  Nitric 


• Sec  his  Table  in  the  Appendix,  showing  the  strength  of  diluted 
acid  of  dilfercnt  densities. 


NITROGEN. 


173 


acid  of  tills  strength  emits  dense,  white,  suflPocatlng  vapours  when  ex- 
posed to  the  atmosphere.  It  attracts  watery  vapour  from  the  air,  where- 
by its  specific  gravity  is  diminished.  A rise  of  temperature  is  occasion- 
ed by  mixing  it  with  a certain  quantity  of  water.  Dr.  Ure  found  that 
when  58  measures  of  nitric  acid,  of  specific  gi’avity  1.5,  are  suddenly 
mixed  with  42  of  water,  the  temperature  rises  from  60  to  140?  F;  and 
the  mixture,  on  cooling  to  60®,  occupies  the  space  of  92.65  measures 
instead  of  100.  From  its  strong  affinity  for  water,  it  occasions  snow  to 
liquefy  witli  great  rapidity;  and  if  the  mixture  is  made  in  due  propor- 
tion, intense  cold  will  be  generated.  (Page  54.) 

Nitric  acid  boils  at  248®  F.  and  may  be  distilled  without  suffering  ma- 
terial change.  An  acid  of  less  specific  gravity  than  1.42  becomes 
stronger  by  being  heated,  because  the  water  evaporates  more  rapidly 
than  the  acid.  An  acid,  on  the  contrary,  which  is  stronger  than  1.42  is 
weakened  by  the  application  of  heat. 

Nitric  acid  may  be  frozen  by  cold.  The  temperature  at  which  con- 
gelation takes  place,  varies  with  the  strength  of  the  acid.  The  strong- 
est acid  freezes  at  about  50  degrees  below  zero.  When  diluted  with 
half  its  weight  of  water,  it  becomes  solid  at  — 1^9  F.  By  the  addition 
of  a little  more  water  its  freezing  point  is  lowered  to  — 45®  F. 

Nitric  acid  acts  powerfully  on  substances  which  are  disposed  to  unite 
with  oxygen;  and  hence  it  is  much  employed  by  chemists  for  bringing 
bodies  to  their  maximum  of  oxidation.  Nearly  all  the  metals  are  oxi- 
dized by  it;  and  some  of  them,  such  as  tin,  copper,  and  mercury,  are 
attacked  with  great  violence.  If  flung  on  burning  charcoal,  it  increases 
the  brilliancy  of  its  combustion  in  a high  degree.  Sulphur  and  phos- 
phorus are  converted  into  acids  by  its  action.  All  vegetable  substances 
are  decomposed  by  it.  In  general  the  oxygen  of  the  nitric  acid  enters 
into  direct  combination  with  the  hydrogen  and  carbon  of  those  com- 
pounds, forming  water  with  the  former,  and  carbonic  acid  with  the  lat- 
ter. This  happens  remarkably  in  those  compounds  in  which  hydrogen 
and  carbon  are  predominant,  as  in  alcohol  and  the  oils.  It  effects  the 
decomposition  of  animal  matters  also.  The  cuticle  and  nails  receive  a 
permanent  yellow  stain  when  touched  with  it;  and  if  applied  to  the 
skin  in  sufficient  quantity  it  acts  as  a powerful  cautery,  destroying  the 
organization  of  the  part  entirely. 

AVhen  oxidation  is  effected  through  the  medium  of  nitric  acid,  the 
acid  itself  is  commonly  converted  into  deutoxide  of  nitrogen.  This  gas 
is  sometimes  given  off’  nearly  quite  pure;  but  in  general  some  nitrous 
acid,  protoxide  of  nitrogen,  or  pure  nitrogen  is  disengaged  at  the  same 
time.  Direct  solar  light  deoxidizes  nitric  acid,  resolving  a portion  of  it 
into  oxygen  and  nitrous  acid.  The  former  escapes  as  gas;  the  latter  is 
absorbed  by  the  nitric  acid,  and  converts  it  into  the  mixed  nitrous  acid 
of  the  shops.  When  the  vapour  of  nitric  acid  is  transmitted  through 
red-hot  porcelain  tubes,  it  suffers  complete  decomposition,  and  a mix- 
ture of  oxygen  and  nitrogen  gases  is  the  product. 

Nitric  acid  may  also  be  deoxidized  by  transmitting  a current  of  deu- 
toxide of  nitrogen  through  it.  That  gas,  by  taking  oxygen  from  the 
nitric,  is  converted  into  nitrous  acid;  and  a portion  of  nitric  acid,  by 
losing  oxygen,  passes  into  the  same  compound.  The  nitrous  acid,  thus 
derived  from  two  sources,  gives  a colour  to  the  nitric  acid,  the  depth 
and  kind  of  which  depend  upon  the  quantity  of  deutoxide  of  nitrogen 
winch  has  been  employed.  The  first  poition  communicates  a pale  straw 
colour,  which  gradually  dee])ens  as  the  absorption  of  the  deutoxide 
continues,  till  the  nitric  acid  has  acquired  a deep  orange  hue,  together 
with  all  the  characters  of  strong  fuming  nitrous  acid.  But  the  solution 
still  continues  to  absorb  the  deutoxide;  and  in  doing  so,  its  colour  passes 

15*^ 


CARBON. 


1T4 

through  different  shades  of  olive  and  green,  till  it  becomes  greenish- 
blue.  By  applying  heat  to  the  blue  liquid,  dcutoxide  of  nitrogen  is 
evolved;  and  in  proportion  as  it  escapes,  the  colour  of  the  solution 
changes  to  green,  olive,  orange,  and  yellow,  at  length  becoming  palo 
as  at  first.  Nitrous  acid  vapours  are  likewise  disengaged  as  well  as  the 
deutoxide.  These  phenomena  are  very  favourable  to  the  view  that  the 
conversion  of  the  orange  colour  into  olive,  green,  and  blue,  is  owing 
to  the  foi’ination  of  hyponitrous  acid. 

All  the  salts  of  nitric  acid  are  soluble  in  water,  and,  therefore,  it  is 
impossible  to  precipitate  that  acid  by  any  reagent.  The  presence  of 
nitric  acid,  when  uncombined,  is  readily  detected  by  its  strong  action 
on  copper  and  mercury,  and  by  its  forming  with  potassa  a neutral  salt, 
which  crystallizes  in  prisms,  and  has  all  the  propeidies  of  nitre.  Gold 
leaf  is  a still  more  delicate  test.  When  muriatic  acid  is  added  to  the 
solution  of  ' a nitrate,  chlorine  is  disengaged,  and  the  liquid  hence  ac- 
quires the  property  of  dissolving  gold  leaf;  but  as  the  action  of  muri- 
atic acid  on  the  salts  or  chloric  and  bromic  acids  likewise  yields  a solu- 
tion capable  of  dissolving  gold,  no  inference  can  be  drawn  from  the 
experiment,  unless  the  absence  of  these  acids  shall  have  been  previous- 
ly demonstrated.  A new  test  of  the  presence  of  nitric  acid  has  recent- 
ly been  proposed  by  Dr.  Liebig.  The  liquid  to  be  examined  must  be 
mixed  with  a sufficient  quantity  of  a solution  of  indigo  in  sulphuric  acid 
for  acquiring  a distinct  blue  colour;  a few  drops  of  sulphuric  acid  must 
be  then  added,  and  the  mixture  boiled.  If  a nitrate  is  present,  the  li- 
quid will  be  bleached,  or,  if  the  quantity  is  very  small,  rendered  yel- 
low. By  this  process  nitric  acid  may  be  detected,  though  diluted 
with  400  times  its  weight  of  water;  or  by  adding  a little  muriate  of 
soda  to  the  liquid  before  applying  heat,  l-500th  part  of  nitric  acid 
may  be  discovered.  (Quarterly  Journal  of  Science  for  July  1827,  p, 
204.) 


SECTION  VI. 

CARBON. 

Weten’  wood  is  heated  to  a certain  degree  in  the  open  air,  it  take* 
fire,  and  burns  with  the  formation  of  water  and  carbonic  acid  gas  till 
the  whole  of  it  is  consumed.  A small  portion  of  ashes,  consisting  of 
ail  the  alkaline  and  earthy  matters  which  had  formed  a part  of  the  wood, 
is  the  sole  residue.  But  if  the  wood  be  heated  to  redness  in  close  ves- 
sels, so  that  atmospheric  air  cannot  have  free  access  to  it,  a large  quan- 
tity of  gaseous  and  other  volatile  matters  is  expelled,  and  a black,  hard, 
porous  substance  is  left,  called  charcoal. 

Charcoal  may  be  procured  from  other  sources.  When  the  volatile 
matters  arc  driven  off  from  coal,  as  in  the  process  for  making  coal  gas, 
,a  peculiar  kind  of  charcoal,  called  coke,  remains  in  the  retort.  Most 
animal  and  vegetable  substances  yield  it  when  ignited  in  close  vessels. 
Tlius,  a very  pure  charcoal  maybe  procured  from  starch  or  sugar;  and 
from  the  oil  of  turpentine  or  spirit  of  wine,  by  passing  their  vapour 
through  tubes  heated  to  redness.  When  bones  are  made  red-hot  in  a 
covered  crucible,  a black  mass  remains,  which  consists  of  charcoal  mix- 
ed with  the  cailhy  matters  of  the  bone.  It  is  called  ivory  black  or  anU 
inal  cJuu'Coal. 


CARBON. 


175 


Charcoal  hard  and  brittle,  conducts  heat  very  slowly,  but  is  a good 
conductor  of  electricity.  Its  density  is  stated  much  too  low  in  chemi- 
cal works: — according  to  Mr.  Leslie,  its  specific  gravity  is  rather  greater 
than  that  of  the  diamond.  It  is  quite  insoluble  in  water,  is  attacked 
with  difficulty  by  nitric  acid,  and  is  little  affected  by  any  of  the  other 
acids,  or  by  the  alkalies.  It  undergoes  little  change  from  exposure  to 
air  and  moisture,  being  less  injured  under  these  circumstances  than 
wood.  It  is  exceedingly  refractory  in  the  fire,  if  excluded  from  the 
air,  supporting  the  most  intense  heat  which  chemists  are  able  to  pro- 
duce without  change. 

Charcoal  possesses  the  property  of  absorbing  a large  quantity  of  air 
or  other  gases  at  common  temperatures,  and  of  yielding  the  greater 
part  of  them  again  when  it  is  heated.  It  appears  from  the  researches 
of  Saussure,  tliat  different  gases  are  absorbed  by  it  in  different  propor- 
tions. His  experiments  were  performed  by  plunging  a piece  of  red-hot 
charcoal  under  mercury,  and  introducing  it  when  cool  into  the  gas  to 
be  absorbed.  He  found  that  charcoal  prepared  from  box-wood  absorbs, 
dui’ing  the  space  of  24  or  36  hours,  of 


Ammoniacal  gas 

90  times  its 

Muriatic  acid 

85 

Sulphurous  acid 

65 

Sulphuretted  hydrogen 

55 

Nitrous  oxide 

40 

Carbonic  acid 

35 

Olefiant  gas  - - - 

35 

Carbonic  oxide 

9.42 

Oxygen  - • . 

9.25 

Nitrogen  - - - 

7.5 

Hydrogen  - - - 

1.75 

volume. 


The  absorbing  power  of  charcoal,  with  respect  to  gases,  cannot  ba 
attributed  to  chemical  action;  for  the  quantity  of  each  gas,  which  is 
absorbed,  bears  no  relation  whatever  to  its  affinity  for  charcoal.  The 
effect  is  in  reality  owing  to  the  peculiar  porous  texture  of  that  sub- 
stance, which  enables  it,  in  common  with  most  spongy  bodigfs',  to  absorb 
more  or  less  of  all  gases,  vapours,  and  liquids,  with  whicn  it  is  in  con- 
tact. This  property  is  most  remarkable  in  charcoal  prepared  from 
wood,  especially  in  the  compact  varieties  of  it,  the  pores  of  which  are 
numerous  and  small.  It  is  materially  diminished  by  reducing  the  char- 
coal to  powder;  and  in  plumbago,  which  has  not  the  requisite  degree 
of  porosity,  it  is  wanting  altogether. 

The  porous  texture  of  charcoal  accounts  for  the  general  fact  of  ab- 
sorption only;  its  power  of  absorbing  more  of  one  gas  than  of  another, 
must  be  explained  on  a different  principle.  This  effect,  though  modi- 
fied to  all  appearance  by  the  influence  of  chemical  attraction,  seems  to 
depend  chiefly  on  the  natural  elasticity  of  the  gases.  Those  which  pos^ 
sess  such  a great  degree  of  elasticity  as  to  have  hitherto  resisted  all  at- 
tempts to  condense  them  into  liquids,  are  absorbed  in  the  smallest  pro- 
portion; while  those  that  admit  of  being  converted  into  liquids  by  com- 
pression, are  absorbed  more  freely.  For  this  reason,  charcoal  absorbs 
vapours  more  easily  tlian  gases,  and  liquids  than  either. 

Messrs.  Allen  and  Pepys  determined  experimentally  the  increase  in 
weight  experienced  by  different  kinds  of  charcoal,  recently  ignited,  after 
a week’s  exposure  to  the  atmosphere.  The  charcoal  from  fir  gained  13 
percent;  that  from  lignum  vitae,  9.6;  that  from  box,  14;  from  beech, 
16.3;  from  oak,  16.5;  and  from  mahogany,  18.  The  absorption  is  most 


176  CAUBON. 

rapid  during*  the  first  24  hours.  Tlie  substance  absorbed  is  both  water 
and  atmospheric  air,  which  the  charcoal  retains  with  such  force,  tliat  it 
cannot  be  completely  separated  from  them  without  exposure  to  a red 
heat.  Vog*el  has  observed  that  charcoal  absorbs  oxygen  in  a much 
gi'catcr  proportion  from  the  air  than  nitrogen.  Thus,  when  recently 
ignited  charcoal,  cooled  under  mercury,  was  ])ut  into  a jar  of  atmospheric 
air,  the  residue  contained  only  8 per  cent  of  oxygen  gas;  and  if  red-hot 
charcoal  be  plunged  into  water,  and  then  introduced  into  a vessel  of  air, 
the  oxygen  disappears  almost  entirely.  It  is  said  that  pure  nitrogen  may 
be  obtained  in  this  way.  (Schweigger’s  Journal,  iv.) 

Charcoal  likewise  absorbs  the  odoriferous  and  colouring  principles  of 
most  animal  and  vegetable  substances.  AVhen  coloured  infusions  of  this 
kind  are  digested  with  a due  quantity  of  charcoal,  a solution  is  obtained, 
which  is  nearly  if  not  quite  colourless.  "iVmted  flesh  may  be  rendered 
sweet  and  eatable  by  this  means,  and  foul  water  may  be  purified  by  fil- 
tration through  charcoal.  The  substance  commonly  employed  to  de- 
colorize fluids  is  animal  charcoal  reduced  to  a fine  powder.  It  loses  the 
property  of  absorbing  colouring  matters  by  use,  but  recovers  it  by  being 
heated  to  redness. 

Charcoal  is  highly  combustible.  When  strongly  heated  in  the  open 
air,  it  takes  fire,  and  burns  slowly.  In  oxygen  gas,  its  combustion  is 
lively,  and  accompanied  with  the  emission  of  sparks.  In  both  cases  it 
is  consumed  without  flame,  smoke,  or  residue,  if  quite  pure;  and  car- 
bonic acid  gas  is  the  product  of  its  combustion. 

The  pure  inflammable  principle,  which  is  the  characteristic  ingredient 
of  all  kinds  of  charcoal,  is  called  carbon.  In  coke  it  is  in  a very  impure 
form.  Wood-charcoal  contains  about  l-50th  of  its  weight  of  alkaline 
and  earthy  salts,  which  constitute  the  ashes  when  this  species  of  char- 
coal is  burned.  In  plumbago,  the  carbon  is  combined  with  a small  por- 
tion of  metallic  iron.  Charcoal  derived  from  spirit  of  wine  is  almost 
quite  pure;  and  the  diamond  is  carbon  in  a state  of  absolute  purity. 

The  diamond  is  the  hardest  substance  in  nature.  Its  texture  is  crys- 
talline in  a high  degree,  and  its  cleavage  very  perfect.  Its  primary 
form  is  the  octohedron.  It  has  a specific  gravity  of  3.520.  Acids  and 
alkalies  do  not  act  upon  it;  and  it  bears  the  most  intense  heat  in  close 
vessels  without  fusing  or  undergoing  any  perceptible  change.  Heated 
to  14°  W,  in  the  open  air,  it  is  entirely  consumed.  Newton  first  sus- 
pected it  to  be  combustible  from  its  great  refracting  power,  a conjec- 
ture which  was  rendered  probable  by  the  experiments  of  the  Florentine 
academicians  in  1694,  and  subsequently  confirmed  by  several  philoso- 
phers. Lavoisier  first  proved  it  to  contain  carbon  by  throwing  the  sun’s 
rays,  concentrated  by  a powerful  lens,  upon  a diamond  contained  in  a 
vessel  of  oxygen  gas.  The  diamond  was  consumed  entirely,  oxygen 
disappeared,  and  carbonic  acid  was  generated.  It  has  since  been  de- 
monstrated by  the  researches  of  Guyton-Morveaii,  Smithson  Tennant, 
Allen  and  Pepys,  and  Sir  H.  Davy,  that  carbonic  acid  is  the  product  of 
its  combustion.  Guyton-Morveau  inferred  from  his  experiments  that 
the  diamond  is  pure  carbon,  and  tluit  charcoal  is  an  oxide  of  carbon. 
Tennant  burned  diamonds  by  heating  them  with  nitre  in  a gold  tube; 
and  comparing  his  own  results  witli  those  of  I.avoisier  on  the  combus- 
tion of  charcoal,  he  concluded  that  equal  weights  of  diamond  and  pure 
charcoal,  in  combining  with  oxygen,  yield  precisely  equal  quantities  of 
car])onic  acid.  He  was  thus  induced  to  adopt  the  opinion,  that  charcoal 
and  the  diamond  arc  chemically  the  .same  substance;  and  that  the  dif- 
ference in  their  physical  character  is  solely  dependent  on  a difference 
of  aggregation.*  This  conclusion  was  confirmed  by  the  experiments 


• Idiilos.  Trans,  for  1797. 


CARBON. 


177 


of  Allen  and  Pepys,*  and  Sir  11.  Davy,f  who  compared  the  product  of 
the  combustion  of  the  diamond  with  that  derived  from  different  kinds  of 
charcoal.  The  latter  chemist  did  indeed  observe  tlie  production  of  a 
minute  quantity  of  water  during’  the  combustion  of  the  purest  charcoal, 
indicative  of  a trace  of  hydrog’en;  but  its  quantity  is  so  exceedingly 
small,  that  it  cannot  be  regarded  as  a necessary  constituent.  It  proves 
only  that  a trace  of  hydrogen  is  retained  by  charcoal  with  such  force, 
that  it  cannot  be  expelled  by  tlie  temperature  of  ignition. 

Carbonic  Jlcid. 

Carbonic  acid  was  discovered  by  Dr.  Black  in  1757,  and  described  by 
him,  in  his  inaugural  dissertation  de,  Magnesia  Alba,  under  the  name  of 
fixed  air.  He  observed  the  existence  of  this  gas  in  common  limestone 
and  magnesia,  and  found  that  it  may  be  expelled  from  these  substances 
by  the  action  of  heat  or  acids.  He  also  remarked  that  the  same  gas  is 
formed  during  respiration,  fermentation,  and  combustion.  Its  composi- 
tion was  first  demonstrated  synthetically  by  Lavoisier,  who  burned  car- 
bon in  oxygen  gas,  and  obtained  carbonic  acid  as  the  product.  The  late 
Ml*.  Smithson  Tennant  illustrated  its  nature  analytically  by  passing  the 
vapour  of  phosphorus  over  chalk,  or  carbonate  of  lime,  heated  to  red- 
ness in  a glass  tube.  The  phosphorus  took  oxygen  from  the  carbonic 
acid,  charcoal  in  the  form  of  a light  black  powder  was  deposited,  and 
the  phosphoric  acid,  which  was  formed,  united  with  the  lime. 

Carbonic  acid  is  most  conveniently  prepared  for  the  purposes  of  ex- 
periment by  the  action  of  muriatic  acid,  diluted  with  two  or  three  times 
its  weight  of  water,  on  fragments  of  marble.  I'he  muriatic  acid  unites 
with  the  lime,  forming  muriate  of  lime,  and  carbonic  acid  gas  escapes 
with  effervescence. 

Carbonic  acid,  as  thus  procured,  is  a colourless,  inodorous,  elastic 
fluid,  which  possesses  all  the  physical  characters  of  the  gases  in  an  emi- 
nent degree,  and  requires  a pressure  of  thirty-six  atmospheres  to  con- 
dense it  into  a liquid.  According  to  the  experiments  of  Dr.  Thomson, 
(First  Principles,  vol.  i.  p.  143.)  100  cubic  inches  of  it,  at  60®  F,  and 
when  the  barometer  stands  at  30  inches,  weigh  46.597  grains;  and  there- 
fore its  specific  gi-avity  is  1.5277. 

Carbonic  acid  extinguishes  burning  substances  of  all  kinds,  and  the 
combustion  does  not  cease  from  the  want  of  oxygen  only.  It  exerts  a 
positive  influence  in  checking  combustion,  as  appears  from  the  fact, 
that  a candle  cannot  burn  in  a gaseous  mixture  composed  of  four  mea- 
sures of  atmospheric  air,  and  one  of  carbonic  acid. 

It  is  not  better  qualified  to  support  the  respiration  of  animals;  for  its 
presence  even  in  moderate  proportion,  is  soon  fatal.  An  animal  cannot 
live  in  air  which  contains  sufficient  carbonic  acid  for  extinguishing  a 
lighted  candle;  and  hence  the  practical  rule  of  letting  down  a burning 
taper  into  old  wells  or  pits  before  any  one  ventures  to  descend.  If  the 
light  is  extinguished,  the  air  is  certainly  impure;  and  there  is  generally 
thought  to  be  no  danger,  if  the  candle  continues  to  burn.  But  some  in- 
stances have  been  known  of  the  atmosphere  being  sufficiently  loaded 
with  carbonic  acid  to  produce  insensibility,  and  yet  not  so  impure  as  to 
extinguish  a burning  candle.  (Christison  on  Poisons,  597.)  When  an 
attempt  is  made  to  inspire  pure  carbonic  acid,  violent  spasm  of  the  glot- 
tis takes  place,  which  prevents  the  gas  from  entering  the  lungs.  If  it 
be  so  much  diluted  with  air  as  to  admit  of  its  passing  the  glottis,  it  then 
acts  as  a narcotic  poison  on  the  system.  It  is  this  gas  which  has  often 
proved  destructive  to  persons  sleeping  in  a confined  room  with  a pan  of 
burning  charcoal. 


Philos.  Trans,  for  1807. 


t Ibid.  1814. 


178 


CATlTiON. 


Carbonic  acid  is  quite  Incombustible,  and  cannot  be  made  to  unite 
with  an  additional  portion  of  oxyg*en.  It  is  a compound,  therefore,  in 
which  carbon  is  in  its  higliest  degree  of  oxidation. 

Lime-water  becomes  turbid  wlien  brought  into  contact  with  carbonic 
acid.  The  lime  unites  with  the  gas,  forming  carbonate  of  lime,  which, 
from  its  insolubility  in  water,  at  first  renders  the  solution  milky,  and  af- 
terwards forms  a white  flaky  precipitate.  Hence  lime-water  is  not  only 
a valuable  test  of  the  presence  of  carbonic  acid,  but  is  frequently  used 
to  withdraw  it  altogether  from  any  gaseous  mixture  that  contains  it. 

Carbonic  acid  is  absorbed  by  water.  This  may  be  easily  demonstrated 
by  agitatingthe  gas  with  that  liquid,  or  by  leaving  a jar  full  of  it  invert- 
ed over  water.  In  the  fij  st  case  the  gas  disappears  in  the  course  of  a 
minute;  and  in  the  latter  it  is  gradually  absorbed.  Recently  boiled 
water  dissolves  its  own  volume  of  carbonic  acid  at  the  common  tempera- 
ture and  pressure;  but  it  will  take  up  much  more  if  the  pressure  be  in- 
creased. The  quantity  of  the  gas  absoi'bed  is  in  exact  ratio  with  the 
compressing  force;  that  is,  water  dissolves  twice  its  volume  when  the 
pressure  is  doubled,  and  three  times  its  volume,  when  the  pressure  is 
trebled. 

A saturated  solution  of  carbonic  acid  may  be  made  by  transmitting  a 
stream  of  the  gas  through  a vessel  of  cold  water  during  the  space  of  half 
an  hour,  or  still  better  by  the  use  of  a Woulfe’s  bottle  or  Nooth’s  appa- 
ratus, so  as  to  aid  the  absorption  by  pressure.  Water  and  other  liquids 
which  have  been  charged  with  carbonic  acid  under  great  pressure,  lose 
the  greater  part  of  the  gas  when  the  pressure  is  removed.  The  effer- 
vescence which  takes  place  on  opening  a bottle  of  ginger  beer,  cider, 
or  brisk  champaign,  is  owing  to  the  escape  of  carbonic  acid  gas.  Water, 
which  is  fully  saturated  with  carbonic  acid  gas,  sparkles  when  it  is  poured 
from  one  vessel  into  another.  The  solution  has  an  agreeably  acidulous 
taste,  and  gives  to  litmus  paper  a red  stain  which  is  lost  on  exposure  to 
the  air.  On  the  addition  of  lime-water  to  it,  a cloudiness  is  produced, 
which  at  first  disappears,  because  the  carbonate  of  lime  is  soluble  in  ex- 
cess of  carbonic  acid;  but  a permanent  precipitate  ensues  when  the  free 
acid  is  neutralized  by  an  additional  quantity  of  lime-water.  The  water 
which  contains  carbonic  acid  in  solution  is  wholly  deprived  of  the  gas  by 
boiling.  Removal  of  pressure  from  its  surface  by  means  of  the  air-pump 
has  a similar  effect. 

The  agreeable  pungency  of  beer,  porter,  and  ale,  is  in  a great  mea- 
sure owing  to  the  presence  of  carbonic  acid;  by  the  loss  of  which,  on 
exposure  to  the  air,  they  become  stale.  All  kinds  of  spring  and  well 
water  contain  carbonic  acid  absorbed  from  the  atmosphere,  and  to  which 
they  are  partly  indebted  for  their  pleasant  flavour:  Boiled  water  has  an 
insipid  taste  from  the  absence  of  carbonic  acid. 

A knowledge  of  the  exact  composition  of  carbonic  acid  gas  is  of  very 
great  importance.  The  researches  of  Allen  and  Pepys,  and  Sir  H.  Davy, 
have  proved  incontestably  that  oxygen  gas  in  combining  with  carbon,  so 
as  to  form  carbonic  acid,  suffers  no  change  of  volume;  or,  in  other  words, 
that  carbonic  acid  contains  its  own  volume  of  oxygen.  It  hence  follows 
that  100  cubic  inches,  or  46.597  grains  of  carbonic  acid,  consist  of  100 
cubic  inches,  or  33.888  grains  of  oxygen,  united  with  12.709  grains 
(46.597  — 33.888)  of  carbon. 

Now,  12.709  : 33.888  : : 6 : 16; 

and  since,  as  will  soon  appear,  6 is  the  combining  proportion  of  carbon, 
carbonic  acid  is  composed  of 

(’arbon  . 6 . one  proportional. 

Oxygen  . 16  . two  proportionals. 


CARBON. 


179 


By  a rule,  which  is  g-iven  at  page  136,  it  may  be  calculated  that  carbon, 
if  supposed  to  exist  in  tlie  form  of  vapour,  would  have  a specific  gravity 
of  0.4166;  from  which  it  follows,  that  100  cubic  inches  of  the  vapour  of 
carbon  at  60®  F,  and  when  tlie  barometer  stands  at  30  inches,  would 
weigh  12.709  grains.  Consequently,  100  cubic  inches  of  carbonic  acid 
gas  are  composed  of 

Oxygen  gas  . 100  cubic  inches. 

Vapour  of  carbon  100  do.* 


* There  is  some  obscurity  in  the  mode  in  which  Dr.  Turner  has  here 
stated  the  composition  of  carbonic  acid,  which  the  beginner  in  chemistry 
may  not  be  able  to  clear  up.  From  the  fact  that  carbonic  acid  contains 
its  volume  of  oxygen,  and  from  our  knowledge  of  the  weight  of  100  cu- 
bic inches  of  this  acid  and  of  oxygen  respectively,  the  author  very  cor- 
rectly deduces  the  weight  and  volume  of  oxygen  united  to  a given  weight 
of  carbon  in  carbonic  acid;  namely,  33.888  grains  or  100  cubic  inches 
of  oxygen  to  12.709  grains  of  carbon;  or  two  proportionals  of  the  for- 
mer to  one  of  the  latter.  To  complete  the  view  of  the  composition  of 
carbonic  acid,  it  only  remains,  then,  to  ascertain  the  volume  of  the  car- 
bon present  considered  as  vapour;  and  as  this  element  is  always  solid 
per  se,  it  is  necessary,  in  doing  this,  to  proceed  on  theoretical  grounds. 
Here,  then,  we  have  only  the  analogy  pointed  out  by  Dr.  Prout  to  guide 
us,  that  as  one  proportional  of  hydrogen,  nitrogen,  and  chlorine,  occupy 
double  the  space  that  is  occupied  by  one  proportional  of  oxygen,  it  is 
probable  that  the  volume  of  one  proportional  of  carbon  also,  is  double  the 
volume  of  one  proportional  of  the  same  element.  On  this  assumption 
then,  one  proportional  of  carbon  vapour  will  occupy  precisely  the  same 
space  as  two  proportionals  of  oxygen;  and  hence,  if  the  33.888  grains  of 
oxygen,  equivalent  to  two  proportionals,  occupy  the  space  of  100  cubic 
inches,  the  12.709  grains  of  carbon,  equal  to  one  proportional,  if  consi- 
dered as  vapour,  must  occupy  the  space  of  100  cubic  inches  also.  In  this 
way  it  is  perceived  how  readily  the  composition  of  carbonic  acid  in  vo- 
lume is  deduced. 

The  rule,  alluded  to  in  the  text  for  calculating  specific  gravities,  em- 
braces the  directions  for  solving  a question  in  the  rule  of  proportion,  the 
bearing  of  which  in  determining  the  specific  gravity  may  not  be  at  once 
obvious  to  the  reader.  From  the  positions  above  taken,  it  will  be  under- 
stood, that  proportional  weights  of  oxygen,  and  of  any  of  the  element- 
ary gases  or  vapours,  correspond  to  volumes  which  are  to  one  another 
as  one  to  two.  -Now  it  is  easy,  when  we  know  the  weights  of  volumes 
which  are  to  one  another  as  one  to  two,  to  ascertain  the  weights  of  equal 
volumes,  that  is,  the  specific  gravity.  In  the  case  of  carbon,  if  we  were 
to  use  the  proportion, — 8 : 6 ::  1.1111  (the  sp.  gr.  of  oxygen);  the 

fourth  term  would  represent  the  weight  of  a volume  of  carbon  va- 
pour, double  the  volume  of  a portion  of  oxygen  which  sliould  weigh 
1.1111;  in  other  words,  twice  the  sp.  gr.  of  the  carbon  vapour.  Using 
this  proportion  then,  it  would  be  necessary,  in  calculating  tlie  sp.  gr.  of 
gaseous  carbon,  to  divide  the  fourth  term  by  2.  But  it  is  obvious  tliat  it 
would  come  to  the  same  thing  to  divide  the  third  term  by  2;  in  which  case 
we  should  have  the  proportion  thus: — as  8 is  to  6,  so  is  0.5555  (half 
the  sp.  gr.  of  oxygen)  to  the  fourth  term,  which  would  give  the  sp.  gr. 
of  the  vapour  of  carbon  at  once.  Now  this  is  the  very  formula  which 
Dr.  Prout  adopts. 

An  easier  way  of  calculating  the  specific  gravity  of  any  elementary 
gas  or  vapour  except  oxygen,  is  from  hydrogen.  The  formula  may  be 
thus  stated  in  general  terms: — As  the  equivalent  of  hydrogen  is  to  the 


180 


CAIinON. 


Carbonic  acid  is  always  present  in  tlie  atmosphere,  even  at  the  sum- 
mit of  the  hig'liest  mountains,  or  at  a distance  of  several  thousand  feet 
above  the  ground.  Its  presence  may  be  demonstrated  l)y  exposing  lime- 
water  in  an  open  vessel  to  tlie  air,  wlicn  its  surface  will  soon  be  covered 
with  a pellicle,  which  is  carbonate  of  lime.  The  origin  of  the  carbonic 
acid  is  obvious.  Ilesides  being  formed  abundantly  by  the  combustion  of 
all  substances  which  coiUain  carbon,  the  respiration  of  animals  is  a fruit- 
ful source  of  it,  as  may  be  proved  by  breatliing  for  a few  minutes  into 
lime-water;  and  it  is  also  generated  in  all  the  spontaneous  changes  to 
which  dead  animal  and  vegetable  matters  are  subject.  The  carbonic 
acid  proceeding  from  sucli  sources,  is  commonly  diffused  equably  through 
the  air;  but  when  any  of  these  processes  occur  in  low  confined  situations, 
as  at  the  bottom  of  old  wells,  tlie  gas  is  then  apt  to  accumulate  there, 
and  form  ah  atmosphere  called  choke  damp,  which  is  fatal  to  any  animals 
that  are  placed  in  it.  'fhese  accumulations  happily  never  take  place, 
except  when  there  is  some  local  origin  for  the  carbonic  acid;  for  exam- 
ple, when  it  is  generated  by  fermentative  processes  going  on  at  the  sur- 
face of  the  ground,  or  when  it  issues  directly  from  the  earth,  as  happens 
at  the  Grotto  del  Cane  in  Italy,  and  at  Pyrmont  in  Westphalia.  Ihere  is 
no  real  foundation  for  the  opinion  that  carbonic  acid  can  separate  itself 
from  the  great  mass  of  the  atmosphere,  and  accumulate  in  a low  situa- 
tion merely  by  the  force  of  gravity.  Such  a supposition  is  contrary  to 
the  well-known  tendency  of  gases  to  diffiise[themselves  equally  through 
each  other.  It  is  also  contradicted.by  observation;  for  many  deep  pits, 
which  are  free  from  putrefying  organic  remains,  though  otherwise  fa- 
vourably situated  for  such  accumulations,  contain  pure  iftmospheric  air. 

Though  carbonic  acid  is  the  product  of  many  natural  operations,  che- 
mists have  not  hitherto  noticed  any  increase  in  the  quantity  contained  in 
the  atmosphere.  The  only  known  process  which  tends  to  prevent  in- 
crease in  its  proportion,  is  that  of  vegetation.  Growing  plants  purify 
the  air  by  withdrawing  carbonic  acid,  and  yielding  an  equal  volume  of 
pure  oxygen  in  return,  but  whether  a full  compensation  is  produced  by 
this  cause,  has  not  yet  been  satisfactorily  determined. 

Carbonic  acid  is  contained  in  the  earth.  Many  mineral  springs,  such 
as  those  of  Tunbridge,  Pyrmont,  and  Carlsbad,  are  highly  charged  with 
it.  In  combination  with  lime  it  forms  extensive  masses  of  rock,  which 
geologists  have  found  to  occur  in  all  countries,  and  in  every  formation. 

Carbonic  acid  unites  witli  alkaline  substances,  and  the  salts  so  con- 
stituted are  called  carbonates.  Its  acid  properties  are  feeble,  so  that  it 
is  unable  to  neutralize  completely  the  alkaline  properties  of  potassa, 
soda,  and  lithia.  For  the  same  reason,  all  the  carbonates,  without  ex- 
ception, are  decomposed  by  the  muriatic  and  all  the  stronger  acids;  car- 
bonic acid  is  displaced,  and  escapes  in  the  form  of  gas. 


equivalent  of  the  given  body,  so  is  the  sp.  gr.  of  hydrogen  to  the  sp.  gr. 
of  the  body.  To  apply  the  mode  of  calculation  to  carbon,  we  have  this 
proportion: — 

1:6::  0.0694  : 0.4166 

This  formula  is  far  preferable  to  the  other,  wherever  both  are  appli- 
cable; for  there  is  no  occasion  for  halving  the  specific  gravity  number 
forming  the  third  term;  aiul  in  all  cases  in  which  the  hydrogen  unit  is 
adopted,  the  aritlimetical  operation  of  dividing  by  the  first  term  is  saved, 
as  this  term  is  unity.  All  that  is  necessary  for  calculating  specific  gravi- 
ties by  this  rule  is,  therefore,  simply  to  multiply  the  equivalent  of  any  ele- 
mcutaiy  body,  except  oxygen,  by  the  specific  gravity  of  hydrogen.  C. 


CARBON. 


181 


Carbonic  Oxide  Gas. 

When  two  parts  of  well-dried  chalk  and  one  of  pure  iron  filings  are  mix- 
ed together,  and  exposed  in  a gun-barrel  to  a red  heat,  a large  quantity  of 
aeriform  matter  is  evolved,  which  may  be  collected  over  water.  On  ex- 
amination, it  is  found  to  contain  two  compounds  of  carbon  and  oxygen, 
one  of  which  is  carbonic  acid,  and  the  other  carbonic  oxide*  By  washing 
the  mixed  gases  with  lime-water,  the  carbonic  acid  is  absorbed,  and  car- 
bonic oxide  gas  is  left  in  a state  of  purity. 

A very  elegant  mode  of  preparing  carbonic  oxide  has  been  suggest- 
ed by  M.  Dumas.  (Edinburgh  Journal  of  Science,  vi.  350.)  The  pro- 
cess consists  in  mixing  binoxalabe  of  potassa  with  five  or  six  times  its 
weight  of  concentrated  sulphuric  acid,  and  heating  the  mixture  in  a 
retort  or  other  convenient  glass  vessel.  Effervescence  soon  ensues, 
owing  to  the  escape  of  gas  consisting  of  equal  measures  of  carbonic 
acid  and  carbonic  oxide  gases;  and  on  absorbing  the  former  by  means  of 
lime-water  or  solution  of  potassa,  the  latter  is  left  in  a state  of  perfect 
purity.  To  comprehend  the  theory  of  the  process  it  is  necessary  to 
premise,  that  oxalic  acid  is  a compound  of  equal  measures  of  carbonic 
acid  and  carbonic  oxide,  or  at  least  its  elements  are  in  the  proportion  to 
form  these  gases;  and  that  it  cannot  exist  unless  in  combination  with 
water  or  some  other  substance.  Now  the  sulphuric  acid  unites  both 
with  the  potassa  and  water  of  the  binoxalate,  and  the  oxalic  acid,  being 
thus  set  free,  is  instantly  decomposed.  Oxalic  acid  may  be  substituted 
in  this  process  for  binoxalate  of  potassa. 

Priestley  discovered  this  gas  by  igniting  chalk  in  a gun-barrel,  and 
afterwards  obtained  it  in  greater  quantity  from  chalk  and  iron  filings. 
He  supposed  it  to  be  a mixture  of  hydrogen  and  carbonic  acid  gases. 
Its  real  nature  was  pointed  out  by  Mr.  Cruickshank,  * and  about  the 
same  time  by  Clement  and  Desormes.-j- 

Carbonic  oxide  gas  is  colourless  and  insipid.  It  does  not  affect  the 
blue  colour  of  vegetables  in  anyway;  nor  does  it  combine,  like  carbo- 
nic acid,  with  lime  or  any  of  the  pure  alkalies.  It  is  very  sparingly 
dissolved  by  water.  Lime-water  does  not  absorb  it,  nor  is  its  transpa- 
rency affected  by  it. 

Carbonic  oxide  is  inflammable.  When  a lighted  taper  is  plunged 
into  a jar  full  of  that  gas,  the  taper  is  extinguished;  but  the  gas  it- 
self is  set  on  fire,  and  burns  calmly  at  its  surface  with  a lambent  blue 
flame.  The  sole  product  of  its  combustion,  when  the  gas  is  quite 
pure,  is  carbonic  acid,  a fact  which  proves  that  it  does  not  contain  any 
hydrogen. 

Carbonic  oxide  gas  cannot  support  respiration.  It  acts  injuriously  on 
the  system;  for  if  diluted  with  air,  and  taken  into  the  lungs,  it  very 
soon  occasions  headach  and  other  unpleasant  feelings;  and  when  breath- 
ed pure,  it  almost  instantly  causes  profound  coma. 

A mixture  of  carbonic  oxide  and  oxygen  gases  may  be  made  to  ex- 
plode by  flame,  by  a red-hot  solid  body,  or  by  the  electric  spark.  If 
they  are  mixed  together  in  the  proportion  of  100  measures  of  carbonic 
oxide  and  rather  more  than  50  of  oxygen,  and  the  mixture  is  inflamed 
in  Volta’s  eudiometer  by  electricity,  so  as  to  collect  the  product  of  the 
combustion,  the  whole  of  the  carbonic  oxide,  together  with  50  mea- 
sures of  oxygen,  disappears,  and  100  measures  of  carbonic  acid  gas 
occupy  their  place.  From  this  fact,  which  was  ascertained  by  Berthol- 


• Nicholson’s  Journal,  4to  Ed.  vol.  v. 
f Annales  de  Chimie,  vol.  xxxix. 

16 


182 


CARBON. 


let,  and  has  been  amply  confirmed  by  subsequent  observation,  the  ex- 
act composition  of  carbonic  oxide  g*as  may  be  easily  deduced.  For  car- 
bonic acid  contains  its  own  bulk  of  oxygen;  and  since  100  measures  of 
carbonic  oxide  with  50  of  oxygen  form  100  measures  of  carbonic  acid, 
it  follows  that  100  of  carbonic  oxide  are  composed  of  50  of  oxygen 
united  with  precisely  the  same  quantity  of  carbon  as  is  contained  in 
100  measures  of  carbonic  acid.  Consequently,  the  composition  of  car- 
bonic acid  being 


By  volume. 

Vapour  of  carbon  100 
Oxygen  gas  100 


By  weight. 
Carbon  6 

Oxygen  16 


100  carbonic  acid  gas,  22  carbonic  acid; 

that  of  carbonic  oxide  must  be 

By  volume.  By  weight. 

Vapour  of  carbon  100  - Carbon  6 

or 

Oxygen  gas  50  - Oxygen  8 


100  carbonic  oxide  gas.  14  carbonic  oxide. 

Grains. 

Also,  since  50  cubic  inches  of  oxygen  gas  weigh  16.944 

and  100  of  the  vapour  of  carbon  12.709 


100  cubic  inches  of  carbonic  oxide  gas  must  weigh  29.653 

Its  specific  gravity  is,  therefore,  0.9722;  and  to  be  satisfied  of  the 
accuracy  of  the  data  on  which  these  calculations  are  founded,  it  is 
sufficient  to  state,  that  its  density,  as  determined  by  Dr.  Thomson,  is 
0.9700,  and  0.9727  according  to  the  observation  of  Berzelius  and  Du- 
long. 

No  compound  of  carbon  and  oxygen  is  known  which  contains  a less 
quantity  of  oxygen  than  carbonic  oxide.  For  this  reason  it  is  regarded 
as  a combination  of  one  proportional  of  carbon  = 6 and  one  of  oxygen 
= 8;  and  carbonic  acid  of  one  proportional  of  carbon  = 6 and  two  of 
oxygen  = 16.  The  combining  proportion  of  carbonic  oxide  is,  there- 
fore, 14,  and  that  of  carbonic  acid  22. 

The  first  process  mentioned  for  generating  carbonic  oxide  will  now 
be  intelligible.  The  principle  of  the  method  is  to  bring  carbonic  acid, 
at  a red  heat,  in  contact  with  some  substance  which  has  a strong  affinity 
for  oxygen.  This  condition  is  fulfilled  by  igniting  chalk,  or  any  car- 
bonate which  can  bear  a red  heat  without  decomposition,  such  as  the 
carbonates  of  baryta,  strontia,  soda,  potassa,  or  lithia,  with  half  its 
weight  of  iron  filings  or  charcoal.  The  carbonate  is  reduced  to  the 
caustic  state,  and  its  carbonic  acid  is  converted  into  carbonic  oxide  by 
yielding  oxygen  to  the  iron  or  charcoal.  When  the  former  is  used, 
oxide  of  iron  is  tlie  product;  when  charcoal  is  employed,  the  charcoal 
itself  is  converted  into  carbonic  oxide.  This  gas  may  likewise  be  gen- 
erated by  heating  to  redness  a mixture  of  almost  any  metallic  oxide 
witli  one-sixth  of  its  weight  of  charcoal  powder.  The  oxides  of  zinc, 
iron,  or  copper,  are  the  cheapest  and  most  convenient.  It  may  also  be 
formed  by  transmitting  a current  of  carbonic  acid  gas  over  ignited  char- 
coal. In  all  these  processes,  it  is  essential  that  the  ingredients  be  quite 
free  from  moisture  and  hydrogen,  otherwise  some  carburetted  hydrogen 


SULPHUR. 


183 


g'as  would  be  g*enerated.  The  product  should  always  be  washed  with 
lime-water  to  separate  it  from  carbonic  acid. 

Dr.  Henry  has  ascertained  that  when  a succession  of  electric  sparks 
is  passed  through  carbonic  acid  confined  over  mercury,  a portion  of  that 
gas  is  converted  into  carbonic  oxide  and  oxygen.  When  a mixture  of 
hydrogen  and  carbonic  acid  gases  is  electrified,  a portion  of  the  latter 
yields  one-half  of  its  oxygen  to  the  former;  water  is  generated,  and 
carbonic  oxide  produced.  On  electrifying  a mixture  of  equal  measures 
of  carbonic  oxide  and  protoxide  of  nitrogen,  both  gases  are  decompo- 
sed without  change  of  volume,  and  the  residue  consists  of  equal  mea- 
sures of  carbonic  acid  and  nitrogen  gases.  The  carbonic  oxide  should 
be  in  very  slight  excess,  in  order  to  ensure  the  success  of  the  experi- 
ment. On  this  fact  is  founded  Dr.  Henry’s  method  of  analyzing  pro- 
toxide of  nitrogen,  and  testing  its  purity,  as  will  be  more  particularly 
mentioned  in  the  fourth  part  of  the  work. 


SECTION  VII. 

SULPHUR. 

Sulphur  occurs  as  a mineral  production  in  some  parts  of  the  earth, 
particularly  in  the  neighbourhood  of  volcanoes,  as  in  Italy  and  Sicily. 
It  is  commonly  found  in  a massive  state;  but  it  is  sometimes  met  with 
crystallized  in  the  form  of  an  oblique  rhombic  octohedron.  It  exists 
much  more  abundantly  in  combination  with  several  metals,  such  as  sil- 
ver, copper,  antimony,  lead,  and  iron.  It  is  procured  in  large  quan- 
tity by  exposing  iron  pyrites  to  a red  heat  in  close  vessels. 

Sulphur  is  a brittle  solid  of  a greenish-yellow  colour,  emits  a peculiar 
odour  when  rubbed,  and  has  little  taste.  It  is  a non-conductor  of  elec- 
tricity, and  is  excited  negatively  by  friction.  Its  specific  gravity  is  1.99. 
Its  point  of  fusion  is  216^  F;  between  230^  and  280?  it  possesses  the 
highest  degree  of  fluidity,  is  then  of  an  amber  colour,  and,  if  cast  into 
cylindrical  moulds,  forms  the  common  roll  sulphur  of  commerce.  It 
begins  to  thicken  near  320?,  and  acquires  a reddish  tint;  and  at  tempe- 
ratures between  428®  and  482®,  it  is  so  tenacious  that  the  vessel  may  be 
inverted  without  causing  it  to  change  its  place.  From  482®  to  its  boil- 
ing point  it  becomes  liquid  again,  but  never  to  the  same  extent  as  when 
at  248?.  When  heated  to  at  least  428^,  and  then  poured  into  water,  it 
becomes  a ductile  mass,  which  may  be  used  for  taking  the  impression 
of  seals.  (Dumas.) 

Fused  sulphur  has  a tendency  to  crystallize  in  cooling.  A crystalline 
arrangement  is  perceptible  in  the  centre  of  common  roU  sulphur;  and 
by  good  management  regular  crystals  may  be  obtained.  For  this  pur- 
pose several  pounds  of  sulphur  should  be  melted  in  an  earthen  cruci- 
ble; and  when  partially  cooled,  the  outer  solid  crust  should  be  pierced, 
and  the  crucible  quickly  inverted,  so  that  the  inner  and  as  yet  fluid 
parts  may  gradually  flow  out.  On  breaking  the  solid  mass,  when  quite 
cold,  crystals  of  sulphur  will  be  found  in  its  interior. 

Sulphur  is  very  volatile.  It  begins  to  rise  slowly  in  vapoUr  even  be- 
fore it  is  completely  fused.  At  550®  or  600®  F.  it  volatilizes  rapidly, 
and  condenses  again  unchanged  in  close  vessels.  Common  sulphur  is 
purified  by  this  process;  and  if  the  sublimation  be  conducted  slowly^ 


184 


SULPHUR. 


tlie  sulphur  collects  in  the  receiver  in  the  form  of  detached  crystalline 
grains,  called  flowers  of  sulphur.  In  this  state,  however,  it  is  not 
quite  pure;  for  the  oxygen  of  the  air  within  the  apparatus  combines 
with  a portion  of  sulphur  during  the  process,  and  forms  sulphurous 
acid.  The  acid  may  be  removed  by  washing  the  flowers  repeatedly  with 
water. 

Sulphur  is  insoluble  in  water,  but  unites  with  it  under  favourable 
circumstances,  forming  the  white  hydrate  of  sulphur,  termed  lat  sul- 
phuris.  It  dissolves  readily  in  boiling  oil  of  turpentine.  The  solution 
has  a reddish-brown  colour  like  melted  sulphur,  and  if  fully  saturated, 
deposites  numerous  small  crystals  in  cooling.  Sulphur  is  also  soluble 
in  alcohol,  if  both  substances  are  brought  together  in  the  form  of  va- 
poui\  The  sulphur  is  precipitated  from  the  solution  by  the  addition  of 
water. 

Sulphur,  like  charcoal,  retains  a portion  of  hydrogen  so  obstinately, 
that  it  cannot  be  wholly  freed  from  it  either  by  fusion  or  sublimation. 
Sir  H.  Davy  detected  its  presence  by  exposing  sulphur  to  the  strong 
heat  of  a powerful  galvanic  battery,  when  some  sulphuretted  hydrogen 
gas  was  disengaged.  The  hydrogen,  from  its  minute  quantity,  can  only 
be  regarded  in  the  light  of  an  accidental  impurity,  and  as  in  nowise  es- 
sential to  the  nature  of  sulphur. 

When  sulphur  is  heated  in  the  open  air  to  300®  F.  or  a little  higher, 
it  kindles  spontaneously,  and  burns  with  a faint  blue  light.  In  oxygen 
gas  its  combustion  is  far  more  vivid;  the  flame  is  much  larger,  and  of  a 
bluish-white  colour.  Sulphurous  acid  is  the  product  in  both  instances; 
— no  sulphuric  acid  is  formed  even  in  oxygen  gas,  unless  moisture  be 
present. 

Compounds  of  Sulphur  and  Oxygen. 


Chemists  are  at  present  acquainted  with  four  compounds  of  sulphur 
and  oxygen,  all  of  which  have  acid  properties.  Their  composition  is 
shown  by  the  following  table. 


Hyposulphurous  acid 
Sulphurous  acid 
Sulphuric  acid 
Hyposulphuric  acid 


Sulphur.  Oxygen. 
32  8 

16  16 

16  24 

32  40  . 


Proportionals. 
Sulphur.  Oxygen. 
Two.  One. 

One.  Two. 

One.  Three. 

Two.  Five. 


Sulphurous  Jlcid  Gas. 

Pure  sulphurous  acid,  at  the  common  temperature  and  pressure,  is  a 
colourless  transparent  gas,  which  was  first  obtained  in  a separate  state 
by  Priestley.  It  is  the  sole  product  when  sulphur  is  burned  in  air  or 
dry  oxygen  gas,  and  is  the  cause  of  the  peculiar  odour  emitted  by  that 
substance  during  its  combustion.  It  may  also  be  prepared  by  depriving 
sulphuric  acid  of  one  proportional  of  its  oxygen.  This  may  be  done  in 
several  ways.  If  chips  of  wood,  straw,  cork,  oil,  or  other  vegetable 
matters,  be  heated  in  strong  sulphuric  acid,  the  carbon  and  hydrogen 
of  those  substances  deprive  the  acid  of  part  of  its  oxygen,  and  convert 
it  into  sulphurous  acid.  Nearly  all  the  metals,  with  the  aid  of  heat, 
have  a similar  effect.  One  portion  of  sulphuric  acid  yields  oxygen  to 
tlie  metal,  and  is  thercl)y  converted  into  sulphurous  acid;  while  the 
metallic  oxide,  at  the  moment  of  its  formation,  unites  with  some  of  the 
undccomposed  sulphuric  acid.  The  best  method  of  obtaining  pure 
sulphurous  acid  gas,  is  by  putting  two  parts  of  mercury  and  three  of 
sulphuric  acid  into  a glass  retort,  the  beak  of  which  is  received  under 


SULPHUR. 


18-5 


mercury,  and  heating*  the  mixture  by  an  Arg*and  lamp.  Effervescence 
soon  takes  place,  a Iarg*e  quantity  of  pure  sulphurous  acid  is  disen- 
g^aged,  and  sulphate  of  the  oxide  of  mercury  remains  in  the  retort. 

Sulphurous  acid  gas  is  distinguished  from  all  other  gaseous  fluids  by 
its  suffocating  pungent  odour.  All  burning  bodies,  when  immersed  in 
it,  are  extinguished  without  setting  fire  to  the  gas  itself.  It  is  fatal  to 
all  animals  which  are  placed  in  it.  A violent  spasm  of  the  glottis  takes 
place,  by  which  the  entrance  of  the  gas  into  the  lungs  is  prevented; 
and  even  when  diluted  with  air,  it  excites  cough,  and  causes  a peculiar 
uneasiness  about  the  chest. 

Recently  boiled  water  dissolves  about  33  times  its  volume  of  sulphu- 
rous acid  at  60®  F.  and  30  inches  of  the  barometer,  forming  a solution 
which  has  the  peculiar  odour  of  that  compound,  and  from  which  the 
gas  may  be  expelled  by  ebullition  without  change. 

Sulphurous  acid  has  considerable  bleaching  properties.  It  reddens 
litmus  paper,  and  then  slowly  bleaches  it.  Most  vegetable  colouring 
matters,  such  as  those  of  the  rose  and  violet,  are  speedily  removed, 
without  being  first  reddened.  It  is  remarkable  that  the  colouring  prin- 
ciple is  not  destroyed;  for  it  may  be  restored  either  by  a stronger  acid 
or  by  an  alkali. 

Sir  H.  Davy  inferred  from  his  experiments  on  the  combustion  of  sul- 
phur in  dry  oxygen  gas,  (Elements,  p.  273,)  that  the  volume  of  the 
oxygen  is  not  altered  during  the  process,  a fact  which  is  now  admitted 
by  most  chemists;  so  that  100  cubic  inches  of  sulphurous  acid  contain 
100  cubic  inches  of  oxygen.  According  to  Dr.  Thomson,  (Annals  of 
Philosophy,  xvi.  256,)  sulphurous  acid  gas  is  just  twice  as  heavy  as  oxy- 
gen; and  the  experiments  of  Davy  and  of  Thenard  correspond  very 
closely  with  his  result.  It  follows,,  therefore,  that  sulphurous  acid  con- 
sists of  equal  weights  of  sulphur  and  oxygen;  and  consequently  that 
100  cubic  inches  weigh  67.776  grains,  and  contain  33.888  grains  of  sul- 
phur. This  proportion  is  also,  established  by  the  researches  of  Berze- 
lius. (An.  de  Ch.  et  de  Ph.  vol.  v.) 

By  the  formula,  page  136,  it  may  be  calculated  that  the  specific  gra- 
vity of  the  vapour  of  sulphur  is  the  same  as  that  of  oxyg’en  gas,  or 
1.1111;  and  hence  100  cubic  inches  of  that  vapour  must  weigh  33.888 
grains.  From  this  it  is  manifest,  that  100  cubic  inches  of  sulphurous 
acid  gas  are  composed  of 

Vapour  of  sulphur  - - - 100  cubic  inches. 

Oxygen  - • - - - 100  do.* 

The  specific  gravity  of  sulphurous  acid  gas  is  of  course  double  that  of 
oxygen,  or  2.2222. 

It  is  inferred  from  the  compounds  of  sulphur  with  oxygen,  hydrogen, 
and  many  other  substances,  that  ! 6 is  the  number  which  expresses  the 
combining  proportion  of  that  substance.  Hence  sulphurous  acid  is  com- 
posed of  16  or  one  proportional  of  sulphur,  and  16  or  two  proportion- 
als of  oxygen.  Its  atomic  weight  is;  therefore,  32. 

Though  sulphurous  acid  cannot  be  made  to  burn  by  the  approach  of' 
flame,  it  has  a very  strong  attraction  for  oxygen,  uniting  with  it  under 
favourable  circumstances,  and  forming  sulphuric  acid.  The  presence  of 
moisture  is  essential  to  this  change.  A mixture  of  sulphurous  acid  and 
oxygen  gases,  if  quite  dry,  may  be  preserved  over  mercury  for  any 
length  of  time  without  chemical  action.  But  if  a little  water  be  admit- 
ted, the  sulphurous  acid  gradually  unites  with  oxygen,  and  sulphuric 


See  note,  page  179.  B. 
16* 


186 


SULPHUR. 


acid  is  generated.  I’he  facility  with  which  this  change  ensues  is  such, 
that  a solution  of  sulphurous  acid  in  water  cannot  be  preserved,  except 
atmospheric  air  be  carefully  excluded.  Many  of  the  chemical  proper- 
ties of  sulphurous  acid  are  owing  to  its  affinity  for  oxygen.  When  mix- 
ed with  peroxide  of  iron  in  solution,  it  deprives  that  compound  of  part 
of  its  oxygen,  and  converts  it  into  the  protoxide.  The  solutions  of  me- 
tals which  have  a weak  affinity  for  oxygen,  such  as  gold,  platinum,  and 
mercury,  are  completely  decomposed  by  it,  these  substances  being  pre- 
cipitated in  the  metallic  form.  Nitric  acid  converts  it  instantly  into  sul- 
phuric acid  by  yielding  some  of  its  oxygen.  Peroxide  of  manganese 
causes  a similar  change,  and  is  itself  converted  into  protoxide  of  man- 
ganese, which  unites  with  the  resulting  sulphuric  acid. 

Sulphurous  acid  gas  may  be  passed  through  red-hot  tubes  without  de- 
composition. Several  substances  which  have  a strong  affinity  for  oxygen, 
such  as  hydrogen,  carbon,  and  potassium,  decompose  it  at  the  tempera- 
ture of  ignition. 

Of  all  the  gases,  sulphurous  acid  is  most  readily  liquefied  by  compres- 
sion. According  to  Mr.  Faraday,  it  is  condensed  by  a force  equal  to  the 
pressure  of  two  atmospheres.  M.  Bussy  (Annals  of  Phil.  viii.  307,  N. 
S.)  has  obtained  it  in  a liquid  form  under  the  usual  atmospheric  pres- 
sure, by  passing  it  through  tubes  surrounded  by  a freezing  mixture  of 
snow  and  salt.  The  anhydrous  liquid  acid  has  a density  of  1.45,  and  it 
boils  at  14^  F.  From  the  rapidity  of  its  evaporation  at  common  tem- 
peratures, it  may  be  used  advantageously  for  producing  an  intense  de- 
gree of  cold.  M,  Bussy  succeeded  in  freezing  mercury  and  liquefying 
several  of  the  gases,  by  the  cold  produced  during  its  evaporation.  De 
la  Rive  states  it  to  be  a non-conductor  of  electricity.  He  adds  also,  that 
when  exposed  to  cold  in  the  moist  state,  a crystalline  solid  hydrate  is 
formed,  which  contains  20  per  cent  of  water,  and  probably  consists  of 
one  equivalent  of  the  acid  to  14  of  water. 

Sulphurous  acid  combines  with  metallic  oxides,  and  forms  salts  which 
are  called  sulphites. 

Sulphuric  Acid, 

Sulphuric  acid,  or  oil  of  vitriol  sls  it  is  often  called,  was  discovered  by 
Basil  Valentine  towards  the  close  of  the  15th  century.  It  is  procured 
for  the  purposes  of  commerce  by  two  methods.  One  of  these  has  been 
long  pursued  in  the  manufactory  at  Nordhausen  in  Germany,  and  con- 
sists in  decomposing  protosulphate  of  iron  (green  vitriol)  by  heat.  This 
salt  contains  seven  proportionals  of  water  of  crystallization;  and  when 
strongly  dried  by  the  fire,  it  crumbles  down  into  a white  powder,  which, 
according  to  Dr.  Thomson,  contains  one  proportional  of  water.  On  ex- 
posing this  dried  protosulphate  to  a red  heat,  its  acid  is  wholly  expel- 
led, the  greater  part  passing  over  unchanged  into  the  receiver,  in  com- 
bination with  the  water  of  the  salt.  Part  of  the  acid,  however,  is  re- 
solved by  the  strong  heat  employed  in  the  distillation  into  sulphurous 
acid  and  oxygen.  The  former  escapes  as  gas  throughout  the  whole 
process;  the  latter  only  in  the  middle  and  latter  stages,  since,  in  the  be- 
ginning of  the  distillation,  it  unites  with  the  protoxide  of  iron.  Per- 
oxide of  iron  is  the  sole  residue. 

The  acid,  as  procured  by  this  process,  is  a dense,  oily  liquid  of  a 
brownish  tint.  It  emits  copious  white  vapours  on  exposure  to  the  air, 
and  is  hence  called  fuming  sulphuric  acid.  Its  specific  gravity  is  stated 
at  1.896  and  1.90.  According  to  Dr.  Thomson  it  consists  of  80  parts  or 
two  equivalents  of  anhydrous  acid,  and  9 parts  or  one  equivalent  of 
water. 


SULPHUR. 


isr 


On  putting  this  acid  into  a glass  retort,  to  which  a receiver  surround- 
ed by  snow  is  securely  adapted,  and  heating  it  gently,  a transparent  col- 
ourless vapour  passes  over,  which  condenses  into  a white  crystalline 
solid.  This  substance  is  shown  by  the  experiments  of  Thomson,  Ure, 
and  Bussy,  to  be  pure  anhydrous  sulphuric  acid.  It  is  tough  and  elas- 
tic, liquefies  at  66°  F,  and  boils  at  a temperature  between  104°,  and 
122°,  forming,  if  no  moisture  is  present,  a transparent  vapour.  Ex- 
posed to  the  air,  it  unites  with  watery  vapour,  and  flies  off  in  the  form 
of  dense  wdiite  fumes.  The  residue  of  the  distillation  is  no  longer  fu- 
ming, and  is  in  every  respect  similar  to  the  common  acid  of  commerce. 

The  other  process  for  forming  sulphuric  acid,  which  is  practised  in  Bri- 
tain and  in  most  parts  of  the  Continent,  is  by  burning  sulphur  previously 
mixed  with  one-eighth  of  its  weight  of  nitrate  of  potassa.  The  mix- 
ture is  burned  in  a furnace  so  contrived  that  the  current  of  air,  which 
supports  the  combustion,  conducts  the  gaseous  products  into  a large 
leaden  chamber,  the  bottom  of  which  is  covered  to  the  depth  of  sev- 
eral inches  with  water.  The  nitric  acid  yields  oxygen  to  a portion  of 
sulphur,  and  converts  it  into  sulphuric  acid,  which  combines  with  the 
potassa  of  the  nitre;  while  the  greater  part  of  the  sulphur  forms  sul- 
phurous acid  by  uniting  with  the  oxygen  of  the  air.  The  nitric  acid,  in 
losing  oxygen,  is  converted,  partly  perhaps  into  nitrous  acid,  but  chief- 
ly, I apprehend,  into  deutoxide  of  nitrogen,  which,  by  mixing  with  air 
at  the  moment  of  its  separation,  gives  rise  to  the  red  nitrous  acid  va- 
pours. The  gaseous  substances,  present  in  the  leaden  chamber,  are, 
therefore,  sulphurous  and  nitrous  acids,  atmospheric  air,  and  watery  va- 
pour. The  explanation  of  the  mode  in  which  these  substances  react  on 
each  other,  so  as  to  form  sulphuric  acid,  was  suggested  by  the  experi- 
ments of  Clement  and  Desormes,  (An.  de  Ch.  lix.)  and  Sir  H.  Davy, 
(Elements,  p.  276.)  When  dry  sulphurous  acid  gas  and  nitrous  acid 
vapour  are  mixed  together  in  a glass  vessel  quite  free  from  moisture,  no 
change  ensues;  but  if  a few  drops  of  water  be  added,  in  order  to  fill 
the  space  with  aqueous  vapour,  a white  crystalline  compound  is  im 
mediately  produced.  The  French  chemists  believed  it  to  consist  of  sul- 
phuric acid,  deutoxide  of  nitrogen,  and  water;  and  they  ascribed  the 
conversion  of  sulphurous  into  sulphuric  acid  to  the  oxygen  supplied  by 
nitrous  acid  during  its  change  into  deutoxide  of  nitrogen.  This  opin- 
ion was  supported  by  the  fact,  that  when  the  crystalline  compound  is 
put  into  water,  a solution  of  sulphuric  acid  is  obtained,  and  deutoxide 
of  nitrogen  is  disengaged  with  effervescence.  Davy  regarded  the  solid 
as  consisting  of  sulphurous  acid,  water,  and  nitrous  acid;  and  supposed 
the  transfer  of  oxygen  from  the  latter  to  the  former  not  to  take  place, 
until  the  compound  was  brought  in  contact  with  the  water.  It  is  doubt- 
ful if  either  of  these  doctrines  is  altogether  correct.  The  more  probable 
theory  is,  that  the  crystalline  matter  contains  sulphuric  and  hyponitrous 
acids;  and  that  when  put  into  water,  the  latter  is  resolved  into  deutoxide 
of  nitrogen,  which  escapes  as  gas,  and  into  nitric  acid  which  remains  in 
solution  together  with  sulphuric  acid.  This  opinion  is  founded,  partly 
on  the  tendency  of  sulphuric  acid  to  unite  with  nitrous  and  hyponitrous 
acids,  but  chiefly  on  the  analysis  by  Dr.  Henry  of  a crystalline  substance, 
similar  to  that  above  alluded  to,  which  was  generated  in  the  leaden 
chamber  of  a manufacturer  of  sulphuric  acid.  (An.  Phil,  xxvii.  367.) 

While  it  is  admitted,  therefore,  that  this  subject  requires  the  aid  of 
further  inquiry,  the  most  probable  account  of  the  phenomena  which 
take  place  within  the  leaden  chambers  is  the  following.  When  moist 
nitrous  and  sulphurous  acids  are  intermixed,  the  former  communicates 
oxygen  to  the  latter,  and  a crystalline  compound  of  water,  hyponitrous 


188 


SULPHUR. 


acid,  and  sulphuric  acid,  in  proportions  not  yet  determined,  is  g’enerat- 
ed.  This  substance,  faHing  into  the  water  at  the  bottom  of  the  leaden 
chamber,  is  there  instantly  resolved,  as  above  mentioned,  into  sulphuric 
and  nitric  acids,  and  deutoxide  of  nitrogen.  The  gas  which  is  tlius  set 
free,  in  mixing  with  atmospheric  air,  is  again  converted  into  nitrous  acid, 
and  thus  gives  rise  to  a second  portion  of  the  crystalline  solid,  which 
undergoes  the  same  change  as  the  first.  When  the  water,  by  these  suc- 
cessive combinations  and  decompositions,  is  sufficiently  charged  with 
acid,  it  is  drawn  off,  and  concentrated  by  evaporation.  During  this 
process  the  nitric  acid,  formed  in  the  leaden  chamber,  is  expelled.  It 
hence  appears  that  the  oxygen,  by  which  the  sulphurous  is* converted 
into  sulphuric  acid,  is  in  reality  supplied  by  the  air;  that  the  combina- 
tion is  effected,  not  directly,  but  through  the  medium  of  nitrous  acid; 
and  that  a small  quantity  of  nitrous  acid  is  sufficient  for  the  production 
of  a large  quantity  of  sulphuric  acid.  The  decomposition  of  the  crys- 
talline solid  by  water  seems  owing  to  the  strong  affinity  of  that  liquid  for 
sulphuric  acid. 

Sulphuric  acid,  as  thus  prepared,  is  never  quite  pure.  It  contains 
some  sulphate  of  potassa  and  of  lead,  the  former  derived  from  the  nitre 
employed  in.  making  it,  and  the  latter  from  the  leaden  chamber.  To 
separate  these  impurities,  the  acid  should  be  distilled  from  a glass  or 
platinum  retort.  The  former  may  be  used  with  safety  by  putting  into 
it  some  fragments  of  platinum  leaf,  which  cause  the  acid  to  boil  freely 
on  the  application  of  heat,  without  danger  of  breaking  the  vessel. 

Pure  sulphuric  acid,  as  obtained  by  the  second  process,  is  a dense, 
colourless,  oily  fluid,  which  boils  at  620®  F,  and  has  a specific  gravity, 
in  its  most  concentrated  form,  of  1.847  or  a little  higher,  never  exceed- 
ing 1. 850.  It  is  one  of  the  strongest  acids  with  which  chemists  are  ac- 
quainted. When  undiluted  it  is  powerfully  corrosive.  It  decomposes 
all  animal  and  vegetable  substances  by  the  aid  of  heat,  causing  deposi- 
tion of  charcoal  and  formation  of  water.  It  has  a strong  sour  taste,  and 
reddens  litmus  paper,  even  though  greatly  diluted.  It  unites  with  al- 
kaline substances,,  and  separates  all  other  acids  more  or  less  completely 
from  their  combinations  with  the  alkalies. 

Sulphuric  acid  in  a very  concentrated  state  dissolves  small  quantities 
of  sulphur,  and  acquires  a blue,  green,  or  brown  tint.  Tellurium  and 
selenium  are  also  sparingly  dissolved,  the  former  causing  a crimson,  and 
the  latter  a green  colour.  By  dilution  with  water,  these  substances  sub- 
side unchanged;  but  if  heat  is  applied,  they  are  oxidized  at  the  expense 
of  the  acid,  and  sulphurous  acid  gas  is  disengaged.  Charcoal  also  ap- 
pears soluble  to  a small  extent  in  sulphuric  acid,  communicating  at  first 
a pink,  and  then  a dark  reddish-brown  tint. 

Sulphuric  acid  has  a very  great  affinity  for  water,  and  unites  with  it 
in  every  proportion.  The  combination  takes  place  with  production  of 
intense  heat.  When  four  parts  by  weight  of  the  acid  are  suddenly 
mixed  with  one  of  water,  the  temperature  of  the  mixture  rises,  accord- 
ing to  Dr.  Ure,  to  300®  F.  By  its  attraction  for  water  it  causes  the 
sudden  liquefaction  of  snow;  and  if  mixed  with  it  in  due  proportion, 
(p,  54),  intense  cold  is  generated.  It  absorbs  watery  vapour  with  avidity 
from  the  air,  and  on  tliis  account  is  employed  in  the  process  for  freez- 
ing water  by  its  own  evaporation.  The  action  of  sulphuric  acid  in  de- 
stroying tlie  texture  of  tlie  skin,  in  forming  ethers,  and  in  decompos- 
ing animal  and  vegetable  substances  in  general,  seems  dependent  on  its 
affinity  for  water. 

It  is  frequently  impoi-tant  to  know  the  quantity  of  real  acid  contained 
in  liquid  sulphuric  acid  of  diff  erent  strengths.  When  great  accuracy  is 
requisite,  this  information  should  always  be  ascertained  by  neutralizing 


SULPHUR. 


189 


a specimen  of  the  acid  with  an  alkali.  For  this  purpose,  dilute  a known 
weig-ht  of  the  acid  moderately  with  water,  and,  while  warm,  add  pure 
anhydrous  carbonate  of  soda,  until  the  solution  is  exactly  neutral.  Every 
54  parts  of  carbonate  of  soda,  required  to  produce  this  effect,  corres- 
pond to  40  parts  of  real  sulphuric  acid.  But  if  minute  precision  is  not 
desired,  the  strength  of  the  acid  may  be  estimated  by  its  specific  g’ravity, 
according  to  the  table  of  Dr.  Ure  inserted  in  the  Appendix. 

Sulphuric  acid  of  commence  freezes  at  — 1 5°  F.  Diluted  with  water  so 
as  to  have  a specific  gravity  of  1.78  it  congeals  even  above  32^,  and  re- 
mains in  the  solid  state,  according  to  Mr.  Keir,  till  the  temperature  rises 
to  45®.  When  mixed  with  rather  more  than  its  weight  of  water,  its 
freezing  point  is  lowered  to  — 36®  F. 

When  sulphuric  acid  is  passed  through  a small  porcelain  tube  heated 
to  redness,  it  is  entirely  decomposed;  and  Gay-Lussac  found  that  it  is 
resolved  into  two  measures  of  sulphurous  acid  and  one  of  oxygen. 
Hence  it  follows  that  real  sulphuric  acid  is  composed  of 

jBy  weight.  By  volume. 

Sulphur  . 16  one  p.  or  Vapour  of  sulphur  100 

Oxygen  . 24  three  p.  Oxygen  gas  . 150; 

and  its  atomic  weight  is  40.  Berzelius  ascertained  its  composition  by 
converting  a known  weight  of  sulphur  into  sulphuric  acid;  and  his  result 
confirms  the  conclusion  of  Gay-Lussac. 

Chemists  possess  an  unerring  test  of  the  presence  of  sulphuric  acid. 
If  a solution  of  muriate  of  baryta  is  added  to  a liquid  containing  sul- 
phuric acid,  it  causes  a white  precipitate,  sulphate  of  baryta,  which  is 
characterized  by  its  insolubility  in  acids  and  alkalies. 

Sulphuric  acid  does  not  occur  free  in  nature,  except  occasionally  in 
the  neighbourhood  of  volcanoes.  In  combination,  particularly  with  lime 
and  baryta,  it  is  very  abundant. 

Hyposulphurous  Acid, — This  acid  may  be  formed  either  by  digesting 
sulphur  in  a solution  of  any  sulphite,  or  by  transmitting  a current  of  sul- 
phurous acid  into  a solution  of  hydrosulphuret  of  lime  or  strontia.  In 
the  former  case,  the  sulphurous  acid  takes  up  an  additional  quantity  of 
sulphur,  and  a salt  of  hyposulphurous  acid  is  obtained;  and  in  the  latter, 
the  sulphurous  acid  is  deprived  of  one-half  of  its  oxygen  by  the  hydrogen 
of  the  sulphuretted  hydrogen,  while  the  other  half  of  its  oxygen  unites 
both  with  the  sulphur  of  the  sulphurous  acid  and  sulphuretted  hydro- 
gen, to  form  hyposulphurous  acid.  If  the  hydrosulphuret  of  lime  em- 
ployed contains  bisulphuretted  hydrogen,  as  is  the  case  when  lime  and 
sulphur  are  boiled  together,  the  action  of  sulphurous  acid  is  accompa- 
nied by  precipitation  of  sulphur.  Mr.  Herschel  states  that  hyposul- 
phurous acid  may  be  formed  by  the  action  of  sulphurous  acid  on  iron 
filings,  but  the  nature  of  the  change  is  not  well  understood. 

The  salts  of  hyposulphurous  acid  were  first  described  by  Gay-Lussac 
in  the  85th  volume  of  the  Annales  de  Chimie,  under  the  name  of  Sul- 
phuretted Sulphites.  Dr.  Thomson  in  his  System  of  Chemistry  suggest- 
ed that  the  acid  of  these  salts  might  be  regarded  as  a compound  of  one 
equivalent  of  sulphur  and  one  of  oxygen,  and  proposed  for  it  the  name 
of  hyposulphurous  acid.  The  subsequent  researches  of  Mr.  Herschel 
(Edinburgh  Philos.  Journal,  i.  8 and  396)  seemed  to  give  such  direct  an- 
alytic proof  of  the  correctness  of  this  opinion,  that  it  was  universally 
adopted;  but  it  appears  from  a recent  essay  by  Dr.  Thomson,  that  this 
view  of  its  composition  is  nevertheless  erroneous,  and  that  the  acid  con- 
sists of  32  parts  or  two  equivalents  of  sulphur,  and  8 parts  or  one  equiv- 
alent of  oxygen.  Its  combining  proportion  is,  therefore,  40.  (On  the 
Compounds  of  Chromium,  Philos.  Trans,  for  1827.) 


190 


SULPHUR. 


Hyposulphurous  acid  cannot  exist  permanently  in  a free  state.  On 
decomposing- a hyposulphite  by  any  stronger  acid,  such  as  the  sulphuric 
or  muriatic,  the  hyposulphurous  acid,  at  the  moment  of  quitting  the  base, 
resolves  itself  into  sulphurous  acid  and  sulphur.  Mr.  Herscliel  succeed- 
ed in  obtaining  free  hyposulphurous  acid,  by  adding  a slight  excess  of 
sulphuric  acid  to  a dilute  solution  of  hyposulphite  of  strontia;  but  its 
decomposition  very  soon  took  place,  even  at  common  temperatures, 
and  was  instantly  effected  by  heat.  Most  of  the  hyposulphites  are  solu- 
ble in  water,  and  have  a bitter  taste;  The  solution  precipitates  nitrate  of 
silver  and  mercury  black,  as  sulphuret  of  the  metals;  and  salts  of  lead 
and  baryta  are  thrown  down  as  white  insoluble  hyposulphites  of  those 
bases.  That  of  baryta  is  soluble  without  decomposition  in  water  acidu- 
lated with  muriatic  acid.  The  solution  of  all  the  neutral  hyposulphites 
has  the  peculiar  property  of  dissolving  recently  precipitated  chloride  of 
silver  in  large  quantity,  and  forming  with  it  a liquid  of  an  exceedingly 
sweet  taste. 

Hr.  Thomson,  in  the  essay  above  quoted,  mentions  that  an  acid  exists 
composed  of  one  equivalent  of  sulphur  and  one  of  oxygen;  but  he  has 
given  no  description  of  it. 

Hyposulphuric  Acid. — This  acid  was  discovered  in  1819  by  Welter  and 
Gay-Lussac,  who  published  their  description  of  it  in  the  10th  vol.  of  the 
An.  de  Ch,  et  de  Physique.  It  is  formed  by  transmitting  a current  of  sul- 
phui’ous  acid  gas  through  water  containing  peroxide  of  manganese  in  fine 
powder.  The  manganese  yields  oxygen  to  the  sulphurous  acid,  con- 
verting one  part  of  it  into  sulphuric,  and  another  part  into  hyposulphuric 
acid,  both  of  which  unite  with  the  protoxide  of  manganese.  To  the 
liquid,  after  filtration,  a solution  of  pure  baryta  is  added  in  slight  ex- 
cess, which  precipitates  the  protoxide  of  manganese,  and  forms  an  in- 
soluble sulphate  of  baryta  with  the  sulphuric,  and  a soluble  hyposul- 
phate  with  the  hyposulphuric  acid.  The  hyposulphate  of  baryta  is  then 
decomposed  by  a quantity  of  sulphuric  acid  exactly  sufficient  for  pre- 
cipitating the  baryta,  and  the  hyposulphuric  acid  is  left  in  solution. 

This  compound  reddens  litmus  paper,  has  a sour  taste,  and  forms  neu- 
tral salts  with  the  alkalies.  It  has  no  odour,  by  which  circumstance  it  is 
distinguished  from  sulphurous  acid.  It  cannot  be  confounded  with  sul- 
phuric acid;  for  it  forms  soluble  salts  with  baryta,  strontia,  lime,  and 
oxide  of  lead,  whereas  the  compounds  which  sulphuric  acid  forms  with 
those  bases  are  all  insoluble.  Hyposulphuric  acid  cannot  be  obtained 
free  from  water.  Its  solution,  if  confined  with  a vessel  of  sulphuric  acid 
under  the  exhausted  receiver  of  an  air-pump,  may  be  concentrated  till 
it  has  a density  of  1.347;  but  if  an  attempt  is  made  to  condense  it  still 
further,  the  acid  is  decomposed,  sulphurous  acid  gas  escapes,  and  sul- 
phuric acid  remains  in  solution.  A similar  change  is  still  more  readily 
produced  if  the  evaporation  is  conducted  by  heat. 

Welter  and  Gay-Lussac  analyzed  hyposulphuric  acid  by  exposing 
neutral  hyposulphate  of  baryta  to  heat.  At  a temperature  a little  above 
212^  F.  tliis  salt  suffers  complete  decomposition;  sulphurous  acid  gas  is 
disengaged,  and  neutral  sulphate  of  baryta  is  obtained.  It  was  thus 
ascertiiined  that  seventy-two  grains  of  hyposulphuric  acid  yield  thirty- 
two  grains  of  sulphurous,  and  forty  of  sulphuric  acid;  from  which  it  is 
inferred  that  hyposulphuric  acid  is  composed  either  of  an  equivalent  of 
each  of  those  acids,  combined  with  each  other,  or  of  two  equivalents 
of  sulphur  and  five  of  oxygen.  Whether  regarded  as  a definite  com- 
pound of  sulphurous  and  sulphuric  acids,  or  of  sulphur  and  oxygen,  it 
consists  of  32  parts  of  sulphur  and  40  of  oxygen,  and,  therefore,  72  is 
its  combining  proportion. 


PHOSPHORUS. 


191 


SECTION  VIIL 

PHOSPHORUS. 

Phosphorus  was  discovered  about  the  year  1669  by  Brandt,  an  alche- 
mist of  Hamburgh.  It  was  Originally  prepared  from  urine;  but  Scheele 
afterwards  described  a method  of  obtaining  it  from  bones.  The  object 
of  both  processes  is  to  bring  phosphoric  acid  in  contact  with  charcoal 
at  a strong  red  heat.  The  charcoal  takes  oxygen  from  the  phosphoric 
acid;  carbonic  acid  is  disengaged,  and  phosphorus  set  free.  When 
urine  is  employed,  the  phosphoric  acid  contained  in  it  should  be  sepa- 
rated by  acetate  of  lead.  Phosphate  of  lead  subsides,  which,  if  heated 
to  redness  with  one-fourth  of  its  weight  of  powdered  charcoal,  yields 
phosphorus  readily.  If  bones  are  used,  they  should  first  be  ignited  in 
an  open  fire  till  they  become  quite  white,  so  as  to  destroy  all  the  ani- 
mal matter  they  contain,  and  oxidize  the  carbon  proceeding  from  its 
decomposition.  The  calcined  bones,  of  which  phosphate  of  lime  con- 
stitutes nearly  four-fifths,  should  be  reduced  to  fine  powder,  and  di- 
gested for  a day  or  two  with  half  their  weight  of  concentrated  sulphuric 
acid,  so  much  water  being  added  to  the  mixture  as  to  give  it  the  con- 
sistence of  thin  paste.  The  phosphate  of  lime  is  decomposed  by  the 
sulphuric  acid,  and  two  new  salts  are  generated, — the  sparingly  soluble 
neutral  sulphate,  and  a soluble  superphosphate  of  lime.  On  the  addi- 
tion of  boiling  water  the  superphosphate  is  dissolved,  and  may  be  sepa- 
rated by  filtration  from  the  sulphate  of  lime.  The  solution  is  then  eva- 
porated to  the  consistence  of  syrup,  mixed  with  one-fourth  of  its  weight 
of  chai’coal  in  powder,  and  heated  in  an  earthen  retort  well  luted  with 
clay.  The  beak  of  the  retort  is  put  into  water,  in  which  the  phos- 
phorus, as  it  passes  over  in  the  form  of  vapour,  is  collected.  When 
first  obtained,  it  is  frequently  of  a reddish-brown  colour,  owing  to  the 
presence  of  phosphuret  of  carbon,  which  is  generally  formed  during 
the  process.  It  may  be  purified  by  being  put  into  hot  water,  and  press- 
ed while  liquid  through  chamois  leather;  or  the  purification  may  be  ren- 
dered still  more  complete  by  a second  distillation. 

Pure  phosphorus  is  transparent  and  almost  colourless.  It  is  so  soft 
that  it  may  be  cut  with  a knife,  and  the  cut  surface  has  a waxy  lustre. 
At  the  temperature  of  108®  F.  it  fuses,  and  at  550®  is  converted  into 
vapour.  It  is  soluble  by  the  aid  of  heat  in  naphtha,  in  fixed  and  vola- 
tile oils,  and  in  chloride,  carburet,  and  phosphuret  of  sulphur.  Quits 
cooling  from  solution  in  the  latter.  Professor  Mitscherlich  obtained  it  in 
regular  dodecahedral  crystals.  By  the  fusion  and  slow  cooling  of  a large 
quantity  of  phosphorus,  M.  Frantween  has  obtained  very  fine  crystals 
of  an  octahedral  form,  and  as  large  as  a cherry-stone. 

Phosphorus  is  exceedingly  inflammable.  Exposed  to  the  air  at  com- 
mon temperatures,  it  undergoes  slow  combustion,  emits  a white  va- 
pour of  a peculiar  alliaceous  odour,  appears  distinctly  luminous  in  the 
dark,  and  is  gradually  consumed.  On  this  account,  phosphorus  should 
always  be  kept  under  water.  The  disap peai^ance  of  oxygen  which  ac- 
companies these  changes  is  shown  by  putting  a stick  of  phosphorus  in  a 
jar  full  of  air,  inverted  over  water.  The  volume  of  the  gas  gradually 
diminishes;  and  if  the  temperature  of  the  air  is  at  60®  F.  the  whole  of 
the  oxygen  will  be  withdrawn  in  the  course  of  12  or  24  hours.  I'he  re- 
sidue is  nitrogen  gas,  containing  about  l-40th  of  its  bulk  of  the  vapour 
of  phosphorus.  It  is  remarkable  that  the  slow  combustion  of  phospho- 


192 


PHOSPHORUS. 


ms  does  not  take  place  in  pure  oxygen,  unless  its  temperature  be  about 
80®.  But  if  the  oxygen  is  diluted  with  nitrogen,  hydrogen,  or  car- 
bonic acid  gas,  the  oxidation  occurs  at  60®;  and  it  takes  place  at  tempe- 
ratures still  lower  in  a vessel  of  pure  oxygen,  rarefied  by  diminished 
pressure.*  Mr.  Graham  finds  that  the  presence  of  certain  gaseous  sub- 
stances, even  in  minute  quantity,  has  a remarkable  effect  in  preventing 
the  slow  combustion  of  phosphorus:  thus  at  66®  F.  it  is  entirely  pre- 
vented by  the  presence,  (Quart.  Journ.  of  Science,  N.  S.  vi.  83.) 


Volumes  of  air» 

of  1 volume  of  olefiant  gas  in  ....  450 

1 ditto  of  vapour  of  sulphuric  ether  in  . 150 

1 ditto  of  vapour  of  naphtha  in  ...  1 820 

1 ditto  of  vapour  of  oil  of  turpentine  in  . 4444 


and  by  an  equally  slight  impregnation  of  the  vapour  of  the  other  essen- 
tial oils.  Their  influence  is  not  confined  to  low  temperatures.  Phos- 
phorus becomes  faintly  luminous  in  the  dark,  in  mixtures  of 


* If  a stick  of  dry  phosphorus  be  dusted  over  with  powdered  resin 
or  sulphur,  and  then  introduced  under  the  receiver  of  an  air-pump,  it 
will  be  found  that,  as  soon  as  the  exhaustion  commences,  the  phospho- 
rus will  become  luminous,  which  appearance  increases  as  the  rarefac- 
tion proceeds,  until  finally  the  phosphorus  inflames.  Van  Bemmelen, 
who  first  attempted  to  account  for  this  phenomenon,  attributes  it  to  the 
combination  of  the  sulphur  or  resin  with  the  phosphorus,  the  union  of 
which,  accelerated  by  the  influence  of  the  vacuum,  gives  rise  to  the 
evolution  of  so  much  heat,  as  to  inflame  the  phosphorus,  or  the  new 
compound  formed.  Berzelius  rejects  this  explanation,  as  it  does  not 
account  for  an  experiment  by  Van  Bemmelen,  in  which  phosphorus  was 
found  to  take  fire  under  an  exhausted  receiver,  when  merely  enveloped 
with  cotton.  Berzelius,  Traite  de  Chimie,  i.  260. 

Professor  A.  D.  Bache,  of  the  University  of  Pennsylvania,  has  re- 
peated and  extended  the  experiments  of  Van  Bemmelen,  and  has  had 
the  goodness  to  communicate  to  me  an  abstract  of  his  results.  He  suc- 
ceeded in  producing  the  inflammation  of  the  phosphorus,  under  the 
circumstances  above  mentioned,  by  means  of  the  following  substances 
in  a finely  divided  state,  in  addition  to  those  employed  by  Van  Bem- 
melen:— 

Carbon,  in  the  form  of  ivory  black 
and  wood-charcoal. 

Spongy  platinum. 

Antimony. 

Arsenic, 

Bisulphuret  of  mercury. 

Sulphuret  of  antimony. 

Silica. 

Sulphur  and  charcoal  were  the  substances  which  succeeded  most 
readily.  Witli  metallic  arsenic  there  was  much  difficulty.  The  tem- 
perature of  the  room  has  great  influence  on  the  success  of  the  experi- 
ments. 

Professor  Bache  is  of  opinion  that  some  of  his  experiments  are  un- 
favourable to  the  explanation  of  Van  Bemmelen;  as  for  example,  those 
with  carbonate  of  lime  and  fluor  spar,  which,  though  incombustible 
substances,  act  with  the  same  energy  as  sulphur  or  carbon.  B. 


Lime. 

Peroxide  of  manganese. 
Hydrate  of  potassa. 
Muriate  of  ammonia. 
Chloride  of  sodium. 
Fluate  of  lime. 
Carbonate  of  lime. 


PHOSPHORUS. 


193 


1 volume  of  air  and  1 volume  of  olefiant  gas  at  200®  F. 

1 . , and  1 ditto  of  vapour  of  ether  at  215® 

111  . . and  1 ditto  of  vapour  of  naphtha  at  170® 

166  . . and  1 ditto  of  vapour  of  turpentine  at  186® 

Phosphorus  may  be  sublimed  at  its  boiling  temperature,  in  air  con- 
taining a considerable  proportion  of  the  vapour  of  oil  of  turpentine, 
without  diminishing  the  quantity  of  oxygen  present,  provided  the  heat 
be  gradually  and  uniformly  applied.  Mr.  Graham  has  also  remarked, 
that  the  oxidation  of  phosphorus  in  air  is  promoted  by  the  presence  of 
muriatic  acid  gas. 

A very  slight  degree  of  heat  is  sufficient  to  inflame  phosphorus  in  the 
open  air.  Gentle  pressure  between  the  fingers,  friction,  or  a tempera- 
ture not  much  above  its  point  of  fusion,  kindles  it  readily.  It  burns 
rapidly  even  in  the  air,  emitting  a splendid  white  light,  and  causing  in- 
tense heat.  Its  combustion  is  far  more  rapid  in  oxygen  gas,  and  the 
light  proportionally  more  vivid. 

Compounds  of  Phosphorus  and  Oxygen, — Phosphoric 

Jicid. 

Recent  observations  appear  to  justify  the  conclusion,  that  under  the 
term phosph(ync  add  chemists  have  hitherto  included  two  distinct  acids, 
phosphoric  2Md.pyropliosphoric.  These  compounds  afford  an  instance 
of  a fact  very  lately  noticed,  and  of  great  interest  in  reference  to  the 
atomic  theory;  viz.,  that  two  substances  may  consist  of  the  same  ingre- 
dients, in  the  same  proportion,  and  nevertheless  differ  essentially  in  their 
chemical  properties.  Such,  at  least,  is  an  obvious  deduction  from  the 
experiments  which  have  been  published  on  the  subject.  But  the  in- 
quiries have  not  yet  been  carried  sufficiently  far  to  admit  of  the  mutual 
relations  of  these  acids  being  stated  with  accuracy;  and,  therefore,  it 
will  be  the  safest  course,  at  present,  to  describe  phosphoric  acid  in  the 
usual  manner,  and  afterwards  to  enumerate  the  facts  known  respecting 
pyrophosphoric  acid. 

Phosphoric  acid  is  commonly  prepared  either  by  the  oxidation  of 
phosphorus,  or  by  the  action  of  sulphuric  acid  on  calcined  bones.  One 
method  of  oxidizing  phosphorus  is  by  its  combustion  in  air  or  oxygen 
gas,  when  phosphoric  acid  appears  in  the  form  of  a copious  white  va- 
pour, which  soon  collects  into  distinct  particles,  and  falls  to  the  bottom 
of  the  vessel  like  flakes  of  snow.  In  this  state  it  is  the  anhydrous  phos“ 
phoric  acid  of  chemists,  and  is  a white,  bulky,  rather  tenacious  solid; 
but  in  the  open  air  its  appearance  soon  changes,  in  consequence  of  its 
attracting  moisture  rapidly  from  the  atmosphere,  and  forming  with  it  a 
dense  acid  solution.  The  conversion  of  all  the  phosphorus  into  phos- 
phoric acid,  rarely,  if  ever,  ensues  in  this  process;  for,  on  the  spot 
where  the  burning  phosphorus  lay,  a small  quantity  of  red  matter  is  al- 
ways found,  which  is  supposed  to  be  an  oxide.  When  the  supply  of 
oxygen  is  insufficient  for  completing  the  combustion,  the  residue  is  a 
mixture  of  this  oxide  and  unburned  phosphorus. 

The  oxidation  of  phosphorus  may  also  be  effected  by  means  of  strong 
nitric  acid,  which  communicates  oxygen  to  the  phosphorus,  and  emits  a 
large  quantity  of  deutoxide  of  nitrogen.  The  unpractised  operator 
should  be  cautious  in  performing  this  experiment,  as  the  disengagement 
of  gas  is  sometimes  so  rapid  as  to  endanger  the  apparatus. 

The  process  is  best  conducted  by  adding  fragments  of  phosphorus  to 
concentrated  nitric  acid  contained  in  a platinum  capsule.  Gentle  heat 
is  applied  so  as  to  commence,  and,  when  necessary,  to  maintain  moderate 

17 


194 


PHOSPHORUS. 


effervescence;  and  when  one  portion  of  phosphorus  disappears,  another 
is  added,  till  the  whole  of  the  nitric  acid  is  exhausted.  The  solution 
is  then  evaporated  to  dryness,  and  exposed  to  a red  heat  to  expel  the 
last  traces  of  nitric  acid.  This  should  always  be  done  in  vessels  of  plat- 
inum, since  phosphoric  acid  acts  chemically  upon  those  of  glass  or  por- 
celain, and  is  thereby  rendered  impure.  In  this  case,  as  in  some  other 
instances  of  the  oxidation  of  combustibles  by  nitric  acid,  water  is  de- 
composed; and  while  its  oxygen  unites  with  phosphorus,  its  hydrogen 
combines  with  nitrogen  of  the  nitric  acid.  A portion  of  ammonia,  thus 
generated,  is  expelled  by  heat  in  the  last  part  of  the  process. 

Phosphoric  acid  may  be  prepared  at  a much  cheaper  rate  from  bones. 
For  this  purpose,  superphosphate  of  lime,  obtained  in  the  way  already 
described,  should  be  boiled  for  a few  minutes  with  excess  of  carbonate 
of  ammonia.  The  lime  is  thus  precipitated  as  the  neutral  phosphate, 
and  the  solution  contains  phosphate,  together  with  a little  sulphate,  of 
ammonia.  The  liquid,  after  filtration,  is  evaporated  to  dryness,  and  then 
ignited  in  a platinum  crucible,  by  which  means  the  ammonia  and  sul- 
phuric acid  are  expelled. 

Solid  phosphoric  acid  unites  with  water  in  every  proportion,  and 
forms,  if  concentrated,  a dense  oily  liquid.  On  heating  the  solution  in 
a platinum  vessel,  the  greater  part  of  the  water  is  driven  off;  the  resi- 
due fuses  at  a low  red  heat,  and  concretes  on  cooling  into  a brittle  glass, 
called  glacial  phosphoric  acid.  This  substance  is  a hydrate,  which  can- 
not be  decomposedby  fire;  for  on  exposing  it  to  a strong  red  heat,  with 
the  view  of  expelling  the  water,  the  compound  itself  is  volatilized,  and 
in  open  vessels  sublimes  with  considerable  rapidity.  It  is  erroneously 
said  to  be  fixed  at  intense  degrees  of  heat,  this  character  applying  to 
the  acid  only  in  its  impure  state,  as  when  combined  with  earthy  or  al- 
kaline substances.  The  composition  of  glacial  phosphoric  acid  is  not 
yet  established;  for  while  M.  Dulong  reports  it  to  contain  17.08  per  cent 
of  water,  M.  Rose  found  only  9.44  per  cent.  (Poggendorff’s  Annalen, 
viii.  201.)  The  analysis  of  Rose,  though  not  rigidly  exact,  is  probably 
not  far  from  the  truth.  The  acid  after  being  fused  in  glass  vessels  is 
anhydrous. 

Phosphoric  acid  is  intensely  sour  to  the  taste,  reddens  litmus  paper 
strongly,  and  neutralizes  alkalies.  It  is,  therefore,  a powerful  acid;  but 
it  does  not  destroy  the  texture  of  the  skin  like  sulphuric  and  nitric  acids. 
It  may  be  distinguished  from  all  other  acids  by  the  following  circum- 
stances:— that  it  neither  suffers  precipitation,  nor  change  of  colour, 
when  a stream  of  sulphuretted  hydrogen  gas  is  passed  through  its  solu- 
tion; and  that  when  carefully  neutralized  by  pure  carbonate  of  potassa 
or  soda,  it  is  precipitated  white  by  acetate  of  lead,  and  yellow  by  nitrate 
of  silver.  The  former  precipitate,  phosphate  of  lead,  dissolves  com- 
pletely on  the  addition  of  nitric  or  phosphoric  acid;  the  latter,  phosphate 
of  silver,  is  dissolved  by  both  these  acids  and  by  ammonia. 

The  composition  of  phosphoric  acid  has  been  investigated  by  Sir  H. 
Davy,  Dr.  'fhomson,  Berzelius,  Dulong,  and  Rose.  The  subject  is  one 
of  much  difficulty,  and  the  results  of  the  two  former  chemists  differ 
widely  from  those  of  the  latter.  Tlie  direct  method  of  burning  a known 
weight  of  phosphorus  in  oxygen  gas  is  ob  jectionable,  on  account  of  the 
difficulty  by  this  process  of  converting  all  the  phosphorus  into  phosphoric 
acid.  Dr.  Thomson  and  others  liave  endeavoured  to  infer  its  constitu- 
tion by  means  of  the  analysis  of  phosphuretted  hydrogen;  but  the  com- 
position and  purity  of  the  gas  employed  in  these  researclies  were  not 
known  with  sufficient  certainty  to  inspire  confidence  in  the  results  which 
were  obtained.  Berzelius  converted  a known  weight  of  phosphorus  into 
phosphoric  acid  by  digestion  in  a neutral  solution  of  muriate  of  gold  or 


PHOSPHORUS. 


195 


sulphate  of  silver,  the  oxygen  required  for  that  change  being  derived 
from  the  metallic  oxide,  and  its  quantity  estimated  by  the  amount  of  me- 
tal reduced.  Dr.  Thomson  infers,  from  experiments  made  by  Sir  H. 
Davy  and  himself,  that  28  is  the  combining  proportion  of  phosphoric 
acid;  and  that  it  consists  of  12  parts,  or  what  he  considers  one  equivalent, 
of  phosphorus,  and  16  parts,  or  two  equivalents  of  oxygen.  Accord- 
ing to  the  researches  of  Berzelius,  as  well  as  of  M.  Dulong,  the  oxygen 
contained  in  phosphorous  and  phosphoric  acids  is  in  the  ratio  of  1.5  to 
2.5,  or  3 to  5;  and  the  former  states  phosphoric  acid  to  be  composed  of 
56  parts  of  oxygen  and  44  of  phosphorus.  Now,  judging  from  these 
data,  and  from  the  composition  of  the  phosphates  analyzed  by  Berzelius 
and  MitscheiTich,  we  may  regard  35.71  as  the  equivalent  of  phosphoric 
acid,  and  the  acid  itself  as  a compound  of  15.71  parts  or  one  equivalent 
of  phosphorus,  and  20  parts  or  two  equivalents  and  a half  of  oxygen. 
Berzelius  believes  that  it  consists  of  two  atoms  of  phosphorus  and  five 
atoms  of  oxygen,  and  therefore  doubles  the  preceding  numbers.  The 
estimate  of  Berzelius  appears  to  me  most  deserving  of  confidence,  and 
1 have  accordingly  adopted  it;  but  that  of  Dr.  Thomson  is  commonly 
employed  in  this  country. 

PyrophosphoricAcid. — It  is  above  remarked,  as  a distinctive  character 
of  phosphoric  acid,  that  it  forms  a yellow  salt  with  oxide  of  silver;  but 
if  crystallized  phosphate  of  soda  be  dried  gently  on  a sand-bath  and 
then  heated  to  redness,  it  afterwards  yields  a white  instead  of  a yellow 
precipitate  with  nitrate  of  silver,  and  is  found  to  have  undergone  an  en- 
tire change  in  its  properties.  It  appears,  nevertheless,  that  in  the  ratio 
of  its  ingredients  no  alteration  is  occasioned,  the  only  visible  effect  of 
heat  being  confined  to  the  expulsion  of  water:  nothing  is  absorbed  from 
the  atmosphere,  and  nothing,  except  water,  is  expelled.  These  re- 
markable facts  were  brought  under  the  notice  of  chemists  in  tlie  year 
1827  by  Mr.  Clarke  of  Glasgow,  who  applied  to  the  new  acid  the  appro- 
priate appellation  of  pyrophosphoric.  (Brewster’s  Journal,  vii.  298.) 
Heat  has  a similar  effect  on  the  phosphate  of  potassa,  and  probably  on 
most  other  phosphates. 

This  interesting  subject  has  lately  occupied  the  attention  of  Gay-Lus- 
sac and  Stromeyer.  The  fact  observed  by  Dr.  Engelhard!,  that  albumen 
is  precipitated  by  a solution  of  recently  ignited  phosphoric  acid,  and  that 
after  keeping  the  solution  a few  days  this  propei’ty  entirely  disappears, 
is  found  by  Gay-Lussac  to  be  allied  to  the  observation  of  Mr.  Clarke. 
Common  phosphoric  acid  is,  in  fact,  converted  by  a red  heat  into  the 
pyrophosphoric,  as  is  inferred  from  its  yielding  a white  precipitate  with 
oxide  of  silver;  but  when  its  solution  is  kept  for  a few  days,  it  is  gradu- 
ally reconverted  into  phosphoric  acid,  as  is  proved  by  its  then  forming 
with  silver  a yellow  precipitate.  In  the  former  state  it  I’enders  turbid  a 
moderately  dilute  solution  of  albumen,  and  in  the  latter  it  does  not  dis- 
turb its  transparency;  so  that  albumen,  as  well  as  the  colour  of  the  salt 
of  silver,  affords  a good  character  for  distinguishing  the  two  acids  from 
each  other.  (An.  de  Ch,  et  de  Ph.  xli.  331.) 

The  observation  of  Gay-Lussac  shows,  that  the  substance  above  des- 
cribed under  the  name  of  glacial  phosphoric  acid  is.  really  hydrated  pyro- 
phosphoric acid;  and  Stromeyer  finds  that  the  white  solid,  procured  by 
the  combustion  of  phosphorus,  is  pyrophosphoric  acid  in  the  dry  state. 
Hence  it  appears  that  solid  phosphoric  acid  is  wholly  unknown.  The 
conversion  of  pyrophosphoric  into  phosphoric  acid,  which  takes  place 
gradually  at  common  temperatures,  is  rapidly  effected  by  boiling  the  so- 
lution; and  even  the  salts  of  pyrophosphoric  acid,  which  may  be  long 
preserved  in  the  liquid  form  without  change,  are  quickly  converted  into 
phosphates  when  heated  with  various  acids,  such  as  thb  nitric,  muriatic,, 


196 


PHOSPHORUS. 


sulphuric,  acetic,  or  phosphoric.  But  the  acid,  which  by  its  presence 
determines  the  chang’e,  does  not  itself  underg'o  the  least  decomposition. 
(Brewster’s  Journal,  N.  S.,  iii.) 

Phosphoric  acid  seems  a stronger  acid  than  the  pyrophosphoric.  Thus, 
if  phosphate  of  soda  is  boiled  with  pyrophosphate  of  silver,  phosphate 
of  silver  is  quickly  generated;  but  pyrophosphate  of  soda  cannot  decom- 
pose any  of  the  insoluble  phosphates.  The  neutralizing  power  of  phos- 
phoric acid  is  likewise  greater.  Stromeyer  states,  for  example,  that  118 
parts  of  oxide  of  silver  combine  with  38.52  parts  of  pyrophosphoric  acid, 
and  with  only  23.4  of  the  phosphoric;  a remarkable  difference  which 
amply  accounts  for  the  uncertainty  which  has  long  prevailed  concerning 
the  equivalent  of  phosphoric  acid,  and  throws  great  doubt  on  the  esti- 
mates above  given  on  the  authority  of  Berzelius  and  Thomson.  The  fore- 
going facts  fully  prove  these  acids  to  be  essentially  distinct;  while,  as  al- 
ready observed,  it  appears  equally  certain  that  in  point  of  composition 
they  differ  neither  in  the  nature  nor  the  proportion  of  their  elements, 
but  solely  in  the  manner  in  which  they  are  arranged.* 

Phosphorous  Acid. — When  phosphorus  is  burned  in  air  highly  rarefied, 
imperfect  oxidation  ensues,  and  phosphoric  and  phosphorous  acids  are 
both  generated,  the  latter  being  obtained  in  the  form  of  a white  vola- 
tile powder.  In  this  state  it  is  anhydrous.  Heated  in  the  open  air,  it 


* Considering  the  uncertainty  in  which  the  composition  of  the  acids 
of  phosphorus  is  still  involved,  if,  is  to  be  regretted  that  Dr.  Turner  has 
thought  proper  to  adopt  the  analytic  results  of  Berzelius  and  Dulong 
respecting  these  compounds,  which  has  the  effect  of  giving  a new  equiv- 
alent number  for  phosphorus,  and  a different  view  of  their  atomic 
composition.  As  the  subject  cannot  yet  be  considered  as  decided,  it 
would  have  been  better  to  wait  until  further  researches  had  finally  set- 
tled the  question  of  their  composition,  rather  than  hastily  reject  the 
numbers,  which  have  heretofore  been  almost  universally  adopted  by 
the  British  and  American  chemists.  It  deserves  to  be  mentioned  that 
the  composition  of  phosphoric  acid,  as  given  by  Dr.  Thomson,  which 
coincides  nearly  with  the  analysis  of  Sir  H.  Davy,  is  not  materially  dif- 
ferent from  the  results  of  Berzelius,  who  states  it  to  be  56  parts  of 
oxygen  and  44  of  phosphorus.  Now  the  proportion  of  16  parts  of 
oxygen  to  12  of  phosphorus,  will  give,  in  the  100  parts,  57.1  parts  of 
oxygen  and  42.9  parts  of  phosphorus.  This  is  a virtual  agreement  in 
the  analysis  of  this  acid,  and,  therefore,  the  discrepancy  relates  to  its 
saline  equivalent.  Berzelius  finds  this  to  be  35.71,  and  Dr.  Thomson 
believes  it  to  be  28.  The  difficulty  certainly  rests  here,  and  it  must  be 
acknowledged  that  there  is  a strong  probability  that  Berzelius’s  number 
is  correct;  as  it  is  not  easy  to  see  how  he  could  be  mistaken  in  his  ana- 
lyses of  the  phosphates.  Still  it  appears  inexpedient  to  abandon  the 
numbers  generally  received,  with  a view  to  adopt  others,  which  cannot 
yet  be  considered  as  fully  established.  The  substitution  in  this  case  is 
peculiarly  unfortunate,  as  it  admits  a fractional  number  to  represent 
phosphorus,  and  causes  the  adoption  of  fractional  equivalents  for  the 
oxygen  both  of  phosphorous  and  phosphoric  acids.  It  ought  to  be  a 
strong  case  of  analytic  proof  that  would  justify  the  author  in  adopting 
numbers  so  little  in  accordance  with  the  laws  of  combination.  B. 

[In  the  interval  which  has  elapsed  since  the  foregoing  note  was  writ- 
ten for  the  preceding  American  edition  of  this  work,  we  deem  the  dis- 
covery of  pyrophosphoric  acid,  and  the  uncertainty  which  still  exists 
as  to  its  nature  and  composition,  as  additional  reasons  why  the  received 
number  for  phosphorus  ought  not  for  the  present  to  be  disturbed.  B.] 


PHOSPHORUS. 


197 


takes  fire,  and  forms  phosphoric  acid;  but  if  exposed  to  heat  in  close 
vessels,  it  is  resolved  into  phosphoric  acid  and  phosphorus.  It  dissolves 
readily  in  water,  has  a sour  taste,  and  smells  somewhat  like  garlic.  It 
unites  with  alkalies,  and  forms  salts  which  are  termed  phosphites.  The 
solution  of  phosphorous  acid  absorbs  oxygen  slowly  from  the  air,  and  is 
converted  into  phosphoric  acid.  From  its  tendency  to  unite  with  an  ad- 
ditional quantity  of  oxygen,  it  is  a powerful  deoxidizing  agent;  and, 
hence,  hke  sulphurous  acid,  precipitates  mercury,  silver,  platinum,  and 
gold,  from  their  saline  conlbinations  in  the  metallic  form.  Nitric  acid,  of 
course,  converts  it  into  phosphoric  acid. 

Phosphorous  acid  may  be  procured  more  conveniently  by  subliming 
phosphorus  through  powdered  corrosive  sublimate,  (a  compound  of 
chlorine  and  mercury,)  contained  in  a glass  tube;  when  a limpid  liquid 
comes  over,  which  is  a compound  of  chlorine  and  phosphorus.  (Davyds 
Elements,  p.  288.)  This  substance  and  water  mutually  decompose  each 
other:  the  hydrogen  of  water  unites  with  the  chlorine,  and  forms  mu- 
riatic acid;  while  the  oxygen  attaches  itself  to  the  phosphorus,  and 
thus  phosphorous  acid  is  produced.  The  solution  is  then  evaporated 
to  the  consistence  of  syrup  to  expel  the  muriatic  acid;  and  the  residue, 
which  is  hydrate  of  phosphorous  acid,  becomes  a crystalline  solid  on 
cooling.  When  this  hydrate  is  heated  in  close  vessels,  the  elements  of 
the  water  and  acid  react  on  each  other,  forming  phosphoric  acid  and  a 
gaseous  compound  of  hydrogen  and  phosphorus.  The  nature  of  this 
gas  will  be  more  particularly  noticed  in  the  section  on  phosphuretted 
hydrogen. 

Phosphorous  acid  is  also  generated  during  the  slow  oxidation  of  phos- 
phorus in  atmospheric  air.  The  product  attracts  moisture  from  the  air,, 
and  forms  an  oil-like  liquid.  M.  Dulong  thinks  that  a distinct  acid  is 
generated  in  this  case,  which  he  phosphatic  acid;  but  the  opinion 
of  Sir  H.  Davy,  that  it  is  merely  a mixture  of  phosphoric  and  phospho- 
rous acids,  is  in  my  opinion  perfectly  correct. 

The  composition  of  phosphorous,  like  that  of  phosphoric  acid,  is  not 
yet  satisfactorily  ascertained.  According  to  Sir  H.  Davy  and  Dr. 
Thomson  the  oxygen  in  the  two  acids  is  in  the  ratio  of  1 to  2,  while  it 
is  stated  by  Dulong  and  Berzelius  to  be  as  3 to  5. 

Hypophosphorous  Acid. — This  acid  was  discovered  in  1816  by  M.  Du- 
long,* and  is  produced  by  the  action  of  water  on  phosphuret  of  baryta. 
Mutual  decomposition  ensues;  and  the  elements  of  water  uniting  with 
different  portions  of  phosphorus,  give  rise  to  the  formation  of  three 
compounds— phosphuretted  hydrogen,  phosphoric  acid,  and  hypophos- 
phorous acid.  - The  former  escapes  in  the  form  of  gas;  and  the  two 
latter  combine  with  the  baryta.  Hypophosphite  of  baryta,  being  solu- 
ble, dissolves  in  the  water,  and  may  consequently  be  separated  by  fil-. 
tration  from  the  phosphate  of  baryta,  which  is  insoluble.  On  adding  a 
sufficient  quantity  of  sulphuric  acid  for  precipitating  the  baryta,  hypo- 
phosphorous  acid  is  obtained  in  a free  state.  On  evaporating  the  solution,, 
a viscid  liquid  remains,  highly  acid  and  even  crystallizable,  which  is 
hydrate  of  hypophosphorous  acid.  When  exposed  to  heat  in  close 
vessels,  it  undergoes  the  same  kind  of  change  as  hydrated  phosphorous 
acid. 

Hypophosphorous  acid  is  a powerful  deoxidizing  agent.  It  unites 
with  alkaline  bases;,  and  it  is  remarkable  that  all  its  salts  are  soluble  in 
water,  'fhe  hypophosphites  of  potassa,  soda,  and  ammonia,  dissolve 
in  every  proportion  in  rectified  alcohol;  and  hypophosphite  of  potassa 


M^m.  d’Arcueil,  vol.  iii.;  or  An.  de  Ch.  et  de  Physique,  vol.  ii. 

17* 


198 


BORON. 


is  even  more  deliquescent  than  chloride  of  calcium.  They  are  all  de- 
composed by  heat,  and  yield  the  same  products  as  the  acid  itself.  They 
are  conveniently  prepared  by  precipitating*  hypophosphite  of  baryta, 
strontia,  or  lime,  with  the  alkaline  carbonates;  or  by  directly  neutraliz- 
in^  these  carbonates  with  hypophosphorous  acid.  The  hypophosphite 
of  baryta,  strontia,  and  lime,  are  formed  by  boiling*  these  earths  in 
the  caustic  state  in  water  together  with  fragments  of  phosphorus. 
The  same  change  occurs  as  during  the  action  of  water  on  phosphuret  of 
baryta. 

M.  Dulong  determined  the  proportion  of  its  elements  by  converting 
it  into  phosphoric  acid  by  means  of  chlorine.  He  infers  from  his  ana- 
lysis that  it  contains  27.25  per  cent,  of  oxygen.  According  to  Sir  H. 
Davy,  it  has  exactly  one  half  less  oxygen  than  phosphorous  acid;  but 
as  the  composition  of  this  acid  is  not  known  with  certainty,  no  infer- 
ence can  be  safely  deduced  from  this  statement.  Professor  Henry  Rose 
finds  that  it  contains  20.31  per  cent,  of  oxygen,  being  the  ratio  of  31.42 
parts  or  two  proportionals  of  phosphorus,  to  8 parts  or  one  proportional 
of  oxygen.  (PoggendorfF’s  Annalen,  ix.  367.)  This  result  is  probably 
more  accurate  than  that  of  M.  Dulong. 

Oxides  of  Phosphorus. — Chemists  have  not  yet  succeeded  in  proving 
the  existence  of  any  oxide  of  phosphorus.  When  phosphorus  is  kept 
under  water  for  some  time,  a white  film  is  formed  upon  its  surface, 
which  some  regard  as  an  oxide  of  phosphorus.  The  red-coloured  mat- 
ter which  remains  after  the  combustion  of  phosphorus,  is  also  supposed 
to  be  an  oxide.  The  nature  of  these  substances  has  not,  however, 
been  determined  in  a satisfactory  manner.  The  formation  of  the  white 
film  is  materially  promoted  by  the  agency  of  light;  and  Mr.  Phillips  has 
observed  this  change  to  be  attended  with  decomposition  of  water,  and 
production,  in  small  quantity,  of  phosphuretted  hydrogen  and  one  of 
the  acids  of  phosphorus.  (An.  of  Phil.  xxi.  470.) 


SECTION  IX. 

BORON. 

Sir  H.  Davy  discovered  the  exigence  of  boron  in  1807  by  exposing 
boracic  acid  to  the  action  of  a powerful  galvanic  battery;  but  he  did 
not  obtain  a sufficient  supply  of  it  for  determining  its  properties.  Gay- 
Lussac  and  Thenard*^  procured  it  in  greater  quantity  in  1808  by  heating 
boracic  acid  with  potassium.  . The  boracic  acid  is  by  this  means  depriv- 
ed  of  its  oxygen,  and  boron  is  set  free.  The  easiest  and  most  economi- 
cal method  of  preparing  this  substance,  according  to  Berzelius,  is  to 
decompose  an  alkaline  borofluate  by  means  of  potassium.  (Annals  of 
Philosophy,  xxvi.  128.) 

'Boron  is  a dark  olive  coloured  substance,  which  has  neither  taste  nor 
smell,  and  is  a non-conductor  of  electricity.  It  is  insoluble  in  w'ater, 
alcohol,  ether,  and  6ils.  It  docs  not  decompose  water  whether  hot  or 
cold.  It  bears  an  intense  heat  ih  close  vessels,  without  fusing  or  under- 
going any  other  change,  except  a slight  increase  of  density.  Its  spe- 


Rechercheg  Physico-chimiques,  vol.  i. 


BORON. 


199 


cific  gravity  is  about  twice  as  great  as  that  of  water.  It  may  be  exposed 
to  the  atmosphere  at  common  temperatures  without  change;  but  if 
heated  to  600°  F.,  it  suddenly  takes  fire,  oxygen  gas  disappears,  and 
boracic  acid  is  generated.  It  experiences  a similar  change  when 
heated  in  nitric  acid,  or  with  any  substance  that  yields  oxygen  with  fa- 
cility. 

Boracic  Acid.  This  is  the  only  known  compound  of  boron  and  oxy- 
gen. As  a natural  product  it  is  found  in  the  hot  springs  of  Lipari, 
and  in  those  of  Sasso  in  the  Florentine  territory.  It  is  a constituent  of 
several  minerals,  among  which  the  datolite  and  boracite  may  in  particu- 
lar be  mentioned.  It  occurs  much  more  abundantly  under  the  form  of 
borax,  a native  compound  of  boracic  acid  and  soda.  It  is  prepared  for 
chemical  purposes  by  adding  sulphuric  acid  to  a solution  of  purified  bo- 
rax in  about  four  times  its  weight  of  boiling  water,  till  the  liquid  ac- 
quires a distinct  acid  reaction.  The  sulphuric  acid  unites  with  the  soda; 
and  the  boracic  acid  is  deposited,  when  the  solution  cools,  in  a confu- 
sed group  of  shining  scaly  crystals.  It  is  then  thrown  on  a filter,  wash- 
ed with  cold  water  to  separate  the  adhering  sulphate  of  soda  and  sul- 
phuric acid,  and  still  further  purified  by  solution  in  boiling  water  and 
re-crystallization.  But  even  after  this  treatment  it  ibapt  to  retain  a lit- 
tle sulphuric  acid;  and  on  this  account,  when  required  to  be  absolutely 
pure,  it  should  be  fused  in  a platinum  crucible,  and  once  more  dissolv- 
ed in  hot  water  and  crystallized. 

Boracic  acid  in  this  state  is  a hydrate.  Its  precise  degree  of  solubility 
in  water  has  not  been  determined  with  accuracy;  but  it  is  much  more 
soluble  in  hot  than  in  cold  water.  Boiling  alcohol  dissolves  it  freely,  and 
the  solution,  when  set  on  fire,  burns  with  a beautiful  green  flame;  a test 
which  affords  the  surest  indication  of  the  presence  of  boracic  acid.  Its 
specific  gravity  is  1.479.  It  has  no  odour,  and  its  taste  is  rather  bitter 
than  acid.  It  reddens  litmus  paper  feebly,  and  effervesces  with  alkaline 
carbonates.  Mr.  Faraday  has  noticed  that  it  renders  turmeric  paper 
brown  like  the  alkalies.  From  the  weakness  of  its  acid  properties,  all 
the  borates,  when  in  solution,  are  decomposed  by  the  stronger  acids. 

When  hydrous  boracic  acid  is  exposed  to  a gradually  increasing  heat 
in  a platinum  crucible,  its  water  of  crystallization  is  wholly  expelled,  and 
a fused  mass  remains  which  bears  a white  heat  without  being  sublimed. 
On  cooling,  it  forms  a hard,  colourless,  transparent  glass,  which  is  an- 
hydrous boracic  acid.  If  the  water  of  crystallization  be  driven  off  by 
the  sudden  application  of  a strong  heat,  a large  quantity  of  boracic  acid 
is  carried  away  during  the  rapid  escape  of  watery  vapour.  The  same 
happens,  though  in  a less  degi^ee,  when  a solution  of  boracic  acid  in 
water  is  boiled  briskly.  Vitrified  boracic  acid  should  be  preserved  in 
well-stopped  vessels;  for  if  exposed  to  the  air,  it  absorbs  water,  and 
gradually  loses  its  transparency.  Its  specific  gravity  is  1.803.  It  is  ex- 
ceedingly fusible,  and  communicates  this  property  to  the  substances 
with  which  it  unites.  For  this  reason  borax  is  often  used  as  a flux. 

The  most  obvious  mode  of  determining  the  composition  of  boracic 
acid  is  to  burn  a known  quantity  of  boron,  and  ascertain  its  increase  of 
weight  when  the  combustion  ceases.  This  method,  however,  though 
apparently  simple,  is  very  difficult  of  execution;  for  the  boracic  acid 
fuses  at  the  moment  of  being  generated,  and  by  glazing  the  surface  of 
the  unconsumed  boron,  protects  it  from  oxidation.  Hence  it  w'as  that 
the  experiments  performed  by  Gay-Lussac  and  Thenard  on  this  subject, 
led  to  results  widely  different  from  those  which  Sir  H.  Davy  obtained 
by  a similar  process.  Dr.  Thomson,  from  data  furnished  partly  by  him  - 
self,  and  partly  by  Sir  H.  Davy,  infers  that  the  atomic  weight  of  boron 
is  8,  and  that  boracic  acid  is  composed  of 


200 


SELENIUM. 


Boron  . . 8,  or  one  equivalent, 

Oxyg-en  . . 16,  or  two  equivalents. 

Consequently,  the  equivalent  of  boracic  acid  is  24. 

Crystallized  boracic  acid,  according*  to  the  same  chemist,  is  compos- 
ed of 

Boracic  acid  . 24,  or  one  equivalent. 

Water  . . 18,  or  two  equivalents; 

and  therefore  its  equivalent  is  42. 

Sulphuret  of  Boron. — This  compound  may  be  formed,  according  to 
Berzelius,  by  igniting  boron  strongly  in  the  vapour  of  sulphur;  and  the 
combination  is  accompanied  with  the  phenomena  of  combustion.  The 
product  is  a white  opake  mass,  which  is  converted  by  the  action  of  wa- 
ter into  sulphuretted  hydrogen  and  boracic  acid;  and  the  liquid  becomes 
milky  at  the  same  time  from  a deposition  of  sulphur.  (Annals  of  Phi- 
losophy, xxvi.  129.) 


SECTION  X. 

SELENIUM. 

Selektium  has  hitherto  been  found  in  very  small  quantity.  It  occurs 
for  the  most  part  in  combination  with  sulphur  in  some  kinds  of  iron 
pyrites.  Stromeyer  has  also  detected  it,  as  a sulphuret  of  selenium, 
among  the  volcanic  products  of  the  Lipari  isles.  It  is  found  likewise  at 
Clausthal,  in  the  Hartz  mountains,  combined,  according  to  Stromeyer 
and  Rose,  with  several  metals,  such  as  lead,  cobalt,  silver,  mercury,  and 
copper.  It  was  discovered  in  1818,  by  Berzelius,  in  the  sulphur  obtain- 
ed by  sublimation  from  the  iron  pyrites  of  Fahlun.  In  a manufactory 
of  sulphuric  acid,  at  which  this  sulphur  was  employed,  iit  was  observed 
that  a reddish-coloured  matter  always  collected  at  the  bottom  of  the  lead- 
en chamber;  and  on  burning  this  substance,  Berzelius  perceived  a strong 
and  peculiar  odour,  similar  to  that  of  decayed  horse-radish,  which  in- 
duced him  to  submit  it  to  a careful  examination,  and  thus  led  to  the  dis- 
covery of  selenium*. 

Selenium,  at  common  temperatures,  is  a brittle  opake  solid  body, 
without  taste  or  odour.  It  has  a metallic  lustre  and  the  aspect  of  lead 
when  in  mass;  but  is  of  a deep  red  colour  when  reduced  to  powder.  Its 
specific  gravity  is  between  4.3  and  4.32.  At  212®  it  softens,  and  is  then 
so  tenacious  that  it  may  be  drawn  out  into  fine  threads  which  are  trans- 
parent, and  appear  red  by  transmitted  light.  It  becomes  quite  fluid  at 
a temperature  somewhat  above  that  of  boiling  water.  It  boils  at  about 
650®,  forming  a vapour  which  has  a deep  yellow  colour,  but  is  free  from 
odour.  It  may  be  sublimed  in  close  vessels  without  change,  and  con- 
denses again  into  dark  globules  of  a metallic  lustre,  or  as  a cinnabar-red 
powder,  according  as  the  space  in  which  it  collects  is  small  or  large. 
Berzelius  at  first  regarded  it  as  a metal;  but,  since  it  is  an  imperfect  con- 
ductor of  caloric  and  electricity,  it  more  properly  belongs  to  the  class 
of  the  simple  non-mctallic  bodies. 


An.  de  Ch.  et  de  Phys.  vol.  ix. ; or  Annals  of  Philosophy,  vol.  xiii. 


SELENIUM. 


201 


Selenium  is  insoluble  in  water.  It  sufTers  no  change  from  mere  ex- 
posure to  the  atmosphere;  but  if  heated  in  the  open  aii;,  it  combines 
readily  with  oxygen,  and  two  compounds,  oxide  of  selenium  and  seleni- 
ous  acid,  are  generated.  If  exposed  to  the  oxidizing  part  of  the  blow- 
pipe flame,  it  tinges  the  flame  with  a light  blue  colour,  and  exhales  so 
strong  an  odour  of  decayed  horse-radish,  that  1.50th  of  a grain  is  said  to 
be  sufficient  to  scent  the  air  of  a large  apartment.  By  this  character  the 
presence  of  selenium  whether  alone  or  in  combination  may  always  be 
detected. 

Oxide  of  Selenium. — This  compound  is  formed  in  greatest  abundance 
by  heating  selenium  in  a limited  quantity  of  atmospheric  air,  and  by  wash- 
ing the  product  to  separate  selenious  acid,  which  is  generated  at  the 
same  time.  It  is  a colourless  gas,  which  is  very  sparingly  soluble  in  wat- 
er, and  does  not  possess  any  acid  properties.  It  is  the  cause  of  the  pe- 
culiar odour  which  is  emitted  during  the  oxidation  of  selenium.  Its 
composition  has  not  been  determined,  but  it  probably  contains  an  atom 
of  each  of  its  elements. 

Selenious  Acid — This  acid  is  most  conveniently  prepared  by  digesting 
selenium  in  nitric  or  nitro-muriatic  acid  till  it  is  completely  dissolved. 
On  evaporating  the  solution  to  dryness,  a white  residue  is  left,  which  is 
selenious  acid.  By  increase  of  temperature,  the  acid  itself  sublimes, 
and  condenses  again  unchanged  into  long  four-sided  needles.  It  attracts 
moisture  from  the  air,  whereby  it  suffers  imperfect  liquefaction.  It  dis- 
solves in  alcohol  and  water.  It  has  distinct  acid  properties,  and  its  salts 
are  called  selenites. 

Selenious  acid  is  readily  decomposed  by  all  substances  which  have  a 
strong  affinity  for  oxygen,  such  as  sulphurous  and  phosphorous  acids. 
When  sulphurous  acid,  or  an  alkaline  sulphite,  is  added  to  a solution  of 
selenious  acid,  a red-coloured  powder,  pure  selenium,  is  thrown  down, 
and  the  sulphurous  is  converted  into  sulphuric  acid.  Sulphuretted  hy- 
drogen also  decomposes  it;  and  an  orange-yellow  precipitate  subsides, 
which  is  a sulphuret  of  selenium. 

The  atomic  weight  of  selenium,  deduced  chiefly  from  the  experiments 
of  Berzelius,  is  40;  and  selenious  acid,  according  to  the  analysis  of  the 
same  chemist,  consists  of  40  parts  or  one  equivalent  of  selenium,  and  16 
parts  or  two  equivalents  of  oxygen. 

Selenic  Acid.  —The  preceding  compound,  discovered  by  Berzelius, 
was  till  lately  the  only  known  acid  of  selenium,  and  has  hitherto  been 
described  in  elementary  works  under  the  name  of  selenic  acid;  but  the 
recent  discovery  of  another  acid  of  selenium  containing  more  oxygen 
than  the  other,, has  rendered  necessary  a change  of  nomenclature.  The 
existence  of  selenic  acid  was  first  noticed  by  M.  Nitzsch,  assistant  of 
Professor  Mitscherlich,  and  its  properties  have  been  examined  and  des- 
cribed by  the  professor  himself.  (Edin.  Journal  of  Science,  viii.  294.) 

This  acid  is  prepared  by  fusing  nitrate  of  potassa  or  soda  with  selenium, 
a metallic  seleniuret,  or  with  selenious  acid  or  any  of  its  salts.  Sele- 
niuret  of  lead,  as  the  most  common  ore  of  selenium,  will  generally  be  em- 
ployed; but  it  is  very  difficult  to  obtain  pure  selenic  acid  by  its  means, 
because  it  is  commonly  associated  with  metallic  sulphurets.  The  ore  is 
first  treated  with  muriatic  acid  to  remove  any  carbonate  that  may  be  pre- 
sent; and  the  insoluble  part,  which  is  about  a third  of  the  mass,  is  mix- 
ed with  its  own  weight  of  nitrate  of  soda,  and  thrown  by  successive  por- 
tions into  a red-hot  crucible.  The  lead  is  thus  oxidized,  and  the  sele- 
nium converted  into  selenic  acid,  which  unites  with  soda.  The  fused 
mass  is  then  acted  on  by  hot  water,  which  dissolves  only  seleniate  of 
soda,  together  with  nitrate  and  nitrite  of  soda;  while  the  insoluble  mat- 
ter, when  well  washed,  is  quite  free  from  selenium.  The  solution  is 


202 


SELENIUM. 


next  made  to  boil  briskly,  when  anhydrous  seleniate  of  soda  is  deposit- 
ed; while,  on  cooling*,  nitrate  of  soda  crystallizes.  On  renewing*  the 
ebullition  and  subsequent  cooling*,  fresh  portions  of  seleniate  and  nitrate 
are  procured;  and  these  successive  operations  are  repeated,  until  the 
former  salt  is  entirely  separated.  This  process  is  founded  on  the  fact, 
that  seleniate  of  soda,  like  the  sulphate  of  the  same  base,  is  more  soluble 
in  water  of  about  90°  F.  than  at  higher  or  lower  temperatures.  I he 
nitrite  of  soda,  formed  during  the  fusion,  is  purposely  reconverted  into 
nitrate  by  digestion  with  nitric  acid. 

The  seleniate  of  soda  thus  procured  always  contains  a little  sulphuric 
acid,  derived  from  the  metallic  sulphurets  of  the  ore;  and  it  is  not  pos- 
sible to  separate  this  acid  by  crystallization.  All  attempts  to  separate  it 
by  means  of  baryta  were  likewnse  fruitless;  and  the  only  method  of  ef- 
fecting this  object  is  by  reducing  the  selenic  acid  into  selenium,  'fliis 
is  done  by  heating  a mixture  of  seleniate  of  soda  and  sal  ammoniac;  when 
mutual  decomposition  ensues,  the  soda  unites  with  muriatic  acid,  the 
hydrogen  of  the  ammonia  combines  with  the  oxygen  of  the  selenic 
acid,  and  selenium  and  nitrogen  are  set  free.  The  selenium  thus  ob- 
tained is  quite  free  from  sulphur.  It  is  then  converted  by  nitric  acid 
into  selenious  acid,  which  should  be  neutralized  with  soda,  and  fused 
with  nitre  or  nitrate  of  soda.  The  pure  seleniate  of  soda,  separated 
from  the  nitrate  according  to  the  foregoing  process,  is  subsequently 
dissolved  in  water,  and  obtained  in  crystals  by  spontaneous  evapo- 
ration. 

To  procure  the  acid  in  a free  state,  seleniate  of  soda  is  decomposed 
by  nitrate  of  lead.  The  seleniate  of  lead,  which  is  as  insoluble  as  the 
sulphate,  after  being  well  washed,  is  exposed  to  a current  of  sulphu- 
retted hydrogen  gas,  which  precipitates  all  the  lead  as  a sulphuret,  but 
does  not  decompose  the  selenic  acid.  The  excess  of  sulphuretted  hy- 
drogen is  driven  off  by  heat,  and  pure  selenic  acid  remains  diluted  with 
water.  The  absence  of  fixed  substances  may  be  proved  by  its  being 
volatilized  by  heat  without  residue;  and  if  free  from  sulphuric  acid,  it 
gives  no  precipitate  with  muriate  of  baryta  after  being  boiled  with  mu- 
riatic acid.  * Any  nitric  acid  which  may  be  present  is  expelled  by  con- 
centrating the  solution  by  means  of  heat. 

Selenic  acid  is  a colourless  liquid,  which  may  be  heated  to  536°  F. 
without  appreciable  decomposition;  but  above  that  point  decomposition 
commences,  and  it  becomes  rapid  at  554°,  giving  rise  to  disengagement 
of  oxygen  and  selenious  acid.  When  concentrated  by  a temperature  of 
329°  its  specific  gravity  is  2.524;  at  512°  it  is  2.60,  and  at  545°  it  is 
2.625,  but  a little  selenious  acid  is  then  present.  When  procured  by 
the  process  above  described,  selenic  acid  alw^ays  contains  water,  but  it 
is  very  difficult  to  ascertain  its  precise  proportion.  Some  acid,  which 
had  been  heated  higher  than  536°,  contained,  subtracting  the  quantity 
of  selenious  acid  present,  15.75  per  cent,  of  water,  which  approximates 
to  the  ratio  of  one  equivalent  of  water  and  one  of  the  acid.  It  is  cer- 
tain tliat  selenic  acid  is  decomposed  by  heat  before  parting  wdth  all  the 
water  wliich  it  contains. 

Selenic  acid  has  a powerful  affinity  for  water,  and  emits  as  much  heat 
in  uniting  with  it  as  sulpluiric  acid  does.  Like  this  acid  it  is  not  de- 
composed by  sulphuretted  hydrogen,  and  hence  this  gas  may  be  em- 


* The  necessity  for  tliis  previous  lioiling  with  muriatic  acid  is  to  con- 
vert the  selenic  into  selenious  acid,  without  which  change  the  muriate 
of  baryta  would  produce  a precijiitate  of  seleniate  of  baryta.  I'he  ra- 
tionale of  the  action  of  muriatic  acid  is  explained  further  on.  B, 


CHLORINE. 


203 


ployed  for  decomposing*  seleniate  of  lead  or  copper.  With  muriatic 
acid  the  chang*e  is  peculiar;  for  on  boiling*  the  mixture,  mutual  decom- 
position ensues,  water  and  selenious  acid  are  formed,  and  chlorine  set 
free;  so  that  the  solution,  like  aqnaregia^  is  capable  of  dissolving  gold 
and  platinum.  Selenic  aoid  dissolves  zinc  and  iron  with  disengagement 
of  hydrogen  gas,  and  copper  with  formation  of  selenious  acid.  It  dis- 
solves gold  also,  but  not  platinum.  Sulphurous  acid  has  no  action  on 
selenic  acid,  whereas  selenious  acid  is  easily  reduced  by  it.  Conse- 
quently, when  it  is  wished  to  precipitate  selenium  from  selenic  acid,  it 
must  be  boiled  with  muriatic  acid  before  sulphurous  acid  is  added. 

Selenic  acid,  in  its  affinity  for  alkaline  bases,  is  little  inferior  to  sul- 
phuric acid;  so  much  so,  indeed,  that  seleniate  of  baryta  cannot  be 
completely  decomposed  by  sulphuric  acid.  It  is,  therefore,  an  acid  of 
great  power.  From  the  analysis  of  this  acid  and  of  the  seleniates  of 
potassa  and  soda,  by  Professor  Mitscherlich,  it  is  established  that  the 
oxygen  combined  in  selenious  and  selenic  acids  with  the  same  quantity 
of  selenium,  is  in  the  ratio  of  2 to  3,  as  is  the  case  with  sulphurous  and 
sulphuric  acids.  Hence  selenic  acid  is  a compound  of  40  parts  or  one 
equivalent  of  selenium,  and  24  parts  or  three  equivalents  of  oxygen; 
and  its  equivalent  is  64. 

Professor  Mitscherlich  has  observed,  that  selenic  and  sulphuric  acids 
are  not  only  analogous  in  composition  and  in  many  of  their  properties, 
but  that  the  similarity  runs  through  their  compounds  with  alkaline  sub- 
kances,  their  salts  resembling  each  other  in  chemical  properties,  con- 
stitution, and  form. 


SECTION  XL 

CHLORINE. 

The  discovery  of  chlorine  was  made  in  the  year  1770  by  Scheele, 
while  investigating  the  nature  of  manganese,  and  he  described  it  under 
the  name  of  dephlogisticated  marine  acid.  The  French  chemists  called 
it  oxygenized  muriatic  acid,  a term  which  was  afterwards  contracted  to' 
oxymuriatic  acid,  from  an  opinion  proposed  by  Berthollct  that  it  is  a 
compound  of  muriatic  acid  and  oxygen.  In  1809  Gay-Lussac  and  The- 
nard  published  an  abstract  of  some  experiments  upon  this  substance, 
which  subsequently  appeared  at  length  in  their  Recherches  Physico-chi- 
miques,  wherein  they  stated  that  oxymuriatic  acid  might  be  regarded  as 
a simple  body,  though  they  gave  the  preference  to  the  doctrine  advanced 
by  Berthollet.  Sir  H.  Davy  engaged  in  the  inquiry  about  the  same 
time;  and  after  having  exposed  oxymuriatic  acid  to  the  most  powerful 
decomposing  agents  which  chemists  possess,  without  being  able  to  effect 
its  decomposition,  he  communicated  to  the  Royal  Society  an  essay,  in 
which'he  denied  its  compound  nature;  and  he  maintained  that,  accord- 
ing to  the  true  logic  of  chemistry,  it  is  entitled  to  rank  with  simple 
bodies.  This  view,  which  is  commonly  termed  the  new  theory  of  chlo- 
rine, though  strongly  objected  to  at  the  time  it  was  first  proposed, 
is  now  almost  universally  received  by  chemists,  and  accordingly  is 
adopted  in  this  work.  The  grounds  of  preference  will  hereafter  be 
briefly  stated. 

Chlorine  gas  is  obtained  by  the  action  of  muriatic  acid  on  peroxide  of 
manganese.  The  most  convenient  method  of  preparing  it  is  by  mixing 


204 


CHLORINE. 


concentrated  muriatic  acid,  contained  in  a glass  flask,  with  half  its 
weight  of  finely  powdered  peroxide  of  manganese.  Effervescence, 
owing  to  the  escape  of  chlorine,  takes  place  even  in  the  cold;  but  the 
gas  is  evolved  much  more  freely  by  the  application  of  a moderate  heat. 
It  should  be  collected  in  inverted  glass  bottles  filled  with  warm  water; 
and  when  the  water  is  wholly  displaced  by  the  gas,  the  bottles  should 
be  closed  with  a well-ground  glass  stopper.  As  some  muriatic  acid  gas 
commonly  passes  over  with  it,  the  chlorine  should  not  be  considered 
quite  pure,  till  after  being  transmitted  through  water. 

Before  explaining  the  theory  of  this  process,  it  may  be  premised  that 
muriatic  acid  consists  of  36  parts  or  one  equivalent  of  chlorine,  and  1 
part  or  one  equivalent  of  hydrogen.  Peroxide  of  manganese,  as  al- 
ready mentioned,  (page  140)  is  composed  of  28  parts  or  one  equivalent 
of  manganese,  and  16  or  two  equivalents  of  oxygen.  When  these 
compounds  react  on  each  other,  one  equivalent  of  each  is  decomposed. 
The  peroxide  of  manganese  gives  one  equivalent  of  oxygen  to  the  hy- 
drogen  of  the  muriatic  acid,  in  consequence  of  which  one  equivalent 
of  water  is  generated,  and  one  equivalent  of  chlorine  disengaged; 
while  the  protoxide  of  manganese  unites  with  an  equivalent  of  unde- 
composed muriatic  acid,  and  forms  an  equivalent  of  muriate  of  the  pro- 
toxide of  manganese.  Consequently,  for  every  44  grains  of  peroxide 
of  manganese,  74  (37  X 2)  grains  of  real  muriatic  acid  disappear;  and 
36  parts  of  chlorine,  9 of  water,  and  73  of  protomuriate  of  manganese, 
are  the  products  of  the  decomposition.  The  affinities  which  determine 
these  changes  are  the  attraction  of  oxygen  for  hydrogen,  and  of  pro- 
toxide of  manganese  for  muriatic  acid. 

When  it  is  an  object  to  prepare  chlorine  at  the  cheapest  rate,  as  for 
the  purposes  of  manufacture,  the  preceding  process  is  modified  in  the 
following  manner.  Three  parts  of  sea-salt  are  intimately  mixed  with 
one  of  peroxide  of  manganese,  and  to  this  mixture  two  parts  of  sul- 
phuric acid,  diluted  with  an  equal  weight  of  water,  are  added.  By  the 
action  of  sulphuric  acid  on  sea-salt,  muriatic  acid  is  disengaged,  which 
reacts  as  in  the  former  case  upon  the  peroxide  of  manganese;  so  that, 
instead  of  adding  muriatic  acid  directly  to  the  manganese,  the  materials 
for  forming  it  are  employed.  In  this  process,  however,  the  protoxide 
of  manganese  unites  with  sulphuric  instead  of  muriatic  acid,  and  the 
residue  is  sulphate  of  manganese  and  sulphate  of  soda. 

Chlorine  (from  <95 j green)  is  a yellowish-green  coloured  gas, 
which  has  an  astringent  taste,  and  a disagreeable  odour.  It  is  one  of 
the  most  suffocating  of  the  gases,  exciting  spasm  and  great  irritation  of 
the  glottis,  even  when  considerably  diluted  with  air.  When  strongly 
and  suddenly  compressed,  it  emits  both  heat  and  light,  a character 
which  it  possesses  in  common  with  oxygen  gas.  According  to  Sir  H. 
Davy,  100  cubic  inches  of  it  at  60^  F.,  and  when  the  barometer  stands 
at  30  inches,  weigh  between  76  and  77  grains.  Dr.  Thomson  states  its 
weight  at  76.25  grains,  and  his  result  agrees  very  nearly  with  that  of 
Gay-Lussac  and  'Fhenard.  Adopting  this  estimate,  its  specific  gravity 
is  2.5.  Under  the  pressure  of  about  four  atmospheres  it  is  a limpid  li- 
quid of  a bright  yellow  colour,  which  does  not  freeze  at  the  tempera- 
ture of  zero,  and  which  assumes  the  gaseous  form  with  the  appearance* 
of  ebullition  when  the  pressure  is  removed. 

In  conse([uencc  of  the  extensive  range  of  affinity  possessed  by  chlo- 
rine, it  is  important  that  its  combining  proportion  should  be  determined 
with  precision.  The  number  stated  by  Berzelius  is  35.43,  and  accord- 
ing to  Dr.  Thomson  36  is  its  equivalent.  The  estimate  of  Dr.  Thomson 
is  usually  employed  in  Britain,  and,  therefore,  for  want  of  better 


CHLORINE. 


205 


g'rounds  of  choice,  1 have  adopted  it  in  this  work;  but  the  subject  is 
exactly  one  of  those,  of  which  a careful  examination  is  much  to  be 
wished. 

Cold  recently  boiled  water,  at  the  common  pressiu-e,  absorbs  twice 
its  volume  of  chlorine,  and  yields  it  again  when  heated.  The  solution, 
which  is  made  by  transmitting  a current  of  chlorine  gas  through  cold 
water,  has  the  colour,  taste,  and  most  of  the  other  properties  of  the 
gas  itself.  When  moist  chlorine  gas  is  exposed  to  a cold  of  32®  F. 
yellow  crystals  are  formed,  which  consist  of  water  and  chlorine  in 
definite  proportions.  They  are  composed,  according  to  Mr.  Faraday, 
of  36  parts  or  one  equivalent  of  chlorine,  and  90  or  ten  equivalents  of 
water. 

Chlorine  experiences  no  chemical  change  from  the  action  of  the  im- 
ponderables. Thus  it  is  not  afiected  chemically  by  intense  heat,  by 
strong  shocks  of  electricity,  or  by  a powerful  galvanic  battery.  Sir  H. 
Davy  exposed  it  also  to  the  action  of  charcoal  heated  to  whiteness  by 
galvanic  electricity,  without  separating  oxygen  from  it,  or  in  any  way 
affecting  its  nature.  Light  does  not  act  on  dry  chlorine;  but  if  water 
be  present,  the  chlorine  decomposes  that  liquid,  unites  with  the  hy- 
drogen to  form  muriatic  acid,  and  oxygen  gas  is  set  at  liberty.  This 
change  takes  place  quickly  in  sunshine,  more  slowly  in  diffused  day- 
light, and  not  at  all  when  light  is  wholly  excluded.  Hence  the  neces- 
sity of  keeping  moist  chlorine  gas,  or  its  solution,  in  a dark  place,  if  it 
is  wished  to  preserve  it  for  any  time. 

Chlorine  unites  with  some  substances  with  evolution  of  heat  and 
light,  and  is  hence  termed  a supporter  of  combustion.  If  a lighted  ta- 
per be  plunged  into  chlorine  gas,  it  burns  for  a short  time  with  a small 
red  flame,  and  emits  a large  quantity  of  smoke.  Phosphorus  takes  fire 
in  it  spontaneously,  and  burns  with  a pale  white  light.  Several  of 
the  metals,  such  as  tin,  copper,  arsenic,  antimony,  and  zinc,  when 
introduced  into  chlorine  in  the  state  of  powder  or  in  fine  leaves,  are 
suddenly  inflamed.  In  all  these  cases  the  combustible  substances  unite 
with  chlorine. 

Chlorine  has  a very  powerful  attraction  for  hydi’ogen;  and  many  of 
the  chemical  phenomena,  to  which  chlorine  gives  rise,  are  owing  to 
this  property.  A striking  example  is  its  power  of  decomposing  water 
by  the  action  of  light,  or  at  a red  heat;  and  most  compound  substances, 
of  which  hydrogen  is  an  element,  are  deprived  of  that  principle,  and 
therefore  decomposed  in  like  manner.  For  the  same  reason,  when 
chlorine,  water,  and  some  other  body  which  has  a strong  affinity  for 
oxygen,  are  presented  to  one  another,  water  is  usually  resolved  into  its 
elements,  its  hydrogen  attaching  itself  to  the  chlorine,  and  its  oxygen 
to  the  other  body.  Hence  it  happens  that  chlorine  is,  indhectly,  one 
of  the  most  powerful  oxidizing  agents  which  we  possess. 

When  any  compound  of  chlorine  and  an  inflammable  is  exposed  to 
the  influence  of  galvanism,  the  inflammable  body  goes  over  to  the  ne- 
gative, and  chlorine  to  the  positive  pole  of  the  battery.  This  esta- 
blishes a close  analogy  between  oxygen  and  chlorine,  bodi  of  them  be- 
ing supporters  of  combustion,  and  both  negative  electrics. 

Chlorine,  though  formerly  called  an  acid,  possesses  no  acid  proper- 
ties. It  has  not  a sour  taste,  does  not  redden  the  blue  colour  of  plants, 
and  shows  comparatively  little  disposition  to  unite  with  alkalies.  Its 
strong  affinity  for  the  metals  is  sufficient  to  prove  that  it  is  not  an  acid; 
for  chemists  are  not  acquainted  with  any  instance  of  an  acid  combining 
directly  in  definite  proportion  with  a metal. 

The  mutual  action  of  chlorine  and  the  pure  alkalies  leads  to  compli- 
cated changes.  If  chlorine  gas  is  passed  into  a solution  of  potassa  till 

18 


206 


CHLORINE. 


all  alkaline  reaction  ceases,  a liquid  is  obtained  which  has  the  odour  of 
a solution  of  chlorine  in  water.  Rut  on  applying  licat,  the  chlorine 
disappears  entirely,  and  the  solution  is  found  to  contain  two  neutral 
salts,  chlorate  and  inuriatc  of  potassa.  'I'lie  production  of  the  two 
acids  is  owing  to  decomposition  of  water,  the  elements  of  which  unite 
v/ith  separate  portions  of  chlorine  and  form  chloric  and  muriatic  acids. 
The  affinities  which  give  rise  to  this  change  arc  the  attraction  of  chlo- 
rine for  hydrogen,  of  chlorine  for  oxygen,  and  of  the  two  residting 
acids  for  the  alkali. 

One  of  the  most  important  properties  of  chlorine  is  its  bleaching 
powers.  All  animal  and  vegetable  colours  are  speedily  removed  by 
chlorine;  and  when  the  colour  is  once  discharged,  it  can  never  be  re- 
stored. Sir  H.  Davy  proved  that  chlorine  cannot  bleach  unless  water 
is  present.  Thus,  dry  litmus  paper  suffers  no  change  in  dry  chlorine; 
but  when  water  is  admitted,  the  colour  speedily  disappears.  It  is  well 
known  also  that  muriatic  acid  is  always  generated  when  chlorine 
bleaches.  From  these  facts  it  is  inferred  that  water  is  decomposed 
during  the  process;  that  its  hydrogen  unites  with  chlorine;  and  that 
decomposition  of  the  colouring  matter  is  occasioned  by  the  oxygen 
wliich  is  liberated.  The  bleaching  property  of  deutoxide  of  hydrogen 
and  chromic  acid,  of  which  oxygen  is  certainly  the  decolorizing  princi- 
ple, leaves  little  doubt  of  the  accuracy  of  the  foregoing  explanation. 

Chlorine  is  useful,  likewise,  for  the  purposes  of  fumigation.  The 
experience  of  Guyton-Morveau  is  sufficient  evidence  of  its  power  in 
destroying  the  volatile  principles  given  off  by  putrefying  animal  matter; 
and  it  probably  acts  in  a similar  way  on  contagious  effluvia.  A peculiar 
compound  of  chlorine  and  soda,  the  nature  of  which  will  be  consider- 
ed in  the  section  on  sodium,  has  been  lately  introduced  for  this  purpose 
by  M.  Labarraque. 

Chlorine  is  in  general  easily  recognised  by  its  colour  and  odour. 
Chemically  it  may  be  detected  by  its  bleaching  property,  added  to  the 
circumstance  that  a solution  of  nitrate  of  silver  occasions  in  it  a dense 
white  precipitate  (a  compound  of  chlorine  and  metallic  silver,)  which 
becomes  dark  on  exposure  to  light,  is  insoluble  in  acids,  and  dissolves 
completely  in  pure  ammonia.  The  whole  of  the  chlorine,  however, 
is  not  thrown  down  by  nitrate  of  silver;  for  the  oxygen  of  the  oxide 
of  silver  unites  with  a portion  of  chlorine,  and  converts  it  into  chloric 
acid. 

The  compounds  of  chlorine,  which  are  not  acid,  are  termed  chlorides 
or  chlorurets.  The  former  expression,  from  the  analogy  between  chlo- 
rine and  oxygen,  is  perhaps  the  more  appropriate. 

Compound  of  Chlorine  and  Hydrogen, — Muriatic  ^cid 

Gas^ 

Muriatic  or  hydrochloric  acid  gas  was  discovered  in  1772  by  Priestley. 
It  may  be  conveniently  prepared  by  putting  an  ounce  of  strong  muria- 
tic acid  into  a glass  flask,  and  heating  it  by  means  of  a lamp  till  the 
liquid  boils.  Pure  muriatic  acid  gas  is  freely  evolved,  and  may  be  col- 
lected over  mercury.  Another  method  of  preparing  it  is  by  the  action 
of  concentrated  sulphuric  acid  on  an  equal  weight  of  sea- salt.  Brisk 
effervescence  ensues  at  the  moment  of  making  the  mixture,  and  on 


* I have  here  deviated  slightly^from  my  arrangement.  I have  done 
so,  because  it  will  facilitate  the  study  of  the  compounds  of  chlorine  with 
the  simple  non-mctallic  bodies,  to  describe  them  in  the  same  section. 
Iodine  and  bromine,  for  a like  reason,  will  be  ti-catedin  a similar  manner. 


CHLORINE. 


207 


the  application  of  heat  a large  quantit)^  of  muriatic  acid  gas  is  disen- 
gaged. In  the  former  process,  muriatic  acid,  previously  dissolved  in 
water,  is  simply  expelled  from  the  solution  by  increased  temperature. 
The  explanation  of  the  latter  process  is  more  complicated.  Sea-salt 
was  formerly  supposed  to  be  a compound  of  mui’iatic  acid  and  soda; 
and,  on  this  supposition,  the  soda  was  believed  merely  to  quit  the  mu- 
riatic and  unite  with  sulphuric  acid.  But  according  to  the  experiments 
of  Gay-Lussac  and  Thenard,  and  Sir  H.  Dav>^  sea-salt  in  its  dry  state 
consists  not  of  muriatic  acid  and  soda,  but  ot  chlorine  and  sodium,  the 
metallic  base  of  soda.  The  proportion  of  its  constituents  are 

Chlorine  36  . vOne  proportional. 

Sodium  24  . one  proportional. 

When  sulphuric  acid  is  added  to  it,  one  proportional  of  water  is  re- 
solved into  its  elements:  its  hydrogen  unites  with  chlorine,  forming 
muriatic  acid,  which  escapes  in  the  form  of  gas;  while  soda  is  genera- 
ted by  the  combination  of  its  oxygen  with  sodium,  which  combines 
with  the  sulphuric  acid,  and  forms  sulphate  of  soda.  The  water  con- 
tained in  liquid  sulphuric  acid  is,  therefore,  essential  to  the  success  of 
the  operation.  The  affinities  which  determine  the  change  are  the  at- 
traction of  chlorine  for  hydrogen,  of  sodium  for  oxygen,  and  of  soda 
for  sulphuric  acid. 

Muriatic  acid  may  be  generated  by  the  direct  union  of  its  elements. 
When  equal  measures  of  chlorine  and  hydrogen  are  mixed  together, 
and  an  electric  spark  is  passed  tlirough  the  mixture,  instantaneous  com- 
bustion takes  place,  heat  and  light  are  emitted,  and  murirdic  acid  is 
generated.  A similar  effect  is  produced  by  flame,  by  a red-hot  body, 
and  by  spongy  platinum.  Light  also  causes  them  to  unite.  A mixture 
of  tixe  two  gases  may  be  preserved  without  change  in  a dark  place;  but 
if  exposed  to  the  diffused  light  of  day,  gradual  combination  ensues, 
wliich  is  completed  in  the  course  of  24  hours.  The  direct  solar  ravs 
produce,  like  flame  or  electricity,  sudden  inflammation  of  the  whole 
mixture,  accompanied  with  explosion;  and,  according  to  Mr.  Brande, 
the  vivid  light  emitted  by  charcoal  intensely  heated  by  galvanic  electri- 
city acts  in  a similar  manner. 

The  experiments  of  Davy,  and  Gay-Lussac  and  Thenard  concur  in 
proving  that  hydrogen  and  chlorine  unite  in  eq\ial  volumes,  and  that  the 
muriatic  acid,  which  is  the  sole  and  constant  product,  occupies  the 
same  space  as  the  gases  from  which  it  is  formed.  From  these  facts  the 
composition  of  muriatic  acid  is  easily  inferred.  For,  as 

Grains, 

50  cubic  inches  of  chlorine  weigh  . , 38.125 

and  50  hydrogen  . . . 1.059 


100  cubic  inches  of  muriatic  acid  gas  must  weigh  39.184 
Its  specific  gravity,  therefore,  is  1.2847.  By  weight  it  consists  of 
Chlorine  . 38.125  . 36 

Hydrogen  . 1.059  . 1 

Since  chlorine  and  hydrogen  unite  in  one  proportion  only,  most  chem- 
ists regard  muriatic  acid  as  a compound  of  one  equivalent  of  each  of 
its  elements;  a conclusion  which  appears  to  be  justified  by  the  pro-  . 
portions  in  which  chlorine  and  hydrogen  unite  with  other  bodies. 
Hence  36  is  one  equivalent  of  chlorine,  and  37  the  equivalent  of  mu- 
riatic acid. 

Muriatic  acid  is  a colourless  gas,  of  a pungent  odour  and  acid  taste.  ^ 


208 


CHLORINE. 


Under  a pressure  of  40  atmosplieres,  and  at  the  temperature  of  50®  F. 
it  is  liquid.  It  is  quite  irrcspiralde,  exciting  violent  spasm  of  the  Ldot- 
tis;  but  when  diluted  with  air,  it  is  far  less  irritating'  than  chlorine.  All 
burning  bodies  are  extinguislicd  by  it,  and  the  gas  itself  docs  not  take 
fire  on  the  approach  of  flame. 

^ Muriatic  acid  gas  is  not  chemically  changed  by  mere  heat,  It  is  rea- 
dily decomposed  by  galvanism,  hydrogen  appearing  at  the  negative, 
and  chlorine  at  the  positive  pole.  It  is  also  decomposed  by  ordinary 
electricity.  I'he  decomposition,  however,  is  incomplete;  for  though 
one  electric  spark  resolves  a portion  of  the  gas  into  its  elements,  the 
next  shock  in  a gi’eat  measure  eflects  their  reunion.  It  is  not  affected 
by  oxygen  under  common  ciicumstances;  but  if  a mixture  of  oxygen 
and  muriatic  acid  gases  is  electrified,  the  oxygen  unites  with  the  hy- 
drogen of  the  muriatic  acid  to  form  water,  aiid  chlorine  is  set  at  liber- 
ty. I'or  this  and  the  preceding  fact  we  are  indebted  to  the  researches 
of  Dr.  Henry. 

One  of  the  most  striking  properties  of  muriatic  acid  gas  is  its  power- 
ful attraction  for  water.  A dense  white  cloud  appears  whenever  muria- 
tic acid  escapes  into  the  air,  owing  to  a combination  which  ensues  be- 
tween the  acid  and  watery  vapour.  When  a piece  of  ice  is  put  into  a jar 
full  of  tlie  gas  confined  over  mercury,  the  ice  liquefies  on  the  instant, 
and  the  whole  of  the  gas  disappears  in  the  course  of  a few  seconds.  On 
opening  a long  wide  jar  of  muriatic  gas  under  water,  the  absorption  of 
tlie  gas  takes  place  so  instantaneously,  that  the  water  is  forced  up  into 
the  jar  with  the  same  violence  as  into  a vacuum, 

A concentrated  solution  of  muriatic  acid  gas  in  water  has  long  been 
known  under  the  names  of  spirit  of  salt,  and  of  marine  or  muriatic  acid. 
It  is  made  by  transmitting  a current  of  gas  into  water  as  long  as  any  of  it 
is  absorbed.  Considerable  increase  of  temperature  takes  place  during 
the  absorption,  and,  therefore,  the  apparatus  should  be  kept  cool  by  ice. 
Sir  H.  Davy  states  (Elements,  p.  252.)  that  water  at  the  temperature  of 
40®  F.  absorbs  480  times  its  volume  of  the  gas,  and  that  the  solution  has 
a density  of  1.2109.  Dr.  Thomson  finds  that  one  cubic  inch  of  water  at 
69°  F.  absorbs  418  cubic  inches  of  gas,  and  occupies  the  space  of  1.34 
cubic  inch.  The  solution  has  a density  of  1.1958,  and  one  cubic  inch  of 
it  contains  311.04  cubic  inches  of  muriatic  acid  gas.  The  quantity  of  real 
acid  contained  in  solutions  of  different  densities  may  be  determined  by 
ascertaining  the  quantity  of  pure  marble  dissolved  by  a given  weight  of 
each.  Every  50  grains  of  marble  correspond  to  37  of  real  acid.  The  fol- 
lowing table  from  Dr,  Thomson’s  “Principles  of  Chemistry,”  is  con- 
structed according  to  this  rule.  The  fii’st  and  second  columns  show  the 
atomic  constitution  of  each  acid. 


CHLORINE. 


209 


Table  exhibiting  the  Specific  Gravity  of  Muriatic  Acid  of  determinate 
Strengths, 


Atoms  of 
acid. 

Atoms  of 
water. 

Real  acid  in  100  of 
the  liquid. 

Specific 

gravity. 

1 

6 

40.659 

1.203 

1 

7 

37.000 

1.179 

1 

8 

33.945 

1.162 

1 

9 

31.346 

1.149' 

1 

10 

29.134 

1.139 

1 

11 

27.206 

1.1285 

1 

12 

25.517 

1.1197 

1 

13 

24.026 

1.1127 

1 

14 

22.700 

1. 1060 

1 

15 

21.512 

1.1008 

1 

16 

20.442 

1.0960 

1 

17 

19.474 

1.0902 

1 

18 

18.590 

1.0860 

1 

18 

17.790 

1.0820 

1 

20 

17.051 

1.0780 

All  the  Pharmacopoeias  give  directions  for  forming  muriatic  acid.  Tlie 
process  recommended  by  the  Edinburgh  College  is  practically  good. 
The  proportions  they  recommend  are  equal  weights  of  sea-salt,  water, 
and  sulphuric  acid,  more  acid  being  purposely  employed  than  is  sum- 
cient  to  form  a neutral  sulphate  with  the  soda,  so  that  the  more  perfect 
decomposition  of  the  sea  salt  may  be  insured.  The  acid,  to  prevent  too 
violent  effervescence  at  first,  is  mixed  with  one-third  of  the  water,  and 
when  the  mixture  has  cooled,  it  is  poured  upon  the  salt  previously  intro- 
duced. into  a glass  retort.  I'he  distillation  is  continued  to  dryness;  and 
the  gas  as  it  escapes,  is  conducted  into  the  remainder  of  the  water.  The 
theory  of  the  process  has  already  been  explained.  The  residue  is  a mix- 
ture of  sulphate  and  bisulphate  of  soda.  The  specific  gravity  of  muriatic 
acid  obtained  by  this  process  is  1.170. 

Muriatic  acid  of  commerce  has  a yellow  colour,  and  is  always  impure. 
Its  usual  impurities  are  nitric  acid,  sulphuric  acid,  and  oxide  of  iron. 
The  presence  of  nitric  acid  may  be  inferred  if  the  muriatic  acid  has  tlie 
property  of  dissolving  gold  leaf.  Iran  may  be  detected  by  ferrocyanate 
of  potassa,  and  sulphuric  acid  by  muriate  of  baryta,  the  suspected  mu- 
riatic acid  being  previously  diluted  with  three  or  four  parts  of  water. 
The  presence  of  nitric  acid  is  provided  against,  by  igniting  the  sea-salt, 
as  recommended  by  the  Edinburgh  College,  in  order  to  decompose  any 
nitre  which  it  may  contain.  The  other  impurities  may  be  avoided  by  em- 
ploying Woulfe’s  apparatus.  A few  drachms  of  water  are  put  into  the 
first  bottle,  to  retain  the  muriate  of  iron  and  sulphuric  acid  which  pass 
over|i%nd  the  muriatic  acid  gas  is  condensed  in  the  second. 

Pure  concentrated  muriatic  acid  is  a colourless  liquid,  which  emits 
white  vapours  when  exposed  to  the  air,  is  intensely  sour,  reddens  litmus 
paper  strongly,  and  unites  with  alkalies.  It  combines  with  water  in 
every  proportion,  and  causes  increase  of  temperature  when  mixed  with 
it,  though  in  a much  less  degree  than  sulphuric  acid.  It  freezes  at  — 60° 
F.;  and  boils  at  110°  F.,  or  a little  higher,  giving  off  pure  muriatic  acid 
gas  in  large  quantity. 

Muriatic  acid  is  decomposed  by  substances  which  yield  oxygen  readily. 
Thus  several  peroxides,  such  as  those  of  manganese,  cobalt,  and  lead, 


210 


CHLORINE. 


effect  its  decomposition.  Chloric,  iodic,  bromic,  and  selenic  acids  acton 
the  same  principle.  The  action  of  nitric  acid  1s  illustrative  of  the  same 
circumstance.  A mixture  of  nitric  and  muriatic  acids,  in  the  proportion 
of  one  measure  of  the  former  to  two  of  the  latter,  has  long  been  known 
under  the  name  of  aqua  regia,  as  a solvent  for  gold  and  platinum.  When 
these  acids  are  mixed  together,  the  solution  instantly  becomes  j^ellow; 
and  on  heating  the  mixture,  pure  chlorine  is  evolved,  and  the  colour  of 
the  solution  deepens.  On  continuing  the  heat,  chlorine  and  nitrous  acid 
vapours  are  disengag'ed.  At  length  the  evolution  of  chlorine  ceases,  and 
the  residual  liquid  is  found  to  be  a solution  of  muriatic  and  nitrous  acids 
which  is  incapable  of  dissolving  gold.  The  explanation  of  these  facts  is 
that  nitric  and  muriatic  acids  decompose  one  another,  giving  rise  to  the 
production  of  water  and  nitrous  acid,  and  the  separation  of  chlorine; 
while  muj’iatic  and  nitrous  acids  may  be  heated  together  without  mutual 
decomposition.  It  is  hence  inferred  that  the  power  of  nitro-muriatic  acid 
in  dissolving  gold  is  owing  to  the  chlorine  which  is  liberated.  (Sir  H. 
Davy  in  the  Quarterly  Journal,  vol.  i.) 

Muriatic  acid  is  distinguished  by  its  odour,  volatility,  and  strong  acid 
properties.  With  nitrate  of  silv’^cr  it  yields  the  same  precipitate  as  chlo- 
rine; but  no  chloric  acid  is  generated,  because  the  oxygen  of  the  oxide 
of  silver  unites  with  the  hydrogen  of  the  muriatic  acid,  and  the  chlorine 
in  consequence  is  entirely  precipitated.  Notwithstanding  that  nitrate  of 
silver  yields  the  same  precipitate  with  chlorine  and  muriatic  acid,  there 
is  no  difficulty  in  distinguishing  between  them;  for  tire  bleaching  pro- 
perty of  the  former  is  a sure  ground  of  distinction. 

Compounds  of  Chlorine  and  Oxygen. 

chlorine  unites  with  oxygen  in  four  different  proportions.  The  leading 
character  of  these  compounds  is  derived  from  the  circumstance  that 
chlorine  and  oxygen,  the  attraction  of  which  for  most  elementary  sub- 
stanep  is  so  energetic,  have  but  a feeble  affinity  for  each  other.  These 
principles,  consequently,  are  never  met  with  in  nature  in  a state  of  com- 
bination. Indeed,  they  cannot  be  made  to  combine  directly;  and  when 
they  do  unite,  very  slight  causes  effect  their  separation.  Notwithstand- 
ing this,  their  union  is  always  regulated  by  the  law  of  definite  propor- 
tions, as  appears  froni  the  following  tabular  view  of  the  constitution  of 
the  compounds  to  which  tliey  give  rise.^ 


Chlorine.  Oxygen. 
Protoxide  of  chlorine  36  . 8 

Peroxide  of  chlorine  36  . 32 

Chloric  acid  36  . 40 

Perchloric  acidf  36  . 56 


Berzelius  contends  for  the  existence  of  a fifth  compound,  intermedi- 
ate between  peroxide  of  chlorine  and  chloric  acid,  and  for  which  he  has 
proposed  the  name  of  chlorous  acid;  but  his  arguments  in  favour  of  this 
opinion,  which  will  be  more  particularly  specified  in  my  general  re- 
marks on  the  metals,  cannot,  I apprehend,  be  admitted  as  decisive. 


* Note  by  Gay-Lussac  in  the  9tli  volume  of  the  An.  de  Ch.  et  de 
Physique. 

I Oxychloric  would  be  a more  appropriate  appellation  for  this  acid, 
as  its  adoption  would  prevent  all  ambiguity  in  naming  its  salts.  This 
name  I proposed  for  it,  in  1819,  in  my  System  of  Chemistry  for  Stu- 
dents of  Medicine;  and  it  may  be  inferred  that  it  has  the  sanction  of 
Bcrzcliug,  as  he  employs  it  in  his  TraiU  de  Chimie.  B. 


CHLORINE. 


211 


Protoxide  of  Chlorine. — This  g'as  was  discovered  in  1811  by  Sir  H, 
Davy,  and  was  described  by  him  in  the  Philosophical  Transactions  for 
that  year  under  the  name  of  euchlorine.  It  is  made  by  the  action  of  mu- 
riatic acid  on  chlorate  of  potassa;  and  its  production  is  explicable  by  the 
fact,  that  muriatic  and  chloric  acids  mutually  decompose  each  other. 
When  muriatic  acid  and  chlorate  of  potassa  are  mixed  together,  part  of 
the  muriatic  acid  unites  with  the  potassa  of  the  salt,  and  thus  sets  chloric 
acid  free,  which  instantly  reacts  on  the  free  muriatic  acid.  The  result 
of  the  reaction  depends  on'  the  relative  quantity  of  the  substances.  If 
chlorate  of  potassa  is  mixed  with  excess  of  concentrated  muriatic  acid, 
the  chloric  acid  undergoes  complete  decomposition.  For  each  equiva- 
lent of  chloric,  five  equivalents  of  muriatic  acid  are  decomposed;  the 
five  equivalents  of  oxygen,  contained  in  the  former,  unite  with  the  hy- 
drogen of  the  latter,  producing  five  equivalents  of  water;  while  the  chlo- 
rine of  both  acids  is  disengaged.  If,  on  the  contrary,  chlorate  of  potassa 
is  in  excess,  and  the  muriatic  acid  diluted,  the  chloric  acid  is  deprived 
of  part  of  its  oxygen  only;  and  the  products  are  water,  protoxide  of 
chlorine,  and  chlorine,  the  two  latter  escaping  in  the  gaseous  form. 
From  the  relative  proportion  in  which  these  g'ases  are  evolved,  it  is  pro- 
bable that  for  each  equivalent  of  chloric,  three  of  muriatic  acid  must  be 
decomposed;  and  that  by  the  reaction  of  their  elements,  they  yield  three 
equivalents  of  water,  two  of  pure  chlorine,  and  two  of  the  protoxide  of 
chlorine. 

The  best  proportion  of  the  ingredients  for  forming  this  compound  is 
two  parts  of  chlorate  of  potassa,  one  of  strong  muriatic  acid,  and  one  of 
water;  and  the  reaction  of  the  materials  should  be  promoted  by  heat 
sufficient  to  produce  moderate  effervescence.  The  gases  should  be 
collected  over  mercury,  which  combines  with  the  chlorine,  and  leaves 
the  protoxide  of  chlorine  in  a pure  state. 

Protoxide  of  chlorine  has  a yellowish-green  colour  similar  to  that  of 
chlorine,  but  considerably  more  brilliant,  which  induced  Sir  H.  Davy  to 
give  it  the  name  of  euchlorine.  Its  odour  is  like  that  of  burned  sugar. 
Water  dissolves  eight  or  ten  times  its  volume  of  the  gas,  and  acquires  a 
colour  approaching  to  orange.  It  bleaches  vegetable  substances,  but 
gives  the  blue  colours  a tint  of  red  before  destroying  them.  It  does 
not  unite  with  alkalies,  and,  therefore,  is  not  an  acid. 

Protoxide  of  chlorine  is  explosive  in  a high  degree.  The  heat  of  the 
hand,  or  the  pressure  occasioned  in  transferring  it  from  one  vessel  to 
another,  sometimes  causes  an  explosion.  This  effect  is  also  occasioned 
by  phosphorus,  which  bursts  into  flame  at  the  moment  of  immersion. 
All  burning  bodies,  by  their  heat,  occasion  an  explosion,  and  then  burn 
vividly  in  the  decomposed  gas.  With  hydrogen  it  forms  a mixture 
which  explodes  by  flame  or  the  electric  spark,  with  production  of  water 
and  muriatic  acid.  The  best  propoi’tion  is  fifty  measures  of  protoxide 
of  chlorine  to  eighty  of  hydrogen. 

Protoxide  of  chlorine  is  easily  analyzed  by  heating  a known  quantity 
of  it  in  a strong  tube  over  mercury.  An  explosion  takes  place;  and  50 
measures  of  the  gas  expand  to  60  measures,  of  which  20  are  oxygen, 
and  40  chlorine.  The  specific  gravity  of  a gas  so  constituted  must  be 
2.444;  and  it  consists  of  36  parts  of  chlorine  and  8 of  oxygen.  Its  atomic 
weight  is  consequently  44. 

Peroxide  of  Chlorine. — This  compound  was  discovered  in  1815  by  Sir 
H.  Davy  (Phil.  Trans,  for  1815,)  and  soon  after  by  Count  Stadion  of 
Vienna.  It  is  formed  by  the  action  of  sulphuric  acid  on  chlorate  of  po- 
tassa. A quantity  of  this  salt,  not  exceeding  50  or  60  grains,  is  reduced 
to  powder,  and  made  into  a paste  by  the  addition  of  strong  sulphuric 
acid.  The  mixture,  which  acquires  a deep  yellow  colour,  is  placed  ia 


212 


CHLORINE. 


a glass  retort,  and  heated  by  warm  water,  the  temperature  of  which  is 
kept  under  212°  F.  A bright  yellowish-green  gas  of  a still  richer  co- 
lour than  piotoxidc  of  chlorine  is  disengaged,  which  has  an  aromatic 
odour  without  any  smell  of  chlorine,  is  absorbed  rapidly  by  water,  to 
which  it  communicates  its  tint,  and  has  no  sensible  action  on  mercury. 
This  gas  is  peroxide  of  chlorine.  ^ * 

The  chemical  changes  which  take  place  in  the  process  are  explained 
in  the  following  manner.  The  sulphuric  acid  decomposes  some  of  the 
chlorate  of  potassa,  and  sets  chloric  acid  at  liberty.  The  chloric  acid, 
at  the  moment  of  separation,  resolves  itself  into  peroxide  of  chlorine 
and  oxygen;  the  last  of  which,  instead  of  escaping  as  free  oxygen  gas, 
goes  over  to  the  acid  of  some  undccomposed  chlorate  of  potassa,  and 
converts  it  into  perchloric  acid.  The  whole  products  are  bisulphate 
and  perchlorate  of  potassa,  and  peroxide  of  chlorine.  It  is  most  proba- 
ble, from  the  data  contained  in  the  preceding  table,  that  every  three 
equivalents  of  chloric  acid  yield  one  equivalent  of  perchloric  acid  and 
two  equivalents  of  peroxide  of  chlorine. 

Peroxide  of  chlorine  does  not  unite  with  alkalies.  It  destroys  most 
vegetable  blue  colours  without  previously  reddening  them.  Phospho- 
rus takes  fire  when  introduced  into  it,  and  occasions  an  explosion.  It 
explodes  violently  when  heated  to  a temperature  of  212°  F.,  emits  a 
strong  light,  and  undergoes  a greater  expansion  than  protoxide  of  chlo- 
rine. According  to  Sir  H.  Davy,  whose  result  is  confirmed  by  Gay- 
Lussac,  40  measures  of  the  gas  occupy  after  explosion  the  space  of  60 
measures;  and  of  these,  20  are  chlorine  and  40  oxygen.  The  peroxide 
is,  therefore,  composed  of  36  parts  or  one  equivalent  of  chlorine,  united 
with  32  or  four  equivalents  of  oxygen;  and  its  specific  gravity  must  be 
2.361.  Count  Stadion  considers  the  chlorine  to  be  united  with  three 
instead  of  four  equivalents  of  oxygen. 

Chloric  Acid. — When  to  a dilute  solution  of  chlorate  of  baryta  a quan- 
tity of  weak  sulphuric  acid,  exactly  sufficient  for  combining  with  the 
baryta,  is  added,  the  insoluble  sulphate  of  baryta  subsides,  and  pure 
chloric  acid  remains  in  the  liquid.  This  acid,  the  existence  of  which 
was  originally  observed  by  Mr.  Chenevix,  was  first  obtained  in  a sepa- 
rate state  by  Gay-Lussac. 

Chloric  acid  reddens  vegetable  blue  colours,  lias  a sour  taste,  and 
forms  neutral  salts,  called  chlorates^  (formerly  hyperoxymuriaies)  with 
alkaline  bases.  It  possesses  no  bleaching  properties,  a circumstance  by 
which  it  is  distinguished  from  chlorine.  It  gives  no  precipitate  in  solu- 
tion of  nitrate  of  silver,  and  hence  cannot  be  mistaken  for  muriatic 
acid.  Its  solution  may  be  concentrated  by  gentle  heat  till  it  acquhes 
an  oily  consistence  without  decomposition;  but  at  a higher  tempera- 
ture, part  of  the  acid  is  volatilized  without  change,  while  another  por- 
tion is  converted  into  chlorine  and  oxygen.  It  is  easily  decomposed  by 
deoxidizing  agents.  Sulphurous  acid,  for  instance,  deprives  it  of  oxy- 
gen, with  formation  of  sulphuric  acid  and  evolution  of  chlorine.  By 
the  action  of  sulphuretted  liydrogen,  water  is  generated,  while  sulphur 
and  chlorine  are  set  free.  The  power  of  muriatic  acid  in  effecting  its 
decomposition  has  already  been  explained. 

Chloric  acid  is  readily  known  by  forming  a salt  with  potassa,  which 
crystallizes  in  taldes  and  luws  a pearly  lustre,  deflagrates  like  nitre  when 
flung  on  burning  charcoal,  and  yields  peroxide  of  chlorine  by  the  action 
of  concentrated  suli)huric  acid.  Chlorate  of  potassa,  like  most  of  the 
chlorates,  gives  off  pure  oxygen  when  heated  to  redness,  and  leaves  a 
residue  of  chloride  of  potassium.  By  this  mode  Gay-Lussac  ascertained 
the  composition  of  chloric  acid,  as  stated  in  the  preceding  table.  (An. 
de  Cliimic,  xci. ) 


CHLORINE. 


213 


Perchloric  Acid, — The  saline  matter  which  remains  in  the  retort  after 
forming"  peroxide  of  chlorine,  is  a mixture  of  perchlorate  and  bisulphate 
of  potassa;  and  by  washing  it  with  cold  water,  the  bisulphate  is  dissolv- 
ed, and  the  perchlorate  is  left.  Perchloric  acid  may  be  prepared  from 
this  salt  by  mixing  it  in  a retort  with  half  its  weight  of  sulphuric  acid, 
diluted  with  one-third  of  water,  and  applying  heat  to  the  mixture.  At 
the  temperature  of  about  284*^  V.  white  vapours  rise,  which  condense 
as  a colourless  liquid  in  the  receiver.  This  is  a solution  of  perchloric 
acid. 

’ The  properties  of  perchloric  acid  have  hitlierto  been  little  examined. 
Count  Stadion,*  its  discoverer,  found  it  to  be  a compound  of  one  equiva- 
lent or  36  parts  of  chlorine,  and  56  or  seven  equivalents  of  oxygenj  and 
his  analysis  has  been  confirmed  by  Gay-Lussac. f 

Chloride  of  Nitrogen. 

The  mutual  affinity  of  chlorine  and  nitrogen  is  very  slight:  they  do 
not  combine  at  all  if  presented  to  each  other  in  their  gaseous  form;  and 
when  combined,  they  are  easily  separated.  Chloride  of  nitrogen  is 
formed  by  the  action  of  chlorine  on  some  salt  of  ammonia.  Its  forma- 
tion is  owing  to  the  decomposition  of  ammonia  (a  compound  of  hydro- 
gen and  nitrogen)  by  chlorine.  The  hydrogen  of  the  ammonia  unites 
with  chlorine,  and  forms  muriatic  acid;  while  the  nitrogen  of  the  am- 
monia, being  presented  in  its  nascent  state  to  chlorine  dissolved  in  the 
solutio IV  enters  into  combination  with  it. 

A convenient  method  of  preparing  chloride  of  nitrogen  is  the  follow- 
ing. An  ounce  of  muriate  of  ammonia  is  dissolved  in  twelve  or  sixteen 
ounces  of  hot  water;  and  when  the  solution  has  cooled  to  the  tempera- 
ture of  90°  F.,  a glass  bottle  with  a wide  mouth,  full  of  chlorine,  is  in- 
verted in  it.  The  solution  gradually  absorbs  the  chlorine,  and  acquires 
a yellow  colour;  and  in  about  twenty  minutes  or  half  an  hour,  minute 
globules  of  a yellow  fluid  are  seen  floating  like  oil  upon  its  surface, 
which,  after  acquiring  the  size  of  a small  pea,  sink  to  the  bottom  of  the 
liquid.  The  drops  of  chloride  of  nitrogen,  as  they  descend,  should  be 
collected  in  a small  saucer  of  lead,  placed  for  that  purpose  under  the 
mouth  of  the  bottle. 

Chloride  of  nitrogen,  discovered  in  1811  by  M.  Dulong,  (An.  de 
Chimie,  vol.  Ixxxvi. ) is  one  of  the  most  explosive  compounds  yet  known, 
having  been  the  cause  of  serious  accidents  both  to  its  discoverer  and  to 
Sir  H.  Davy.:}:  Its  specific  gravity  is  1.653.  It  does  not  congeal  in  the 
intense  cold  produced  by  a mixture  of  snow  and  salt.  It  may  be  distil- 
led at  160°  F.;'but  at  a temperature  between  200°  and  212°  it  explodes. 
It  appears  from  the  investigation  of  Messrs.  Porrett,  Wilson,  and  Kirk,§ 
that  its  mere  contact  witli  some  substances  of  a combustible  nature 
causes  detonation  even  at  common  temperatures.  This  result  ensues 
particularly  with  oils,  both  volatile  and  fixed.  I have  never  known 
olive  oil  fail  in  producing  the  effect.  The  products  of  the  explosion  are 
chlorine  and  nitrogen. 

Sir  H.  Davy  analyzed  chloride  of  nitrogen  by  means  of  mercury, 
which  unites  with  chlorine,  and  liberates  the  nitrogen.  He  inferred 
from  his  analysis  that  its  elements  are  united  in  the  proportion  of  four 
measures  of  chlorine  to  one  of  nitrogen;  and  it  hence  follows  that,  by 


* Annales  de  Ch.  et  de  Physique,  vol.  viii.  f Ibid.  vol.  ix, 

t Philosophical  Transactions,  1813. 

§ Nicholson’s  Journal,  vol.  xxxiv. 


214 


CHLORINE. 


weight,  it  consists  of  144  parts  or  four  equivalents  of  chlorine,  and  14 
pai'ts  or  one  equivalent  of  nitrogen.* 

Compounds  of  Chlorine  and  Carbon. — Per  chloride  of 
Carbon. 

For  the  knowledge  of  the  compounds  of  chlorine  and  carbon,  chemists 
are  indebted  to  tlie  ingenuity  of  Mr.  Faraday.  When  olefiant  gas  (a 
compound  of  carbon  and  hydrogen)  is  mixed  with  chlorine,  combination 
takes  place  between  them,  and  an  oil-like  liquid  is  generated,  which 
consists  of  chlorine,  carbon,  and  hydrogen.  On  exposing  this  liquid  in 
a vessel  full  of  chlorine  gas  to  the  direct  solar  rays,  the  chlorine  acts 
upon  and  decomposes  the  liquid,  muriatic  acid  is  set  free,  and  the  car- 
bon, at  the  moment  of  separation,  unites  with  the  chlorine.f 

Perchloride  of  carhon,  as  this  compound  is  named  by  Mr.  Faraday,  is 
solid  at  common  temperatures,  has  an  aromatic  odour  approaching  to 
that  of  camphor,  is  a non-conductor  of  electricity,  and  refracts  light  very 
powerfully.  Its  specific  gi’avity  is^  exactly  double  that  of  water.  It 
fuses  at  320®  F. , and  after  fusion  it  is  colourless  and  very  transparent. 
It  boils  at  360®,  and  may  be  distilled  without  chang'e,  assuming  a crystal- 
line arrangement  as  it  condenses.  It  is  sparingly  soluble  in  water,  but 
dissolves  in  alcohol  and  ether,  especially  by  the  aid  of  heat.  It  is  solu- 
ble also  in  fixed  and  volatile  oils. 

Perchloride  of  carbon  burns  with  a red  light  when  held  in* the  flame 
of  a spirit-lamp,  g'iving  out  acid  vapours  and  smoke;  but  the  combustion 
ceases  as  soon  as  it  is  withdrawn.  It  burns  vividly  in  oxygen  gas.  Alka- 
lies do  not  act  upon  it,  nor  is  it  changed  by  the  stronger  acids,  such  as 
the  muriatic,  nitric,  or  sulphuric  acids,  even  with  the  aid  of  heat.  When 
its  vapour  is  mixed  with  hydrogen,  and  passed  through  a red-hot  tube, 
charcoal  is  separated,  and  muriatic  acid  gas  evolved.^  On  passing  its 
vapour  over  the  peroxides  of  metals,  such  as  that  of  mercury  and  copper, 
heated  to  redness,  a chloride  of  the  metal  and  carbonic  acid  are  gene- 
rated. Protoxides,  under  the  same  treatment,  yield  carbonic  oxide  %a3 
and  metallic  chlorides.  Most  of  the  metals  decompose  it  also  at  the  tem- 
perature of  ignition,  uniting  with  its  chlorine,  and  causing  deposition 
of  charcoal. 

From  the  proportions  of  chlorine  and  olefiant  gas  employed  in  form- 
ing perchloride  of  carbon,  and  from  its  analysis,  made  by  passing  it  over 


* Berzelius  states  the  composition  of  this  compound  to  be  three  vol- 
umes of  chlorine  to  one  of  nitrogen,  corresponding  to  three  equivalents’ 
of  the  former  to  one  of  the  latter.  These  proportions,  if  found  to  be 
coiTect,  will  render  the  chloride  and  iodide  of  nitrogen  analogous  in 
composition.  B. 

f The  reader  will  find  the  details  of  this  process  in  the  Philosophical 
Transactions  for  1821,  or  in  the  second  volume,  N.  S.,  of  the  Annals  of 
Philosophy. 

t As  the  text  originally  stood,  it  read  as  follows: — “Alkalies  do  notact 
upon  it;  nor  is  it  changed  by  the  stronger  acids,  such  as  the  muriatic, 
nitric,  or  sulphuric  acids,  even  with  the  aid  of  heat;  charcoal  is  sepa- 
rated, and  muriatic  acid  gas  evolved.”  There  is  evidently  some  omis- 
sion here,  as  the  last  clause  of  the  sentence  does  not  make  sense  with 
what  precedes  it.  "J'he  words  which  have  been  supplied  are  evidently 
necessary  to  complete  the  sense;  but  before  1 felt  satisfied  to  insert  them, 
I consulted  the  original  jiajier  of  Mr.  Faraday  in  the  Philosophical 
Transactions,  and  find  that  it  clearly  justifies  U.ie  addition  wliich  1 have 
made.  B, 


CHLORINE. 


215‘ 


peroxide  of  copper  at  the  temperaUirq  of  ig’nition,  Mr.  Faraday  infers 
that  this  compound  consists  of  108  parts  or  three  equivalents  of  chlorine, 
and  12  parts  or  two  equivalents  of  carbon. 

Proiochloride  of  Carbon, — When  the  vapour  of  perchloride  of  carbon 
is  passed  througdi  a red-hot  glass  or  porcelain  tube,  containing  fragments 
of  rock  crystal  to  increase  the  extc^it  of  heated  surface,  partial  decom- 
position takes  place;  chlorine  gas  escapes,  and  a fluid  passes  over  which 
Ikli*.  Faraday  calls  protocliloride  of  carbon. 

Protochloride  of  carbon  is  a limpid  colourless  fluid,  which  does  not 
congeal  at  zero  of  Fahrenheit,  and  at  160^  or  170°  F.  is  converted  into 
vapour.  It  may  be  distilled  repeatedly  without  change;  but  when  ex- 
posed to  a red  lieat,  some  of  it  is  resolved  into  its  elements.  Its  specific 
gravity  is.  1.5526.  In  its  chemical  relations  it  is  very  analogous  to  pfer- 
chloride  of  carbon.  Mr.. Faraday  analyzed  it  by  transmitting  its  vapour 
over  ignited  peroxide  of  copper;  and  he  infers  from  the  products  of  its 
decomposition — carbonic  acid  and  chloride  of  copper — that  it  is  com- 
posed of  36  parts  or  one  equivalent  of  chlorine,  and  6 parts  or  one  equiv- 
alent of  carbon. 

A third  compound  of  chlorine  and  carbon  is  described  in  volume  xvii. 
of  the  Annals  of  Philosophy.  It  was  brought  from  Sweden  by  M.  Ju- 
lin,  and  is  said  to  have  been  formed  during  the  distillation  of  nitric  acid 
from  crude  nitre  and  sulphate  of  iron.  It  occurs  in  small,  soft,  adhe- 
sive fibres  of  a white  colour,  which  have  a peculiar  odour,  somewhat 
resembling  spermaceti.  It  fuses  on  the  application  of  heat,  and  boils 
at  a temperature  between  350?  and  450°  F.  At  250°  F.  it  subhmes 
slowly,  and  condenses  again  in  the  form  of  long  needles.  It  is  insolu- 
ble in  water,  acids,  and  alkalies;  but  is  dissolved  by  hot  oif  of  turpen- 
tine or  by  alcohol,  and  forms  acicular  crystals  as  the  solution  cools.  It 
burns  with  a red  flame,  emitting  much  smoke  and  fumes  of  muriatic 
acid  gas. 

The  nature  of  this  substance  is  showmby  the  following  circumstance. 
When  its  vapour  is  exposed  to  a red  heat,  evolution  of  chlorine  gas  en- 
sues, and  charcoal  is  deposited.  A similar  deposition  of  charcoal  is 
produced  by  heating  it  with  phosphorus,  iron,  or  tin;  and  a chloride 
is  formed  at  the  same  time.  Potassium  burns  vividly  in  its  vapour,  with 
formation  of  chloride  of  potassium  and  separation  of  charcoal.  On  de- 
tonating a mixture  of  its*vapour  with  oxygen  g*as  over  mercury,  a chloride 
of  that  metal  and  carbonic  acid  are  generated.  From  these  facts,  the 
greater  part  of  which  were  ascertained  by  Messrs.  Phillips  and  Faraday, 
it  follows  that  the  substance  brought  from  Sweden  by  M.  Jufin  is  a 
compound  of  chlorine  and  carbon;  and  the  same  able  chemists  con- 
clude, from  their  analysis,  that  its  elements  are  united  in  the  ratio  of 
one  equivalent  of  chlorine  to  two  equivalents  of  carbon.  (An.  of  Pliil. 
xviii.  150.) 

Chloride  of  Sulphur, 

Chloride  of  sulphur  was  discovered  in  the  year  1804  by  Dr.  Thomson,* 
and  was  afterwards  examined  by  Berthollet.-j-  It  is  most  conveniently 
prepared  by  passing  a current  of  chlorine  gas  over  flowers  of  sulphur 
gently  heated.  Direct  combination  takes  place,  and  the  product  is  ob- 
tained under  the  form  of  a liquid  which  appears  red  by  reflected,  and 
yellowish-green  by  transmitted  light.  Its  density  is  1.6.  It  is  volatile 
below  200°  F.,  and  condenses  again  without  change  in  cooling.  When 
exposed  to  the  air  it  emits  acrid  fumes,  which  irritate  the  eyes  power- 


Nicholson’s  Journal,  vol,  vi. 


f Memoires  d’Ai’cueil,  vol.  i. 


216 


CHLORINE. 


fully,  and  have  an  odour  somewhat  rcscmblinj^  sea-weed,  but  much 
strong*er.  Dry  litmus  paper  is  not  reddened  by  it,  nor  does  it  unite 
with  alkalies.  It  acts  with  energ'y  on  water;  mutual  decomposition 
ensues,  the  water  becomes  cloudy  from  deposition  of  sulphur,  a solu- 
tion is  obtained,  in  which  muriatic,  sulphurous,  and  sulphuric  acids  may 
be  detected.  Similar  phenomena  ensue  when  it  is  mixed  with  alcohol 
or  ether. 

According*  to  Sir  H.  Davy,  chloride  of  sulphur  is  composed  of  30 
parts  of  sulphur,  and  68.4  of  chlorine;  a proportion  which  leaves  little 
doubt  of  its  being  a compound  of  36  or  one  equivalent  of  chlorine,  and 
16  or  one  equivalent  of  sulphur.  (Elements,  p.  280.) 

Compounds  of  Chlorine  and  Phosphorus, 

There  are  two  definite  compounds  of  chlorine  and  phosphorus,  the 
nature  of  which  was  first  satisfactorily  explained  by  Sir  II.  I)avy.  (Ele- 
ments, p.  290.)  When  phosphorus  is  introduced  into  a jar  of  dry  chlo- 
rine, it  inflames,  and  on  the  inside  of  the  vessel  a white  matter  collects, 
which  \?i  perchloride  of  phosphorus.  It  is  very  volatile,  a temperature 
much  below  2128  F.  being  sufficient  to  convert  it  into  vapour.  Under 
pressure  it  may  be  fused,  and  it  yields  transparent  prismatic  crystals  in 
cooling. 

Water  and  perchloride  of  phosphorus  mutually  decompose  each, 
other;  and  the  sole  products  are  muriatic  and  phosphoric  acids.  Now 
in  order  that  these  products  should  be  formed,  consistently  with  the 
constitution  of  phosphoric  acid,  as  stated  at  page  195,  the  perchloride 
must  consist  of  15.71  parts  or  one  equivalent  of  phosphorus,  and  90 
parts  dr  two  equivalents  and  a half  of  chlorine.  One  equivalent  of  the 
chloride  and  two  and  a half  of  water  will  then  mutually  decompose 
each  other  without  any  element  being  in  excess,  and  yield  one  equiva- 
lent of  phosphoric,  and  two  and  a half  equivalents  of  muriatic  acid. 
This  proportion  is  not  far  from  the  truth;  for,  according  to  Sir  H. 
Davy,  one  grain  of  phosphorus  is  united  in  the  perchloride  with  six  of 
chlorine. 

Protochloride  of  phosphorus  may  be  made  either  by  heating  the  per- 
chloride with  phosphorus,  or  by  passing  the  vapour  of  phosphorus,  over 
corrosive  sublimate  contained  in  a glass  tube.  It  is  a clear  liquid  like 
water,  of  specific  gravity  1.45;  emits  acid  fumes  when  exposed  to  the 
air,  owing  to  the  decomposition  of  watery  vapour;  but  when  pure  it 
does  not  redden  dry  litmus  paper.  On  mixing  it  with  water,  mutual 
decomposition  ensues,  heat  is  evolved,  and  a solution  of  muriatic  and 
phosphorous  acids  is  obtained.  It  hence  appears  to  consist  of  15.71  parts 
or  one  proportional  of  phosphorus,  and  54  parts  or  one  proportional 
and  a half  of  chlorine. 

When  sulphuretted  hydrogen  gas  is  transmitted  through  a vessel  con- 
taining perchloride  of  phosphorus,  muriatic  acid  is  disengaged,  and  a 
liquid  produced  which  Serullus  states  to  be  a compound  of  three 
equivalents  of  chlorine,  one  of  phosphorus,  and  one  of  sulphur..  (An. 
de  Ch.  etde  Ph.  xlii.  25.) 

Chlorocarbonic  Jicid  Gas. 

Tins  compound  was  discovered  in  1812  by  Dr.  John  Davy,  who  de- 
scribed it  in  tlic  Philosopliical  Transactions  for  that  year,  under  the 
name  of  phosgene  gas.*  It  is  made  b}/-  exposing  a mixture  of  equal 
measures  of  dry  cldorine  and  carbonic  oxide  gases  to  sunshine,  when 
rapid  but  silent  combination  ensues,  and  they  contract  to  one-half  theif 


From  light,  and  yewcea  I produce. 


CHLORINE.  2ir 

volume.  Diffused  day-light  also  effects  their  union  slowly;  but  they  do , 
not  combine  at  all  when  the  mixture  is  wholly  excluded  from  light. 

Chhrocarhonic  acid  gas  is  colourless,  has  a strong  odour,  and  reddens 
dry  litmus  paper.  It  combines  with  four  times  its  volume  of  ammonia- 
cal  gas,  forming  a white  solid  salt;  so  that  it  possesses  the  characteristic 
property  of  acids.  It  is  decomposed  by  contact  with  water.  One 
equivalent  of  each  compound  undergoes  decomposition;  and  as  the 
hydrogen  of  the  water  unites  with  chlorine,  ar.d  its  oxygen  with  car- 
bonic oxide,  the  products  are  carbonic  and  muriatic  acids.  When 
tin  is  heated  in  chlorocarbonic  acid  gas,  chloride  of  tin  is  generated, 
and  carbonic  oxide  gas  set  free,  which  occupies  exactly  the  same  space 
as  the  chlorocarbonic  acid  which  was  employed.  A similar  change  oc- 
curs when  it  is  heated  in  contact  with  antimony,  zinc,  or  arsenic. 

As  chlorocarbonic  acid  gas  contains  its  own  volume  of  each  of  its 
constituents,  it  follows  that  100  cubic  inches  of  that  gas,  at  the  standard 
temperature  and  pressure,  must  weigh  105.9  grains;  namely,  76.25  of 
chlorine  added  to  29.65  of  carbonic  oxide.  Its  specific  gravity  is, 
therefore,  3.4721;  and  it  consists  of  36  parts  or  one  equivalent  of  chlo- 
rine, and  14  parts  or  one  equivalent  of  carbonic  oxide. 

Chloride  of  Boron. 

Sir  H.  Davy  noticed  that  recently  prepared  boron  takes  fire  sponta- 
neously in  an  atmosphere  of  chlorine,  and  emits  a vivid  light;  but  he  did 
not  examine  the  product.  Berzelius  remarked,  that  if  the  boron  has 
been  previously  heated,  whereby  it  is  rendered  more  compact,  the 
combustion  does  not  take  place  till  heat  is  applied.  This  observation 
led  him  to  expose  boron,  thus  rendered  dense,  in  a glass  tube  to  a cur- 
rent of  dry  chlorine;  and  to  heat  it  gently,  as  soon  as  the  atmospheric 
air  was  completely  expelled,  in  order  to  commence  the  combustion. 
The  resulting  compound  proved  to  be  a colourless  gas;  and  on  collect- 
ing it  over  mercury,  which  absorbed  free  chlorine,  he  procured  the 
chloride  of  boron  in  a state  of  purity.  This  gas  is  rapidly  absorbed  by 
water  ; but  double  decomposition  takes  place  at  the  same  instant,  giving 
rise  to  the  production  of  muriatic  and  boracic  acids.  The  watery  va- 
pour of  the  atmosphere  occasions  a similar  change;  so  that  when  the 
gas  is  mixed  with  air  containing  hygrometric  moisture,  a dense  white 
cloud  is  produced.  The  specific  gravity  of  the  gas,  according  to  Du- 
mas, is  3.942.  It  is  soluble  in  alcohol,  and  communicates  to  it  an 
ethereal  odour,  apparently  by  the  action  of  muriatic  acid.  It  unites 
witli  ammoniacal  gas,  forming  a fluid  volatile  substance,  the  nature  of 
which  is  unknown. — (Annals  of  Phil,  xxvi.  129.) 

M.  Dumas  finds  that  chloride  of  boron  may  be  generated  by  the  ac- 
tion of  dry  chlorine  on  a mixture  of  charcoal  and  boracic  acid  heated  to 
redness  in  a porcelain  tube.  M.  Despretz  also  appears  to  have  invented 
a similar  process.  (Philos.  Magazine  and  Annals,  i,  469.) 

The  composition  of  the  chloride  of  boron  may  be  inferred  from  its 
action  on  water.  If  the  constitution  of  boracic  acid,  as  estimated  by 
Dr.  Thomson,  is  correct,  page  199,  the  chloride  of  boron  should  consist 
of  72  parts  or  two  equivalents  of  chlorine,  and  8 parts  or  one  equiva- 
lent of  boron ; for  one  equivalent  of  such  a compound,  with  two  of 
water,  will  yield  one  of  boracic  and  two  equivalents  of  muriatic  acid. 

On  the  Nature  of  Chlorine. 

The  change  of  opinion  which  has  gradually  taken  place  among  che- 
mists concerning  the  nature  of  chlorine,  is  a remarkable  fact  in  tlic 
history  of  the  science.  The  hypothesis  of  Berthollet,  unfounded  as  it 

19 


218 


CHLORINE. 


is,  prevailed  at  one  time  universally.  It  explained  phenomena  so  satis- 
factorily, and  in  a manner  so  consistent  with  the  received  chemical  doc- 
ti’ine,  that  for  some  years  no  one  thought  of  calling  its  correctness  into 
question.  A singular  reverse,  however,  has  taken  place;  and  this 
hypothesis,  though  it  has  not  hitherto  been  rigidly  demonstrated  to  be 
erroneous,  has  within  a short  period  been  generally  abandoned,  even  by 
persons  who,  from  having  adopted  it  in  early  life,  were  prejudiced  in 
its  favour.  The  reason  of  this  will  readily  appear  on  comparing  it  with 
the  opposite  theory,  and  examining  the  evidence  in  fiivour  of  each. 

Chlorine,  according  to  the  new  theory,  is  maintained  to  be  a simple 
body,  because,  like  oxygen,  hydrogen,  and  other  analogous  substances, 
it  cannot  be  resolved  into  more  simple  parts.  It  does  not  indeed  follow 
that  a body  is  simple,  because  it  has  not  hitherto  been  decomposed  ; 
but  as  chemists  have  no  other  mode  of  estimating  the  elementary  nature 
of  bodies,  they  must  necessarily  adopt  this  one,  or  have  none  at  all.  Muria- 
tic acid,  by  the  same  rule,  is  considered  to  be  a compound  of  chlorine 
and  hydrogen.  For  when  it  is  exposed  to  the  agency  of  galvanism,  it  is 
resolved  into  these  substances ; and  by  mixing  the  two  gases  in  due 
proportion,  and  passing  an  electric  spark  through  the  mixture,  muriatic 
acid  gas  is  the  product.  Chemists  have  no  other  kind  of  proof  of  the 
composition  of  water,  of  potassa,  or  of  any  other  compound. 

Very  dilFerentis  the  evidence  in  support  of  the  theory  of  Berthollet. 
According  to  that  view,  muriatic  acid  gas  is  composed  of  ahsoliite  mu^ 
riatic  acid  and  water  or  its  elements;  chlorine  consists  of  absolute  miv- 
ncf/zc  ctac?  and  oxygen ; omU  absolute  muriatic  acid  is  a compound  of  a 
certain  unknown  base  and  oxygen  gas.  Now  all  these  propositions  are 
gratuitous.  For,  in  the  first  place,  muriatic  acid  gas  has  not  been 
proved  to  contain  water.  Secondly,  the  assertion  that  chlorine  contains 
oxygen  is  opposed  to  direct  experiment,  the  most  powerful  deoxidizing 
agents  having  been  unable  to  elicit  from  that  gas  a particle  of  oxygen. 
Thirdly,  the  existence  of  such  a substance  as  absolute  muriatic  acid  is 
wholly  without  proof,  and  therefore  its  supposed  base  is  also  imaginary. 

But  this  is  not  the  only  weak  point  of  the  doctrine.  Since  chlorine 
*iS  admitted  by  this  theory  to  contain  oxygen,  it  was  necessary  to  explain 
how  it  happens  that  no  oxygen  can  be  separated  from  it.  For  instance 
on  exposing  chlorine  to  a powerful  galvanic  battery,  oxygen  gas  does 
not  appear  at  the  positive  pole,  as  occurs  when  other  oxidized  bodies 
are  subjected  to  its  action;  nor  is  carbonic  acid  or  carbonic  oxide 
evolved,  when  chlorine  is  conducted  over  ignited  charcoal.  To  account 
for  the  oxygen  not  appearing  under  these  circumstances,  it  was  assumed 
that  absolute  muriatic  acid  is  unable  to  exist  in  an  uncombined  state,  and, 
therefore,  cannot  be  separated  from  one  substance  except  by  uniting 
with  another.  This  supposition  was  thought  to  be  supported  by  the  ana- 
logy of  certain  compounds,  such  as  nitric  and  oxalic  acids,  which  appear 
to  be  incapable  of  existing  except  when  combined  with  water  or  some 
other  substance.  The  analogy,  however,  is  incomplete;  for  the  decompo- 
sition of  such  compounds,  when  an  attempt  is  made  to  procure  them  in 
an  insulated  state,  is  manifestly  owing  to  the  tendency  of  their  elements 
to  enter  into  new  combinations. 

Admitting  the  various  assumptions  which  have  been  stated,  most  of 
tlie  phenomena  receive  as  consistent  an  explanation  by  the  old  as  by  the 
new  theory.  Thus,  when  muriatic  acid  gas  is  resolved  by  galvanism 
into  chlorine  and  liydrogen,  it  ma}^  Im  supposed  tluit  absolute  muriatic 
acid  attaches  itself  to  the  oxygen  of  the  water,  and  forms  chlorine;  while 
tlie  hydrogen  of  the  water  is  attracted  to  the  opposite  pole  of  the  bat- 
tery, AVlicn  chlorine  and  hydrogen  enter  into  combination,  tlie  oxygen 
of  the  former  may  be  said  to  unite  with  the  latter;  and  that  muriatic  acid 


CHLORINE, 


219 


gas  is  generated  by  the  water  so  formed  combining  with  the  absolute 
muriatic  acid  of  the  chlorine.  The  evolution  of  chlorine,  which  ensues 
on  mixing  muriatic  acid  and  peroxide  of  manganese,  is  explained  on  the 
supposition  that  absolute  muriatic  acid  unites  Erectly  with  the  oxygen  of 
the  black  oxide  of  manganese. 

It  will  not  be  difficult,  after  these  observations,  to  account  for  the 
preference  shown  to  the  new  theory.  In  an  exact  science,  such  as 
chemistry,  every  step  of  which  is  required  to  be  matter  of  demonstra- 
tion, there  is  no  room  to  hesitate  between  two  modes  of  reasoning,  one 
of  which  is  hypothetical,  and  the  other  founded  on  experiment.  Nor 
is  there,  in  the  present  instance,  temptation  to  deviate  from  the  strict 
logic  of  the  science;  for  there  is  not  a single  phenomenon  which  may 
not  be  fully  explained  on  the  new  theory,  in  a manner  quite  consistent 
with  the  laws  of  chemical  action  in  general.  It  was  supposed,  indeed, 
at  one  time,  that  the  sudden  decomposition  of  water,  occasioned  by  the 
action  of  that  liquid  on  the  compounds  of  chlorine  with  some  simple 
substances,  constitutes  a real  objection  to  the  doctrine;  but  it  will  after- 
wards appear,  that  the  acquisition  of  new  facts  has  deprived  this  argu- 
ment of  all  its  force.  While  nothing,  therefore,  can  be  gained,  much 
may  be  lost  by  adopting  the  doctrine  of  Berthollet.  If  chlorine  is  re- 
garded as  a compound  body,  the  same  opinion,  though  in  direct  opposi- 
tion to  the  result  of  observation,  ought  to  be  extended  to  iodine  and 
bromine;  and  as  other  analogous  substances  may  hereafter  be  discover- 
ed, in  regard  to  which  a similar  hypothesis  will  apply,  it  is  obvious  that 
this  view,  if  proper  in  one  case,  may  legitimately  be  extended  to  others. 
One  encroachment  on  the  method  of  strict  induction  would  consequent- 
ly open  the  way  to  another,  and  thus  the  genius  of  the  science  would 
eventually  be  destroyed. 

An  able  attempt  was  made  some  years  ago  by  the  late  Dr.  Murray,  to 
demonstrate  the  presence  of  water  or  its  elements  as  a constituent  part 
of  muriatic  acid  gas,  and  thus  to  establish  the  old  theory  to  the  subver- 
sion of  the  new.  Into  this  discussion,  however,  I shall  not  enter  here, 
as  it  would  lead  into  details  too  minute  for  an  elementary  treatise.  I may 
only  observe,  in  referring  the  reader  to  the  original  papers  on  the  sub- 
ject,* that  Dr.  Murray  did  not  succeed  in  establishing  his  point;  and 
that  his  arguments,  though  exceedingly  plausible  and  ingenious,  were 
fully  answered  by  Sir  Humphry  and  Dr.  John  Davy.  I must  also  state, 
that  the  history  of  the  only  experiment  which  strictly  bears  upon  the 
question, — that,  namely,  in  which  muriatic  acid  and  ammoniacal  gases 
were  mixed  together, — amounts  very  nearly  to  a demonstration  of  the 
absence  of  combined  water  in  muriatic  acid  gas.  The  traces  of  humid- 
ity, which  were  observed,  may  easily  be  accounted  for  by  the  difficulty 
of  rendering  gases  absolutely  dry,  which  have  themselves  a strong 
affinity  for  moisture;  whereas  the  absence  of  so  large  a quantity  of  wa- 
ter, as  ought,  according  to  Dr.  Murray’s  argument,  to  be  present  in 
muriatic  acid  gas,  does  not  admit  of  a satisfactory  explanation,  except 
by  supposing  that  gas  to  be  anhydrous. 


* In  Nicholson’s  Journal,  vols.  xxxi.  xxxii.  and  xxxiv.  Edinburgh 
Philos.  Trans,  vol.  viii.  and  Philos.  Trans,  for  1818. 


220 


IODINE. 


SECTION  XII. 

IODINE. 

Iodine  was  discovered  in  the  year  1812  by  M.  Courtois,  a manufac- 
turer of  saltpetre  at  Paris.  In  preparing  carbonate  of  soda  from  the 
ashes  of  sea-weeds,  he  observed  that  the  residual  liquor  corroded  me- 
tallic vessels  powerfully;  and,  investigating  the  cause  of  the  corrosion, 
he  noticed  that  sulphuric  acid  threw  down  a dark  coloured  matter, 
whicli  was  converted  by  the  application  of  heat  into  a beautiful  violet 
vapour.  Struck  with  its  appearance,  he  gave  some  of  the  substance  to 
M.  Clement,  who  recognised  it  as  a new  body,  and  in  1813  described 
some  of  its  leading  properties  in  the  Royal  Institute  of  France.  Its 
real  nature  was  soon  after  determined  by  Gay-Lussac  and  Sir  II.  Davy, 
each  of  whom  proved  tliat  it  is  a simple  non-metallic  substance,  exceed- 
ingly analogous  to  chlorine.* 

lo.line,  at  coTT^mon  temperatures,  is  a soft  friable  opake  solid,  of  a 
bluish-black  cob.  r,  and  metallic  lustre.  It  occurs  usually  in  crystalline 
scales,  having  the  appearance  of  micaceous  iron  ore;  but  it  sometimes 
crystallizes  in  large  rhomboidal  plates,  the  primitive  form  of  which  is  a 
rhombic  octohedron.  The  crystals  are  best  prepared  by  exposing  to 
the  air  a solution  of  iodine  in  Jiydriodic  acid.  Its  specific  gravity, 
according  to  Gay-Lussac,  is  4.948;  but  Dr.  Thomson  found  it  only 
3.0844.  At  225^  F.  it  is  fused,  and  enters  into  ebullition  at  347*^;  but 
when  moisture  is  present,  it  is  sublimed  rapidly  even  below  the  degree 
of  boiling  water,  and  suffers  a gradual  dissipation  at  low  temperatures. 
Its  vapour  is  of  an  exceedingly  rich  violet  colour,  a character  to  which  it 
owes  the  name  of  (From  violet-coloured.)  This  va- 

pour is  remarkably  dense,  its  specific  gravity,  as  calculated  by  the  for- 
mula of  page  136,  being  8.6102;  or  8.716  as  directly  observed  by  M. 
Dumas.  Hence  100  cubic  inches,  at  the  standard  temperature  and 
pressure,  m ist  weigh  262.612  grains.  Dr.  Thomson  infers,  partly 
from  the  experiments  of  Gay-Lussac,  and  partly  from  his  own  researches, 
that  the  atomic  weight  of  iodine  is  124;  but  according  to  the  experi- 
ments of  Berzelius  its  equivalent  is  126.26. 

Iodine  is  a non-conductor  of  electricity,  and,  like  oxygen  and  chlo- 
rine, is  a negative  electric.  It  has  a very  acrid  taste,  and  its  odour  is 
almost  exactly  similar  to  that  of  chlorine,  when  much  diluted  with  air. 
It  acts  energetically  on  the  ani,mal  system  as  an  irritant  poison,  but  is 
employed  medicinally  in  very  small  doses  with  advantage. 

Iodine  is  very  sparingly  soluble  in  water,  requiring  about  7000 
times  its  weight  of  that  liquid  for  solution.  It  communicates,  however, 
even  in  this  minute  quantity,  a brown  tint  to  the  menstruum.  Alcohol 
and  ether  dissolve  it  freely,  and  the  solution  has  a deep  reddish-brown 
colour. 

Iodine  possesses  an  extensive  range  of  affinity.  It  destroys  vegeta- 
ble colours,  though  in  a much  less  degree  than  chlorine.  It  manifests 
little  disposition  to  combine  with  metallic  oxides;  but  it  has  a strong  at- 
traction for  tlic  pure  metals,  and  for  most  of  the  simple  non-metallic 
substances,  producing  compounds  which  are  termed  iodides' ov  iodurets. 


* The  original  papers  on  this  subject  arc  in  the  Annales  de  Chimie, 
vols.  Ixxxviii.  xc.  and  xci.;  and  in  the  Philos.  Trans,  for  1814  and 
1815, 


IODINE. 


221 


It  is  not  inflammable;  but  under  favourable  circumstances  may,  like 
chlorine,  be  made  to  unite  with  oxygen.  A solution  of  the  pure  alka- 
lies acts  upon  it  in  the  same  manner  as  upon  chlorine,  giving  rise  to 
decomposition  of  water,  and  the  formation  of  iodic  and  hydriodic 
acids. 

Pure  iodine  is  not  influenced  chemically  by  the  imponderables.  Ex- 
posure to  the  direct  solar  rays,  or  to  strong  shocks  of  electricity,  does 
not  change  its  nature.  It  may  be  passed  through  red-hot  tubes,  or 
over  intensely  ignited  chalrcoal,  without  any  appearance  of  decomposi- 
tion; nor  is  it  affected  by  the  agency  of  galvanism.  Chemists,  indeed, 
are  unable  to  resolve  it  into  more  simple  parts,  and  consequently  it  is 
regarded  as  an  elementary  principle. 

The  violet  hue  of  the  vapour  of  iodine  is  for  many  purposes  a suf- 
ficiently sure  indication  of  its  presence.  A far  more  delicate  test,  how- 
ever, was  discovered  by  MM.  Colin  and  Gaultier  de  Claubry.  They 
found  that  iodine  has  tlie  property  of  uniting  with  starch,  and  of  form- 
ing with  it  a compound  insoluble  in  cold  water,  which  is  recognised 
with  certainty  by  its  deep  blue  colour.  This  test,  according  to  Profes- 
sor Stromeyer,  is  so  delicate,  that  a liquid  containing  1-450,000  of  its 
weight  of  iodine,  receives  a blue  tinge  from  a solution  of  starch.  Two 
precautions  should  be  observed  to  insure  success.  In  the  first  place, 
the  iodine  must  be  in  a free  state;  for  it  is  the  iodine  itself  only  and 
not  its  compounds  which  unite  with  starch.  Secondly,  the  solution 
should  be  quite  cold  at  the  time  of* adding  the  starch;  for  boiling 
water  decomposes  the  blue  compound,  and  consequently  removes  its 
colour. 

Iodine  and  Hydrogen — Hydriodic  Acid  Gas. 

When  a mixture  of  hydrogen  and  the  vapour  of  iodine  is  trans- 
mitted through  a red-hot  porcelain  tube,  direct  combination  takes 
place  between  them,  and  a colourless  gas,  possessed  of  acid  proper- 
ties, is  the  product.  To  this  substance  the  term  hydriodic  acid  gas  is 
applied. 

This  gas  may  be  obtained  quite  pure  by  the  action  of  water  on  iodide 
of  phosphorus.  Any  convenient  quantity  of  the  iodide  is  put  into  a 
small  glass  retort,  together  with  a little  water,  and  a gentle  heat  is  ap- 
plied.  Mutual  decomposition  ensues;  the  oxygen  of  the  water  unites 
with  phosphorus,  and  its  hydrogen  with  iodine,  giving  rise  to  the  for- 
mation of  phosphoric  and  hydriodic  acid,  the  latter  of  which  passes 
over  in  the  form  of  a colourless  gas.  The  preparation  of  the  iodide 
requires  care;  since  phosphorus  and  iodine  act  so  energetically  on  each 
other  by  mere  contact,  that  the  phosphorus  is  generally  inflamed,  and 
a great  part  of  the  iodine  expelled  in  the  form  of  vapour.  This  incon- 
venience is  avoided  by  putting  the  phosphorus  into  a tube  sealed  at  one 
end,  and  about  twelve  inches  long,  displacing  the  air  by  a current  of 
dry  carbonic  acid  gas,  and  then  adding  the  iodine  by  degrees.  The 
action  sliould  be  promoted  towards  the  close  by  a gentle  heat.  The 
materials  should  be  well  dried  with  bibulous  paper,  and  the  phosphuret 
preserved  in  a well  stopped  dry  vessel;  for  even  atmospheric  humi- 
dity gives  rise  to  copious  white  fumes  of  hydriodic  acid.  The  propor- 
tions usually  employed  are  one  part  of  phosphorus  to  about  twelve  of 
iodine. 

Another  process  has  been  recommended  by  M.  F.  d’Ai’cet,  which 
consists  in  evaporating  hypophosphorous  acid  until  it  begins  to  yield 
phosphuretted  hydrogen,  mixing  it  with  an  equal  weight  of  iodine,  and 
applying  a gentle  heat.  Hydriodic  acid  gas  of  great  purity  is  tlien  ra- 

19* 


222 


IODINE. 


pklly  dlsengag*ed,  its  production  depending,  as  in  the  former  process, 
on  the  decomposition  of  water. 

Hydriodic  acid  gas  has  a very  sour  taste,  reddens  vegetable  blue  co- 
lours without  destroying  them,  produces  dense  white  fumes  when  mixed 
with  atmospheric  air,  and  has  an  odour  similar  to  that  of  muriatic  acid 
gas.  It  combines  with  alkalies,  forming  salts  which  are  called  Jiydrio- 
dates.  Like  muriatic  acid  gas  it  cannot  be  collected  over  water;  for 
that  liquid  dissolves  it  in  large  quantity, 

Hydriodic  acid  is  decomposed  by  several  substances  which  have  a 
strong  affinity  for  either  of  its  elements.  Thus  oxygen  gas,  when 
heated  with  it,  unites  with  its  hydrogen,  and  liberates  the  iodine.  Chlo- 
rine effects  the  decomposition  instantly;  muriatic  acid  gas  is  produced, 
and  the  iodine  appears  in  the  form  of  vapour.  With  strong  nitrous  acid 
it  takes  fire,  and  the  vapour  of  iodine  is  set  free.  It  is  also  decompos- 
ed b}^  mercury.  The  decomposition  begins  as  soon  as  hydriodic  acid 
comes  in  contact  with  mercury,  and  proceeds  steadily,  and  even  quick- 
ly if  the  gas  is  agitated,  till  nothing  but  hydrogen  remains.  Gay-Lus- 
sac ascertained  by  this  method  that  100  measures  of  hydriodic  acid  gas 
contain  precisely  half  their  volume  of  hydrogen.  This  result  induced 
him  to  suspect  that  the  composition  of  hydriodic  must  be  analogous  to 
that  of  muriatic  acid  gas;^  that,  as  100  measures  of  the  latter  contain  50 
of  hydrogen  and  50  of  chlorine,  100  measures  of  the  foi-mer  consist  of 
50  of  hydrogen  and  50  of  the  vapour  of  iodine.  If  this  view  be  cor- 
rect, then  the  composition  of  hydriodic  acid  gas,  by  weight,  may  be 
determined  by  calculation.  For  since 

Grains, 

50  cubic  inches  of  the  vapour  of  iodine  weigh  . 131.306 

50  hydrogen  gas  ....  1.059 

100  hydriodic  acid  gas  must  weigh  132.365; 

and  its  specific  gravity  will  be  4.3398.  Now  Gay-Lussac  ascertained, 
by  weighing  hydriodic  acid  gas,  that  its  density  is  4.443, — a number 
which  corresponds  so  closely  with  the  preceding,  as  to  leave  no  doubt 
that  tlie  principle  of  the  calculation  is  correct.  There  is  good  reason 
to  believe,  indeed,  that  the  calculated  result,  if  not  rigidly  exact,  is 
very  near  the  truth;  for  Gay-Lussac  states,  that  the  number  determined 
by  him  directly  is  too  high.  (An.  de  Chimie,  vol.  xci.  p.  16.) 

Hydriodic  acid  is  regarded  as  a compound  of  one  equivalent  of  each 
element, — an  opinion  supported  both  by  the  proportions  in  which 
iodine  combines  with  other  substances,  and  by  the  analogy  of  mu- 
riatic acid.  The  constitution  of  hydriodic  acid  may,  therefore,  be  thus 
stated ; 

By  volume.  By  weight. 

Iodine  . . 50  . . 124  or  one  proportional, 

Hydrogen  . 50  . . 1 or  one  proportional; 

100  125 

and  its  combining  proportion  is  125. 

When  hydriodic  acid  gas  is  conducted  into  water  till  that  liquid  is 
fully  chui-gcd  witli  it,  a colourless  acid  solution  is  obtained,  which  emits 
white  fumes  on  exposure  to  tlie  air,  and  has  a density  of  1.7.  It  may 
l)e  ])re])ared  also  by  tj-ansmilting  a current  of  sulphuretted  hydrogen 
gas  through  water  in  which  iodine  in  fine  powder  is  suspended.  The 
iodine,  from  having  a greater  affinity  than  sulphur  for  hydrogen,  decom- 
po.sea  the  suJjihuretted  hydrogen;  and  lienee  sulphur  is  set  free,  and 


IODINE. 


223 


hydriodic  acid  produced.  As  soon  as  the  iodine  has  disappeared, 
and  the  solution  become  colourless,  it  is  heated  for  a short  time  to  expel 
the  excess  of  sulphuretted  hydrog*en,  and  subsequently  filtered  to  sepa- 
rate free  sulphur. 

The  solution  of  hydriodic  acid  is  readily  decomposed.  Thus,  on  ex- 
posure during*  a few  hours  to  the  atmosphere,  the  oxyg*en  of  the  air 
forms  water  with  the  hydrog*en  of  the  acid,  and  sets  iodine  free.  The 
solution  is  found  to  have  acquired  a yellow  tint  from  the  presence  of 
uncombined  iodine,  and  a blue  colour  is  occasioned  by  the  addition  of 
starch.  Nitric  and  sulphuric  acids  likewise  decompose  it  by  yielding 
oxygen,  the  former  being  at  the  same  time  converted  into  nitrous,  and 
the  latter  into  sulphurous  acid.  Chlorine  unites  directly  with  the  hy- 
drogen of  the  hydriodic  acid,  and  muriatic  acid  is  formed.  The  sepa- 
ration of  iodine  in  all  these  cases  may  be  proved  in  the  way  ju^t  men- 
tioned. These  circumstances  afford  a sure  test  of  the  presence  of  hy- 
driodic acid,  whether  free  or  in  combination  with  alkalies.  All  that  is 
necessary,  is  to  mix  a cold  solution  of  starch  with  the  liquid,  previousl3«- 
concentrated  by  evaporation  if  necessary,  and  then  add  a few  drops  of 
strong  sulphuric  acid.  A blue  colour  will  make  its  appearance  if  hy- 
di’iodic  acid  is  present. 

Hydriodic  acid  is  frequently  met  with  in  nature  in  combination  with 
potassa  or  soda.  Under  this  form  it  occurs  in  many  salt  and  other  min- 
eral springs,  both  in  England  and  on  the  continent.  It  has  been  de- 
tected in  the  water  of  the  Mediterranean,  in  the  oyster  and  some  other 
marine  molluscous  animals,  in  sponges,  and  in  most  kinds  of  sea-weed. 
In  some  of  these  productions,  such  as  the  Fucus  serratus  and  Fucus 
digitatiis^  it  exists  ready  formed,  and  according  to  Dr.  Fyfe  (Edinburgh 
Philos.  Journal,  i.  254.)  may  be  separated  by  the  action  of  water;  but 
in  others  it  can  be  detected  onl}"  after  incineration.  Marine  animals  and 
plants  doubtless  derive  the  hydriodic  acid  which  they  contain  from  the 
sea.  Vauquelin  has  found  it  also  in  the  mineral  kingdom,  in  combina- 
tion with  silver.  (Annales  de  Chimie  et  de  Physique,  vol.  xxix.) 

All  the  iodine  of  commerce  is  procured  from  the  impure  carbonate  of 
soda,  called  kelp,  which  is  prepared  in  large  quantity  on  the  northern 
shores  of  Scotland,  by  incinerating  sea-weeds.  The  kelp  is  employed 
by  soap-makers  for  the  preparation  of  carbonate  of  soda;  and  the  dark 
residual  liquor,  remaining  after  that  salt  has  crystallized,  contains  a con- 
siderable quantity  of  hydriodic  acid,  combined  with  soda  or  potassa. 
By  adding  a sufficient  quantity  of  sulphuric  acid,  the  hydriodic  acid  is 
separated  from  the  alkali,  and  then  decomposed.  The  iodine  sublimes 
when  the  solution  is  boiled,  and  may  be  collected  in  cool  glass  receiv- 
ers. A more  convenient  process  is  to  employ  a moderate  excess  of  sul- 
phuric acid,  and  then  add  some  peroxide  of  manganese  to  the  mixture. 
The  oxygen  of  the  manganese  decomposes  the  hydriodic  acid,  and 
protosulphate  of  manganese  is  formed.  (Dr.  Ure’s  Paper  in  the  50th 
volume  of  the  Philosophical  Magazine.)  Another  method,  proposed 
by  M.  Soubeiran,  is  by  adding  to  the  ley  from  kelp  a solution  made  with 
one  part  of  sulphate  of  copper  and  two  and  a quarter  of  protosulphate 
of  iron,  both  in  crystals,  as  long  as  a white  precipitate  appears:  The 
protiodide  of  copper  is  thus  thrown  down;  and  it  may  be  decomposed 
either  by  peroxide  of  manganese  alone,  or  by  manganese  and  .sulphuric 
acid.  By  means  of  the  former,  the  iodine  passes  over  quite  dry;  but  a 
strong  heat  is  requisite. 

Iodine  and  Oxygen. — Iodic  Acid. 

Iodic  acid  was  discovered  about  the  saipe  time  b^^  Gay-Lussac  and  Sir 
H.  Davy;  but  the  latter  first  succeeded  in  obtaining  it  in  a state  of  per- 


224 


IODINE 


feet  purity.  When  Iodine  is  brought  into  contact  witli  protoxide  of 
chlorine,  immediate  action  ensues;  the  clilorine  of  tlie  protoxide  unites 
witli  one  portion  of  iodine,  and  its  oxygen  with  anotlier,  forming  tvv'o 
compounds,  a volatile  orange-coloured  matter,  chloriodic  acid,  and  a 
white  solid  substance,  which  is  iodic  acid.  On  applying  licat,  the  for- 
mer passes  off  in  vapour,  and  the  latter  remains.  (Philos.  Trans,  for 
1815.)  Serullus  has  obtained  it,  in  the  form  of  hexagonal  laminrc,  by 
evaporating  in  a warm  place  its  solution  either  in  water,  or  in  sulphuric 
or  nitric  acid.  The  method  which  he  found  most  convenient  is  by 
forming  a solution  of  iodate  of  soda  in  a considerable  excess  of  sul- 
phuric acid,  keeping  it  at  a boiling  temperature  for  twelve  or  fifteen 
minutes,  and  then  setting  it  aside  to  crystallize.  (An.  de  Ch.  et  dc 
Ph.  xliii.  216.) 

This  compound,  which  w'as  termed  by  Sir  II.  Davy,  is  anhy^ 

drous  iodic  acid.  It  is  a white  semitransparent  solid,  which  has  a strong 
astringent  sour  taste,  but  iio  odour.  Its  density  is  considerable,  as  it 
sinks  rapidly  in  sulphuric  acid.  When  heated  to  the  temperature  of 
about  500?  F.  it  is  fused,  and  at  the  same  time  resolved  into  oxygen  and 
iodine. 

Iodic  acid  deliquesces  in  a moist  atmosphere,  and  is  very  soluble  in 
water.  The  liquid  acid  thus  formed  reddens  vegetable  blue  colours, 
and  afterwards  destroys  them.  On  evaporating  the  solution,  a thick 
mass  of  the  consistence  of  paste  is  left,  which  is  hydrous  iodic  acid,  and 
which,  by  the  cautious  application  of  heat,  may  be  rendered  anhydrous. 
It  acts  powerfully  on  inflammable  substances.  With  charcoal,  sulphur, 
sugar,  and  similar  combustibles,  it  forms  mixtures  which  detonate  when 
heated.  It  enters  into  combination  with  metallic  oxides,  and  the  resulting 
salts  are  called  iodates.  These  compounds,  like  the  chlorates,  yield  pure 
oxygen  by  heat,  and  deflagrate  when  thrown  on  burning  charcoal. 

Iodic  acid  was  said  by  Davy  to  unite  with  several  acids,  such  as  the 
sulphuric,  nitric,  phosphoric,  and  boracic  acids,  and  to  form  crystalliza- 
ble  compounds  with  the  three  former;  but  Serullus  denies  the  existence 
of  such  compounds.  It  is  decomposed  by  sulphurous,  phosphorous, 
and  hydriodic  acids,  and  by  sulphuretted  hydrogen.  Iodine  in  each 
case  is  set  at  liberty,  and  may  be  detected  as  usual  by  starch.  Muriatic 
and  iodic  acids  decompose  each  other,  water  and  chloriodic  acid  b^ing 
generated. 

Sir  11.  Davy  analyzed  iodic  acid  by  determining  the  quantity  of  oxy- 
gen which  it  evolves  when  decomposed  by  heat.  Gay-Lussac  effected 
tlie  same  object  by  heating  iodate  of  potassa,  when  pure  oxygen  was 
given  off,  and  iodide  of  potassium  remained.  From  the  result  of  these 
analyses,  it  appears  that  iodic  acid  is  a compound  of  124  parts  or  one 
equivalent  of  iodine,  and  40  parts  or  five  equivalents  of  oxygen.  The 
sum  of  these  numbers,  or  164,  is,  therefore,  the  combining  proportion 
of  the  acid. 

lodous  acid. — This  name  was  applied  to  a compound  prepared  in  1824 
by  Professor  Sementini  of  Naples  by  the  action  of  iodine  on  chlo- 
rate of  potassa.  (Quarterly  Journal  of  Science,  xvii.  381.)  Equal 
weights  of  the  materials  well  triturated  together  were  exposed  to  heat 
in  a retort,  wlicn  a yellow  volatile  liquid  of  the  consistence  of  oil,  the 
supposed  iodo\is  acid,  passed  over  into  the  receiver.  Put  it  appears 
from  the  subsequent  experin\ents  of  Wohler,  that  this  matter  does  not 
consist  of  iodine  and  oxygen,  but  of  iodine  and  chlorine.  Its  formation 
is  owing  to  part  of  the  chloric  acid  being  decomposed.  Its  elements 
unite  with  separate  ])ortions  of  iodine,  and  generate  two  compounds; 
iodic  acid,  which  remains  in  the  retort  combined  with  potassa,  and  chlo- 
ride of  iodine,  similar  to  that  described  by  Gay-Lussac,  which  is  sublimed. 


IODINE. 


225 


(Edin.  Joum.  of  Science,  No.  xii.  352.)  From  some  other  experiments, 
however,  M.  Sementini  has  almost  proved  the  existence  both  of  iodous 
acid  and  an  oxide  of  iodine.  He  states  that  on  bringing  together  the 
vapour  of  iodine  and  oxygen  gas  considerably  heated,  the  violet  tint  of 
the  former  disappears,  and  a yellow  matter  of  the  consistence  of  solid 
oil  is  generated.  This  he  regards  as  oxide  of  iodine;  and  if  the  supply 
of  oxygen  is  kept  up  after  its  formation,  it  is  converted  into  a yellow 
liquid,  which  he  supposes  to  be  iodous  acid#  From  the  moc^  in  which 
the  process  is  described,  there  can  scarcely  1^  a doubt  thatfbme  com- 
pound of  iodine  and  oxygen  is  thus  formed;  *ut,  at  the  same  time,  the 
new  compounds  have  not  been  examined  analytically,  nor  has  the 
chemical  constitution  of  the  substances  hitherto  prepared  by  M,  Semen- 
tini been  determined  with  that  accuracy  which  is  required  for  inspiring 
confidence  in  his  results.  (Quarterly  Journal  of  Science,  N.  S.  i.  478.) 

Mitscherlich  has  observed,  that  on  dissolving  iodine  in  a rather  dilute 
solution  of  soda,  until  the  solution  began  to  acquire  a red  tint,  perma- 
nent crystals  were  obtained  by  spontaneous  evaporation.  They  had  the 
form  of  a six-sided  prism,  and  dissolved  in  cold  water  without  change; 
but  by  the  action  of  water  moderately  heated,  or  by  alcohol,  they  were 
converted  into  iodate  of  soda  and  iodide  of  sodium.  On  the  addition  of 
an  acid,  iodine  and  iodic  acid  were  set  at  liberty.  From  these  facts  the 
crystals  were  inferred  to  be  iodite  of  soda.  (An.  de  Ch.  et  de  Fh. 
XXX.  84.) 

Chloriodic  Acid, 

chlorine  is  absorbed  at  common  temperatures  by  dry  iodine  with  evo- 
lution of  caloric,  and  a solid  compound  of  iodine  and  chlorine  results, 
which  was  discovered'both  by  Sir  H.  Davy  and  Gay  Lussac.  The  colour 
of  the  product  is  orange  yellow  when  the  iodine  is  fully  saturated  with 
chlorine,  but  is  of  a reddish-orange  if  iodine  is  in  excess.  It  is  con- 
verted by  heat  into  an  orange-coloured  liquid,  which  yields  a vapour  of 
the  same  tint  on  increase  of  temperature.  It  deliquesces  in  the  open 
air,  and  dissolves  freely  in  water.  Its  solutionis  colourless,  is  very  sour 
to  the  taste,  and  reddens  vegetable  blue  colours,  but  afterwards  destroys 
them.  From  its  acid  properties  Sir  H.  Davy  gave  it  the  name  of  chlo- 
riodic acid,  Gay-Lussac,  on  the  contrary,  calls  it  chloride  of  iodine^  con- 
ceiving that  the  acidity  of  its  solution  arises  from  the  presence  of  mu- 
riatic and  iodic  acids,  which  he  supposes  to  be  generated  by  decompo- 
sition of  water.  The  opinion  of  Sir  H.  Davy  appears  to  me  more  pro- 
bable; for  we  know  that  free  muriatic  and  iodic  acids  mutually  decom- 
pose each  other,  and,  therefore,  could  hardly  be  generated  by  the  ac- 
tion of  water  on  the  compound  of  iodine  and  chlorine.  A fact  greatly 
in  favour  of  this  opinion  has  been  added  by  Serullus;  namel}^  that  chlo- 
ride of  iodine  is  precipitated  from  its  solution  by  gradually  adding  a 
large  quantity  of  sulphuric  acid,  and  at  the  same  time  preventing  a rise 
of  temperature  by  the  application  of  cold.  He  also  found  that  on 
mixing  solutions  of  iodic  and  muriatic  acid,  and  then  adding  sulphuric 
acid  as  before,  chloriodic  acid  was  precipitated  Blit  this  compound 
does  not  unite  with  alkaline  substances.  On  mixing  it,  for  example, 
with  baryta,  muriate  and  iodate  of  baryta  are  obtained.  From  this  it 
may  be  infeiTed,  that  water  and  chloriodic  acid  decompose  each  other 
when  an  alkali  is  present. 

The  composition  of  chloriodic  acid  is  not  known  with  precision. 

Iodide  of  Nitrogen. — From  the  weak  affinity  that  exists  between 
iodine  and  nitrogen,  these  substances  cannot  be  made  to  unite  directly. 
But  when  iodine  is  put  into  a solution  of  ammonia,  the  alkali  is  decom- 
posed; its  elements  unite  with  different  portions  of  iodine,  and  thus 


226 


BROMINE. 


cause  the  formation  of  hydrlodic  acid  and  iodide  of  nitrog“en.  The  lat- 
ter subsides  in  the  form  of  a dark  powder,  which  is  characterized,  like 
chloride  of  nitrogen,  by  its  explosive  property.  It  detonates  violently 
as  soon  as  it  is  dried;  and  slight  pressure,  while  moist,  produces  a similar 
effect.  Heat  and  light  are  emitted  during  tlie  explosion,  and  iodine 
and  nitrogen  are  set  free.  According  to  the  experiments  of  M.  Colin, 
iodide  of  nitrogen  consists  of  one  proportional  of  nitrogen  and  three  of 
iodine.  # 

It  is  coi#enientl^mad^  according  to  Serullas,  by  saturating  alcohol 
of  0.852  with  iodine,  admng  a large  quantity  of  pure  ammonia,  and 
agitating  the  mixture.  On  diluting  with  water,  iodide  of  nitrogen  sub- 
sides, which  should  be  washed  by  repeated  affusion  of  water  and  decan- 
tation. As  thus  prepared  it  is  very  finely  divided,  and  may  be  pressed 
under  water  witliout  detonating  ; but  if,  subsequently  to  its  formation, 
it  is  put  in  contact  with  pure  ammonia,  it  will  afterwards  detonate  with 
the  same  facility  as  that  prepared  in  the  usual  manner. 

Serullas  has  also  remarked  that  water  and  iodide  of  nitrogen  mutually 
decompose  each  other,  giving  rise  to  the  formation  of  hydriodic  and 
iodic  acids  and  ammonia.  The  change  takes  place  slowly  in  cold  water; 
but  it  is  completed  in  a few  minutes,  and  with  scarcely  any  disengage- 
ment of  nitrogen,  when  gentle  heat  is  applied.  When  a little  nitric  or 
sulphuric  acid  is  used,  ammonia  and  iodic  acid  are  alone  produced.  (An. 
de  Ch.  et  de  Ph.  xlii.  201. 

Iodide  of  Phosphorus. — Iodine  and  phosphorus  combine  readily  in 
the  cold,  evolving  so  much  caloric  as  to  kindle  the  phosphorus,  if  the 
experiment  is  made  in  the  open  air;  but  in  close  vessels  no  light  ap- 
pears. The  combination  takes  place  in  several  proportions,  which 
have  not  been  determined.  Its  most  interesting  property  is  that 
of  decomposing  water,  with  formation  of  hydriodic  and  phosphoric 
acids. 

Iodide  of  Sulphur, — This  compound  is  formed  by  heating  gently  a 
mixture  of  iodine  and  sulphur.  The  product  has  a dark  colour  and 
radiated  appearance  like  antimony.  Its  elements  are  easily  disunited  by 
heat. 

Periodideof  Carhon. — When  a solution  of  pure  potassa  in  alcohol  is 
mixed  with  an  alcoholic  solution  of  iodine,  a portion  of  alcohol  is  de- 
composed; and  its  hydrogen  and  carbon,  uniting  separately  with  iodine, 
give  rise  to  periodide  of  carbon  and  hydriodic  acid.  The  latter  com- 
bines with  the  potassa,  and  remains  in  solution.  The  former  has  a yel- 
low colour  like  sulphui^  and  forms  scaly  crystals  of  a pearly  lustre;  its 
taste  is  very  sweet,  and  it  has  a strong  aromatic  odour  resembling  saf- 
fron. It  was  discovered  by  Serullas,  and  described  by  him  as  a hydro- 
carburet  of  iodine;  but  its  real  nature  was  pointed  out  by  Mitscherlich. 
(An.  de  Ch.  et  de  Ph.  xxxvii.  86.) 

The  protiodide  is  formed  by  distilling  a mixture  of  the  preceding  com- 
pound with  corrosive  sublimate.  It  is  a liquid  of  a sweet  taste,  and  has 
a penetrating  ethereal  odour. 


SECTION  XIIL 

BROMINE. 

This  peculiarly  interesting  substance  was  discovered  about  two  years 
ago  by  M.  Balard  of  Montpellier,  and  tlie  first  description  of  its  proper- 


BROMINE. 


227 


ties  appeared  in  the  Annales  de  Chimie  et  de  Physique  for  August,  1826. 
The  name  originally  applied  to  it  was  muride;  but  it  has  been  since 
changed  to  hrome^  a word  derived  from  the  Greek  graveolentia, 

signifying  a strong  or  rank  odour.  This  appellation  may  be  convenient- 
ly changed  in  English  into  that  of  bromine. 

.Bromine  in  its  chemical  relations  bears  a close  analogy  to  chlorine  and 
iodine,  and  has  hitherto  been  always  found  in  nature  associated  with  the 
former,  and  sometimes  also  with  the  latter.  It  exists  in  sea  water  in 
the  form  of  hydrobromic  acid,  combined,  in  the  opinion  of  M.  Balard, 
with  magnesia.  Its  relative  quantity,  however,  is  very  minute;  and 
even  the  uncrystallizable  residue  called  bittern,  left  after  muriate  of 
soda  has  been  separated  from  sea  water  by  crystallization,  contains  it  in 
small  proportion.  It  may  apparently  be  regarded  as  an  essential  ingi’e- 
dient  of  the  saline  matter  of  the  ocean;  for  it  has  been  detected  in  the 
waters  of  the  Mediterranean,  Baltic,  North  Sea,  and  Frith  of  Forth. 
It  has  also  been  found  in  the  waters  of  the  Dead  Sea,  and  in  a variety 
of  salt  springs  in  Germany.^  Dr.  Daubeny  has  detected  it  in  several 
mineral  springs  in  England;  and  states  that  it  is  rarely  wanting  in  those 
springs  which  contain  much  common  salt,  except  that  of  Droitwich  in 
Worcestershire.  M.  Balard  found  that  it  exists  in  marine  plants  grow- 
ing on  the  shores  of  the  Mediterranean,  and  he  has  procured  it  in  ap- 
preciable quantity  from  the  ashes  of  the  sea^weeds  that  furnish  iodine. 
He  has  likewise  detected  its  presence  in  the  ashes  of  some  animals, 
especially  in  those  of  the  Janthina  violacea,  one  of  the  testaceous  mol- 
lusca. 

At  common  temperatures  bromine  is  a liquid,  the  colour  of  which  is 
blackish-red  when  viewed  in  mass  and  by  reflected  light,  but  appears 
hyacinth-red  when  a thin  stratum  is  interposed  between  the  light  and 
the  observer.  Its  odour,  which*  somewhat  resembles  that  of  chlorine, 
is  very  disagreeable,  and  its  taste  powerful.  Its  specific  gravity  is  about 
3.  Its  volatility  is  considerable;  for  at  common  temperatures  it  emits 
red  coloured  vapours,  which  are  very  similar  in  appearance  to  those 
of  nitrous  acid;  and  at  116.5^  F.  it  enters  into  ebullition.  By  a tem- 
perature between  zero]  and — >4^  F.‘ it  is  congealed,  and  in  that  state 
is  brittle.  The  density  of  its  vapour,  as  calculated  by  Berzelius,  is 
5.3933.  ^ 

Bromine  is  a non-conductor  of  electricity,  and  undergoes  no  chemi- 
cal change  whatever  from  the  agency  of  the  imponderables.  It  may  be 
transmitted  through  a red-hot  glass  tube,  and  be  exposed  to  the  agency 
of  galvanism,  without  evincing  the  least  trace  of  decomposition.  Like 
oxygen,  chlorine,  and  iodine,  it  is  a negative  electric.  Bromine  is  so- 
luble in  water,  alcohol,  and  ether,  the  latter  being  its  best  solvent.  It 
does  not  redden  litmus  paper,  but  bleaches  it  rapidly  like  chlorine;  and 
it  likewise  discharges  tlie  blue  colour  from  a solution  of  indigo.  Its  va- 
pour extinguishes  a lighted  taper;  but  before  going  out,  it  burns  for  a 
few  seconds  with  aflame  which  is  green  at  its  base  and  red  at  its  upper 
part.  Some  inflammable  substances  take  fire  by  contact  with  bromine 
in  the  same  manner  as  when  introduced  into  an  atmosphere  of  chlorine. 
It  acts  with  energy  on  organic  matters,  such  as  wood  or  cork,  and 
corrodes  the  animal  texture;  but  if  applied  to  the  skin  for  a short  time 


* Some  of  the  salt  springs  of  Germany  furnish  a good  deal  of  bro- 
mine. The  saline  at  Theodorshalle,  near  Kreuznach,  contains  a suf- 
ficient quantity  to  make  its  extraction  profitable.  A quintal  (100  lbs.) 
of  the  mother-waters  of  this  spring  yields  two  ounces  and  one  drachm 
of  bromine. — Berzelius,  Traite  de  Chimie,  i.  293.  B. 


228 


BROMINE. 


only  it  communicates  a yellow  stain,  which  is  less  intense  than  that 
produced  by  iodine,  and  soon  disappears.  To  animal  life  it  is  highly 
destructive,  one  drop  of  it  placed  on  the  beak  of  a bird  having  proved 
fatal. 

From  the  close  resemblance  observable  between  chlorine  and  bro- 
mine, M.  Balard  was  of  course  led  to  examine  its  relations  with  hydro- 
gen, and  found  that  these  substmees  may  readily  be  made  to  unite;  the 
product  of  the  combination  being  a gas  very  similar  to  muriatic  and  hy- 
driodic  acid  gases,  whence  it  lias  received  tl^  name  of  hydrohromic  acid 
gas.  In  its  action  on  metals,  also,  bromine  presents  the  closest  simi- 
larity to  that  which  chlorine  exerts  on  the  same  substances.  Antimony 
and  tin  take  fire  by  contact  with  bromine;  and  its  union  with  potassium 
is  attended  with  such  intense  disengagement  of  heat  as  to  cause  a vivid 
flash  of  light,  and  often  to  burst  tlie  vessel  in  which  the  experiment  is 
performed.  Its  affinity  for  metallic  oxides  is  feeble,  but  it  has  a strong 
attraction  for  metals.  By  the  action  of  alkalies  it  is  resolved  into  hydro- 
bromic  and  bromic  acids,  suffering  the  same  kind  of  change  as  chlorine 
or  iodine  when  similarly  treated. 

Bromine  is  usually  extracted  from  bittern,  and  its  mode  of  prepara- 
tion is  founded  on  the  property  which  chlorine  possesses  of  decompos- 
ing hydrohromic  acid,  uniting  with  its  hydrogen,  and  setting  bromine 
at  liberty.  Accordingly,  on  adding  chlorine  to  bittern,  the  free  bro- 
mine immediately  communicates  an  orange-yellow  tint  to  the  liquid; 
and  on  heating  the  solution  to  its  boiling  point,  the  red  vapours  of  bro- 
mine are  expelled,  and  may  be  condensed  by  being  conducted  into  a 
tube  surrounded  with  ice.  It  was  this  change  of  colour  produced  by 
chlorine  that  led  to  the  discovery  of  bromine.  The  method  recom- 
mended by  M.  Balard  for  procuring  this  substance,  as  well  as  for  de- 
tecting the  presence  of  hydrohromic  acid,  is  to  transmit  a current  of 
chlorine  gas  through  bittern,  and  then  to  agitate  a portion  of  sulphuric 
ether  with  the  liquid.  The  ether  dissolves  the  whole  of  the  bromine, 
from  which  it  receives  a beautiful  hyacinth-red  tint,  and  on  standing  it 
rises  to  tlie  surface.  When  the  ethereal  solution  is  agitated  with  caustic 
potassa,  its  colour  entirely  disappears,  owing  to  the  formation  of  hydro- 
bromate  and  bromate  of  potassa;  and  the  former  salt  is  obtained  in  cu- 
bic crystals  by  evaporation.  The  bromine  may  then  be  set  free  by 
means  of  chlorine,  and  separated  by  heat.*  M.  Balard  has  subse- 
quently improved  the  mode  of  preparation  so  much,  that  it  is  now  pro- 


* According  to  the  authorities  of  Berzelius  and  Thenard,  whose 
treatises  I have  consulted,  the  mode  of  treating  the  cubic  crystals, 
(which  consist  of  bromide  of  potassium,  and  not  hydrobromate  of  po- 
tassa as  stated  by  Dr.  Turner)  in  order  to  extract  the  bromine,  is  to  mix 
them  in  a small  retort,  with  the  peroxide  of  manganese  in  powder,  and 
act  on  the  mixture  with  sulphuric  acid,  diluted  with  half  its  weight  of 
water,  with  the  assistance  of  heat.  The  beak  of  the  retort  must  plunge 
under  cold  water.  As  the  distillation  proceeds,  the  bromine  passes 
over  in  red  vapours,  and  condenses  under  the  water  in  the  form  of 
brown  and  heavy  drops. — Berzelius^  Trade  de  Cldrn.  i.  293. 

It  is  certainly  true  that  chlorine  will  disengage  bromine  from  the  bro- 
mide of  potassium,  as  mentioned  by  Dr.  Turner;  and  it  is  possible  tliat 
>1.  Balard  may  have  recently  modified  his  process  in  this  particular. 
But  supposing  this  to  be  the  case,  it  is  remarkable,  that  neither  Ber- 
zelius nor  Henry,  in  their  treatises,  should  have  alluded  to  the  circum- 
stance, B. 


BROMINE.  229 

duced  in  considerable  quantity,  and  sold  in  Paris  as  an  article  of  com- 
merce. 

According  to  all  the  experiments  hitherto  made,  bromine  appears  to 
be  an  element.  It  is  so  very  similar  in  most  respects  to  chlorine  and 
iodine,  and,  in  the  order  of  its  chemical  relations,  is  so  constantly  in- 
termediate between  them,  that  M.  Balard  at  first  suspected  it  to  be  some 
unknown  compound  of  these  substances.  There  seems,  however,  to 
be  no  good  ground  for  the  supposition;  but,  on  the  contrary,  an  expe- 
riment performed  by  M.  De  la  Rive  affords  a very  strong  argument 
against  it.  He  finds  that  when  a compound  of  bromine  and  iodine  is 
mixed  with  starch,  and  exposed  to  the  influence  of  galvanism,  bromine 
appears  at  the  positive  and  iodine  at  the  negative  wire,  where  the 
starch  acquires  a blue  tint.  On  making  the  experiment  with  bromine 
containing  a little  bromide  of  iodine,  the  same  appearance  ensues;  but 
if  iodine  is  not  previously  added,  the  starch  does  not  receive  a tint  of 
blue. 

Bromine  is  in  most  cases  easily  detected  by  means  of  chlorine;  for 
this  substance  displaces  bromine  from  its  combination  with  hydrogen, 
metals,  and  most  other  bodies.  The  appearance  of  its  vapour  or 
the  colour  of  its  solution  in  ether  will  then  render  its  presence  ob- 
vious. 

The  combining  proportion  of  bromine,  according  to  the  composition 
of  bromide  of  silver,  as  determined  by  Berzelius,  is  78.26. 

Bromine,  like  chlorine,  forms  a crystalline  hydrate  when  exposed  to 
32?  F.  in  contact  with  water.  The  crystals  are  octohedral,  of  a beauti- 
ful red  tint,  and  suffer  decomposition  at  54^.  (Lowig.) 

Hydrobromic  Acid  Gas, 

No  chemical  action  takes  place  between  the  vapour  of  bromine  and 
hydrogen  gas  at  common  temperatures,  not  even  by  the  agency  of  the 
direct  solar  rays;  but  on  introducing  a lighted  candle,  or  a piece  of 
red-hot  iron,  into  the  mixture,  combination  ensues  in  the  vicinity  of  the 
heated  body,  though  without  extending  to  the  whole  mixture,  and  with- 
out explosion.  The  combination  is  readily  effected  by  the  action  of 
bromine  on  some  of  the  gaseous  compounds  of  hydrogen.  Thus  on 
mixing  the  vapour  of  bromine  with  hydriodic  acid,  sulphuretted  hydro- 
gen, or  phosphuretted  hydrogen  gas,  decomposition  ensues,  and  hydro- 
bromic acid  gas  is  generated.  It  may  be  conveniently  made  for  experi- 
mental purposes  by  a process  similar  to  that  for  forming  hydriodic 
acid.  A mixture  of  bromine  and  phosphorus,  slightly  moistened, 
yields,  by  the  aid  of  a gentle  heat,  a large  quantity  of  pure  hydrobro- 
mic acid  gas,  which  should  be  collected  either  in  dry  glass  bottles,  or 
over  mercury. 

Hydrobromic  acid  gas  is  colourless,  has  an  acid  taste,  and  pungent 
odour.  It  irritates  the  glottis  powerfully  so  as  to  excite  cough,  and, 
when  mixed  with  moist  air,  yields  white  vapours,  which  are  denser  than 
those  occasioned  under  the  same  circumstances  by  muriatic  acid  gas.  It 
undergoes  no  decomposition  when  transmitted  through  a red-hot  tube 
either  alone,  or  mixed  with  oxygen.  It  is  not  affected  by  iodine;  but 
chlorine  decomposes  it  instantly,  with  production  of  muriatic  acid  gas, 
and  deposition  of  bromine.  It  may  be  preserved  without  change  over 
mercury;  but  potassium  and  tin  decompose  it  with  facility,  the  former 
at  common  temperatures,  and  the  latter  by  the  aid  of  heat. 

Hydrobromic  acid  gas  is  very  soluble  in  water.  The  aqueous  solution 
may  be  made  by  treating  bromine  with  sulphuretted  hydrogen  dissolved 
in  water,  or  still  better,  by  transmitting  a current  of  hydrobromic  acid 
gas  through  pure  water.  The  liquid  becomes  hot  during  the  conden- 

20 


230 


BROMINE- 


sation,  acquires  great  density,  increases  in  volume,  and  emits  whItt 
fumes  when  exposed  to  the  air.  This  acid  solution  is  colourless  when 
pure,  but  possesses  the  property  of  dissolving  a large  quantity  of  bro- 
mine, and  then  receives  the  tint  of  that  substance. 

Chlorine  decomposes  the  solution  of  hydrobromic  acid  in  an  instant* 
Nitric  acid  likewise  acts  upon  it,  though  less  suddenly,  occasioning  the 
disengagement  of  bromine,  and  probably  the  formation  of  water  and 
nitrous  acid.  Nitro-hydrobromic  acid  is  analogous  to  aqua  and 

possesses  the  property  of  dissolving  gold. 

The  elements  of  sulphuric  and  hydrobromic  acids  react  on  each  other 
in  a slight  degree;  and  hence,  on  decomposing  hydrobromate  of  potassa 
by  sulphuric  acid,  the  hydrobromic  is  generally  mixed  with  a httle  sul- 
phurous acid  gas. 

Metallic  oxides,  as  might  be  expected,  do  not  act  in  a uniform  man- 
ner  on  hydrobromic  acid.  The  alkalies,  earths,  oxides  of  iron,  and 
peroxide  of  copper  and  mercury,  form  compounds  which  may  be  re- 
garded as  hydrobromates;  whereas  oxide  of  silver  and  protoxide  of  lead 
give  rise  to  double  decomposition,  in  consequence  of  which  water  and 
a metallic  bromide  result. 

The  composition  of  hydrobromic  acid  gas  is  easily  inferred  from  the 
two  following  facts.  1.  On  decomposing  hydrobromic  acid  gas  by  po- 
tassium, a quantity  of  hydrogen  remains,  precisely  equal  to  half  the 
volume  of  the  gas  employed;  and,  2.  when  hydriodic  acid  gas  is  de- 
composed by  bromine,  the  resulting  hydrobromic  acid  occupies  the 
very  same  space  as  the  gas  which  is  decomposed.  It  is  hence  apparent 
that  hydrobromic  is  analogous  to  hydriodic  and  muriatic  acid  gases^ 
or,  in  other  words,  that  100  measures  of  hydrobromic  acid  gas  contain 
50  measures  of  the  vapour  of  bromine,  and  5p  of  hydrogen.  By 
weight  it  may  be  regarded  as  a compound  of  one  proportional  of  each 
element. 

Since  bromine  decomposes  hydriodic,  and  chlorine  hydrobromic  acid, 
it  is  obvious  that  bromine,  in  relation  to  hydrogen,  is  intermediate  be- 
tween chlorine  and  iodine;  for  it  has  a stronger  affinity  for  hydrogen 
than  iodine,  and  a weaker  than  chlorine.  The  affinity  of  bromine 
and  oxygen  for  hydrogen  appears  nearly  similar;  for  while  oxygen  can- 
not detach  hydrogen  from  bromine,  bromme  does  not  decompose  wa- 
tery vapour. 

The  salts  of  hydrobromic  acid  are  termed  hydrohromates.  Like  the 
free  acid,  they  are  decomposed,  and  the  presence  of  bromine  is  de- 
tected, by  means  of  chlorine.  On  mixing  a soluble  hydrobromate  with 
nitrate  of  lead,  silver,  and  of  protoxide  of  mercury,  white  precipitates 
are  obtained,  which  are  very  similar  in  appearance  to  the  chlorides  of 
those  metals,  but  which  are  metallic  bromides.  On  the  addition  of  chlo- 
rine, the  vapour  of  bromine  is  evolved. 

Bromic  Jlcid. 

The  only  compound  yet  known  of  bromine  and  oxygen  is  that  form- 
ed by  the  action  of  pure  potassa  on  bromine,  when  by  decomposition  of 
water,  and  the  union  of  its  elements  witli  separate  portions  of  bromine, 
bromic  and  hydrobromic  acids  are  generated.  Of  the  bromate  and  hy- 
drobromate of  potassa  thus  produced,  the  former  is  much  less  soluble 
in  water  tl)an  the  latter,  and  by  means  of  this  difference  in  solubility  the 
two  salts  are  easily  separated.  The  bromate  of  the  otlier  alkalies  and 
alkaline  earths  may  be  prei)ared  in  a similar  manner. 

The  bromates  arc  analogous  to  the  chlorates  and  iodates.  Thus  bro- 
mate of  potassa  is  converted  by  heat  into  bromide  of  potassium  witli 
disengagement  of  pure  oxygen  gas,  deflagrates  like  nitre  when  tlrrown 


BROMINE. 


231 


burning-  charcoal,  and  forms  with  sulphur  a mixture  which  detonates 
by  percussion.  The  acid  of  the  bromates  is  decomposed  by  deoxidiz- 
ing-  ag-ents,  such  as  sulphurous  acid  and  sulphuretted  hydrogen,  in  the 
same  manner  as  the  acid  of  the  iodates.  The  bromates  likewise  suffer 
decomposition  from  the  action  of  hydrobromic  and  muriatic  acids. 

Bromate  of  potassa  is  said  not  to  precipitate  the  salts  of  lead,  but  to 
occasion  a white  precipitate  with  nitrate  of  silver,  and  a yellowish- 
white  with  protonitrate  of  mercury;  characters  which,  if  true,  serve  as 
a good  test  to  distinguish  bromate  from  iodate  and  chlorate  of  potassa. 

Bromic  acid  may  be  procured  in  a separate  state  by  decomposing  a 
dilute  solution  of  bromate  of  baryta  with  sulphuric  acid,  so  as  to  preci- 
pate  the  whole  of  the  baryta.  The  resulting  solution  of  bromic  acid 
maybe  concentrated  by  slow  evaporation  until  it  acquires  the  consist- 
ence of  syrup;  but  on  raising  the  temperature,  in  order  to  expel  all  the 
water,  one  part  of  the  acid  is  volatilized,  and  the  other  resolved  into 
oxygen  and  bromine.  A similar  result  took  place  when  the  evaporation 
was  conducted  in  vacuo  w\t\\  sulpliuric  acid;  and  accordingly  all  attempts 
to  procure  anhydrous  bromic  acid  have  hitherto  failed. 

Bromic  acid  has  scarcely  any  odour,  but  its  taste  is  very  acid,  though 
not  at  all  corrosive.  It  reddens  litmus  paper  powerfully  at  first,  and 
soon  after  destroys  its  colour.  It  is  not  affected  by  nitric  or  sulphuric 
acid  except  when  the  latter  is  highly  concentrated,  in  which  case  bro- 
mine is  set  free,  and  effervescence,  probably  owing  to  the  escape  of 
oxygen  gas,  ensues.  From  the  analysis  of  bromate  of  potassa,^  bromic 
acid  is  obviously  similar  in  constitution  to  iodic,  chloric,  and  nitric  acids; 
that  is,  it  consists  of  one  proportional  of  bromine  united  with  five  of 
oxygen. 

Chloride  of  Bromine. — This  compound  maybe  formed  at  common 
temperatures  by  transmitting  a current  of  chlorine  through  bromine, 
and  condensing  the  disengaged  vapours  by  means  of  a freezing  mixture. 
The  resulting  chloride  is  a volatile  fluid  of  a reddish-yellow  colour, 
much  less  intense  than  that  of  bromine;  its  odour  is  penetrating  and 
causes  a discharge  of  tears  from  the  eyes;  and  its  taste  very  disagreea- 
ble. . Its  vapour  is  a deep  yellow,  like  the  oxides  of  chlorine,  and  it 
enables  metals  to  burn  as  in  an  atmosphere  of  chlorine,  doubtless  giving 
rise  to  the  formation  of  metallic  chlorides  and  bromides. 

Chloride  of  bromine  is  soluble  in  water  without  decomposition;  for 
the  solution  possesses  the  colour,  odour,  and  bleaching  properties  of 
the  compound,  and  discharges  the  colour  of  litmus  paper  without  pre- 
viously reddening  it.  By  the  action  of  the  alkalies  it  is  decomposed, 
being  converted,  by  means  of  the  elements  of  water,  into  muriatic  and 
bromic  acids. 

Bromide  of  Iodine. — These  substances  act  readily  on  each  other,  and 
appear  capable  of  uniting  in  two  proportions.  The  protobromide  is  a 
solid,  convertible  by  heat  into  a reddish-brown  vapour,  which,  in  cool- 
ing, condenses  into  crystals  of  tlie  same  colour,  and  of  a^form  resemb- 
ling that  of  fern  leaves.  An  additional  quantity  of  bromine  converts 
these  crystals  into  a fluid,  which  in  appearance  is  like  a strong  solution 
of  iodine  in  hydriodic  acid.  This  compound  dissolves  without  decom- 
position in  water,  but  with  the  alkalies  yields  hydrobromic  and  iodic 
acids. — The  existence  of  two  bromides  of  iodine  can  scarcely  be  regard- 
ed as  satifactorily  established. 

Bromide  of  Sulphur, — On  pouring  bromine  on  sublimed  sulphur, 
combination  ensues,  and  a fluid  of  an  oily  appearance  and  reddish  tint 
is  generated.  In  odour  it  somewhat  resembles  chloride  of  sulphur,  and 
like  that  compound  emits  white  vapours  when  exposed  to  the  air;  but 
its  Qolour  is  deeper.  It  reddens  litmus  paper  fain^^ly  when  dry,  but. 


232 


FLUORINE. 


strongly  when  water  is  added.  Cold  water  acts  slowly  upon  bromida 
of  sulphurj  but  at  a boiling  temperature  the  action  is  so  violent  that  a 
slight  detonation  occurs,  and  three  compounds,  hydrobromic  and  sul- 
phuric acids  and  sulphuretted  hydrogen,  are  formed.  The  formation 
of  these  substances  is  of  course  attributable  to  decomposition  of  water, 
and  die  union  of  its  elements  with  bromine  and  sulphur.  Bromide  of 
sulphur  is  likewise  decomposed  by  chlorine,  which  unites  with  sulphur 
and  displaces  bromine. 

Bromide  of  Phosphorus. — When  bromine  and  phosphorus  are 
brought  into  contact  in  a flask  filled  with  carbonic  acid  gas,  they  act 
suddenly  on  each  other  with  evolution  of  heat  and  light,  and  two  com- 
pounds are  generated;  one  a crystalline  solid,  which  is  sublimed  and 
collects  in  the  upper  part  of  the  flask,  and  the  other  a fluid,  which  re- 
mains at  the  bottom.  The  latter  is  regarded  by  M.  Balard  as  a proto- 
bromide, and  the  former  as  a deutobromide  of  phosphorus. 

The  protobromide  retains  its  liquid  form  even  at  52®  F.  It  is  readily 
converted  into  vapour  by  heat,  and  on  exposure  to  the  air  emits  pene- 
ti’ating  fumes.  It  reddens  litmus  paper  faintly,  an  eflect  which  is  pro- 
bably owing  to  the  presence  of  moisture.  With  water  it  acts  energeti- 
cally and  with  free  disengagement  of  caloric,  hydrobromic  acid  gas 
being  evolved  when  only  a few  drops  of  water  are  employed;  but  if  a 
lai’ge  quantity  is  used,  the  gas  is  dissolved,  and  the  acid  solution  leaves 
by  evaporation  a residuum,  which  burns  slightly  when  dried,  and  is  con- 
verted into  phosphoric  acid. 

The  deutobromide  is  yellow  in  its  solid  state;  but  with  gentle  heat  it 
becomes  a red-coloured  liquid,  which  by  increase  of  temperature  is 
converted  into  vapour  of  the  same  tint.  On  cooling  after  fusion  it  yields 
rhombic  crystals;  but  when  its  vapour  is  condensed*,  the  crystals  are 
acicular.  It  is  decomposed  by  metals,  probably  with  the  formation  of 
metallic  bromides  and  phosphurets.  It  emits  dense  penetrating  fumes 
on  exposure  to  the  air,  and  with  water  gives  rise  to  the  production  of 
hydrobromic  and  phosphoric  acids. 

Chlorine  has  a greater  affinity  for  phosphorus  than  bromine,  and  de- 
composes both  the  bron^ides  with  evolution  of  the  vapour  of  bromine. 
These  compounds  are  not  decomposed  by  iodine;  but  on  the  contrary 
bromine  decomposes  iodide  of  phosphorus. 

Bromide  of  Carbon. — This  compound  is  formed  by  the  action  of 
bromine  on  half  its  weight  of  periodide  of  carbon,  when  bromide  of 
carbon  and  a subbromide  of  iodine  are  formed,  the  latter  of  which  is 
removed  by  a solution  of  caustic  potassa.  At  common  temperatures  it 
is  liquid,  but  crystallizes  at  32®  F.  Its  taste  is  sweet,  and  it  has  a pene- 
trating ethereal  odour.  It  resembles  protochloride  of  carbon  in  many 
respects;  but  is  distinguished  from  it  by  the  vapour  which  it  emits  on 
exposure  to  heat  (Serullas,  in  the  An.  de  Ch.  et  de  Ph.  xxxix.  225.) 


SECTION  XIV. 

FLUORINE. 

Tur  niibstance  to  which  this  name  is  applied  has  not  hitherto  been 
obtained  in  an  insulated  form,  and,  tlicrcfore,  the  properties  which  are 
pecubar  to  it  in  that  state  are  entirely  unknown.  From  the  nature  of 


FLUORINE. 


233 


its  compounds  it  appears  to  belong  to  the  class  of  negative  electrics,  and 
like  oxygen  and  chlorine  to  have  a powerful  affinity  for  hydiogen  and 
metallic  substances.  With  hydrogen  it  constitutes  a peculiar  and  very 
powerful  acid,  the  liydrofluoricy  the  history  of  which  will  occupy  the 
greater  part  of  tliis  section. 

Hydrofluoric  Acid, 

This  acid  was  first  procured  in  its  pure  state  in  the  year  1810  by  MM. 
Gay-Lussac  and  Thenard,  and  described  in  the  second  volume  of  their 
Recherches  Pkysico^chimiques,  tt  is  prepared  by  acting  on  the  mineral 
called  Jliior  spar,  carefully  separated  from  siliceous  earth  and  reduced  to 
fine  powdei’,  with  twice  its  weight  of  concentrated  sulphui’ic  acid.  The 
mixture  is  made  in  a leaden  retort^  and  on  applying  heat,  an  acid  and 
highly  corrosive  vapour  distils  over,  which  must  be  collected  ia  a re- 
ceiver of  the  same  metal  surrounded  with  ice.  As  the  matei'ials  swell 
up  considerably  during  the  process,  owing  to  a quantity  of  vapour 
forcing  its  way  through  a viscid  mass,  the  retort  should  be  capacious. 
At  the  close  of  the  operation  pure  hydrofluoric  acid  is  found  in  the  re- 
ceiver, and  the  retort  contains  dry  sulphate  of  lime.  The  chemical 
changes  are  similar  to  those  which  occur  in  the  decomposition  of  chlo- 
ride of  sodium  by  sulphuric  acid,  as  explained  at  page  209.  Fluor  spar 
consists  of  fluorine  and  calcium,  and  when  acted  on  by  oil  of  vitriol, 
the  water  of  that  acid  is  resolved  into  its  elements;  the  hydrogen  uni- 
ting with  fluorine  generates  hydrofluoric  acid,  and  the  lime,  formed  by 
the  union  of  the  oxygen  of  water  and  calcium,  combines  with  sulphuric 
acid.  If  the  oil  of  vitriol  is  of  sufficient  strength,  all  its  water  is  de- 
composed, and  the  resulting  hydrofluoric  acid  is  anhydrous. 

Hydrofluoric  acid,  at  the  temperature  of  32^^  F.,  is  a colourless  fluid, 
and  remains  in  that  state  at  59®  if  preserved  in  well  stopped  bottles; 
but  when  exposed  to  the  air,  it  flies  off  in  dense  white  fumes,  which 
consist  of  the  acid  vapour  combined  with  the  moisture  of  the  atmosphere. 
Its  specific  gravity  is  1.0609;  but  its  density  may  be  increased  to  1.25  by 
gradual  additions  of  water.  Its  affinity  for  this  liquid  far  exceeds  that 
of  the  strongest  sulphuric  acid,  and  the  combination  is  accompanied 
with  a hissing  noise,  as  when  red-hot  iron  is  quenched  by  immersion  in 
water. 

The  vapour  of  hydrofluoric  acid  is  much  more  pungent  than  chlorine 
or  any  of  the  irritating  gases.  Of  all  known  substances,  it  is  the  most 
destructive  to  animal  matter.  When  a drop  of  the  concentrated  acid 
of  the  size  of  a pin’s  head  comes  in  contact  with  the  skin,  instantaneous 
disorganization  ensues,  and  deep  ulceration  of  a malignant  character  is 
produced.  On  this  account  the  greatest  care  is  requisite  in  the  prepa- 
ration of  pure  hydrofluoric  acid. 

This  acid  when  concentrated  acts  energetically  on  glass.  The 
transparency  of  the  glass  is  instantly  destroyed,  caloric  is  evolved,  and 
the  acid  boils,  and  in  a short  time  entirely  disappears.  A colourless  gas 
commonly  known  by  the  name  Jluosilicic  acid  gas,  the  sole  product. 
This  compound  is  always  formed  when  hydrofluoric  acid  comes  in  con- 
tact with  a siliceous  substance.  For  this  reason  it  cannot  be  preserved 
in  glass;  but  must  be  prepared  and  kept  in  metallic  vessels.  Those 
of  lead,  from  their  cheapness,  are  often  used;  but  vessels  of  silver  or 
platinum  are  preferable.  In  consequence  of  its  powerful  affinity  for 
siliceous  matter,  hydrofluoric  acid  may  be  employed  for  etching  on 
glass;  and  when  used  with  this  intention,  it  should  be  diluted  with  thrCQ 
or  four  times  its  weight  of  water. 

Hydrofluoric  acid  has  all  the  usual  characters , of  a powerful  acid.  It 
has  a strong  sour  taste,  reddens  litmus  paper,  and  with  alkaline  PUb* 
20* 


234 


FLUOIUNE. 


stances  forms  salts*  wliich  are  termed  hydrojluates.  All  these  salts  art 
decomposed  by  strong  sulphuric  acid  with  the  aid  of  heat,  and  the  hy* 
drofluoric  acid  while  escaping  may  be  detected  by  its  action  on  glass. 

Hydrofluoric  acid  acts  violently  on  some  of  the  metals,  especially  on 
the  bases  of  the  alkalies.  Thus  when  potassium  is  brought  in  con- 
tact with  the  concentrated  acid  an  explosion  attended  with  heat  and 
light  ensues;  hydrogen  gas  is  disengaged,  and  a white  compound,  fluo- 
ride of  potassium,  is  generated.  It  is  a solvent  for  some  elementary 
principles  which  resist  the  action  even  of  nitro-muriatic  acid.  Thus  it 
dissolves  silicium,  zirconium,  and  columbium,  with  evolution  of  hydro- 
gen gas;  and  when  mixed  with  nitric  acid,  it  proves  a solvent  for  sili- 
cium which  has  been  condensed  by  heat,  and  for  titanium.  Nitro-hydro- 
fiuoric  acid,  however,  is  incapable  of  dissolving  gold  and  platinum. 
Several  oxidized  bodies,  wdiich  are  not  attacked  by  sulphuric,  nitric  or 
muriatic  acid,  are  readily  dissolved  by  hydrofluoric  acid.  As  examples 
of  this  fact,  several  of  the  w'eaker  acids,  such  as  silica  or  silicic  acid, 
titanic,  columbic,  molybdic,  and  tungstic  acids  maybe  enumerated. 
(Berzelius.) 

Chemists  are  not  agreed  as  to  the  precise  combining  proportion  of 
fluorine.  According  to  the  experiments  of  Dr,  Thomson,  18  is  the 
true  atomic  weight  of  this  substance;  but  as  Berzelius  has  far  more 
practical  knowledge  of  the  compounds  of  fluorine  than  other 
chemists,  his  result  is  probably  nearer  the  truth.  He  found  that  100 
parts  of  pure  fluoride  of  calcium,  prepared  with  the  greatest  care, 
yielded  with  sulphuric  acid  175  parts  of  sulphate  of  lime.  According 
to  these  numbers,  fluoride  of  calcium  consists  of  20  parts  or  one 
proportional  of  calcium,  and  18.86  parts  or  one  proportional  of  fluorine, 
giving  38.86  as  the  equivalent  of  the  compound;  and  as  the  constitu- 
tion of  hydrofluoric  is  analogous  to  that  of  muriatic  and  hydriodic  acids, 
it  is  composed  of  18.86  parts  of  fluorine  and  1 part  of  hydrogen. 

A different  view  of  the  compounds  of  fluorine  was  originally  taken 
by  Gay-Lussac  and  Thenard,  and  is  still  held  by  some  chemists.  They 
adopted  the  opinion  that  hydrofluoric  acid  is  a compound  of  a certain 
inflammable  principle  and  oxygen,  and  applied  to  it  the  name  of  Jiucyric 
acid,  previously  introduced  by  Scheele.  Fluor  spar  on  this  view  is  a 
fluate  of  lime,  and  when  this  salt  is  decomposed  by  oil  of  vitriol,  the 
fluoric  is  merely  displaced  by  the  sulphuric  acid,  and  the  former  passes 
off  combined  with  the  water  of  the  latter.  What  I have  described  as 
anhydrous  hydrofluoric  acid  is,  according  to  this  hypothesis,  hydrated 
fluoric  acid;  and  when  acted  on  by  potassium,  this  metal  is  oxidized  at 
the  expense  of  the  water,  and  potassa,  thus  generated,  unites  with  fluoric 
acid,  forming,  not  fluoride  of  potassium,  but  fluate  of  potassa.  The 
combining  proportion  of  fluoric  acid,  as  inferred  from  the  analysis  of 
Berzelius,  is  10.86;  for  38.86  parts  or  one  equivalent  of  fluorspar  is 
supposed  to  contain  28  parts  of  lime  (20  calcium  and  8 oxygen,)  thus 
leaving  10.86  as  the  equivalent  of  the  acid. 

The  theory,  according  to  which  fluor  spar  is  a compound  of  fluorine 
and  calcium,  originated  as  a suggestion  with  M.  Ampere  of  Paris,  and 
was  afterwards  supported  experimentally  by  Sir  H.  Davy.  It  was  found 
tliatpure  hydrofluoric  acid  evinces  no  sign  of  containing  either  oxygen 
or  water.  Charcoal  may  be  intensely  heated  in  the  vapour  of  the  acid 
without  the  production  of  carbonic  acid.  When  hydrofluoric  acid  w'as 
neutralized  with  dry  ammoniacal  gas,  a white  salt  resulted,  from 
wliich  no  water  could  be  separated;  and  on  treating  this  salt  with 
potassium,  no  evidence  could  be  obtained  of  the  presence  of  oxygen. 
On  exposing  the  acid  to  the  agency  of  galvanism  there  was  a disen- 
gagement at  the  negative  pole  of  a small  quantity  of  gas,  which 


FLUORINE. 


235 


from  its  combustibility  was  inferred  to  be  hydrog’en;  while  the  pla- 
tinum wire  of  the  opposite  side  of  the  battery  was  rapidly  corroded^ 
and  became  covered  with  a chocolate-coloured  powder.  Sir 
Davy  explained  these  phenomena  by  supposing*  that  hydrofluoric  acid 
was  resolved  into  its  elements;  and  that  fluorine,  at  the  moment  of  ar- 
riving* at  the  positive  side  of  the  battery,  entered  into  combination  with 
tlie  platinum  wire  which  was  employed  as  a conductor.  Unfortunately 
however,  he  did  not  succeed  in  obtaining  fluorine  in  an  insulated  state- 
Indeed,  from  the  noxious  vapours  that  arose  during  the  experiment,  it 
was  impossible  to  watch  its  progress,  and  examine  the  different  pro- 
ducts with  that  precision  which  is  essential  to  the  success  of  minute 
cliemical  inquiries,  and  which  Sir  H.  Davy  has  so  frequently  displayed 
on  other  occasions. 

Though  these  researches  led  to  no  conclusive  result,  they  afforded  so 
strong  a presumption  in  favour  of  the  opinion  of  Ampere  and  Davy, 
tliat  it  was  adopted  by  several  other  chemists.  This  view  has  very  re- 
cently received  strong  additional  support  from  the  experiments  of  M. 
Kuhlman.  (Quarterly  Journal  of  Science  for  July  1827,  p.  205.)  It  was 
found  by  this  chemist  that  fluor  spar  is  not  in  the  slightest  degree  de- 
composed by  the  action  of  anhydrous  sulphuric  acid,  whether  at  com- 
mon temperatures  or  at  a red  heat.  The  experiment  was  made  both  by 
ti’ansmitting  the  vapour  of  anhydrous  sulphuric  acid  over  fluor  spar 
heated  to  redness  in  a tube  of  platinum,  and  by  putting  the  mineral 
into  the  liquid  acid.  In  neither  case  did  decomposition  ensue  ^ but 
when  the  former  experiment  was  repeated  with  the  difference  of  em- 
ploying concentrated  hydrous  instead  of  anhydrous  sulphuric  acid,  evo- 
lution of  hydrofluoric  acid  was  produced.  M.  Kuhlman  also  transmitted 
dry  muriatic  acid  gas  over  fluor  spar  at  a red  heat,  when  hydrofluoric 
acid  \yas  disengaged,  without  any  evolution  of  hydrogen,  and  chloride 
of  calcium  remained.  I am  aware  of  no  satisfactory  explanation  of 
these  facts,  except  by  regarding  fluor  spar  as  a compound  of  fluorine 
and  calcium,  and  hydrofluoric  acid  as  a compound  of  fluorine  and 
hydrogen.  I shall  accordingly  adopt  this  view  in  the  subsequent 
pages,  and  never  employ  the  term  fluoric  acid,  except  when  explaining 
phenomena  according  to  the  theory  of  Gay-Lussac. 

Fluohoric  Jlcid  Gas. 

The  chief  difficulty  in  determining  the  nature  of  hydrofluoric  acid 
arises  from  the  water  of  the  sulphuric  acid  which  is  employed  in  its 
preparation.  To  avoid  this  source  of  uncertainty,  Gay-Lussac  and  The- 
nard  made  a mixture  of  vitrified  boracic  acid  and  fluor  spar,  and  expos- 
ed it  in  a leaden  retort  to  heat,  under  the  expectation  that  as  no  water 
was  present,  anhydrous  fluoric  acid  would  be  obtained.  In  this,  how- 
ever, they  were  disappointed;  but  a new  gas  came  over,  to  which  they 
applied  the  term  of  jfluohoric  acid  gas.  A similar  train  of  reasoning  led 
Sir  H.  Davy  about  the  same  time  to  the  same  discovery;  though  the 
French  chemists  had  the  advantage  of  priority  of  publication.  Fluo- 
boric  acid  gas  may  be  prepared  more  conveniently  by  mixing  one  part 
of  vitrified  boracic  acid,  and  two  of  fluor  spar,  with  twelve  parts  of 
strong  sulphuric  acid,  and  heating  the  mixture  gently  in  a glass  retorL 
(Dr.  John  Davy,  Philos.  Trans,  for  1812. ) When  thus  prepared,  how- 
ever, it  contains  fluosilicic  acid,  according  to  Berzelius,  in  considerable 
quantity;  and  Dr.  Thomson  detected  in  it  traces  of  sulphuric  acid.  The 
gas  may  likewise  be  formed  by  the  action  of  hydrofluoric  acid  on  a so- 
lution of  boracic  acid. 

In  the  decomposition  of  fluor  spar  by  vitrified  boracic  acid,  the  fo> 
mer  and  part  of  the  latter  undergo  an  interchange  of  elements.  The 


FLUORINE. 


^6 

fluorine  uniting*  with  boron  gives  rise  to  fluoboric  acid  gas;  and  by  the 
union  of  calcium  and  oxygen,  lime  is  generated,  which  combines  with 
boracic  acid,  and  is  left  in  the  retort  as  borate  of  lime.  Fluoboric  acid 
gas,  therefore,  is  composed  of  boron  and  fluorine.  Those  who  adopjt 
the  theory  of  Gay-Lussac  give  a different  explanation,  and  regard  this 
gas  as  a compound  of  fluoric  and  boracic  acids.  The  lime  of  fluor  spar 
is  supposed  to  unite  with  one  portion  of  boracic  acid,  and  fluoric  acid 
at  the  moment  of  separation  with  another  portion,  yielding  borate  of 
lime  and  fluoboric  acid  gas. 

Fluoboric  acid  gas  is  colourless,  has  a penetrating  pungent  odour, 
and  extinguishes  flame  on  the  instant.  Its  specific  gravity,  according 
to  Dr.  Thomson,  is  2.3622.  It  reddens  litmus  paper  as  powerfully  as 
sulphuric  acid,  and  forms  salts  with  alkalies  wliich  are  called  Jluohorates, 
It  has  a singularly  great  affinity  for  water.  When  it  is  mixed  with  air 
or  any  gas  wliich  contains  watery  vapour,  a dense  white  cloud  appears, 
which  is  a combination  of  water  and  fluoboric  acid  gas.  From  this  cir- 
cumstance it  affords  an  exceedingly  delicate  test  of  the  presence  of 
moisture  in  gases.  Fluoboric  acid  gas  is  rapidly  absorbed  by  water.  • 
According  to  Dr.  John  Davy,  water  absorbs  700  times  its  volume. 
Caloric  is  evolved  during  the  absorption,  and  the  water  acquires  an  in- 
crease of  volume.  The  saturated  solution  is  limpid,  fuming,  and  very 
caustic.  On  the  application  of  heat,  part  of  the  gas  is  disengaged;  but 
afterwards  the  whole  solution  is  distilled. 

Gay-Lussac  and  Thenard,  and  Dr.  Davy  were  of  opinion  that  fluobo- 
ric acid  gas  is  dissolved  by  water  without  decomposition;  but  Berzelius 
denies  the  accuracy  of  their  observation.  On  transmitting  the  gas  into 
water  until  the  liquid  acquires  a sharply  sour  taste,  but  is  far  from  be- 
ing saturated,  a white  powder  begins  to  subside;  and,  on  cooling,  a 
considerable  quantity  of  boracic  acid  is  deposited  in  crystals.  It  ap- 
pears that  in  a certain  state  of  dilution,  part  of  the  fluoboric  acid  and 
water  mutually  decompose  each  other,  with  formation  of  boracic  and 
hydrofluoric  acids.  The  latter  unites,  according  to  Berzelius,  with  un- 
decomposed fluoboric  acid,  forming  what  he  has  called  horo-hydrojluoric 
acid.  On  concentrating  the  liquid  by  evaporation,  the  boracic  and  hy- 
drofluoric acids  decompose  each  other,  and  the  original  compound  is 
re-produced. 

Fluoboric  acid  gas  does  not  act  on  glass,  but  attacks  animal  and  ve- 
getable matters  with  energy,  converting  them  like  sulphuric  acid  into  a 
carbonaceous  substance.  This  action  is  most  probably  owing  to  its 
affinity  for  water. 

When  potassium  is  heated  in  fluoboric  acid  gas,  the  metal  takes  fire, 
and  a chocolate-coloured  solid,  wholly  devoid  of  metallic  lustre,  is 
formed.  This  substance  is  a mixture  of  fluoride  of  potassium,  and  bo- 
ron, from  which  the  former  is  dissolved  by  water,  and  the  boron  is  left 
in  a solid  state! 

The  composition  of  fluoboric  acid  gas  has  not  hitherto  been  deter- 
mined by  direct  experiment.  Dr.  Davy  ascertained  that  it  unites  with 
an  equal  measure  of  ammoniacal  gas,  forming*  a solid  salt;  and  that  it 
also  coml>incs  with  twice  and  tlirce  times  its  volume  of  ammonia, 
yielding  liquid  compounds.  In  the  former  salt  the  relative  weights  of 
tJie  constituent  gases  arc  in  the  ratio  of  tlieir  specific  gravities;  and  if 
the  compound  consists  of  one  proportional  of  each,  it  will  be  thus  con- 
glituted, 

Fluoboric  acid  gas  . 2.3622  . 68.04  one  proportional, 

Ammoniacal  gas  . 0.5902  , 17  one  proportional 

so  that  the  combining  proportion  of  the  acid  may  be  assumed  in  round 


FLUORINE. 


237 


numbers  to  be  68.*  Now  supposing  this  acid  to  be  formed  of  three 
proportionals  of  fluorine  and  one  of  boron,  its  equivalent  will  be  64.58, 
a number  which  approximates  to  the  preceding.  But  this  view  is  quite 
hypothetical.  Dr.  Thomson  considers  34  as  the  equivalent  of  fluoboric 
acid  gas,  and  believes  it  to  consist  of  one  proportional  of  fluorine  and 
two  of  boron.  His  opinion,  however,  is  very  improbable;  for  the 
formation  of  the  gas  from  a mixture  of  boracic  acid  and  fluor  spar,  ac- 
cording to  this  supposition,  appears  quite  inexplicable.  These  remarks 
will  serve  to  show  that  the  data  for  forming  an  opinion  on  this  subject 
are  uncertain. 


• It  is  more  probable  that  the  first  salt  consists  of  two  proportionals 
of  the  acid  combined  with  one  of  ammonia.  It  is  a well  known  fact, 
that  combining  weights  or  equivalents  of  the  great  majority  of  the  gases, 
whether  simple  or  compound,  occupy  the  same  volume;  while  the  com- 
bining weights  of  a few,  such  as  ammonia,  muriatic  acid,  deutoxide  of 
nitrogen,  have  a volume  double  the  usual  volume.  Now  it  is  most  pro- 
bable that  fluoboric  acid  conforms,  in  its  constitution,  to  the  general 
rule,  and  that,  therefore,  one  proportional  of  it  fills  but  half  the  space 
tliat  is  occupied  by  one  proportional  of  ammonia.  Admitting  this  view, 
a combination  of  equal  volumes  of  these  gases  must  be  a bifluoborate, 
and  the  equivalent  of  fluoboric  acid  will  be  34,02,  or  only  half  as  greai 
as  that  given  by  Dr.  Turner.  B, 


HYDROGEN  AND  NITROGEN. 


OiV  THE  COMPOUNDS  OF  THE  SIMPLE  NONMETJLLIC 
ACIDIFMBLE  COMBUSTIBLES  WITH  EACH  OTHER. 


SECTION  I. 

HYDROGEN  AND  NITROGEN— AMMONIACAL  GAS. 

Spirit  of  liartsliorn  has  been  long  known  to  chemists;  the  existence  of 
ammonia  as  a gas  was  first  noticed  by  Dr.  Priestley,  and  was  described 
by  him  in  his  works  under  the  name  of  alkaline  air.  It  is  sometimes 
called  the  volatile  alkali;  but  the  terms  ammonia  and  ammoniacal  gas  are 
now  more  commonly  employed. 

The  most  convenient  method  of  preparing*  ammoniacal  g’as  for  the 
purposes  of  experiment  is  by  applying*  a g*entle  heat  to  the  concen- 
trated solution  of  ammonia,  contained  in  a glass  vessel.  It  soon  en- 
ters into  ebullition,  and  a large  quantity  of  pure  ammonia  is  disen- 
gaged. 

Ammonia  is  a colourless  gas,  which  has  a strong  pungent  odour,  and 
acts  powerfully  on  the  eyes  and  nose.  It  is  quite  irrespirable  in  its  pure 
form,  but  when  diluted  with  air,  it  may  be  taken  into  the  lungs  with 
safety.  Burning  bodies  are  extinguished  by  it,  nor  is  the  gas  inflamed 
by  their  approach.  Ammonia,  however,  is  inflammable  in  a low  de- 
gree; for  when  a lighted  candle  is  immersed  in  it,  the  flame  is  some- 
what enlarged,  and  tinged  of  a pale  yellow  colour  at  the  moment  of 
being  extinguished;  and  a small  jet  of  the  gas  will  burn  in  an  atmos- 
phere of  oxygen.  A mixture  of  ammoniacal  and  oxygen  gases  deto- 
nates by  the  electric  spark;  water  being  formed,  and  nitrogen  set  free- 
A little  nitric  acid  is  generated  at  the  same  time,  except  when  a 
smaller  quantity  of  oxygen  is  employed  than  is  sufficient  for  combining 
with  all  the  hydrogen  of  the  ammonia.  (Dr.  Henry  in  the  Philos.  Trans- 
fer 1809.) 

Ammoniacal  gas  at  the  temperature  of  50®  F.  and  under  a pressure 
^ual  to  6.5  atmospheres,  becomes  a transparent  colourless  liquid.  It 
is  also  liquefied,  according  to  Guyton-Morveau,  under  the  common 
pressure,  by  a cold  of  70  degrees  below  zero  of  Fahrenheit;  but  there 
is  no  doubt  that  the  liquid  which  he  obtained  was  a solution  of  ammonia 
in  water. 

Ammonia  has  all  the  properties  of  an  alkali  in  a very  marked  manner, 
llius  it  has  an  acrid  taste,  and  gives  a brown  stain  to  turmeric  paper; 
tliough  tlie  yellow  colour  soon  re-appears  on  exposure  to  the  air,  owing 
to  the  volatility  of  the  alkali.  It  combines  also  with  acids,  and  neu- 
tralizes their  properties  completely.  All  these  salts  suff'er  decomposi- 
tion by  being  heated  with  the  fixed  alkalies  or  alkaline  earths,  such  as 
pota.ssa  or  lime,  the  union  of  which  with  the  acid  of  the  salt  causing 
tlie  separation  of  its  ammonia.  None  of  the  ammoniacal  salts  can  sus- 
tain a red  heat  without  being  dissipated  in  vapour  or  decomposed,  a 
character  which  manifestly  arises  from  the  volatile  nature  of  the  alkali. 
If  combined  with  a volatile  acid,  such  as  the  muriatic,  the  compound 
itself  sublimes  unchanged  by  heat;  but  if  it  is  in  combination  with  an 


HYDROGEN  AND  NITROGEN. 

acid,  such  as  the  phosphoric,  which  is  fixed  at  a low  red  heat,  the  aftii- 
monia  alone  is  expelled. 

Hydrogen  and  nitrogen  gases  do  not  unite  directly,  and,  therefore, 
chemists  have  no  synthetic  proof  of  the  constitution  of  ammonia.  Its 
composition,  however,  has  been  determined  analytically  with  great  ex- 
actness. When  a succession  of  electric  sparks  is  passed  through  ammo- 
niacal  gas,  it  is  resolved  into  its  elements;  and  the  same  effect  is  pro- 
duced by  conducting  ammonia  through  porcelain  tubes  heated  to  red- 
ness. The  late  A.  Berthollet  analyzed  ammonia  in  both  ways,  and 
ascertained  that  200  measures  of  that  gas,  on  being  decomposed,  occu- 
py the  space  of  400  measures,  300  of  which  are  hydrogen,  and  100 
nitrogen.  Dr.  Hemy  has  made  an  analysis  of  ammonia  by  means  of 
electricity,  and  his  experiment  proves  beyond  a doubt  that  the  pro- 
portions above  given  are  rigidly  exact.  (Annals  of  Philosophy,  xxiv. 
346.) 

Grains^ 

Now  since  150  cubic  inches  of  hydrogen  weigh  3.177 

and  50  of  nitrogen 14.826 


100  cubic  inches  of  ammonia  must  weigh  18.003; 

and  it  is  composed  by  weight  of 

Hydrogen  . 3.177  . 3 . or  three  proportional®. 

Nitrogen  . 14.826  . 14  . or  one  proportional. 

Its  equivalent,  therefore,  is  17. 

The  specific  gravity  of  ammonia,  according  to  this  calculation,  is 
0.5902,  a number  which  agrees  closely  with  those  ascertained  directly 
by  Sir  H.  Davy  and  Dr.  Thomson. 

Ammoniacal  gas  has  a powerful  affinity  for  water,  and  for  this  reason 
must  always  be  collected  over  mercury.  Owing  to  this  attraction,  a 
piece  of  ice,  when  introduced  into  a jar  full  of  ammonia,  is  instantly 
liquefied,  and  the  gas  disappears  in  the  course  of  a few  seconds.  Sir 
H.  Davy,  in  his  Elements,  stated  that  water  at  50°  F.,  and  when  the 
barometer  stands  at  29.8  inches,  absorbs  670  times  its  volume  of  am- 
monia; and  that  the  solution  has  a specific  gravity  of  0.875.  According 
to  Dr.  Thomson,  water  at  the  common  temperature  and  pressure  takes 
up  780  times  its  bulk.  By  strong  compression,  water  absorbs  the  gas  in 
still  greater  quantity.  Caloric  is  evolved  during  its  absorption;  and  a 
considerable  expansion,  independently  of  the  increased  temperature, 
occurs  at  the  same  time. 

The  concentrated  solution  of  ammonia,  commonly  though  incorrectly 
termed  liquid  ammonia^  is  made  by  transmitting  a current  of  the  gas,  as 
long  as  it  continues  to  be  absorbed,  into  distilled  water,  which  is  kept 
cool  by  .means  of  ice  or  moist  cloths.  The  gas  may  be  prepared  from 
any  salt  of  ammonia  by  the  action  of  any  pure  alkali  or  alkaline  earth; 
but  muriate  of  ammonia  and  lime,  from  economical  considerations,  are 
always  employed.  The  proportions  to  which  I give  the  preference  are 
equal  parts  of  muriate  of  ammonia  and  well- burned  quicklime,  consi- 
derable excess  of  lime  being  taken,  in  order  to  decompose  the  muriate 
more  expeditiously  and  completely.  The  lime  is  slaked  by  the  addition 
of  water;  and  as  soon  as  it  has  fallen  into  powder,  it  should  be  placed 
in  an  earthen  pan  and  be  covered  till  it  is  quite  cold,  in  order  to  protect 
it  from  the  carbonic  acid  of  the  air.  It  is  then  mixed  in  a mortar  with 
the  muriate  of  ammonia,  previously  reduced  to  a fine  powder;  and  the 
mixture  is  put  into  a retort  or  other  convenient  glass  vessel.  Heat  is 
then  applied,  and  the  temperature  gradually  increased  as  long  as  a free 
evolution  of  gas  continues.  The  ammonia  should  be  conducted,  by 


240 


COMPOUNDS  OF  HYDROGEN  AND  CARBON. 


means  of  a safety  tube  of  Welter,  into  a quantity  of  distilled  water 
equal  to  the  weight  of  the  salt  employed.  The  residue  consists  of 
muriate  of  lime,  or  strictly  chloride  of  calcium,  and  lime. 

The  concentrated  solution  of  ammonia,  as  thus  prepared,  is  a clear 
colourless  liquid,  of  specific  gravity  0.936.  It  possesses  the  peculiar 
pungent  odour,  taste,  alkalinity,  and  other  properties  of  the  gas  it- 
self. On  account  of  its  great  volatility  it  should  be  preserved  in  well- 
stopped  bottles,  a measure  which  is  also  required  to  prevent  the  ab- 
sorption of  carbonic  acid.  At  a temperature  of  130^  F.  it  enters  into 
ebullition,  owing  to  the  rapid  escape  of  pure  ammonia;  but  the 
whole  of  the  gas  cannot  be  expelled  by  this  means,  as  at  last  the  solu- 
tion itself  evaporates.  It  freezes  at  about  the  same  temperatiu*e  as 
mercury.  - 

The  following  table,  from  Sir  H.  Davy’s  Elements  of  Chemical  Phi- 
losophy, shows  the  quantity  of  real  ammonia  contained  in  100  parts  of 
solutions  of  different  densities,  at  59®  F.  and  when  the  barometer 
stands  at  30  inches.  The  specific  gravity  of  water  is  supposed  to  be 
10,000:— 


Table  of  the  Quantity  of  real  Ammonia  in  Solutions  of  differ^ 
Densities. 


100  parts  of 
sp.  gravity. 

of  real 
Ammonia, 

100  pai’ls  of 
sp.  gravity. 

of  real 
Ammonia, 

8750 

32.5 

9435 

14.53 

8875 

c 

29.25 

9476 

.c 

13.46 

9000 

*cS 

+-> 

26.00 

9513 

ci 

•4-> 

c 

12.40 

9054 

o 

25.37 

9545 

O 

o 

11.56 

9166 

22.07 

9573 

10.82 

9255 

19.54 

9597 

10.17 

9326 

17.52 

9619 

9.60 

9385 

15.88 

9692 

■ 9.50 

The  presence  of  free  ammoniacal  gas  may  always  be  detected  by  its 
odour,  by  its  temporary  action  on  yellow  turmeric  paper,  and  by  its 
forming  dense  white  fumes  (muriate  of  ammonia),  when  a glass  rod 
moistened  with  muriatic  acid  is  brought  near  it 


SECTION  IL 

COMPOUNDS  OF  HYDROGEN  AND  CARBON. 

CnEMTSTs  have  for  several  years  been  acquainted  with  two  distinct 
compounds  of  carbon  and  hydrogen,  viz.  carburetted  hydrogen  and 
olefiant  gas;  but  the  researclics  of  Mr.  Faraday  have  enriched  the 
science  by  tlic  discovery  of  two  new  substances  of  a similar  nature,  and 
the  same  able  chemist  hasdcmonsU'ated  the  existence  of  others,  though 
he  has  hitherto  been  unable  to  obtain  them  in  an  insulated  form.  Ao 
cording  to  Dr.  Thomson,  naphtha  and  naphthaline  are  likewise  pure 
carburets  of  hydrogen. 


COMPOUNDS  OF  HYDROGEN  AND  CARBON. 


241 


Light  Carhuretted  Hydrogen. 

This  gas  is  sometimes  called  heavy  inflammable  air,  the  inflammalk 
air  of  marshes,  hydrocar  buret,  and  protocarburet  of  hydrogen.  Dr. 
Thomson  proposed  the  term  of  bihydroguret  of  carbon;  but  it  is  more 
generally  known  by  the  name  of  light  carburetted  hydrogen.  It  is  form- 
ed abundantly  in  stagnant  pools  during  the  spontaneous  decomposition 
of  dead  vegetable  matter;  and  it  may  readily  be  procured  by  stirring 
the  mud  at  the  bottom  of  them,  and  collecting  the  gas,  as  it  escapes, 
in  an  inverted  glass  vessel.  In  this  state  it  is  found  to  contain  l-20th  of 
carbonic  acid  gas,  which  may  be  removed  by  means  of  lime-water  or  a 
solution  of  pure  potassa,  and  l-15th  or  l-20th  of  nitrogen.  This  is  the 
only  convenient  method  of  obtaining  it. 

Light  ca.rburetted  hydrogen  is  tasteless  and  nearly  inodorous,  and  it 
does  not  change  the  colour  of  litmus  or  turmeric  paper.  Water,  ac- 
cording to  Dr.  Henry,  absorbs  about  l-60th  of  its  volume.  It  extin- 
guishes all  burning  bodies,  and  is  of  course  unable  to  support  the  res- 
piratioyi  of  animals.  It  is  highly  inflammable;  and  when  a jet  of  it  is 
set  on  fire,  it  burns  with  a yellow  flame,  and  with  a much  stronger  liglit 
than  is  occasioned  by  hydrogen  gas.  With  a due  proportion  of  atmos- 
pheric air  or  oxygen  gas,  it  forms  a mixture  which  detonates  powerfully 
with  the  electric  spark,  or  by  the  contact  of  flame.  The  sole  products 
of  the  explosion  are  water  and  carbonic  acid. 

Mr.  Dalton  first  ascertained  the  real  nature  of  light  carburetted  hy- 
drogen, and  it  has  since  been  particularly  examined  by  Dr.  Thomson, 
Sir  H.  Davy,  and  Dr.  Henry.  When  100  measures  are  detonated  with 
rather  more  than  twice  their  volume  of  oxygen  gas,  the  whole  of  the  in- 
flammable gas  and  precisely  200  measures  of  the  oxygen  disappear,  water 
is  condensed,  and  100  measures  of  carbonic  acid  are  produced.  From 
this  it  may  be  inferred  (page  135),  that  100  cubic  inches  of  light  carbu- 
retted hydrogen  contain  100  cubic  inches  of  the  vapour  of  carbon,  and 
200  cubic  inches  of  hydrogen  gas;  and  that  it  is  composed  by  weight  of 
6 parts  or  one  equivalent  of  carbon,  and  2 parts  or  two  equivalents  of 
‘hydrogen.  Consequently,  8 is  its  equivalent. 

From  the  same  data  it  follows  that  100  cubic  inches  of  light  carburet- 
ted hydrogen,  at  60?  F.,  and  when  the  barometer  stands  at  30  inches, 
must  weigh  16.944  grains;  and  its  specific  gravity  is,  therefore,  0.5555. 
This  calculated  result  is  almost  identical  with  the  specific  gi’avity  of  the 
gas  as  determined  directly  by  Dr.  Henry  and  Dr.  Thomson. 

Light  carburetted  hydrogen  is  not  decomposed  by  electricity,  or  by 
being  passed  through  red-hot  tubes,  unless  the  temperatoe  is  very 
great.  It  may  be  inferred  from  the  experiments  of  Berthollet,  and 
from  the  phenomena  that  attend  the  formation  of  oil  gas  at  high  tem- 
peratures, that  light  carburetted  hydrogen  is  resolved  into  its  elements 
at  least  in  part,  when  the  heat  is  very  intense.  It  follows  from  the 
nature  of  the  gas,  that  for  each  volume  so  decomposed,  two  volumes 
of  hydrogen  must  be  set  free. 

Chlorine  and  light  carburetted  hydrogen  do  not  act  on  each  other  at 
common  temperatures,  when  quite  dry,  even  if  they  are  exposed  to  tlie 
(firect  solar  rays.  If  the  gases  are  moist,  and  the  mixture  is  kept  in  a 
dark  place,  still  no  action  ensues;  but  if  light  be  admitted,  particularly 
sunshine,  decomposition  follows.  The  nature  of  the  product  depencls 
upon  the  proportion  of  the  gases.  If  four  measures  of  chlorine  and 
one  of  light  carburetted  hydrogen  are  present,  carbonic  and  muriatic 
acid  gases  will  be  produced.  For  during  this  action,  tw'o  volumes  of 
chlorine  combine  with  two  volumes  of  hydrogen  contained  in  the  car- 


242  COMPOUNDS  OF  HYDROGEN  AND  CARBON 

buretted  hydrogen,  and  the  other  two  volumes  of  chlorine  decom- 
pose so  much  water  as  will  likewise  give  two  volumes  of  liydrogcn, 

which  forms  muriatic  acid^  while  the  oxygen  of  the  water  unites  with 
tlxe  carbon,  and  converts  it  into  carbonic  acid.  If  tliere  are  tlirce  instead 
of  four  volumes  of  chlorine,  carbonic  oxide  will  be  generated  instead 
of  carbonic  acid,  because  one  half  less  water  will  be  decomposed. 
(Dr.  Henry.)  If  a mixture  of  chlorine  and  light  carburetted  hydrogen 
is  electrified  or  exposed  to  a red  heat,  mm*iatic  acid  is  formed,  and 
charcoal  deposited. 

It  was  first  ascertained  by  Dr.  Henry  (Nicholson’s  Journal,  vol.  xix.) 
and  his  conclusions  have  been  fully  confirmed  by  the  subsequent  re- 
searches of  Sir  H.  Davy,  that  the  fire-damp  of  coal  mines  consists  al- 
most solely  of  light  carburetted  hydrogen.  This  gas  often  issues  in 
large  quantity  from  between  beds  of  coal,  and  by  collecting  in  mines, 
owing  to  deficient  ventilation,  gi’adually  mingles  with  atmospheric  air, 
and  forms  an  explosive  mixture.  The  first  unprotected  light,  which 
then  approaches,  sets  fire  to  the  whole  mass,  and  a dreadful  explosion 
ensues.  These  accidents,  which  were  formerly  so  frequent  and  so 
fatal,  are  now  comparatively  rare,  owing  to  the  employment  of  the 
safety  lamp;  and  I conceive  it  to  be  demonstrable,  on  the  view  that 
light  carburetted  hydrogen  is  tlie  sole  constituent  of  fire-damp,  that 
accidents  of  the  land  cannot  occur  at  all,  provided  the  gauze  lamp  is 
in  a due  state  of  repair,  and  employed  with  the  requisite  precautions* 
Foa*  this  invention  we  are  indebted  to  Sir  H.  Davy;  and  we  must  in 
justice  remember  that  it  is  not,  like  many  discoveries,  the  offspring  of 
diance,  but  the  fmit  of  elaborate  experiment  and  close  induction;  an 
invention  which  originated  solely  with  that  philosopher,  and  which  may 
be  regarded  as  one  of  the  happiest  efforts  of  his  genius.  (Essay  on 
Flame.) 

Sir  H.  Davy  commenced  the  inquiry  by  determining  the  best  propor- 
tion of  air  and  light  carburetted  hydrogen  for  forming  an  explosive 
mixture.  When  the  inflammable  gas  is  mixed  with  three  or  four  times 
its  volume  of  air,  it  does  not  explode  at  all.  It  detonates  feebly  when 
mixed  with  five  or  six  times  its  bulk  of  air,  and  powerfully  when  one  to 
seven  or  one  to  eight  is  the  proportion.  With  fourteen  times  its  volume 
it  still  forms  a mixture  which  is  explosive;  but  if  a larger  quantity  of 
ajr  be  admitted,  a taper  burns  in  it  only  with  an  enlarged  flame. 

The  temperature  which  is  required  for  causing  an  explosion  was  next 
ascertained.  It  was  found  that  the  strongest  explosive  mixture  may 
come  in  contact  with  iron  of  other  solid  bodies  heated  to  redness,  or 
even  to  whiteness,  without  detonating,  provided  they  are  not  in  a state 
of  actual  combustion;  whereas  the  smallest  point  of  flame,  owing  to 
its  higher  temperature,  instantly  causes  an  explosion. 

Tlie  last  important  step  in  the  inquiiT  was  the  observation  that  flame 
cannot  pass  through  a narrow  tube.  This  led  Sir  II.  Davy  to  the  dis- 
covery, thattlie  power  of  tubes  in  preventing  the  transmission  of  flame 
is  not  necessarily  connected  with  any  particular  length;  and  that  a very 
ftliort  one  will  have  the  effect,  provided  its  diameter  is  proportionally 
reduced-  Thus  a piece  of  fine  wire  gauze,  which  may  be  regarded  as 
an  assemblage  of  shoi’t  narrow  tubes,  is  quite  impermeable  to  flame; 
and  consequently  if  a common  oil  lamp  be  completely  surrounded  with 
a cage  of  such  gauze,  it  may  be  introduced  into  an  explosive  atmosphere 
cif  fire-damp  and  air,  without  kindling  the  mixture.  This  simple  con- 
tidvance,  which  is  appropriately  termed  the  safety-lamp,  not  only  pre- 
vents explosion,  but  indicates  the  precise  moment  of  danger.  When 
the  lamp  is  carried  into  an  atmosphci’c  charged  with  fire-damp,  the 
flame  begins  to  enlarge;  and  tlie  mixture,  if  highly  explosive,  takes  (irp 


COMPOUNDS  OF  HYDROGEN  AND  CARBON- 


24fi 


as  soon  as  it  has  passed  tlirough  the  gauze  and  burns  on  its  inner  sur- 
face, while  the  light  in  the  centre  of  the  lamp  is  extinguished.  When- 
ever this  appearance  is  observed,  the  miner  must  instantly  withdraw; 
for  though  the  flame  cannot  communicate  to  the  explosive  mixture  on 
the  outside  of  the  lamp,  as  long  as  the  texture  of  the  gauze  remains 
entire,  yet  the  heat  emitted  during  the  combustion  is  so  great,  that  the 
wire,  if  exposed  to  it  for  a few  minutes,  would  suffer  oxidation,  and 
fall  to  pieces. 

The  peculiar  operation  of  small  tubes  in  obstructing  the  passage  of 
flame  admits  of  a very  simple  explanation.  Flame  is  gaseous  matter 
heated  so  intensely  as  to  be  luminous;  and  Sir  H.  Davy  has  shown  that 
the  temperature  necessary  for  producing  this  effect  is  far  higher  tlmn 
the  white  heat  of  solid  bodies.  Now  when  flame  comes  in  contact  with 
the  sides  of  very  minute  apertures,  as  when  wire  gauze  is  laid  upon  a 
burning  jet  of  coal  gas,  it  is  deprived  of  so  much  caloric  that  its  tem- 
perature instantly  falls  below  the  degree  at  which  gaseous  matter  is 
luminous;  and  consequently,  though  the  gas  itself  passes  freely  through 
the  interstices,  and  is  still  very  hot,  it  is  no  longer  incandescent.  Nor 
does  this  take  place  when  the  wire  is  cold  only;  the  effect  is  equaUy 
certain  at  £lny  degree  of  heat  which  the  flame  can  communicate  to  it. 
For  since  the  gauze  has  a large  extent  of  surface,  and  from  its  metallic 
nature  is  a good  conductor  of  caloric,  it  loses  heat  with  great  rapidity. 
Its  temperature,  therefore,  though  it  may  be  heated  to  whiteness,  is  al- 
ways so  far  below  that  of  flame,  as  to  exert  a cooling  influence  over 
the  burning  gas,  and  reduce  its  heat  below  the  point  at  which  it  is  in- 
candescent 

Olefiant  Gas, 

This  gas  was  discovered  in  1796  by  some  associated  Dutch  chemists, 
who  gave  it  the  name  of  olefiant  gasy  from  its  property  of  forming  an 
dl-like  liquid  with  chlorine.  It  is  sometimes  called  bicarhuretted  or  per- 
carburetted  hydrogen  and  hydroguret  of  carbon;  but  as  none  of  these 
terms  convey  a precise  idea  of  its  nature,  I shall  employ  the  appellation 
proposed  by  its  discoverers. 

Olefiant  gas  is  prepared  by  mixing  in  a capacious  retort  six  measures 
of  strong  alcohol  with  sixteen  of  concentrated  sulphuric  acid,  and  heat- 
ing the  mixture  as  soon  as  it  is  made,  by  means  of  an  Argand  lamp. 
The  acid  soon  acts  upon  the  alcohol,  effervescence  ensues,  and  olefiant 
gas  passes  over.  The  chemical  changes  which  take  place  are  of  a com- 
plicated nature,  and  the  products  numerous.  At  the  commencement 
of  the  process,  the  olefiant  gas  is  mixed  only  with  a little  ether;  but  in 
a short  time  the  solution  becomes  dark,  the  formation  of  ether  declines, 
and  the  odour  of  sulphurous  acid  begins  to  be  perceptible:  towards  the 
close  of  the  operation,  though  olefiant  gas  is  still  the  chief  product, 
sulphurous  acid  is  freely  disengaged,  some  carbonic  acid  is  formed,  and 
charcoal  in  large  quantity  deposited.  The  olefiant  gas  may  be  collected 
either  over  water  or  mercury.  The  greater  part  of  the  ether  condenses 
spontaneously,  and  the  sulphur^«^»  and  carbonic  acids  may  be  separated 
by  washing  the  gas  with  l’»*’^“Water,  or  a solution  of  pure  potassa. 

The  olefiant  ttiis  process  is  derived  solely  from  the  alcohol; 

and  its  proauction  is  owing  to  the  strong  affinity  of  sulphuric  acid  for 
water.  Alcohol  is  composed  of  carbon,  hydrogen,  and  oxygen;  and 
from  the  proportion  of  its  elements  it  is  inferred  to  be  a compound  of 
1,4  parts  or  one  equivalent  of  olefiant  gas,  united  with  9 parts  or  one 
equivalent  of  water.  It  is  only  necessary,  therefore,  in  order  to  obtain 
ojefiant  gas,  to  deprive  alcohol  of  the  water  which  is  essential  to  its 
constitution;  and  this  is  effected  by  sulphuric  acid.  The  formation  of 


244 


COMPOUNDS  OF  HYDROGEN  AND  CARBON. 


ether,  which  occurs  at  the  same  time,  will  be  explained  hereafter. 
The  other  phenomena  are  altog’ether  extraneous.  They  almost  always 
ensue  when  substances  derived  from  the  animal  and  vegetable  kingdoms 
are  subjected  to  the  action  of  sulphuric  acid.  They  occur  chiefly  at 
the  close  of  the  preceding  process,  in  consequence  of  the  excess  of 
acid  which  is  then  present. 

Olefiant  gas  is  a colourless  elastic  fluid,  which  has  no  taste,  and 
scarcely  any  odour  when  pure.  Water  absorbs  about  one-eighth  of  its 
volume.  Like  the  preceding  compound  it  extinguishes  flame,  is  una- 
ble to  support  the  respiration  of  animals,  and  is  set  on  fire  when  a lighted 
candle  is  presented  to  it,  burning  slowly  with  the  emission  of  a dense 
white  light.  With  a proper  quantity  of  oxygen  gas,  it  forms  a mixture 
which  may  be  kindled  by  flame  or  the  electric  spark,  and  which  ex- 
plodes with  great  violence.  To  burn  it  completely,  it  should  be  deto- 
nated with  four  or  five  times  its  volume  of  oxygen.  On  conducting 
this  experiment  with  the  requisite  care.  Dr.  Henry  finds  that  for  each 
measure  of  olefiant  gas,  precisely  three  of  oxygen  disappear,  deposi- 
tion of  water  takes  place,  and  two  measures  of  carbonic  acid  are  pro- 
duced. From  these  data  the  proportion  of  its  constituents  may  easily 
be  deduced  in  the  following  manner.  Two  measures  of  carbonic  acid 
contain  two  measures  of  the  vapour  of  carbon,  which  must  have  been 
present  in  the  olefiant  gas,  and  two  measures  of  oxygen.  Two-thirds 
af  tlie  oxygen  which  disappeared  are  thus  accounted  for;  and  the  other 
third  must  have  combined  with  hydrogen.  But  one  measure  of  oxygen 
requires  for  forming  water  precisely  two  measures  of  hydrogen,  which 
must  likewise  have  been  contained  in  the  olefiant  gas.  It  hence  follows 
that  100  cubic  inches  contain, 

Grains. 

200  cubic  inches  of  the  vapour  of  carbon,  which  weigh  25.418 

200  . - hydrogen  gas,  which  weigh  4.236; 


and  consequently 

100  cubic  inches  of  olefiant  gas  must  weigh  - . 29. 654. 

Its  specific  gi'avity,  accordingly,  is  0.9722:  whereas  its  specific  gravity, 
as  taken  directly  by  Saussure,  is  0.9852;  by  Hemy,  0.967;  and  by 
Tliomson,  0.97. 

Olefiant  gas,  by  weight,  consists  of 

Carbon  . 25.418  12  or  two  proportionals. 

Hydrogen  . 4.236  2 or  two  pi'oportionals; 

and  its  atomic  weight  is  14. 

Olefiant  gas,  when  a succession  of  electric  sparks  is  passed  through 
it,  is  resolved  into  charcoal  and  hydrogen;  and  the  latter  of  course  occu- 
pies twice  as  much  space  as  the  gas  from  which  it  was  derived.  Ole- 
fiant gas  is  decomposed  by  being  passed  through  red-hot  tubes  of 
porcelain.  The  nature  of  the  products  varies  with  the  temperature. 
By  employing  a very  low  degree  of  heat,  it  may  probably  be  converted 
solely  into  carbon  and  light  carbuvotted  hydrogen;  and  in  this  case  no 
inci-ease  of  volume  can  occur,  because  tlitun  two  gases,  for  equal  bulks, 
contain  the  same  quantity  of  hydrogen.  Bui  if  the  temperature  is 
high,  then  a great  increase  of  volume  takes  place;  circumstance 
which  indicates  the  evolution  of  free  hydrogen,  and  consequently  the 
total  decomposition  of  some  of  the  olefiant  gas. 

Chlorine  acts  powerfully  on  olefiant  gas.  When  these  gases  are 
mixed  together  in  the  proportion  of  two  measures  of  the  former  to  one 
of  the  latter,  they  form  a mixture  which  takes  fire  on  the  approach  of 
flame,  and  which  burns  rapidly  with  formation  of  muriatic  acid  gas, 


COMPOUNDS  OP  HYDROGEN  AND  CARBON. 


24$ 


and  deposition  of  a large  quantity  of  charcoal.  But  if  the  gases  are 
allowed  to  remain  at  rest  after  being  mixed  together,  a very  different 
action  ensues.  The  chlorine,  instead  of  decomposing  the  olefiant  gas, 
enters  into  direct  combination  with  it,  and  a yellow  liquid  like  oil  is 
generated.  This  substance  is  sometimes  called  chloric  ether;  but  the 
term  hydrocarhuret  of  chlorine^  as  indicative  of  its  composition,  is  more 
appropriate.  The  name  hydrochloride  of  carbon  has  also  been  applied 
to  it 

Hydrocarhuret  of  chlorine  was  discovered  by  the  Dutch  chemists; 
but  Dr.  Thomson*  first  ascertained  that  it  is  a compound  of  olefiant  gas 
and  chlorine;  and  its  nature  has  since  been  more  fully  elucidated  by 
the  researches  of  MM.  Robiquet  and  Colin. f To  obtain  it  in  a pure 
and  dry  state,  it  should  be  well  washed  with  water,  and  then  distilled 
from  chloride  of  calcium.  Thus  purified,  it  is  a colourless  volatile 
liquid,  of  a peculiar  sweetish  taste  and  ethereal  odour.  Its  specific 
gravity  at  45^  F.  is  1,2201.  It  boils  at  152®  F.  and  may  be  distilled 
without  change.  It  suffers  complete  decomposition  when  its  vapour  is 
passed  through  a red-hot  porcelain  tube,  being  resolved  into  charcoal, 
light  carburetted  hydrogen,  and  muriatic  acid  gas. 

The  composition  of  hydrocarhuret  of  chlorine  is  readily  inferred  from 
the  fact,  that  in  whatever  proportions  olefiant  gas  and  chlorine  may  be 
mixed  together,  they  always  unite  in  equal  volumes.  Consequently 
they  combine  by  weight  according  to  the  ratio  of  their  densities,  so  that 
hydrocarhuret  of  chlorine  consists  of 

Chlorine  . ,2.5  . 36  one  proportional. 

Olefiant  gas  * . 0.9722  14  one  proportional; 


3.4722  $0 

and  its  atomic  weight  is  50,  This  estimate  is  confirmed  by  the  analysis  of 
Robiquet  and  Cohn;  but  a different  view  of  its  composition  has  been 
lately  proposed  by  M.  Morin.  (An.  de  Ch.  et  de  Ph.  xliii.  244.)  He 
contends  that  the  chlorine,  instead  of  uniting  directly  with  olefiant  gas, 
decomposes  a portion  of  it,  and  is  equally  divided  between  its  hydrogen 
and  carbon,  forming  muriatic  acid  and  protochloride  of  carbon;  and 
that  the  latter  unites  with  the  remaining  elements  of  the  olefiant  gas 
which  was  employed.  Hydrocarhuret  of  chlorine  would  hence  consist 
of  one  equivalent  of  chlorine,  four  of  carbon,  and  three  of  hydrogen; 
but  the  experiments  on  which  this  statement  is  founded  require  confir- 
mation. 

Hydrocarhuret  of  chlorine  forms  a veiy  dense  vapour,  its  specific 
gravity,  according  to  Gay-Lussac,  being  3.4434.  This  is  very  near  the 
united  densities  of  chlorine  and  olefiant  gas,  a circumstance  greatly  in 
favour  of  the  general  opinion  concerning  the  constitution  of  the  hydro- 
carburet. 

Dr.  Henry  has  demonstrated  that  light  is  not  essential  to  the  action 
of  cl  Jorine  on  olefiant  gas.  On  this  he  lias  founded  an  ingenious  and 
perfectly  efficacious  method  of  separating  olefiant  gas  from  light  car- 
buretted hydrogen  and  carbonic  oxide  gases,  neither  of  which  is  acted 
on  by  chlox’ine  unless  light  is  present.  (Philos.  Trans,  for  1821.) 

Olefiant  gas  unites  also  with  iodine.  This  compound  was  discovered 
by  Mr.  Faraday  (Philos.  Trans,  for  1821)  by  exposing  olefiant  gas  and 
iodine,  contained  in  the  same  vessel,  to  the  direct  rays  of  the  sun.  Hydro- 


* Memoirs  of  the  Wernerian  Society,  vol.  i. 
f An.  de  Ch.  et  de  Ph.  vol.  i.  and  ii. 

21* 


246 


COMPOUNDS  OF  HYDROGEN  AND  CARBON. 


carburet  of  iodine^  or  hydriodide  of  carbon,  is  a solid  white  crystalline 
body,  which  has  a sweet  taste  and  aromatic  odour.  It  sinks  rapidly  in 
strong  sulphuric  acid.  It  is  fused  by  heat,  and  then  sublimed  without 
ciiange,  condensing  into  crystals,  which  are  either  tabular  or  prismatic. 
On  exposure  to  strong  heat,  it  is  decomposed,  and  iodine  escapes.  It 
buinis,  if  held  in  the  flame  of  a spirit  lamp,  with  evolution  of  iodine  and 
some  hydriodic  acid.  It  is  insoluble  both  in  water  and  in  acid  or  alkaline 
solutions.  Alcohol  and  etlier  dissolve  it,  and  on  evaporating  the  solu- 
tion it  crystallizes. 

Hydrocarburet  of  iodine  is  composed,  according  to  the  analysis  of 
Mr.  Faraday,  of  124  parts  or  one  equivalent  of  iodine,  and  14  parts  or 
one  equivalent  of  olefiant  gas.  (Quarterly  Journal  of  Science,  xiii.) 

Hydroearhuret  of  Bromine. — This  compound  was  formed  by  M.  Se- 
rullas  by  adding  one  part  of  hydrocarburet  of  iodine  to  two  parts  of 
bromine  contained  in  a glass  tube.  Instantaneous  reaction  ensues, 
attended  with  disengagement  of  caloric  and  a hissing  noise,  and  two 
compounds,  the  bromide  of  iodine  and  a liquid  hydrocarburet  of  bro- 
mine, are  generated.  By  means  of  water  the  former  is  dissolved;  while 
the  latter,  coloured  by  bromine,  collects  at  the  bottom  of  the  liquid. 
The  decoloration  is  then  effected  by  means  of  caustic  potassa.  In  order 
that  the  process  should  succeed,  tlie  hydrocarburet  of  iodine  must  not 
be  in  excess. 

Hydrocarburet  of  bromine,  after  being  washed  with  a‘  solution  of 
potassa,  is  colourless,  heavier  than  water,  very  volatile,  of  a penetrating 
ethereal  odour,  and  of  an  exceedingly  sweet  taste,  which  it  communi- 
cates to  water  in  which  it  is  placed,  in  consequence  of  being  slightly 
soluble  in  that  liquid.  It  becomes  solid  at  a temperature  between  21^ 
and  23®  F.  This  compound  is  identical  with  that  w^hich  M.  Balard 
formed  by  letting  a drop  of  bromine  fall  into  a flask  full  of  olefiant  gas. 
(An.  de  Ch.  et  de  Physique,  xxxiv.) 

On  the  new  Carburets  of  Hydrogen  discovered  by  Mr. 
Faraday."^' 

In  the  process  of  compressing  oil  gas  in  Mr.  Gordon’s  apparatus,  du- 
ring w'hich  operation  the  gas  is  subjected  to  a force  equal  to  the  pres- 
sure of  thirty  atmospheres,  a considerable  quantity  of  liquid  collects, 
which  retains  its  fluidity  at  the  common  atmospheric  pressure.  This  li- 
quid, w'hen  recently  received  from  the  vessel,  boils  at  60?  F.  But  as 
soon  as  the  more  volatile  portions  are  dissipated,  which  happens  before 
one-tenth  is  thrown  off,  the  point  of  ebullition  rises  to  IQO®;  and  the 
temperature  gradually  ascends  to  250?  before  all  the  liquid  is  volatilized. 
This  indicated  the  presence  of  several  compounds,  which  differ  in  vo- 
latility; and  Mr.  Faraday  remarked  that  the  boiling  point  was  more  con- 
stant between  176?  and  190®  F.  than  at  any  other  temperature.  He  was 
hence  led  to  search  for  a definite  compound  in  the  fluid  which  came 
(wer  at  that  period;  and  at  length,  by  repeated  distillations,  and  expos- 
ing the  distilled  liquid  to  a temperature  of  zero,  he  succeeded  in  ob- 
taining a suijstance,  to  wliich  he  has  applied  tlie  term  of  hicarhuret  of 
hydrogen. 

Bicarburct  of  liydrogen,  at  common  temperatures,  is  a colourless  trans- 
parent liquid,  which  smells  like  oil  gas,  and  has  also  a slight  odoiu*  of 
almonds.  Its  specific  gravity  is  nearly  0.85  at  60®  F.  At  32®  it  is  con- 
gealed, and  forms  dendritic  ciystals  on  tlie  sides  of  tlie  glass.  At  zero 


* Philos.  Transactions  for  1825,  Part  H.  or  Annals  of  Philosophy, 
xxvii.  44. 


COMPOUNDS  OF  HYDROGEN  AND  CARBON.  247 

it  is  transparent,  brittle,  and  pulverulent,  and  is  nearly  as  hard  as  loaf- 
sugar.  When  exposed  to  the  air  at  the  ordinary  temperature  it  evapo- 
rates, and  boils  at  186^.  The  density  of  its  vapour  at  60?,  and  when 
the  barometer  stands  at  29.98  inches,  is  nearly  2.7760, 

Bicarb uret  of  hydrogen  is  very  slightly  soluble  in  water;  but  it  dis- 
solves freely  in  fixed  and  volatile  oils,  in  ether,  and  in  alcohol,  and  the 
alcohohc  solution  is  precipitated  by  water.  It  is  not  acted  on  by  alka- 
lies. It  is  combustible,  and  burns  with  a bright  flame  and  much  smoke. 
When  admitted  to  oxygen  gas,  so  much  vapour  rises  as  to  make  a pow- 
erfully detonating  mixture.  Potassium  heated  in  it  does  not  lose  its 
lustre.  On  passing  its  vapour  through  a red-hot  tube,  it  gradually 
deposites  charcoal,  and  yields  carburetted  hydrogen  gas.  Chlo- 
rine, by  the  aid  of  sunshine,  decomposes  it  with  evolution  of  muriatic 
acid.  Two  triple  compounds  of  chlorine,  carbon,  and  hydrogen  are 
formed  at  the  same  time,  one  of  which  is  a crystalline  solid,  and  the 
other  a dense  thick  fluid. 

Bicarburet  of  hydrogen  was  analyzed  in  two  ways.  In  the  first,  its 
vapour  was  passed  over  oxide  of  copper  heated  to  redness;  and  in  the 
second,  it  was  detonated  with  oxygen  gas.  Carbonic  acid  and  water 
were  the  sole  products:  and  as  the  absence  of  oxygen  is  established  by 
the  inaction  of  potassium,  it  follows  that  the  bicarburet  consists  of  car- 
bon and  hydrogen  only.  Mr.  Faraday  infers  from  his  analyses,  that  100 
measures  of  the  inflammable  vapour  require  750  of  oxygen  for  com- 
plete combustion;  that  150  measures  of  oxygen  unite  with  300  of  hy- 
drogen; and  that  the  remaining  600  combine  with  600  of  the  vapour  of 
carbon,  forming  600  measures  of  carbonic  acid  gas.  Consequently, 
100  measures  of  the  vapour  are  composed  of 

Carbon  . (0.4166x6)  . 2.4996  . 36  . six  proportionals, 

Hydrogen  . (0.0694x3)  . 0.2082  . 3 . three  proportionals. 

Its  atomic  weight  is,  tlierefore,  39;  and  its  specific  gravity  by  calcula- 
tion, 2.7078. 

The  second  carburet  of  hydrogen  discovered  by  Mr-  Faraday,  to 
which  he  has  not  given  a name,  was  derived  from  the  same  souix;e  as 
the  preceding,  [t  is  obtained  by  heating  with  the  hand  the  condensed 
liquid  from  oil  gas,  and  conducting  the  vapour  which  escapes  through 
tubes  cooled  artificially  to  zero.  A liquid  is  thus  procured,  which  boils 
by  slight  elevation  of  temperature,  and  before  the  thermometer  rises  to 
32°  F.  is  wholly  reconverted  into  vapour. 

This  vapour  is  highly  combustible,  and  burns  with  a brilliant  flame- 
Its  specific  gravity,  at  60°  F.  and  29.94  of  the  barometer,  is  about 
1.9065.  On  being  cooled  to  zero,  it  is  again  condensed,  and  the  speci- 
fic gravity  of  this  liquid  at  54°  is  0.627;*  so  that  among  solids  and  liquids 
it  is  the  lightest  body  known. 

Water  absorbs  the  vapour  sparingly;  but  alcohol  takes  it  up  in  large 
quantity,  and  the  solution  effervesces  on  being  diluted  with  -water.  AJ^ 
kalies  and  muriatic  acid  do  not  affect  it.  Sulphuric  acid,  on  the  contra- 
ry, absorbs  more  than  100  times  its  volume  of  the  vapour.  A dark 
coloured  solution  is  formed,  but  no  sulphurous  acid  is  disengaged. 


* This  statement  seems  to  require  some  explanation;  as  it  is  not  easy 
to  understand  how  the  specific  gravity  of  a liquid,  which  becomes  a 
vapour  under  32°,  could  be  ascertained  at  54°.  The  fact  is  that  it  was 
examined  in  a tube  hermetically  sealed,  and,  therefore,  under  considera- 
ble pressure;  in  consequence  of  which  it  retained  its  liquid  form  at  the 
temperature  above-mentioned.  B. 


248 


COMPOUNDS  OF  HYDROGEN  AND  CARBON. 


From  the  analysis  of  this  vapour,  made  by  detonatinij  it  with  oxyg-en 
gtis,  Mr.  Faraday  infers  that  each  volume  requires  six  of  oxygen  for 
complete  combustion,  and  yields  four  volumes  of  carbonic  acid.  It 
hence  follows  that  100  measures  of  the  vapour  contain  400  measures  of 
tlie  vapour  of  carbon  and  400  of  hydrogen  gas,  and  that  tliis  carburet 
of  hydrogen  consists,  by  weight,  of 

Carbon  , (0.4166x4)  1.6664  , 24  . four  proportionals. 

Hydrogen  . (0.0694x4)  . 0.27^6  . 4 . four  proportionals. 

Its  equivalent  is,  therefore,  28.  Its  specific  gravity  must  be  1.9440; 
and  Mr.  Faraday  regards  this  estimate  of  its  specific  gravity  as  nearer 
the  truth  than  that  above  stated.  The  composition  of  this  substance 
was  calculated  by  Dr.  Thomson  (Principles  of  Chemistry,  vol.  i.  p.  151) 
before  the  compound  itself  had  been  obtained  in  an  insulated  form. 
He  terms  it  quadrocarhuretted  hydrogen^  and  is  of  opinion  that  it  exists 
in  sulphuric  ether,  combined  with  one  equivalent  of  water.  This  view 
is  justified  by  the  proportion  in  which  the  elements  of  ether  are  united. 

The  discovery  of  this  substance  has  established  a fiict  which  is  alto- 
gether new  to  chemists.  The  elements  of  the  new  carburet  are  united 
in  the  proportion  of  24  to  4,  and  those  of  olefiant  gas  in  that  of  12  to  2; 
that  is,  the  carbon  and  hydrogen  in  both  are  in  the  ratio  of  6 to  1,  and 
therefore,  each  may  be  regarded  as  a compound  of  one  atom  of  its  com- 
ponent principles.  Hence  it  appears  that  two  substances  may  be  iden- 
tical with  respect  to  the  proportion  of  their  constituents,  and  yet  be 
quite  distinct  in  their  physical  and  chemical  properties. 

This  peculiarity  is  explicable  on  the  supposition  that  the  ultimate 
atoms  of  such  compounds  are  differently  disposed.  It  is  to  be  presumed 
that  tlie  smallest  possible  particle  of  olefiant  gas  contains  two  atoms  of 
carbon  and  two  atoms  of  hydrogen;  and  that,  in  like  manner,  an  inte- 
grant particle  of  the  new  compound  of  Mr.  Faraday  contains  four  atoms 
of  each  element.  Neither  of  these  substances  could,  I conceive,  be 
formed  by  direct  union  of  a single  atom  of  carbon  and  a single  atom  of 
hydrogen.  If  a combination  of  the  kind  were  to  occur,  a new  compound 
different  from  any  known  at  present,  would  be  the  result.  Such  appears 
to  me  the  only  satisfactory  mode  of  accounting  for  the  phenomena.  A 
similar  instance  has  already  been  noticed  in  the  section  on  phosphorus. 

Naphtha  from  Coal  Tar, 

This  substance  is  obtained  by  the  distiUation  of  coal  tar,  and  is  termed 
naphtha  from  its  similarity  to  mineral  naphtha.  It  has  a strong  and  pecu- 
liar empyreumatic  odour,  and  is  highly  inflammable.  Potassium  may 
be  preserved  in  it  without  losing  its  lustre,  which  is  a sufficient  proof 
that  it  contains  no  oxygen.  According  to  Dr.  Thomson,  one  measure 
of  the  vapour  of  naphtha  contains  six  measures  of  the  vapour  of  carbon, 
and  six  of  hydrogen  gas;  or,  by  weight,  consists  of  36  or  six  propor- 
tionals of  cai’bon,  and  6 or  six  proportionals  of  hydrogen. 

Naphthaline. 

This  compound  is  likewise  derived  from  coal  tar.  If  the  distillation  is 
conducted  at  a very  gentle  heat,  the  naphtha,  from  its  greater  volatility, 
first  passes  over;  and  afterwards  the  naphthaline  rises  in  vapour,  and 
condenses  in  the  neck  of  the  retort  as  a white  crystalline  solid.  (Dr. 
Kid  in  the  Phil.  Trans,  for  1821,  page  216.*) 


* See  also  a paper  by  Mr.  Brande  in  the  Quarterly  Journal  of  Science, 
viii.  289;  and  Annals  of  Pliilosophy,  N,  S.vi.  136. 


COMPOUNDS  OF  HYDROGEN  AND  CARBON. 


249 


Pure  naphthaline  is  heavier  than  water,  has  a pungent  aromatic  taste, 
and  a peculiar,  faintly  aromatic,  odour,  not  unlike  that  of  the  narcissus* 
It  is  smooth  and  unctuous  to  the  touch,  is  perfectly  white,  and  has  a sil- 
very lustre.  It  fuses  at  180°,  and  assumes  a crystalline  texture  in  cool- 
ing*. It  volatilizes  slowly  at  common  temperatures,  and  boils  at  410?  F. 
Its  vapour,  in  condensing*,  crystallizes  with  remarkable  facility  in  tliin 
transparent  laminse. 

Naphthaline  is  not  veiy  readily  inflamed;  but  when  set  on  fire  it 
burns  rapidly,  and  emits  a larg'e  quantity  of  smoke.  It  is  insoluble  in 
cold,  and  very  sparingly  dissolved  by  hot  waters  Its  proper  solvents  are 
alcohol  and  ether,  and  especially  the  latter.'  It  is  likewise  soluble  in 
olive  oil,  oil  of  turpentine,  and  naphtha. 

The  alkalies  do  not  act  upon  naphthaline.  The  acetic  and  oxalic 
acids  dissolve  it,  forming  pink-coloured  solutions.  Sulphuric  acid  en- 
ters into  direct  combination  with  it,  and  forms  a new  and  peculiar  acid, 
which  IMr.  Faraday  has  described  in  the  Philosophical  Transactions  for 
1826,  under  the  name  of  sulplionaphthalic  arAd, 

Naphthaline,  according  to  the  analysis  of  Dr.  Thomson,  is  a sesquU 
carburet  of  hydrogen;  that  is,  a compound  of  9 parts  or  an  equivalent 
and  a half  of  carbon,  and  1 part  or  one  equivalent  of  hydrogen.  It  is 
desirable,  however,  that  this  analysis  should  be  repeated. 

Sulphonaphthalic  acid  is  made  by  melting  naphthaline  with  half  its 
weight  of  strong  sulphuric  acid,  when  a red-coloured  liquid  is  formecl, 
which  becomes  a crystalline  solid  in  cooling.  The  mass  is  soluble  in 
water,  and  the  solution  contains  a mixture  of  sulphuric  and  sulpho- 
naphthalic acids.  On  neutralizing  with  carbonate  of  baryta,  the  insolu- 
ble sulphate  subsides,  while  the  soluble  sulphonaphthalate  remains  in 
solution;  and  on  decomposing  this  salt  by  a quantity  of  sulphuric  acid 
precisely  sufficient  for  precipitating  the  baryta,  pure  sulphonaphthalie 
acid  is  obtained. 

The  aqueous  solution  of  the  acid,  as  thus  formed,  reddens  litmus  pa- 
per powerfully,  and  has  a bitter  acid  taste.  On  concentrating  by  heat, 
the  liquid  at  last  acquires  a brown  tint,  and  if  then  taken  from  the  fire 
becomes  solid  as  it  cools.  If  the  concentration  is  effected  by  means  of 
sulphuric  acid  in  an  exhausted  receiver,  the  acid  becomes  a soft  white 
solid,^  apparently  dry,  and  at  length  hard  and  brittle.  In  this  state  it  is 
chemically  united  with  water,  and  dcli<]^ucooco  on  exposure  to  the  air^ 
but  in  close  vessels  it  undergoes  no  change  during  several  months.  Its 
taste,  besides  being  bitter  and  sour,  leaves  a metallic  flavour  like  that 
of  cupreous  salts.  When  heated  in  a tube  at  temperatures  below  212^^ 
it  is  fused  without  undergoing  any  other  change,  and  crystallizes  from 
centres  in  cooling.  When  more  strongly  heated,  water  is  expelled, 
and  the  acid  appears  to  be  then  anhydrous;  but  at  the  same  time  it  ac- 
quires a red  tint,  and  a minute  trace  of  free  sulphuric  acid  may  be  de- 
tected,— circumstances  which  indicate  commencing  decomposition.  On 
raising  the  temperature  still  higher,  the  red  colour  first  deepens,  then 
passes  into  brown,  and  at  length  the  acid  is  resolved  into  naphthaline, 
sulphurous  acid,  and  charcoal;  but  in  order  thus  to  decompose  all  the 
acid,  a red  heat  is  requisite. 

Sulphonaphthalic  acid  is  readily  soluble  in  water  and  alcohol,  and  is 
also  dissolved  by  oil  of  turpentine  and  olive  oil,  in  proportions  depend- 
ent on  the  quantity  of  water  which  it  contains.  By  the  aid  of  heat  it 
unites  with  naphthaline.  It  combines  with  alkaline  bases,  and  forms 
neutral  salts,  which  are  called  sulphonaphthalates.  All  these  salts  are 
soluble  in  water,  and  most  of  them  in  alcohol,  and  when  exposed  to 
heat  in  the  open  air,  take  fire,  leaving  sulphates  or  sulphurets  accord- 
ing to  circumstances. 


250 


COMPOUNDS  OF  HYDROGEN  AND  CARBON. 


From  Mr.  Faraday’s  analysis  of  the  neutral  sulpbonaphthalate  of 
baryta,  it  appears  that  78  parts  or  one  proportional  of  baryta  are  com- 
bined with  208  parts,  or  what  may  be  regarded  as  one  equivalent,  of 
sulphonaphthalic  acid.  These  208  parts  were  found  to  consist  nearly  of 
80  parts  or  two  equivalents  of  sulphuric  acid,  120  parts  or  twenty  equiv- 
alents of  carbon,  and  8 parts  or  eight  equivalents  of  hydrogen.  It  has 
not  been  demonstrated  that  sulphuric  acid  exists  as  such  in  the  com- 
pound, nor  is  it  known  how  its  elements  are  arranged;  but  from  some 
interesting  facts  noticed  by  Mr.  Hennel,  to  be  mentioned  in  the  section 
on  ether,  it  appears  vefy  probable  that  sulphonaphthalic  acid  is  com- 
posed of  two  proportionals  of  sulphuric  acid  united  with  twenty  equiv- 
alents of  carbon  and  eight  of  hydrogen,  the  two  latter  existing  as  a 
carburet  of  hydrogen. 

On  Coal  and  Oil  Gas. 

The  nature  of  the  inflammable  gases  derived  from  the  destructive 
distillation  of  coal  and  oil  was  first  ascertained  by  Dr.  Henry,*  who 
showed,  in  several  elaborate  and  able  essays,  that  these  gaseous  pro- 
ducts do  not  differ  essentially  from  each  other,  but  consist  of  a few 
well-known  compounds,  mixed  in  different  and  very  variable  propor- 
tions. The  chief  constituents  were  found  to  be  light  carburetted  hy- 
drogen and  olefiant  gases;  but  besides  these  ingredients,  they  contain 
an  inflammable  vapour,  free  hydrogen,  carbonic  acid,  carbonic  oxide, 
and  nitrogen  gases.  The  discoveries  of  Mr.  Faraday  have  elucidated 
the  subject  still  further,  by  proving  that  there  exists  in  oil  gas,  and  by 
inference  in  coal  gas  also,  the  vapour  of  several  definite  compounds  of 
carbon  and  hydrogen,  the  presence  of  which,  for  the  purposes  of  illu^ 
mination,  is  exceedingly  important. 

The  illuminating  power  of  the  ingredients  of  coal  and  oil  gas  is  very 
unequal.  Thus  the  carbonic  oxide  and  carbonic  acid  are  positively 
hurtful;  that  is,  the  other  gases  would  give  more  light  without  them. 
The  nitrogen  of  course  can  be  of  no  service.  The  hydrogen  is  actually 
prejudicial;  because,  though  it  evolves  a large  quantity  of  caloric  in 
burning,  it  emits  an  exceedingly  feeble  light.  The  carburets  of  hydro- 
gen are  the  real  illuminating  agents,  and  the  degree  of  light  emitted  by 
Siese  is  dependent  on  the  quantity  of  carbon  whieh  they  contain.  Thus 
olefiant  gas  illuniinates  much  mure  powerfully  than  light  carburetted 
hydrogen;  and  for  the  same  reason,  the  dense  vapour  of  the  quadro- 
carburet  of  hydrogen  emits  a far  greater  quantity  of  light,  for  equal 
volumes,  than  olefiant  gas. 

From  these  facts,  it  is  obvious  that  the  comparative  illuminating  power 
of  different  kinds  of  coal  and  oil  gas  may  be  estimated,  approximately 
at  least,  by  determining  the  relative  quantities  of  the  denser  carburets 
of  hydrogen  which  enter  into  their  composition.  This  may  be  done  in 
three  ways,  1.  By  their  specific  gravity.  2.  By  the  relative  quantities 
of  oxygen  required  for  their  complete  combustion.  3.  By  the  relative 
quantity  of  gaseous  matter  condensible  by  chlorine  in  the  dark;  for 
chlorine,  when  light  is  excluded,  condenses  all  the  hydrocarburets,  ex- 
cepting liglit  caibiiretted  hydrogen.  Of  these  methods,  tlie  last  is,  I 
coinceive,  tlic  least  exceptionable. f 


• Nicholson’s  Journal  for  1805.  Philosophical  Transactions  for  1808. 
Ibid,  for  1821.  . ^ , 

f For  a discussion  of  this  and  other  questions  relative  to  oil  and  coal 
gas,  tlie  reader  may  consult  an  essay  by  Dr.  Christison  and  myself  in 
the  Edinburgh  Philosophical  Journal  for  1825, 


COMPOUNDS  OF  HYDROGEN  AND  CARBON. 


251 


The  formation  of  coal  and  oil  gas  is  a process  of  considerable  delica- 
cy. Coal  gas  is  prepared  by  heating  coal  to  redness  in  iron  retorts.  The 
quality  of  the  gas,  as  made  at  difterent  places,  or  at  tlie  same  place  at 
different  times,  is  very  variable,  the  specific  gravity  of  some  specimens 
having  been  found  as  low  as  0.443,  and  that  of  others  as  high  as  0.700. 
These  differences  arise  in  part  from  the  nature  of  the  coal,  and  partly 
from  the  mode  in  which  the  process  is  conducted.  The  regulation  of 
the  degree  of  heat  is  the  chief  circumstance  in  the  mode  of  operating, 
by  which  the  quality  of  the  gas  is  affected.  That  the  quality  of  the 
gas  may  be  influenced  from  this  cause  is  obvious  from  the  fact,  that  all 
She  dense  hydrocarburets  are  resolved  by  a strong  red  heat  either  into 
chaixoal  and  light  carburetted  hydrogen,  or  into  charcoal  and  hydrogen 
gas.  Consequently  the  gas  made  at  a very  high  temperature,  though 
its  quantity  may  be  comparatively  great,  has  a low  specific  gravity,  and 
illuminates  feebly.  It  is,  thei-efore,  an  object  of  importance  that 
the  temperature  should  not  be  greater  than  is  required  for  decomposing 
the  coal  effectually,  and  that  the  retorts  be  so  contrived  as  to  prevent 
the  gas  from  passing  over  a reddiot  surface  subsequently  to  its  form- 
ation. 

These  remarks  apply  with  still  greater  force  to  the  manufacture  of 
oil  gas,  because  oil  is  capable  of  yielding  a much  larger  quantity  of  the 
heavy  hydrocarburets  than  coal.  The  quality  of  oil  gas  from  the  same 
material  is  liable  to  such  great  variation  from  the  mode  of  manufacture, 
that  the  density  of  some  specimens  has  been  found  as  low  as  0.464,  and 
that  of  others  as  high  as  1.110.  The  average  specific  gravity  of  good 
oil  gas  is  0.900,  and  it  should  never  be  made  higher.  The  true  interest 
of  the  manufacturer  is  to  form  as  much  olefiant  gas  as  possible,  with 
only  a small  proportion  of  the  heavier  hydrocarburets.  If  the  latter 
predominate,  the  quantity  of  gas  derived  from  a given  weight  of  oil  is 
greatly  diminished;  and  a subsequent  loss  is  experienced  by  the  conden- 
sation of  the  inflammable  vapours  when  the  gas  is  compressed,  or  while 
it  is  circulating  through  the  distributing  tubes. 

Coal  gas,  when  first  prepared,  always  contains  sulphuretted  hydro- 
gen, and  for  this  reason  must  be  purified  before  being  distributed  for 
burning.  The  process  of  purificatiuu  consists  In  passing  the  gas  under 
strong  pressure  through  milk  of  lime,  or  causing  it  to  descend  through 
successive  layers  of  dry  hydrate  of  lime.  This  latter  method,  which  is 
practised  with  great  success  at  Perth  under  the  able  direction  of  Mr. 
Anderson  of  that  city,  has  this  advantage  over  the  former,  that  while  it 
deprives  the  gas  completely  of  sulphuretted  hydrogen,  there  is  no  loss 
from  absorption  of  olefiant  gas  or  the  heavy  hydrocarburets,  as  invaria- 
bly ensues  when  milk  of  lime  is  employed.  But  coal  gas,  after  being 
thus  purified,  still  retains  some  compound  of  sulphur,  most  probably, 
as  Mr.  Brande  conjectures,  sulphuret  of  carbon,  owing  to  the  presence 
of  which  a minute  quantity  of  sulphurous  acid  is  generated  during  its 
combustion.  Oil  gas,  on  the  contrary,  needs  no  purification;  and  as  it 
is  free  from  all  compounds  of  sulphur,  it  does  not  yield  any  sulphurous 
acid  in  burning,  and  is,  thq^efore,  better  fitted  for  lighting  dwelling- 
houses  than  coal-gas. 

With  respect  to  the  relative  economy  of  the  two  gases,  I may  ob- 
serve that  the  illuminating  power  of  oil  gas,  of  specific  gravity  0.900, 
is  about  double  that  of  coal  gas,  of  0.600.  In  coal  districts,  however, 
oil  gas  is  fully  three  times  the  price  of  coal  gas,  and,  therefore,  in 
such  situations,  the  latter  is  considerably  cheaper.  (Essay  above 
quoted. ) 

^ A successful  attempt  has  been  made  by  IMr.  Daniell  to  procure  a gas, 
similar  to  that  from  oil  la  being  free  from  sulphur,  but  made  with 


252  COMPOUNDS  OF  HYDROGEN  AND  SULPHUR. 

cheaper  materials.  The  substance  employed  for  this  purpose  is  a sola- 
tion  of  common  resin  in  oil  of  turpentine.  The  combustible  liquid  is 
made  to  drop  into  red-hot  retorts  in  the  same  manner  as  oil;  and  the  oil 
of  turpentine,  which  from  its  volatility  is  driven  off  in  vapour,  is  col- 
lected, and  again  used  as  a menstruum.  For  this  process  Mr.  Daniell 
has  taken  out  a patent,  and  the  gas  so  prepared  is  employed  by  Mr. 
Gordon  for  filling  his  portable  lamps.  The  gas,  when  properly  made, 
is  said  to  be  of  very  superior  quality,  and  nearly  if  not  quite  equal  to 
oil  gas.  ^ A patent  has  also  been  taken  for  the  formation  of  gas  from  a 
volatile  oil,  prepared  during  the  destructive  distillation  of  resin,  and  a 
manufacture  both  of  the  oil  and  gas  is  established  at  Hammersmith,  near 
Uondon. 


SECTION  III. 

CO>n>OUNDS  OF  HYDROGEN  AND  SULPHUR.— -SULPHURET- 
TED HYDROGEN. 

The  best  method  of  preparing  pure  sulphuretted  hydrogen  is  by 
heating  sulphuret  of  antimony  in  a retort,  or  any  convenient  glass  flask, 
with  four  or  five  times  its  weight  of  strong  muriatic  acid.  An  inter- 
change of  elements  takes  place  between  water  and  the  sulphuret  of 
antimony,  in  consequence  of  which,  sulphuretted  hydrogen  and  pro- 
toxide of  antimony  are  generated.  The  former  escapes  with  efferves- 
cence, while  the  latter  unites  with  muriatic  acid.  The  affinities  which 
determine  these  changes  are  the  attraction  of  hydrogen  for  sulphur,  of 
oxygen  for  antimony,  and  of  muriatic  acid  for  protoxide  of  antimony. 
This  process  may  be  explained  differently.  Instead  of  water,  muriatic 
acid  may  be  supposed  to  undergo  decomposition,  and,  yielding  its  hy- 
drogen to  the  sulphur  and  its  chlorine  to  the  metal,  give  rise  to  sulphu- 
retted hydrogen  and  ehlurlde  of  antimony.  It  is  quite  doubtful  which 
explanation  is  the  true  one,  and  accordingly  some  chemists  adopt  one 
opinion,  and  others  the  other. 

Sulphuretted  hydrogen  is  also  formed  by  the  action  of  sulphuric  or 
muriatic  acid,  diluted  with  three  or  four  parts  of  water,  on  protosulphu- 
ret  of  iron;  and  the  theory  of  the  phenomena  is  similar  to  the  first  of 
the  two  explanations  just  mentioned.  Protosulphuret  of  iron  may  be 
procimed  either  by  igniting  common  iron  pyrites  (deutosulphuret  of 
iron),  by  which  means  one  proportional  of  sulphur  is  expelled;  or  by 
exposing  to  a low  red  heat  a mixture  of  two  parts  of  iron  filings  and 
rather  more  than  one  part  of  sulphur.  The  materials  should  be  placed 
in  a common  eaidhen  or  cast  iron  crucible,  and  be  protected  as  much  as 
possible  from  the  air  during  the  process.  The  protosulphuret  procured 
from  iron  filings  and  sulphur  always  contains  some  uncombined  iron, 
and,  thcrcfoi’c,  the  gas  obtained  from  it  is  never  quite  pure,  being  mix- 
ed with  a little  free  hydrogen.  This,  however,  lor  many  pm’poses,  is 
quite  immaterial. 

Sulphuretted  liydrogcn  is  a colourless  gas,  and  is  distinguished  from 
all  other  gaseous  substances  by  its  offensive  taste  and  odour,  which  is 
similar  to  that  of  putrefying  eggs,  or  the  water  of  sulpbimous  springs. 
Under  a pressure  of  17  atmospheres,  at  50?  F.  it  is  compressed  into  a 
limpid  liquid,  which  resumes  the  gaseous  state  as  soon  as  the  pressure  is 
removed. 


COMPOUNDS  OF  HYDROGEN  AND  SULPHUR. 


253 


Sulphuretted  hydrog*en  is  very  injurious  to  animal  life.  According* 
to  the  experiments  of  Dupuytren  and  Thenard,  the  presence  of 
l-1500th  of  sulphuretted  hydrog*en  in  air  is  instantly  fatal  to  a small 
bird;  l-800tli  killed  a middle-sized  dog*,  and  a horse  died  in  an  atmos- 
phere which  contained  l-250th  of  its  volume. 

Sulphuretted  hydrogen  extinguishes  all  burning  bodies;  but  the  gas 
takes  fire  when  a lighted  candle  is  immersed  in  it,  and  burns  with  a pale 
blue  flame.  Water  and  sulphurous  acid  are  the  products  of  its  combus- 
tion, and  sulphur  is  deposited.  With  oxygen  gas  it  forms  a mixture 
which  detonates  by  the, application  of  flame  or  the  electric  spark.  If 
100  measures  of  sulphuretted  hydrogen  are  exploded  with  150  of  oxy- 
gen, the  former  is  completely  consumed,  the  oxygen  disappears,  water 
is  deposited,  and  100  measures  of  sulphurous  acid  gas  remain.  (Dr. 
Thomson.)  From  the  result  of  this  experiment;  the  composition  of 
sulphuretted  hydrogen  may  be  inferred;  for  it  is  clear,  from  the  com- 
position of  sulphurous  acid,  (page  184,)  that  two-thirds  of  the  oxygen 
must  have  combined  with  sulphur;  and,  therefore,  that  the  remaining 
one-third  contributed  to  the  formation  of  water.  Consequently,  sul- 
phuretted hydrogen  contains  its  own  volume  of  the  vapour  of  sulphur 
and  of  hydrogen  gas;  and  since 

Grains. 

100  cubic  inches  of  the  vapour  of  sulphur  weigh  , 33.888 

100  cubic  inches  of  hydrogen  gas  weigh  . . 2.118 


100  cubic  inches  of  sulphuretted  hydrogen  gas  must  weigh  36.006 
and  its  specific  gravity  is  1.1805. 

The  accuracy  of  this  estimate  is  confirmed  by  several  circumstances. 
Thus,  according  to  Gay-Lussac  and  Thenard,  the  weight  of  100  cubic 
inches  of  sulphuretted  hydrogen  is  36.33  grains;  and  Sir  H.  Davy  and 
Dr.  Thomson  found  it  somewhat  lighter.  When  sulphur  is  heated  in 
hydrogen  gas,  sulphuretted  hydrogen  is  generated  without  any  change 
of  volume.  On  igniting  platinum  wires  in  it  by  means  of  the  voltaic 
apparatus,  sulphur  is  deposited,  and  an  equal  volume  of  pure  hydrogen 
remains.  A similar  effect  is  produced,  though  more  slowly,  by  a suc- 
cession of  electric  sparks.  (Elements  of  Sir  H.  Davy,  p.  282.)  Gay- 
Lussac  and  Thenard  have  given  ample  demonstration  of  the  same  fact. 
Thus  on  heating  tin  in  sulphuretted  hydrogen  gas,  a sulphuret  of  tin  is 
formed;  and  when  potassium  is  heated  in  it,  vivid  combustion  ensues, 
with  formation  of  sulphuret  of  potassium.  In  both  cases,  pure  hydro- 
gen is  left,  which  occupies  precisely  the  same  space  as  the  gas-  from 
which  it  was  derived.  (Recherches  Physico-chimiques,  vol  i.) 

From  the  data  above  stated,  it  follows  that  sulphuretted  hydrogen  is  • 
composed,  by  weight,  of 

Sulphut'  . 33.888  . 16  . one  proportional, 

Hydrogen  . 2.118.  . 1 . one  proportional. 

Sulphuretted  hydrogen  has  decidedly  acid  properties;  for  it  reddens 
litmus  paper,  and  forms  salts  with  alkalies.  It  is  hence  sometimes  called 
hydrosulphuric  acid.  Its  salts  are  termed  Jiydrosidphurets  or  hydrosul- 
phates. All  the  hydrosulphurets  are  decomposed  by  muriatic  or  sulphu- 
ric acid,  and  sulpluiretted  hydrogen  is  disengaged  with  effervescence. 

Recently  boiled  water  absorbs  its  own  volume  of  suphuretted  hydro- 
gen, and  acquires  the  peculiar  taste  and  odour  of  sulphurous  springs. 
The  gas  is  expelled  witliout  change  by  boiling. 

The  elements  of  sulphuretted  hydrogen  may  easily  be  sepamted 
from  one  another.  Thus  on  p,y,tting  a solution  of  sulphuretted  hydro- 

22 


254  COMPOUNDS  OF  HYDROGEN  AND  SULPHUR. 


gen  into  an  open  vessel,  the  oxygen  absorbed  from  the  air  gradually 
unites  with  the  hydrogen  of  the  sulphuretted  hydrogen,  water  is  formed, 
and  sulphur  deposited.  Sulphuretted  hydrogen  and  sulphurous  acid 
mutually  decompose  each  other,  with  formation  of  water  and  deposition 
of  sulphur.  If  a drachm  of  fuming  nitrous  acid  is  poured  into  a bottle 
full  of  sulphuretted  hydrogen  gas,  a bluish-white  flame  passes  rapidly 
through  the  vessel,  sulphur  and  nitrous  acid  fumes  make  their  appear- 
ance, and  of  course  water  is  generated.  Chlorine,  iodine,  and  bromine 
decompose  sulphuretted  hydrogen,  with  separation  of  sulphur,  and  for- 
mation either  of  muriatic,  hydriodic,  or  hydrobromic  acid.  An  atmos- 
phere charged  with  sulphuretted  hydrogen  gas  may  be  purified  by  means 
of  chlorine  in  the  space  of  a few  minutes. 

Sulphuretted  hydrogen,  from  its  affinity  for  metallic  substances,  is  a 
chemical  agent  of  great  importance.  It  tarnishes  gold  and  silver  pow- 
erfully, forming  with  them  metallic  sulphurets.  'VVhite  paint,  owing  to 
the  lead  which  it  contains,  is  blackened  by  it;  and  the  salts  of  nearly 
all  the  common  metals  are  decomposed  by  its  action.  In  most  cases, 
the  hydrogen  of  the  sulphuretted  hydrogen  combines  with  the  oxygen 
of  the  oxide,  and  the  metal  unites  with  the  sulphur. 

Sulphuretted  hydrogen  is  readily  distinguished  from  other  gases  by 
its  odour.  The  most  delicate  chemical  test  of  its  presence  is  carbonate 
of  lead  (white  paint)  mixed  with  water  and  spread  upon  a piece  of 
white  paper.  So  minute  a quantity  of  sulphuretted  hydrogen  may  by 
this  means  be  detected,  that  one  measure  of  the  gas  mixed  with  20,000 
times  its  volume  of  air,  hydrogen,  or  carburetted  hydrogen,  gives  a 
brown  stain  to  the  whitened  surface.  (Dr.  Henry.) 

Bisulphur et ted  Hydrogen. 

Though  Scheele  discovered  this  compound,  it  was  first  particularly 
described  by  Berthollet.  (An.  de  Chimie,  vol.  xxv.)  It  may  be  made 
conveniently  by  boiling  equal  parts  of  recently  slaked  lime  and  flowers 
of  sulphur  with  five  or  six  of  water,  when  a deep  orange-yellow  solu- 
tion is  formed,  which  contains  a hydrosulphuret  of  lime  with  excess  of 
sulphur.  On  pouring  this  liquid  into  strong  muriatic  acid,  copious  de- 
position of  sulphur  takes  place;  and  the  greater  part  of  the  sulphuretted 
hydrogen,  instead  of  escaping  with  effervescence,  is  retained  by  the 
sulphur.  After  some  minutes,  a yellowish  semifluid  matter  like  oil  col- 
lects at  the  bottom  of  the  vessel,  which  is  hisulpJiuretted  hydrogen. 

From  the  facility  with  which  this  substance  resolves  itself  into  sul- 
phur and  sulphuretted  hydrogen,  its  history  is  imperfect,  and  in  some 
respects  obscure.  It  is  viscid  to  the  touch,  and  has  the  peculiar  odour 
and  taste  of  sulphuretted  hydrogen,  though  in  a slighter  degree.  It 
appears  to  possess  the  properties  of  an  acid;  for  it  unites  with  alkalies 
and  the  alkaline  earths,  forming  salts  which  are  termed  sulphuretted  hy- 
drosulphurets.  According  to  Mr.  Dalton,  bisulphuretted  hydrogen  con- 
sists of  one  equivalent  of  hydrogen  and  two  equivalents  of  sulphur; 
and  consequently  its  combining  proportion  is  33.  This  view  of  its  com- 
position is  corroljoratcd  by  Mr.  Herschel’s  analysis  of  the  sulphuretted 
hydrosulphuret  of  lime.  (Edinburgh  Philos.  Journal,  vol.  i.  p.  13.) 

The  salts  of  bisulphuretted  hydrog'cn  may  be  prepared  by  digesting 
sulphur  in  solutions  of  the  alkaline  or  earthy  hydrosulphurets.  They 
are  also  generatcal  when  alkalies  or  alkaline  earths  are  boiled  with  sul- 
phur and  water;  but  in  this  case,  another  salt  is  formed  at  the  same  time. 
Thus,  on  boiling  together  lime  and  sulphur,  as  in  the  preceding  process, 
the  only  mode  i)y  which  sulphuretted  hydrogen  can  be  formed  at  all,  is 
by  decomposition  of  water;  but  since  no  oxygen  escapes  during  the 


HYDROGEN  AND  SELENIUM. 


255 


ebullition,  it  is  manifest  that  the  elements  of  that  liquid  must  have  com- 
bined with  separate  portions  of  sulphur,  and  have  formed  two  distinct 
acids.  One  of  these,  in  all  probability,  is  hyposulphurous  acid;  and 
the  other  is  sulphuretted  hydrog'en. 

The  salts  of  bisulphuretted  hydrogen  absorb  oxygen  from  the  air, 
and  pass  gradually  into  hyposulphites.  A similar  change  is  speedily 
effected  by  the  action  of  sulphurous  acid.  Dilute  muriatic  and  sulphu- 
ric acids  produce  in  them  a deposition  of  sulphur,  and  evolution  of  sul- 
phuretted hydrogen  gas. 


SECTION  IV. 

Hydrogen  and  Selenium, — Hydroselenic  Acid, 

Selenium,  like  sulphur,  forms  a gaseous  compound  with  hydrogen, 
which  has  distinct  acid  properties,  and  is  termed  seleniuretted  hydrogen, 
or  hydroselenic  acid.  This  gas  is  disengaged  when  muriatic  acid  is  added 
to  a concentrated  solution  of  any  hydroseleniate.  It  may  also  be  pro- 
cured by  heating  seleniuret  of  iron  in  muriatic  acid.  By  decomposition 
of  watex’,  oxide  of  iron  and  hydroselenic  acid  are  generated;  and  while 
the  former  unites  with  muiiatic  acid,  the  latter  escapes  in  the  form  of 
gas. 

Hydroselenic  acid  gas  is  colourless.  Its  odour  is  at  fii'st  similar  to  that 
of  sulphuretted  hydrogen;  but  it  afterwards  iiTitates  the  lining  mem- 
brane of  the  nose  powerfully,  excites  catari*hal  symptoms,  and  destroys 
for  some  houi’s  the  sense  of  smelling.  It  is  absoi’bed  freely  by  water, 
forming  a colourless  solution,  which  reddens  litmus  papei',  and  gives  a 
brown  stain  to  the  skin.  The  acid  is  soon  decomposed  by  exposure  to 
the  atmosphei’e;  for  the  oxygen  of  the  air  unites  with  the  hydrogen  of 
the  hydroselenic  acid,  and  selenium,  in  the  form  of  a red  powder,  sub- 
sides. 

All  the  salts  of  the  common  metals  are  decomposed  by  hydroselenic 
acid.  The  hydi’ogen  of  that  acid  combines  with, the  oxygen  of  the 
oxide,  and  a seleniuret  of  the  metal  is  genei^ated. 

Hydroselenic  acid  gas  is  composed,  according  to  the  analysis  of  Ber- 
zelius, of  one  equivalent  of  each  of  its  constituents. 


SECTION  V. 

COMPOUNDS  OF  HYDROGEN  AND  PHOSPHORUS. 

Much  uncertainty  still  pi*evails  concerning  the  nature  of  these  com- 
pounds. Even  their  number  is  doubtful;  though  two  are  generally  ad- 
mitted by  chemists.  Some  of  the  difficulties  have,  however,  been 
lately  removed.  The  observations  of  Dumas,  relative  to  the  constitu- 
tion of  protophosphui’etted  hydi’ogen,  have  been  confirmed  by  M.  Buff; 
and,  therefore,  the  unexpected  statement  of  Rose,  that  this  compound 
contains  more  phosphorus  than  perphosphui^etted  hydrogen,  may  be  in- 


256  COMPOUNDS  OF  HYDROGEN  AND  PHOSPHORUS. 


ferred  to  be  incorrect.  (An.  de  Cli.  et  de  Ph.  xxxi.  113.  et  xli.  220; 
and  Pog'g*cndorfi'’s  Annalen,  viii.  192.) 

ProtophospJmretted  Hydrogen.  T his  gas,  which  was  discovered  in 
1812  by  Sir  H.  Davy,  is  colourless,  and  has  a disagreeable  odour,  some- 
what like  that  of  garlic.  Water  absorbs  about  one-eighth  of  its  vol- 
ume. It  does  not  take  fire  spontaneously,  as  perphosphurettcd  hydro- 
gen does,  when  mixed  with  air  or  oxygen  at  common  temperatures; 
but  the  mixture  detonates  with  the  electric  spark,  or  by  a temperature 
of  300^  F.  Even  diminished  pressure  causes  an  explosion;  an  effect 
which,  in  operating  with  a mercurial  trough,  is  produced  simply  by 
raising  the  tube,  so  that  the  level  of  the  mercury  within  may  be  a few 
inches  higher  than  at  the  outside.  Admitted  into  a vessel  of  chlorine  it 
inflames  instantly,  and  emits  a white  light,  a property  which  it  possesses 
in  common  with  perphosphurettcd  hydrogen.  Its  specific  gravity 
was  found  by  Dumas  to  be  1.214,  and  100  cubic  inches  weigh  37.027 
grains. 

Sir  H.  Davy  prepared  this  gas  by  heating  hydrated  phosphorous  acid 
in  a retort  (page  197);  and  it  is  also  evolved  from  hydrous  hypophospho- 
rous  acid  by  similar  treatment.  It  is  also  formed,  according  to  Dumas, 
by  the  action  of  strong  muriatic  acid  on  phosphuret  of  lime;  and 
likewise  by  the  spontaneous  decomposition  of  perphosphurettcd  hy- 
drogen. 

Dr.  Thomson  states  that  when  sulphur  is  heated  in  100  measures  of 
protophosphuretted  hydrogen,  sulphuret  of  phosphorus  and  200  mea- 
sures of  sulphuretted  hydrogen  are  generated;  and  he  hence  infers  that 
the  former  contains  twice  its  volume  of  hydrogen  gas.  But  this  mode 
of  analysis  is  inaccurate,  since  a considerable  quantity  of  sulphuretted 
hydrogen  is  always  absorbed  by  the  excess  of  sulphur  employed  in  the 
experiment.  Dumas,  who  detected  this  error,  has  also  proved  proto- 
phosphuretted hydrogen  to  contain  once  and  a half  its  volume  of  hydro- 
gen. His  experiments  were  made  by  introducing  into  a tube  contain- 
ing the  gas,  a fragment  of  bichloride  of  mercury  (corrosive  sublimate,) 
and  applying  heat  so  as  to  convert  it  into  vapour.  Mutual  decomposi- 
tion instantly  took  place:  phosphuret  of  mercury  and  muriatic  acid  were 
generated,  and  100  measures  of  gas,  thus  decomposed,  yielded  300 
measures  of  muriatic  acid  gas,  corresponding  to  150  of  hydrogen.  The 
quantity  of  hydrogen  contained  in  any  given  volume  of  protophosphu- 
retted hydrogen  is  thus  given;  and  by  subtracting  the  weight  of  the  for- 
mer from  that  of  the  latter,  the  compound  is  found  to  consist  of  1 part 
of  hydrogen  to  10.65  of  phosphorus.  But  though  this  calculation  is 
founded  on  data  which  appear  to  be  correct,  the  equivalent  of  phos- 
phorus, deducible  from  it,  does  not  correspond  with  that  formerly  stat- 
ed. (Page  194.) 

It  is  affirmed  by  Dr.  Thomson  that  when  protophosphuretted  hydro- 
gen is  detonated  with  1.5  its  volume  of  oxygen  gas,  the  only  products 
are  water  and  phosphorous  acid;  but  when  the  oxygen  is  in  considera- 
ble exce.ss,  two  volumes  disappear  for  one  of  the  compound,  and  water 
and  ])hosphoric  acid  are  generated.  Now  the  hydrogen  contained  in 
one  volume  of  j)rotophosphuretted  hydrogen  is  equal  to  1.5,  and  it 
unites  with  0.75  of  oxygen.  Hence  if  0.75,  or  3-4,  be  deducted  from 
1.5  and  from  2,  the  remainders,  3-4  and  5-4,  represent  the  relative  quan- 
tity of’  oxygen  whicli  is  reejuired  to  convert  the  same  weight  of  phos- 
phorus into  phosphorous  and  phos])h()ric  acid.  These  numbers  are  ob- 
viously in  the  ratio  of  3 to  5,  as  already  stated  on  the  authority  of  Ber- 
zelius. (Ikige  194.)  The  eh  inents  of  the  calculation  have  been  con- 
firmed both  by  Dumas  and  Buff. 

It  frequently  happens  in  the  preparation  of  protophosphuretted  by- 


COMPOUNDS  OF  HYDROGEN  AND  PHOSPHORUS.  257 

drog*en,  especially  when  heat  is  incautiously  applied,  that  it  is  mixed 
with  variable  quantities  of  free  hydrogen,  which  has  been  doubtless 
often  overlooked,  and  thus  the  frequent  cause  of  error.  Dumas  ob- 
viated this  source  of  fallacy  by  agitating  portions  of  the  gas,  which  he 
employed,  with  a cold,  saturated  solution  of  sulphate  of  Copper. 
This  substance  has  the  property  of  absorbing  both  the  compounds 
of  phosphorus  and  hydrogen  entirely,  with  production  of  phosphuret 
of  copper;'  while  the  free  hydrogen  is  left,  and  the  purity  of  the 
gas  ascertained.  Sulphuric  acid  and  chloride  of  lime  act  in  a similar 
manner. 

Perphosphurdted  Hydrogen,  The  gas,  to  which  this  name  is  applied, 
was  discovered  in  the  year  1783  by  M.  Gengembre,  and  has  since  been 
particularly  examined  by  Mr.  Dalton,  Dr.  Thomson,  M.  Dumas,  and 
Professor  H.  Rose.  It  may  be  prepar,ed  in  several  ways.  The  first  me- 
tliod  is  by  heating  phosphorus  in  a strong  solution  of  pure  potassa.  The 
second  consists  in  heating  a mixture  made  of  small  pieces  of  phospho- 
rus and  recently  slaked  lime,  to  which  a quantity  of  water  is  added 
sufficient  to  give  it  the  consistence  of  thick  paste/  The  third  method 
is  by  the  action  of  dilute  muriatic  acid,  aided  by  moderate  heat,  on 
phosphuret  of  lime.  In  these  processes,  three  compounds  of  phospho- 
rus are  generated; — phosphoric  acid,  hypophosphorous  acid,,  and  per- 
phosphuretted  hydrogen — all  of  which  are  produced  by  decomposition 
of  water,  and  the  union  of  its  elements  with  separate  portions  of  phos- 
phorus. The  last  method  appears  to  yield  the  purest  gas. 

The  gas  obtained  by  either  of  these  processes  is  said  by  Mr.  Dalton 
to  be  generally,  and  by  M.  Dumas  to  be  always,  mixed  with  variable 
proportions  of  hydrogen;  but  Rose  denies  that  free  hydrogen  gas  is 
evolved,  except  when  the  heat  is  so  great  as  to  decompose  the  hypo- 
phosphite,  a temperature  wiiich  is  never  attained  so  long  as  the  mate- 
rials are  moist.  It  has  a peculiar  odour,  resembling  that  of  garlic,  and 
a bitter  taste.  Its  specific  gravity  according  to  Dr.  Thomson  is  0.9027, 
according  to  Dalton  1.1  nearly,  and  1.761  according  to  Dumas.  It  does 
not  support  flame  or  respiration. 

Recently  boiled  water,  according  to  Dalton,  absorbs  fully  one-eighth 
of  its  bulk  of  this  gas,  most  of  which  is  again  expelled  by  boiling  or 
agitation  with  other- gases;  but  Dr.  Thomson  states  that  water  takes  up 
only  about  five  per  cent,  of  its  volume.  The  aqueous  solution  does 
not  redden  litmus  paper,  nor  does  the  gas  itself  possess  any  of  the 
properties  of  acids.  The  gas  is  freely  and  completely  absorbed  by  a 
solution  of  sulphate  of  copper  or  chloride  of  lime,  by  which  means  its 
purity  may  be- ascertained,  and  the  presence  of  hydrogen  detected. 

This,  as  well  as  the  other  compound  of  phosphorus  and  hydrogen, 
sometimes  decomposes  metallic  solutions  in  the  same  manner  as  sulphur 
retted  hydrogen,  giving  rise  to  the  formation  of  water  and  a phosphu- 
ret of  the  metal.  But  if  -the  metal  has  a feeble  affinity  for  oxygen,  it 
is  thrown  down  in  the  metallic  state,  and  water  and  phosphoric  acid 
are  generated.  This  is  the  case,  according  to  Rose,  with  solutions  of 
gold  and  silver. 

The  most  remarkable  character  of  this  compound,  by  which  it  is 
distinguished  from  all  other  gases,  is  the  spontaneous  combustion  which 
it  undergoes  when  mixed  with  air  or  oxygen  gas.  If  the  beak  of  the 
retort  from  which  it  issues  is  plunged  under  water,  so  that  successive 
bubbles  of  the  gas  may  arise  through  the  liquid,  a very  beautiful  ap- 
pearance takes  place.  Each  bubble,  on  reaching  the  surface  of  the 
water,  bursts  into  flame,  and  forms  a ring  of  dense  white  smoke,  which 
enlarges  as  it  ascends,  and  retains  its  shape,  if  the  air  is  tranquil,  until 
it  disappears.  The  wreath  is  formed  by  the  products  of  the  combus- 

22* 


258  COMPOUNDS  OF  HYDROGEN  AND  PHOSPHORUS. 


tion — phosphoric  acid  and  water.  If  received  in  a vessel  of  oxygen 
gas,  the  entrance  of  each  bubble  is  instantly  followed  by  a strong  con- 
cussion, and  a flash  of  white  light  of  extreme  intensity.  It  is  remark- 
able that,  whatever  may  be  the  excess  of  oxygen,  traces  of  phosj)ho- 
rus  always  escape  combustion;  but  that  if  the  gas  be  previously  mixed 
with  three  times  its  volume  of  carbonic  acid,  and  be  then  mixed  with 
oxygen,  the  combustion  is  perfect.  Mr.  Dalton  observed  that  it  may  be 
mixed  with  pure  oxygen  in  a tube  of  three-tenths  of  an  inch  in  diame- 
ter without  taking  fire;  but  that  the  mixture  detonates  when  an  electric 
spark  is  transmitted  through  it. 

In  consequence  of  the  combustibility  of  perphosphuretted  hydrogen, 
it  would  be  hazardous  to  mix  it  in  any  quantity  with  air  or  oxygen  gas 
in  close  vessels.  For  the  same  reason  care  is  necessaiy  in  the  formation 
of  this  gas,  lest,  in  mixing  with  the  air  of  the  apparatus,  an  explosion 
ensue,  and  the  vessel  burst.  The  risk  of  such  an  accident  is  avoided, 
when  phosphuret  of  lime  is  used,  by  filling  the  flask  or  retort  entirely 
with  dilute  acid;  and  in  either  of  the  other  processes,  by  causing  the 
phosphuretted  hydrogen  to  be  formed  slowly  at  first,  in  order  that  the 
oxygen  gas  within  the  apparatus  may  be  gradually  consumed.  A very 
simple  method  of  averting  all  danger  has  been  lately  mentioned  to  me 
by  Mr.  Graham.  It  consists  in  moistening  the  interior  of  the  retort 
with  one  or  two  drops  of  ether,  the  vapour  of  which,  when  mixed  with 
atmospheric  air  even  in  small  proportion,  effectually  prevents  the  com- 
bustion of  phosphuretted  hydrogen. 

Perphosphuretted  hydrogen  gas  is  resolved  into  its  elements  by  ex- 
posure to  strong  heat,  or  by  successive  sparks  of  electricity;  and  when 
sulphur  is  volatilized  in  this  gas,  the  phosphuretted  is  converted  into 
sulphuretted  hydrogen.  Dr.  Thomson  states  that  the  pure  hydrogen 
in  the  former  case,  and  in  the  latter  the  sulphuretted  hydrogen,  retain 
precisely  the  same  volume  as  the  gas  from  which  they  were  derived. 
He  hence  infers  that  the  phosphuretted  hydrogen  contains  its  own  vol- 
ume of  hydrogen  gas;  but  this  fact  is  disputed  by  other  chemists,  and 
particularly  by  M.  Dumas,  who  finds  that  100  measures  of  the  former 
contain  150  of  the  latter.  (An.  de  Ch.  et  de  Ph.  xxxi.  153.)  The  quan- 
tity of  oxygen  required  to  effect  the  complete  combustion  of  phosphu- 
retted hydrogen,  tiiat  is,  to  convert  it  into  water  and  phosphoric  acid, 
is  also  uncertain.  Dalton  and  Dumas  agree  in  the  opinion  that  phos- 
phuretted hydrogen  requires  about  twice  its  volume  for  this  purpose; 
while  Dr.  Thomson  states  that  only  one  and  a half  times  its  volume  are 
requisite. 

When  perphosphuretted  hydrogen  is  allowed  to  stand  for  a few  days 
over  water,  it  deposites  part  of  its  phosphorus  without  change  of  vol- 
ume, and  ceases  to  be  spontaneously  combustible  when  mixed  with  at- 
mospheric air.  According  to  Dr.  Thomson,  the  perphosphuretted 
hydrogen  parts  with  l-4th  of  its  phosphorus  under  these  circumstances, 
and  a peculiar  gas,  which  ho  has  called  suhphosphuretted  hydrogen,  is 
generated;  but  M.  Dumas  maintains  that  l-3d  of  the  phosphorus  is  de- 
posited, and  that  the  new  gas  is  identical  with  protophosphuretted  hy- 
drogen. 

Fcrj)hosphuretted  hydrogen,  according  to  Dr.  Thomson,  is  composed 
of  1 part  of  liydrogen  to  12  of  phosphorus;  the  proportion  as  stated  by 
Rose  is  as  1 to  10.52;  and  according  to  Dumas,  it  is  as  1 to  15.9.  Such 
results,  it  is  manifest,  ])rovc  nothing  but  the  uncertainty  of  our  chemi- 
cal knowledge  relative  to  this  subject.  The  cause  of  the  discordance 
is,  indeed,  fully  cxj)lained  by  M.  Ruff,  for  the  gas  is  not  only  always 
mixed  with  more  or  less  free  hydrogen  at  the  moment  of  its  formation, 
but  is  so  extremely  liable  to  spontaneous  decomposition,  even  at  com- 


COMPOUNDS  OF  NITROGEN  AND  CARBON. 


259 


mon  temperatures,  that  the  same  specimen  will  vary  in  its  constitution 
during  the  course  of  an  hour.* 


SECTION  VI. 

COMPOUNDS  OF  NITROGEN  AND  CARBON. 

Bicarburet  of  Nitrogen^  or  Cyanogen  Gas, 

CvATfOGEx  gas,  the  discovery  of  which  was  made  in  1815  by  M.  Gay- 
Lussac,  ( Annales  de  Chimie,  vol.  xcv. ) is  prepared  by  heating  bicyan- 
uret  of  mercury,  carefully  dried,  in  a small  glass  retort,  by  means  of  a 
spirit  lamp.  This  cyanuret  which,  on  the  supposition  of  its  being  a 
compound  of  oxide  of  mercury  and  prussic  acid,  was  formerly  called 
prussiate  of  mercury^  is  in  reality  composed  of  metallic  mercury  and 
cyanogen.  On  exposing  it  to  a low  red  heat,  it  is  resolved  into  its  ele- 
ments. The  cyanogen  passes  over  in  the  form  of  gas,  and  the  metallic 
mercury  is  sublimed.  The  retort,  at  the  close  of  the  process,  contains 
a small  residue  of  charcoal,  derived  from  the  cyanogen  itself,  a portion 
of  which  is  decomposed  by  the  temperature  employed  in  its  formation; 
but  Gay-Lussac  states  that  no  free  nitrogen  is  disengaged  till  towards 
the  close  of  the  process. 

Cyanogen  gas  is  colourless,  and  has  a strong  pungent  and  very  pecu- 
liar odour.  At  the  temperature  of  45?  F.  and  under  a pressure  of  3.6 


* Of  the  different  results  given  in  the  text  in  relation  to  the  composi- 
tion of  the  two  phosphuretted  hydrogens,  those  of  Dumas  are  most 
consistent.  If  we  assume  the  number  of  Berzelius  for  phosphorus  as 
correct,  and  that  one  equivalent  of  hydrogen  and  of  the  vapour  of 
phosphorus  respectively  occupies  the  space  of  one  volume,  it  will  be 
found  that  the  proportions  obtained  by  Dumas,  favour  the  supposition 
that  protophosphuretted  hydrogen  consists  of  2 volumes  of  the  vapour 
of  phosphorus  to  3 volumes  of  hydrogen,  condensed  into  2 volumes; 
or  two  proportionals  of  phosphorus  31.42,  to  three  proportionals  of  hy- 
drogen 3.  Taking  the  same  chemist’s  composition  of  perphosphuretted 
hydrogen,  it  will  consist  of  3 volumes  of  the  vapour  of  phosphorus  to 
3 volumes  of  hydrogen,  condensed  into  2 volumes;  or  three  propor- 
tionals of  phosphorus  47.13,  to  three  proportionals  of  hydrogen  3. 
The  composition  of  the  gases  stated  in  this  manner,  shows  that  they  con- 
tain the  same  quantity  of  hydrogen  in  a given  volume,  and  that  the  differ- 
ence between  tliem  consists  in  the  quantity  of  phosphorus  present.  At 
the  same  time  it  serves  to  make  more  clearly  intelligible,  the  statement 
made  in  the  text  on  the  authority  of  Dumas,  that  perphosphuretted 
hydrogen,  by  depositing  one-third  of  its  phosphorus,  is  converted  into 
protophosphuretted  hydrogen. 

Assuming  Berzelius’s  composition  of  phosphoric  acid,  protophos- 
phuretted hydrogen  would  require  twice  its  volume  of  oxygen  for  com- 
plete combustion,  as  mentioned  by  Dr.  I'urner,  p.  256;  but  the  same 
proportion  of  oxygen  is  obviously  insufficient  for  perpliosphuretted  hy- 
drogen. By  calculation,  this  gas  would  require  for  every  volume,  2 
and  5*8ths  of  a volume.  B. 


260 


COMPOUNDS  OF  NITROGEN  AND  CARBON. 


atmospheres,  it  is  a limpid  liquid,  which  resumes  the  g’aseous  form 
when  the  pressure  is  removed.  It  exting-uishes  burning  bodies;  but  it 
is  inflammable,  and  burns  with  a beautiful  and  characteristic  purple 
flame.  It  can  support  a strong  heat  without  decomposition.  Wa- 
ter, at  the  temperature  of  60®  F.,  absorbs  4.5  times,  and  alcohol  23 
times  its  volume  of  the  gas.  The  aqueous  solution  reddens  litmus  pa- 
per,* but  this  effect  is  not  to  be  ascribed  to  the  gas  itself,  but  to  the 
presence  of  acids  which  are  generated  by  the  mutual  decomposition  of 
cyanogen  and  water.  It  appears  from  a recent  observation  of  Wohler, 
that  two  of  the  products  are  cyanous  acid  and  ammonia;  which,  uniting 
together,  generate  urea.  (An.  de  Ch.  et  de  Ph.  xliii.  73.) 

The  composition  of  cyanogen  may  be  determined  by  mixing  that  gas 
with  a due  proportion  of  oxygen,  and  inflaming  the  mixture  by  elec- 
tricity. Gay-Lussac  ascertained  in  this  way  that  100  measures  of  cyan- 
ogen require  200  of  oxygen  for  complete  combustion,  that  no  water  is 
formed,  and  that  the  products  are  200  measures  of  carbonic  acid  gas 
and  loo  of  nitrogen.  Hence  it  follows  that  cyanogen  contains  its  own 
bulk  of  nitrogen,  and  twice  its  volume  of  the  vapour  of  carbon.  Con- 
sequently, since 

Grains, 

100  cubic  inches  of  nitrogen  gas  weigh  . . . 29.652 

200  the  vapour  of  carbon  weigh  . . 25.418 

100  cubic  inches  of  cyanogen  gas  must  weigh  . , 55.070 

And  it  consists  by  weight  of 

Nitrogen  . 29.652  . 14  . one  equivalent. 

Carbon  . 25.418  . 12  . two  equivalents. 

The  specific  gravity  of  a gas  so  constituted  is  1.8054,  whereas  Gay- 
Lussac  found  it,  by  weighing,  to  be  1.8064. 

Cyanogen,  from  this  view  of  its  composition,  is  a bicarhuret  of  nitro- 
gen; but  for  the  sake  of  convenience  I shall  employ  the  term  cyanogen^ 
proposed  by  its  discoverer.*  All  the  compounds  of  cyanogen,  which 
are  not  acids,  are  called  cyanurets  or  cyanides. 

Cyanogen,  though  a compound  body,  has  a remarkable  tendency  to 
combine  with  elementary  substances.  Thus  it  is  capable  of  uniting 
with  the  simple  non-metallic  bodies,  and  evinces  a strong  attraction  for 
metals.  When  potassium,  for  instance,  is  heated  in  cyanogen  gas, 
such  energetic  action  ensues,  that  the  metal  becomes  incandescent, 
and  cyanuret  of  potassium  is  generated.  The  affinity  of  cyanogen  for 
metallic  oxides,  on  the  contrary,  is  comparatively  feeble.  It  enters 
into  direct  combination  with  a few  alkaline  bases  only,  and  these  com- 
pounds are  by  no  means  permanent.  From  these  remai’ks  it  is  apparent 
that  cyanogen  has  no  claim  to  be  regarded  as  an  acid. 

Hydrocyanic  or  Prussic  Acid. 

Prussic  acid  was  discovered  in  the  year  1782  by  Scheele,  and  Berthol- 
let  afterwards  ascertained  that  it  contains  carbon,  nitrogen,  and  hydro- 
gen; but  Gay-Lussac  first  procured  it  in  a pure  state,  and  by  the  dis- 
covery of  cyanogen  was  enabled  to  determine  its  real  nature.  The 
substance  prepared  by  Scheele  was  merely  a solution  of  prussic  acid  in 
water. 

Pure  hydrocyanic  or  prussic  acid  maybe  prepared  by  heating  bicyan- 


* From  JtJotvo?  blue,  and  ymuu  I generate;  because  it  is  an  essential 
ingredient  of  Prussian  blue. 


COMPOUNDS  OF  NITROGEN  AND  CARBON. 


261 


urct  of  mercury  in  a g'lass  retort  with  two-thirds  of  its  weight  of  con- 
centrated muriatic  acid.  By  an  interchange  of  elements  similar  to  that 
which  was  explained  in  the  first  process  for  fox’ining  sulphuretted  hydro- 
gen (p.  252,)  the  cyanogen  of  the  cyanuret  unites  with  the  hydrogen 
either  of  water  or  muriatic  acid,  forming  hydrocyanic  acid;  while  a 
solution  of  corrosive  sublimate  remains  in  the  retort.  The  vapour  of 
hydrocyanic  acid,  as  it  rises,  is  mixed  with  moisture  and  muriatic  acid. 
It  is  separated  from  the  latter  by  being  conducted  through  a narrow 
tube  over  fragments  of  marble,  with  the  lime  of  which  the  muriatic  acid 
unites.  It  is  next  dried  by  means  of  chloride  of  calcium,  and  is  subse- 
quently collected  in  a tube  surrounded  with  ice  or  snow. 

Vauquelin  proposes  the  following  process  as  affording  a more  abund- 
ant product  than  the  preceding.  It  consists  in  filling  a narrow  tube, 
placed  horizontally,  with  fragments  of  bicyanuret  of  mercury,  and 
causing  a current  of  dry  sulphuretted  hydrogen  gas  to  pass  slowly  along 
it.  The  instant  that  gas  comes  in  contact  with  the  bicyanuret,  double 
decomposition  ensues,  and  hydrocyanic  acid  and  bisulphuret  of  mercu- 
ry are  generated.  The  progress  of  the  sulphuretted  hydrogen  along 
the  tube  may  be  distinctly  traced  by  the  change  of  colour,  and  the  ex- 
periment should  be  closed  as  soon  as  the  whole  of  the  bicyanuret  has 
become  black.  It  then  onl}^  remains  to  expel  the  hydroc5^anic  acid  by 
a gentle  heat,  and  collect  it  in  a cool  receiver.  This  process  is  elegant, 
easy  of  execution,  and  productive. 

Pure  hydrocyanic  acid  is  a limpid  colourless  fluid,  of  a strong  odour, 
similar  to  that  of  peach-blossoms.  It  excites  at  first  a sensation  of  cool- 
ness on  the  tongue,  which  is  soon  followed  by  heat;  but  when  diluted, 
it  has  the  flavour  of  bitter  almonds.  Its  specific  gravity  at  45®  F.  is 
0.7058.  It  is  so  exceedingly  volatile,  that  its  vapour  during  warm 
weather  may  be  collected  over  mercury.  Its  point  of  ebullition  is  79® 
F.,  and  at  zero  it  congeals.  When  a drop  of  it  is  placed  on  a piece  of 
glass,  it  becomes  solid,  because  the  cold  produced  by  the  evaporation 
of  one  portion  is  so  great  as  to  freeze  the  remainder.  It  unites  with 
water  and  alcohol  in  every  proportion. 

Pure  hydrocyanic  acid  is  a powerful  poison,  producing  in  poisonous 
doses  insensibility  and  convulsions,  which  are  speedily  followed  by 
death.  A single  drop  of  it  placed  on  the  tongue  of  a dog  causes  death 
in  the  course  of  a very  few  seconds;  and  small  animals,  when  confined 
in  its  vapour,  are  rapidly  destroyed.  On  inspiring  the  vapour,  diluted 
with  atmospheric  air,  headach  and  giddiness  supervene;  and  for  this 
reason  the  pure  acid  should  not  be  made  in  close  apartments  during 
warm  weather.  The  distilled  water  from  the  leaves  of  the  Prunus 
lauro-cerasus  owes  its  poisonous  quality  to  the  presence  of  this  acid.  Its 
effects  are  best  counteracted  by  diffusible  stimulants,  and  of  such  re- 
medies solution  of  ammonia  appears  to  be  the  most  beneficial.  The 
aqueous  solution  of  chlorine  may  be  used  as  an  antidote,  which  decom- 
poses prussic  acid  instantly,  with  formation  of  muriatic  acid.  In  some 
experiments  recently  described  by  MM.  Persoz  and  Nonat,  symptoms 
of  poisoning,  induced  by  prussic  acid  applied  to  the  globe  of  the  eye, 
ceased  on  the  internal  administration  of  chlorine.  It  would  hence  ap- 
pear, that  both  substances  were  absorbed  into  the  circulating  fluids,  and 
there  reacted  on  each  other.  (An.  de  Ch.  et  de  Ph.  xliii.  324.) 

Pure  hydrocyanic  acid,  even  when  excluded  from  air  and  moisture, 
is  very  liable  to  sponlaiieous  changes,  owing  to  the  tendency  of  its  ele- 
ments to  form  new  combinations.  These  changes  sometimes  commence 
within  an  hour  after  the  acid  is  made,  and  it  can  rarely  be  preserved  for 
more  than  two  weeks.  The  commencement  of  decomposition  is  mark- 
ed by  the  liquid  acquiring  a reddish-brown  ting-e.  The  colour  then 


262 


COMPOUNDS  OF  NITROGEN  AND  CARBON. 


gradually  deepens,  a matter  like  cliarcoal  subsides,  and  ammonia  is  gen- 
erated. On  analyzing  tlie  black  matter,  it  was  found  to  contain  carbon 
and  nitrogen.  I’he  acid  may  be  preserved  for  a longer  period  if  diluted 
with  water,  but  even  then  it  undergoes  gradual  decomposition. 

Hydrocyanic  acid  reddens  litmus  paper  feebly,  and  unites  with  most 
alkaline  bases,  forming  salts  which  are  prussiates  or  hydrocyan- 

ates.  It  is  a weak  acid;  for  it  does  not  decompose  the  carbonates,  and 
no  quantity  of  it  can  destroy  the  alkaline  reaction  of  potassa.  Its  salts 
are  poisonous;  they  are  all  decomposed  by  carbonic  acid,  and  have  the 
odour  of  hydrocyanic  acid,  a character  by  which  the  hydrocyanates  may 
easily  be  recognised.  ^ 

Hydrocyanic  acid  is  resolved  by  galvanism  into  liydrogen  and  cyano- 
gen, the  former  of  which  appears  at  the  negative,  and  tlie  latter  at  the 
positive  pole.  When  its  vapour  is  conducted  through  a red-hot  porce- 
lain tube,  partial  decomposition  ensues.  Charcoal  is  deposited,  and  ni- 
trogen, hydrogen,  and  cyanogen  gases  are  set  atlibei’ty;  but  the  greater 
part  of  the  acid  passes  over  unchanged.  Electricity  produces  a similar 
effect.  The  vapour  of  hydroc3^anic  acid  takes  fire  on  the  approach  of 
flame;  and  with  oxygen  ga^  it  forms  a mixture  which  detonates  with 
the  electric  spark.  The  products  of  the  combustion  are  nitrogen,  wa- 
ter, and  carbonic  acid. 

The  composition  of  hydrocyanic  acid  is  shown  by  the  following  sim- 
ple but  decisive  experiment  of  Gay-Lussac.  If  a quantity  of  potassium 
precisely  sufficient  for  absorbing  50  measures  of  pure  cyanogen  gas,  is 
•heated  in  100  measures  of  hydrocyanic  acid  vapour,  cyanuret  of  potas- 
sium is  generated,  diminution  of  50  measures  takes  place,  and  the  resi- 
due is  pure  hydrogen.  From  this  it  appears,  that  hydrocyanic  acid 
vapour  is  composed  of  equal  volumes  of  cyanogen  and  hydrogen,  united 
without  any  condensation;  and,  consequently,  these  two  gases  combine, 
by  weight,  according  to  the  ratio  of  their  densities.  The  composition  of 
hydrocyanic  acid  may,  therefore,  be  thus  stated; — 

By  volume.  By  weight. 

Cyanogen  50  . 1.8054  26,  one  equivalent, 

Hydrogen  50  . 0.0694  1,  one  equivalent. 

100  acid  vapour. 

The  atomic  weight  of  hydrocyanic  acid  Is  27.  The  specific  gravity  of 
its  vapour  is,  of  course,  intermediate  between  that  of  its  constituents, 
or  0.9374;  as  determined  directly  by  Gay  Lussac  its  density  is  0.9476. 

From  the  powerful  action  of  hydrocyanic  acid  on  the  animal  economy 
tills  substance,  in  a diluted  form,  is  sometimes  employed  in  medical 
practice  to  diminish  pain  and  nervous  irritability.  It  may  be  procured 
of  any  given  strength  by  dissolving  bicyanuret  of  mercury  in  water, 
and  transmitting  a current  of  sulphuretted  hydrogen  gas  through  the 
solution  till  the  whole  of  the  cyanuret  is  decomposed.  The  decompo- 
sition is  known  to  be  complete  by  the  filtered  liquid  remaining  colour- 
less and  transparent  when  mixed  with  a solution  of  sidphiq;etted  hydro- 
gen; for  should  any  undccoinposed  cyanuret  of  mercury  be  present,  a 
Idack  ])rccipitatc,  bisulphurct  of  mcrcuiy,  will  be  formed.  This  test 
of  the  complete  dccomjiosition  of  the  cyanuret  of  mercury  should  ne- 
ver be  neglected.  The  excess  of  sul})huretted  hjnlrogen  is  removed 
by  agitation  with  carbonate  of  lead,  and  the  hydrocyanic  acid  is  then 
separated  from  the  insoluble  matters  by  filtration,  'flie  process  adopted 
at  Apothecaries’  Hall,  London,  is  to  mix  in  a retort  one  part  of  bicy- 
anuret of  mercury,  one  ])art  of  muriatic  acid  of  specific  gravity  1.15, 
and  six  parts  of  water;  and  to  distil  the  mixture  until  a quantity  of  acid 


COMPOUNDS  OP  NITROGEN  AND  CARDON. 


263 


equal  to  that  of  the  water  employed,  is  collected.  The  product  has  a 
density  of  0.995.  (Braude’s  Manual  of  Chemistry.)  In  this  process, 
a little  muriatic  acid  is  apt  to  pass  over  into  the  recipient,  and  render 
the  product  impure.  Its  presence,  in  a medical  point  of  view,  cannot 
be  very  material;  but  it  may  be  separated  by  mixing*  the  impure  acid 
with  a little  chalk,  and  distilling  to  dryness.  The  muriatic  acid  unites 
with  lime  and  is  retained  in  the  retort,  where  it  may  be  detected  by  its 
appropriate  test.  Muriatic  when  mixed  with  hydrocyanic  acid  cannot 
be  detected  by  nitrate  of  silver;  because  cyanuret  of  silver  is  very  simi- 
lar to  the  chloride  both  in  its  appearance,  and  in  several  of  its  leading 
properties. 

The  quality  of  dilute  hydrocyanic  acid,  however  prepared,  is  very 
variable,  owing  to  the  volatility  of  the  acid,  and  its  tendency  to  sponta- 
neous decomposition.  On  this  account,  it  should  be  made  only  in  small 
quantities  at  a time,  kept  in  well-stopped  bottles,  and  excluded  from 
light.  The  best  way  of  estimating  the  strength  of  any  solution  is  that 
proposed  by  Dr.  Ure.  To  100  grains  or  any  other  convenient  quantity 
of  the  acid,  contained  in  a phial,  small  quantities  of  peroxide  of  mercu- 
ry in  fine  powder  are  successively  added,  till  it  ceases  to  be  dissolved. 
The  weight  of  the  peroxide  which  is  dissolved,  divided  by  four,  gives 
the  quantity  of  real  hydrocyanic  acid  present.  (Quarterly  Journal,  vol. 
xiii.) 

The  presence  of  free  hydrocyanic  acid  is  easily  recognised  by  its 
odour.  Chemically  it  may  be  detected  by  agitating  the  fluid  supposed 
to  contain  it  with  peroxide  of  mercury  in  fine  powder.  Double  decom- 
position ensues,  by  which  water  and  bicyanuret  of  mercury  are  genera- 
ted; and  on  evaporating  the  solution  slowly,  the  latter  is  obtained  in 
the  form  of  crystals. 

A test  of  far  greater  delicacy,  originally  noticed  by  Scheele,  is  the 
following.  To  the  liquid  supposed  to  contain  hydrocyanic  acid,  add  a 
solution  of  green  vitriol,  throw  down  the  protoxide  of  iron  by  a slight 
excess  of  pure  potassa,  and  after  exposure  to  the  air  for  four  or  five 
minutes,  acidulate  with  muriatic  or  sulphuric  acid,  so  as  to  redissolve 
the  precipitate.  Prussian  blue  will  then  make  its  appearance,  if  prus- 
sic acid  had  been  originally  present.  I'he  nature  of  the  chemical 
change  will  be  explained  in  the  section  on  the  salts  of  ferrocyanic  acid, 
when  describing  the  manufacture  of  Prussian  blue.  M.  Lassaigne,  who 
has  written  an  essay  on  the  tests  of  this  acid,  (An.  de  Ch.  et  de  Ph. 
xxvii.  200,)  speaks  of  the  joersulphate  as  the  proper  re-agent  for  this 
experiment;  but  according  to  my  observation,  the  presence  of  the  pro- 
toxide is  essential  to  its  success.  If  the  iron  is  strictly  at  its  maximum 
of  oxidation,  Prussian  blue  will  not  be  formed  at  all,  as  was  proved  long 
ago  by  Scheele  and  Proust. 

As  hydrocyanic  acid  is  sometimes  administered  with  criminal  designs, 
the  chemist  may  be  called  on  to  search  for  its  presence  in  the  stomach 
after  death.  This  subject  has  been  investigated  experimentally  by  MM. 
Leuret  and  Lassaigne,  and  the  process  they  have  recommended  is  the 
following.  T-he  stomach  or  other  substances  to  be  examined  are  cut 
into  small  fragments,  and  introduced  into  a retort  along  with  water;  the 
mixture  being  slightly  acidulated  with  sulphuric  acid.  The  distillation 
is  then  conducted  at  a temperature  of  212®  F,  the  volatile  products  are 
collected  in  a receiver  surrounded  with  ice,  and  the  presence  of  hydro- 
cyanic acid  in  the  distilled  matter  is  tested  by  the  method  above  men- 
tioned. These  gentlemen  found,  that  prussic  acid  may  be  thus  detected 
two  or  three  days  after  death;  butnot  after  a longer  period.  The  disappear- 
ance of  die  acid  appears  owing  partly  to  its  volatility,  and  partly  to  the 


264 


COMPOUNDS  OF  NITROGEN  AND  CARBON. 


facility  with  which  it  underg'oes  spontaneous  decomposition.  (Journal 
de  Chimie  Medicale,  &c.  ii.  p.  561.) 

Cyanic  Acid, 

In  the  last  edition  of  this  work  two  compounds  were  described  under 
the  name  of  cyanic  acid^  one  discovered  by  Wohler,  and  tlie  other  by 
Liebig-,  both  consisting*  of  the  same  elements  in  the  same  proportion, 
and  yet  essentially  different  from  each  other  in  their  chemical  proper- 
ties. The  discovery  of  another  compound  of  cyanog*en  and  oxyg*en, 
containing*  twice  as  much  oxyg'en  as  the  others,  has  since  been  made  by 
Serullas,  and  hence  a change  of  nomenclature  is  necessary.  The  acids 
formerly  described  under  the  name  of  cyanic  must  now  be  termed  cyan- 
ous  acid-^  and  the  new  compound  will  receive  its  proper  appellation  of 
cyanic  acid.  (An.  de  Ch.  et  de  Ph.  xxxviii.  379.) 

When  bichloride  of  cyanogen,  which  consists,  as  its  name  implies, 
of  two  equivalents  of  chlorine  and  one  of  cyanogen,  is  gently  boiled 
with  water,  mutual  decomposition  ensues;  and  each  equivalent  of  the 
bichloride  reacts  on  two  equivalents  of  water.  Every  72  parts  of  chlo- 
rine combine  with  2 parts  of  hydrogen,  yielding  two  equivalents  of  mu- 
riatic acid;  while  the  corresponding  26  parts,  or  one  equivalent,  of 
cyanogen,  unite  with  16  parts  of  oxygen,  and  constitute  one  equiva- 
lent of  cyanic  acid.  The  solution  is  then  evaporated  until  nearly  all  the 
muriatic  acid  is  expelled,  and  on  cooling  the  cyanic  acid  is  deposited  in 
oblique  rhomboidal  prisms.  They  are  purified  by  a second  solution  and 
ciystallization. 

These  crystals  are  colourless  and  transparent  when  recent,  but  be- 
come opake  by  exposure  to  the^air,  and  if  gently  heated,  lose  23.4  per 
cent,  of  water.  They  are  insoluble  in  cold  water;  but  they  are  dissolv- 
ed by  this  menstruum,  as  also  by  sulphuric,  nitric,  and  muriatic  acid> 
with  the  aid  of  heat.  They  have  little  taste,  redden  litmus  paper,  and 
are  rather  lighter  than  sulphuric  acid.  One  of  the  most  remarkable 
characters  of  the  acid  is  its  permanence.  For  instance,  it  may  be  boil- 
ed in  strong  nitric  or  sulphuric  acid  without  decomposition;  and  by 
evaporating  its  solution  in  the  former,  it  is  obtained  very  white  and 
pure.  It  is  volatile  at  a lower  temperature  than  boiling  mercury,  and 
condenses,  unchanged,  in  the  form  of  acicular  crystals.  When  heated 
with  potassium  it  is  decomposed,  yielding  potassa  and  cyanuret  of  po- 
tassium. With  metallic  oxides  it  forms  permanent  salts,  which  do  not 
detonate. 

Anhydrous  cyanic  acid,  first  noticed  by  Wbliler,  is  obtained  by  cool- 
ing from  a hot  concentrated  solution  of  the  crystals  in  sulphuric  or  mu- 
riatic acid.  The  figure  of  its  crystals,  when  they  are  regularly  form- 
ed, is  that  of  an  octohedron  with  a square  base.  When  the  anhy- 
drous acid  is  sharply  heated,  part  of  it  sublimes  without  change;  but 
pai-t  is  decomposed,  and  pure  cyanous  acid  is  formed  in  considerable 
quantity. 

I/icbig  and  Wohler  have  remarked,  that  the  substance  called  pyro- 
uric  acid,  which  sublimes  when  uric  acid  is  decomposed  by  lieat,  is 
cyanic  acid.  'I'bis  compound  is  also  formed,  according  to  Liebig,  by 
transmitting  chlorine  gas  through  water  in  whicli  cyanite  of  silver  is 
suspended;  cldoride  of  silver,  carbonic  acid,  and  ammonia  being  gen- 
erated at  the  same  time.  'Vo  this  result  the  elements  of  water  mani- 
festly contril)Ute,  l>y  yielding  oxygen  to  the  carbon,  and  hydrogen  to 
the  nitrogen,  of  a portion  of  cyanogen,  l.iebig  also  states,  that  on 
heating  dry  uric  acid  in  di*y  chlorine  g:is,  a large  quantity  of  cyanic  and 
muriatic  acids  is  generated,  lie  adds,  further,  that  cyanite  of  potassa, 


265 


COMPOUNDS  OF  NITROGEN  AND  CARBON, 

when  heated  in  strong*  acetic  acid,  is  converted  into  cyanate  of  potassa. 
(An.  de  Ch.  et  de  Pli.  xli.  225.  and  xliii.  64.) 

Cyanous  Acid  of  Wohler. — It  was  stated  by  Gay-Lussac  in  the  essay 
already  quoted,  that  cyanogen  gas  is  freely  absorbed  by  pure  alkaline 
solutions;  and  he  expressed  his  opinion  that  the  alkali  combines  directly 
with  the  cyanogen.  It  appears,  however,  from  the  experiments  of 
Wohler,  that  hydrocyanic  and  cyanous  acids  are  formed  under  these  cir- 
cumstances; and,  consequently,  that  alkaline  solutions  act  upon  cyano- 
gen in  the  same  manner  as  on  chlorine,  iodine,  bromine,  and  sulphur. 
But  the  salts  of  cyanous  acid  cannot  conveniently  be  procured  in  this 
way,  owing  to  the  difficulty  of  separating  the  cyanite  from  the  hydrocy- 
anate  with  which  it  is  accompanied.  Wohler  finds  that  cyanite  of  po- 
tassa may  be  procured  in  large  quantity  by  mixing  ferrocyanate  of  po- 
tassa with  an  equal  weight  of  peroxide  of  manganese  in  fine  powder, 
and  exposing  the  mixture  to  a low  red  heat.  The  cyanogen  of  the  fer- 
rocyanic  acid  receives  oxygen  from  the  manganese,  and  is  converted  into 
cyanous  acid,  which  unites  with  the  potassa.  The  ignited  mass  is  then 
boiled  in  alcohol  of  86  per  cent;  and  as  the  solution  cools,  the  cyanite 
is  deposited  in  small  tabular  crystals  resembling  chlorate  of  potassa. 
The  only  precaution  necessary  in  this  process  is  to  avoid  too  high  a tem- 
perature. 

Cyanous  acid  is  characterized  by  the  facility  with  which  it  is  resolved 
by  water  into  carbonic  acid  and  ammonia.  This  change  is  effected 
merely  by  boiling  an  aqueous  solution  of  cyanite  of  potassa;  and  it 
takes  place  still  more  rapidly  when  an  attempt  is  made  to  decompose 
the  cyanite  by  means  of  another  acid.  If  the  acid  is  diluted,  cyanous 
acid  is  instantly  .decomposed,  and  carbonic  acid  escapes  with  efferves- 
cence. But,  on  the  contrary,  if  a concentrated  acid  is  employed,  then 
the  cyanous  acid  resists  decomposition  for  a short  time,  and  emits  a 
strong  odour  of  vinegar.  According  to  Liebig,  the  acid  may  be  obtained 
in  a free  state  by  transmitting  sulphuretted  hydrogen  gas  through  water 
in  which  cyanite  of  silver  is  suspended;  but  the  operation  should  be 
discontinued  before  all  tlie  cyanite  is  decomposed,  otherwise  the  free 
sulphuretted  liydrogen  would  react  on  the  cyanous  acid,  and  effect  its 
decomposition.  The  acid  thus  formed  is  permanent  only  for  a few  hours. 
Wohler  has  himself  lately  procured  it  by  distilling  anhydrous  cyanic 
acid  and  transmitting  the  products  through  a cool  dry  receiver;  when  a 
clear,  colourless,  and  very  volatile  liquid  collected,  which  was  pure  an- 
hydrous cyanous  acid.  (An.  de  Ch.  et  de  Ph.  xxxiii.  207.  and  xliii.  64.) 

Cyanous  acid  forms  a soluble  salt  with  baryta,  but  insoluble  ones  with 
oxide  of  lead,  mercury,  and  silver.  If  cyanite  of  potassa  is  quite  pure, 
it  gives  a white  precipitate  with  nitrate  of  silver,  and  the  cyanite  of 
silver  so  formed  dissolves  without  residue  in  dilute  nitric  acid.  With 
ammonia  it  forms  a compound  which  has  all  the  properties  of  urea. 

Cyanous  acid,  according  to  the  analysis  of  \\  ohler,  is  composed  of 
26  parts  or  one  equivalent  of  cyanogen,  and  8 parts  or  one  equivalent 
of  oxygen.  The  accuracy  of  this  result  was  at  first  doubted  by  Liebig, 
but  it  is  now  admitted  to  be  correct.  (An.  de  Ch.  et  de  Ph.  xx.  and 
xxvii.) 

The  existence  of  cyanous  acid  was  suspected  by  M.  Vauquelin  be- 
fore it  was  actually  discovered  by  Wohler.  The  experiments  of  the 
former  chemist  led  him  to  the  opinion  that  a solution  of  cyanogen  in 
water  is  gradually  converted  into  hydrocyanic,  cyanous,  and  carbonic 
acids,  and  ammonia;  and  he  supposed  alkalies  to  produce  a similar 
change.  lie  did  not  establish  the  fact,  however,  in  a satisfactory  man- 
ner. (An.  de  Ch.  et  de  Ph.  vol.  ix.) 

Cyanous  Acidoi  M.  Liebig. — A powerfully  detonating  compound  of 


266  COMPOUNDS  OF  NITROGEN  AND  CARBON. 

mercury  was  described  in  the  Philosophical  Transactions  for  1800  by 
Mr.  E.  Howard.  It  is  prepared  by  dissolving*  one  hundred  g’rains  of 
mercury  in  a measured  ounce  and  a half  of  nitric  acid  of  specific  gravity 
1.3;  and  adding*,  when  the  solution  has  become  cold,  two  ounces  by 
measure  of  alcohol,  the  density  of  which  is  0.849.  The  mixture  is 
then  heated  till  moderately  brisk  effervescence  takes  place,  during^ 
which  the  fulminating*  compound  is  generated.  A similar  substance 
may  be  made  by  treating  silver  in  the  same  manner.  I'he  conditions 
necessary  for  forming  these  compounds  are,  that  the  silver  or  mercury 
be  dissolved  in  a fluid  which  contains  so  much  free  nitric  acid  and  alcohol, 
that,  on  the  application  of  heat,  nitric  ether  shall  be  freely  disengaged. 
Fulminating  silver  and  mercury  bear  the  lieat  of  212°  or  even  260  F., 
without  detonating;  but  a higher  temperature  or  slight  percussion  be- 
tween two  hard  bodies,  causes  them  to  explode  with  violence.  The  na- 
ture of  these  compounds  was  discovered  in  1823  by  Liebig,*  who  de- 
monstrated that  they  are  salts  composed  of  a peculiar  acid,  which  he 
termed  fulminic  acid,  in  combination  with  oxide  of  mercury  or  silver. 
According  to  an  analysis  of  fulminating  silver  made  by  Liebig  and  Gay- 
Lussac,-)-  the  acid  of  the  salt  is  composed  of  26  parts  or  one  proportion- 
al of  cyanogen,  and  8 parts  or  one  proportional  of  oxygen.  It  is  there- 
fore, a real  cyanous  acid,  and  its  salts  are  cyanites;  but  in  order  not  to 
apply  the  same  appellation  to  two  different  compounds,  it  will  be  con- 
venient to  retain  the  term  oi  fulminic  acid  originally  proposed  by  Liebig. 
Fulminating  silver,  therefore,  is  a fulminate  of  the  oxide  of  silver;  and 
it  is  found  to  contain  one  equivalent  of  each  constituent. 

It  is  remarkable  that  the  oxide  of  silver  cannot  be  entirely  separated 
from  fulminic  acid  by  means  of  an  alkali.  On  digesting  fulminate  of 
silver  in  potassa,  for  example,  one  equivalent  of  oxide  of  silver  is  sepa- 
rated, and  a double  fulminate  is  formed,  which  consists  of  two  equiva- 
lents of  fulminic  acid,  one  of  oxide  of  silver,  and  one  equivalent  of  po- 
tassa. Similar  compounds  may  be  procured  by  substituting  other  alka- 
line substances,  such  as  baryta,  lime,  or  magnesia,  for  the  potassa. 
These  double  fulminates  are  capable  of  crystallizing;  and  they  all  pos- 
sess detonating  properties. 

From  the  presence  of  oxide  of  silver  in  the  double  fulminates,  it  was 
at  first  imagined  that  this  oxide  actually  constitutes  a part  of  the  acid; 
but  since  several  other  substances,  such  as  oxide  of  mercury,  zinc,  and 
copper,  may  be  substituted  for  that  of  silver,  this  view  can  no  longer  be 
admitted. 

Fulminic  acid  has  not  hitherto  been  obtained  in  an  insulated  form; 
for  while  some  acids  do  not  decompose  the  fulminates,  others  act  on 
fulminic  acid  itself,  and  give  rise  to  new  products.  Muriatic  acid,  for 
example,  causes  the  formation  of  hydrocyanic  acid,  and  of  a new  acid 
containing  chlorine,  carbon,  and  nitrogen,  the  nature  of  which  has  not 
been  determined.  Hydriodic  acid  acts  in  a similar  manner;  and  a pecu- 
liar acid  is  likewise  produced  by  the  action  of  sulphuretted  hydrogen. 
From  subsequent  researches  Liebig  suspects  that  this  acid  is  composed 
of  sulphur,  cyanogen,  and  oxygen  in  the  ratio  of  two  equivalents  of  the 
first  substance,  one  of  the  second,  and  one  of  the  third;  but  the  accu- 
racy of  this  view  has  not  been  demonstrated  in  a conclusive  manner. 

Chloride  of  Cyanogen. 

The  existence  of  this  compound  was  first  noticed  by  Berthollet,  who 
named  it  oxyyrumc  acid,  on  the  supposition  of  its  containing  prussic 


An.  de  Ch.  et  de  Ph.  vol.  xxiv. 


■\  Ibid.  XXV. 


COMPOUNDS  OF  NITROGEN  AND  CARBON. 


267 


acid  and  oxygen;  and  it  was  afterwards  described  by  Gay-Lussac,  in. 
his  essay  on  cyanogen,  under  the  appellation  of  chlorocyanic  add.  It 
was  procured  by  this  chemist  by  transmitting  chlorine  gas  into  an 
aqueous  solution  of  hydrocyanic  acid  until  the  liquid  acquired  bleaching 
properties,  removing  the  excess  of  chlorine  by  agitation  with  mercury, 
and  then  heating  the  mixture,  so  as  to  expel  the  gaseous  chloride  of 
cyanogen.  The  chemical  changes  which  take  place  during  this  pro- 
cess are,  complicated.  At  first  the  elements  of  hydrocyanic  acid  unite 
with  separate  portions  of  chlorine,  and  give  rise  to  muriatic  acid  and 
chloride  of  cyanogen;  and  when  heat  is  applied,  the  elements  of 
the  chloride  and  water  react  on  each  other,  in  consequence  of  which 
muriatic  acid,  ammonia,  and  carbonic  acid  are  generated.  Owing  to  this 
circumstance,  the  chloride  of  cyanogen  was  always  mixed  with  carbonic 
acid,  and  its  properties  imperfectly  understood. 

Dui’ing  the  course  of  last  year  M.  Serullas  succeeded  in  procuring 
this  compound  in  a pure  state,  by  exposing  bicyanuret  of  mercury,  in 
powder  and  moistened  with  water,  to  the  action  of  chlorine  gas  con- 
tained in  a well  stopped  phial.  'I'he  vessel  is  kept  in  a dark  place;  and 
after  ten  or  twelve  hours  the  colour  of  the  chlorine  is  no  longer  per- 
ceptible, bichloride  of  mercury  is  found  at  the  bottom  of  the  phial, 
and  its  space  is  filled  with  the  vapour  of  chloride  of  cyanogen.  The 
bottle  is  then  cooled  down  to  zero  by  freezing  mixtures  of  snow  and 
salt,  at  which  temperature  chloride  of  cyanogen  is  solid.  Some  chlo- 
ride of  calcium  is  then  introduced,  the  stopper  replaced,  and  the  bottle 
kept  in  a moderately  warm  situation,  in  order  that  the  moisture  within 
may  be  completely  absorbed.  The  chloride  of  cyanogen  is  then  again 
solidified  by  cold,  the  phial  completely  filled  with  dry  and  cold  mercury, 
and  a bent  tube  adapted  to  its  aperture  by  means  of  a cork.  The  solid 
chloride,  which  remains  adhering  to  the  inner  surface  of  the  phial,  is 
converted  into  gas  by  gentle  heat,  and,  passing  along  the  tube,  is  col- 
lected over  mercury.  Exposure  to  the  direct  solar  rays  interferes  with 
the  success  of  this  process.  Muriate  of  ammonia,  together  with  a little 
carbonic  acid,  is  then  generated,  and  a yellow  liquid  collects;  which  ap- 
pears to  be  a mixture  of  chloride  of  carbon  and  chloride  of  nitrogen. 
(An.  de  Ch.  etde  Ph.  xxxv.  291.) 

Chloride  of  cyanogen  is  solid  at  zero  of  Fahrenheit’s  thermometer, 
and  in  congealing  crystallizes  in  very  long  slender  needles.  At  tem- 
peratures between  5®  F.  and  10.5^  it  is  liquid,  and  also  at  68®  under  a 
pressure  of  four  atmospheres;  but  at  the  common  pressure,  and  when 
the  thermometer  is  above  10.5®  or  11®  F.  it  is  a colourless  gas.  In  the 
liquid  state  it  is  as  limpid  and  colourless  as  water.  It  has  a very  offen- 
sive odour,  irritates  the  eyes,  is  corrosive  to  the  skin,  and  highly  inju- 
rious to  animal  life. 

Chloride  of  cyanogen  is  very  soluble  in  water  and  alcohol.  The 
former  under  the  common  pressure,  and  at  68®  F.,  dissolves  twenty-five 
times  its  volume.  Alcohol  takes  up  100  times  its  volume,  and  the  ab- 
sorption is  effected  almost  with  the  same  velocity  as  tl^t  of  ammonia- 
cal  gas  by  water.  ^ These  solutions  are  quite  neutral  with  respect  to 
litmus  and  turmeric  paper,  and  may  be  kept  without  apparent  change. 
The  gas  may  even  be  separated  without  decomposition  by  boiling.  The 
chloride  of  cyanogen,  accordingly,  does  not  possess  the  characters  of 
an  acid. 

The  changes  induced  by  the  action  of  alkalies  do  not  appear  to  be 
very  clearly  understood.  M.  Serullas  agrees  with  Gay-Lussac  in  stating 
that  if  to  a solution  of  chloride  of  cyanogen  a pure  alkali  is  added,  and 
then  an  acid,  effervescence  ensues  from  the  escape  of  carbonic  acid 


268  COMP(iuNl)S  OF  NITROGEN  AND  CARBON. 


gas.  Ammonia,  and  probably  muriatic  and  hydrocyanic  acid,  are  also 
generated. 

The  statement  of  Gay-Lussac  relative  to  the  composition  of  chloride 
of  cyanogen  is  confirmed  by  the  analysis  of  M.  Serullas.  According  to 
these  chemists,  it  is  composed  of  equal  measures  of  chlorine  and  cya- 
nogen gases,  united  without  any  condensation;  orby  weiglit,  of  36  parts 
or  one  equivalent  of  chlorine,  and  26  parts  or  one  equivalent  of  cyano- 
gen. Its  equivalent  is,  therefore,  62,  and  its  specific  gravity  in  the 
gaseous  state  2.1527. 

Bichloride  of  Cyanogen. — This  compound,  which  contains  twice  as 
much  chlorine  as  the  preceding,  was  prepared  by  Serullas  by  the  ac- 
tion of  dry  chlorine  on  anhydrous  prussic  acid,  muriatic  acid  being 
generated  at  the  same  time.  It  is  solid  at  common  temperatures,  and 
occurs  in  white  acicular  crystals.  At  284®  F.  it  fuses,  and  enters  into 
ebdllition  at  374®.  Its  vapour  is  acrid  and  excites  a flow  of  tears,  and 
it  is  very  destructive  to  animals.  Its  odour  somewhat  resembles  that  of 
chlorine,  and  is  very  similar  to  that  of  mice.  It  is  very  soluble  in  alco- 
hol and  ether,  and  is  precipitated  from  them  by  water  which  dissolves 
it  in  small  quantity.  When  boiled  in  water,  or  solution  of  potassa,  it  is 
converted  into  muriatic  and  cyanic  acids.  (An.  de  Ch.  et  de  Ph. 
xxxviii.  370.)- 

Iodide  of  Cyanogen, 

Iodide  of  cyanogen,  which  was  discovered  in  1824  by  M.  Serullas, 
(An.  de  Ch.  et  de  Ph.  vol.  xxvii.)  may  be  prepared  by  the  following 
process: — Two  parts  of  bicyanuret  of  mercury  and  one  of  iodine  are 
intimately  and  quickly  mixed  in  a glass  mortar,  and  the  mixture  is  in- 
troduced into  a phial  with  a wide  mouth.  On  applying  heat,  the  violet 
vapours  of  iodino  appear;  but  as  soon  as  the  cyanuret  of  mercury  be- 
gins to  be  decomposed,  the  vapour  of  iodine  is  succeeded  by  white 
fumes,  which,  if  received  in  a cool  glass  receiver,  condense  upon  its 
sides  into  flocks  like  cotton  wool.  The  action  is  found  to  be  promoted 
by  the  presence  of  a little  water. 

Iodide  of  cyanogen,  when  slowly  condensed,  occurs  in  very  long  and 
exceedingly  slender  needles,  of  a white  colour.  It  has  a very  caustic 
taste  and  penetrating  odour,  and  excites  a flow  of  tears.  It  sinks  ra- 
pidly in  sulphuric  acid.  It  is  very  volatile,  and  sustains  a temperature 
much  higher  than  212®  F.  without  decomposition;  but  it  is  decom- 
posed by  a red  heat.  It  dissolves  in  water  and  alcohol,  and  forms  solu- 
tions which  do  not  redden  litmus  paper.  Alkalies  act  upon  it  in  the 
same  manner  as  on  chloride  of  cyanogen,  a compound  to  which  it  is 
very  analogous. 

Sulphurous  acid,  when  water  is  present,  has  a very  powerful  action 
on  iodide  of  cyanogen.  On  adding  a few  drops  of  this  acid,  iodine  is 
set  free,  and  hydrocyanic  acid  produced;  but  when  more  of  the  sulphu- 
rous acid  is  employed,  the  iodine  disappears,  and  the  solution  is  found 
to  contain  liydrlodic  acid.  These  changes  are  of  course  accompanied 
with  formation  of  sulphuric  acid,  and  decomposition  of  water. 

Iodide  of  cyanogen  has  not  been  analyzed  with  accuracy;  but  M.  Se- 
rullas infers  from  an  approximative  anal}'sis,  that  it  is  composed  of  one 
equivalent  of  iodine  and  one  of  cyanogen. 

Bromide  of  Cyanogen, 

This  substance  has  been  ])rcparcd  ])y  Liebig  by  a process  very  simi- 
lar to  that  described  for  procuring  iodide  of  cyanogen.  At  tlie  bottom 
of  a small  tubulated  retort,  or  a rather  long  tube,  is  placed  some  bicy- 
anuret of  mercury  slightly  moistened,  and  after  cooling  the  apparatus 


1 


COMPOUNDS  OF  NITROGEN  AND  CARBON.  269 

by  cold  water,  or  still  better  by  a freezing*  mixture,  a precaution  which 
is  indispensable  in  summer,  half  its  weight  of  bromine  is  introduced. 
Strong  reaction  instantly  ensues,  and  caloric  is  so  freely  evolved,  that  a 
considerable  quantity  of  the  bromide  would  be  dissipated,  unless  the 
temperature  of  the  retort  had  been  previously  reduced.  The  new 
products  are  bromide  of  mercury  and  bromide  of  cyanogen,  the  latter 
of  which  collects  in  the  upper  part  of  the  tube  in  the-  form  of  long 
needles.  After  allowing  any  vapour  of  bromine,  which  may  have 
risen  at  the  same  time,  to  condense  and  fall  back  upon  the  cyanuret  of 
mercury,  the  bromide  of  cyanogen  is  expelled  by  a gentle  heat,  and 
collected  in  a recipient  carefully  cooled. 

As  thus  formed,  the  bromide  is' crystallized,  sometimes  in  small  regu- 
lar colourless  and  transparent  cubes,  and  sometimes  in  long  and  very 
slender  needles.  In  its  physical  properties  it  is  so  very  similar  to  iodide 
of  cyanogen,  that  they  may  easily  be  mistaken  for  each  other,  especially 
when  the  crystals  of  the  bromide  possess  the  acicular  form.  They 
agree  closely  in  odour  and  volatility,  but  the  bromide  is  even 'more 
volatile  than  the  iodide  of  cyanogen.  It  is  converted  into  vapour  at 
59*^  F.,  and  crystallizes  suddenly  on  cooling.  Its  solubility  in  water 
and  alcohol  is  likewise  greater  than  that  of  iodide  of  cyanogen.  By  a 
solution  of  caustic  potassa  it  is  converted  into  hydrocyanate  and  hydro- 
bromate  of  potassa. 

Bromide  of  cyanogen  is  highly  deleterious.  A grain  of  it  dissolved  in 
a little  water,  and  introduced  into  the  oesophagus  of  a rabbit,  proved 
fatal  on  the  instant,  acting  with  the  same  rapidity  as  prussic  acid.  In 
consequence  of  the  volatility  and  noxious  quality  of  this  substance,  ex- 
periments with  it  should  be  conducted  with  great  circumspection.  The 
danger  from  this  cause,  together  with  a deficient  supply  of  bromine, 
prevented  M.  Serullas  from  continuing  the  investigation  of  its  proper- 
ties. (Edin.  Journal  of  Science,  vii.  189.) 

Ferrocyanic  Acid, 

Ferrocyanic  acid  has,  within  these  few  years,  been  the  subject  of  able 
researches  by  Mr.  Porrett,*  Berzelius, -j-  and  M.  Robiquet.i:  Mr.  Por- 
rett  recommends  two  methods  for  obtaining  ferrocyanic  acid,  by  one 
of  which  it  is  procured  in  crystals,  and  by  the  other  in  a state  of  solu- 
tion. The  first  process  consists  in  dissolving  58  grains  of  crystallized  tar- 
taric acid  in  alcohol,  and  mixing  the  liquid  with  50  grains  of  ferrocyanate 
of  potassa  dissolved  in  the  smallest  possible  quantity  of  hot  water.  Bi- 
tartrate of  potassa  is  precipitated,  and  the  clear  solution,  on  being  al- 
lowed to  evaporate  spontaneously,  gradually  deposites  ferrocyanic  acid 
in  the  form  of  small  cubic  crystals  of  a yellow  colour.  In  the  second 
process,  ferrocyanate  of  baryta,  dissolved  in  water,  is  mixed  with  a 
quantity  of  sulphuric  acid  precisely  sufficient  for  combining  with  the 
baryta;  when  the  insoluble  sulphate  of  baryta  subsides,  and  ferrocyanic 
acid  remains  in  solution.  According  to  Mr.  Porrett,  every  10  grains  of 
ferrocyanate  of  baryta  require  so  much  liquid  sulphuric  acid  as  is  equiva- 
lent to  2.53  grains  of  real  acid. 

Ferrocyanic  acid  is  neither  volatile  nor  poisonous  in  small  quantities, 
and  has  no  odour.  It  is  gradually  decomposed  by  exposure  to  the  light, 
forming  hydrocyanic  acid  and  Prussian  blue;  but  it  is  far  less  liable  to 


* Philosophical  Transactions  for  1814  and  1815.  Annals  of  Philosophv, 
vol.  xiv. 

•(*  Annales  de  Chimie  et  de  Physique,  vol.  xv. 
i Ibid.  vol.  xvii. 


270  CbMI^otjNDS  OF  NITROGEN  AND 


CARBON. 


spontaneous  decomlpositlon  than  hydrocyanic  acid.  It  differs  also  from 
this  acid  in  possessing*  tlie  properties  of  acidity  in  a much  greater  de- 
gree. Thus  it  reddens  litmus  paper  permanently,  neutralizes  alkalies, 
and  separates  the  carbonic  and  acetic  acids  from  their  combinations.  It 
even  decomposes  some  salts  of  the  more  powerful  acids.  Peroxide  of 
iron,  for  example,  unites  with  ferrocyanic  in  preference  to  sulphuric 
acid,  unless  tlie  latter  is  concentrated. 

Different  opinions  liave  prevailed  as  to  the  nature  of  ferrocyanic  acid. 
Berzelius  maintains  that  it  is  a super-hydrocyanate  of  the  protoxide  of 
iron;  but  M.  llobiquet  has  shown  by  arguments  wliich  appear  to  me 
unanswerable,  that  this  supposition  is  inconsistent  with  the  phenomena. 
The  view  which  is  now  commonly  taken  of  the  composition  of  this  acid 
was  suggested  by  an  experiment  made  by  Mr.  Porrett.  On  exposing 
ferrocyanate  of  soda  to  the  agency  of  galvanism,  the  soda  was  observed 
to  collect  at  the  negative  pole,  while  oxide  of  iron,  together  with  the 
elements  of  hydrocyanic  acid,  appeared  at  the  opposite  end  of  the  bat- 
tery. From  this  he  inferred,  that  the  iron  does  not  act  tlie  part  of  an 
alkali  in  the  salt,  for  on  that  supposition  it  should  have  accompanied  the 
soda,  but  that  it  enters  into  the  constitution  of  the  acid  itself.  Mr.  Por- 
rett at  first  considered  the  iron  to  be  in  the  state  of  an  oxide;  but  he 
concludes  from  subsequent  researches,  that  ferrocyanic  acid  contains  no 
oxygen,  and  that  its  sole  elements  are  carbon,  hydrogen,  nitrogen, 
and  metallic  iron.  To  the  acid  thus  constituted,  he  proposes  the  name 
of  ferruretted  chyazic*  acid,  but  the  term  ferrocyanic  acid,  introduced 
by  the  French  chemists,  is  more  generally  employed. 

This  view  has  the  merit  of  accounting  for  the  fact,  that  iron,  though 
contained  in  ferrocyanic  acid  and  all  its  salts,  cannot  be  detected  in 
them  by  the  usual  tests  of  iron.  For  the  liquid  tests  are  fitted  only  for 
detecting  oxide  of  iron  as  existing  in  a salt,  and,  therefore,  cannot  be 
expected  to  indicate  the  presence  of  metallic  iron  while  forming  one  of 
the  elements  of  an  acid.  We  may  now  also  understand  how  it  happens 
that  ferrocyanic  should  actually  contain  the  elements  of  hydrocyanic 
acid,  and  yet  differ  from  it  totally  in  its  properties. 

According  to  the  experiments  of  Mr.  Porrett,  ferrocyanic  acid  is 
composed  of  one  equivalent  of  iron,  one  of  hydrocyanic  acid,  and  two 
equivalents  of  carbon.  M.  Robiquet  states,  however,  that  its  ele- 
ments are  in  such  proportion  as  to  form  cyanuret  of  iron,  and  hydro- 
cyanic acid;  and  the  result  of  his  researches,  together  with  the  ana- 
lysis of  Berzelius,  appears  to  justify  the  conclusion  that  ferrocyanic  acid 
is  composed  of 

Hydrogen  . « two  equivalents. 

Iron  . . one  equivalent. 

Cyanogen  . . three  equivalents; 

or  of 


Hydrocyanic  acid  . two  equivalents, 

Cyanuret  of  iron  . one  equivalent,  j" 


Ferrocyanic  acid  is,  therefore,  analogous  to  several  acids,  such  as 
tlie  muriatic,  hydriodic,  and  hydrosulphuric  acids,  all  of  which  con- 
tain liydrogcn  as  an  essential  element,  and  wliich  for  this  reason  are 
termed  hydracida.  Under  this  point  of  view,  ferrocyanic  acid  may  be 
regarded  as  a compound  of  a certain  radical  and  hydrogen.  This 


* Chyazic  from  the  initials  of  carbon,  hydrogen,  and  azote. 

I See  a notice  on  the  triple  prussiates  in  the  An.  de  Ch.  et  de  Ph. 
vol.  xxii. 


COMPOUNDS  OF  NITROGEN  AND  CARBON.  271 

radical,  which  has  not  been  obtained  in  an  insulated  state,  is  composed 
of 

Cyanogen  three  equiv. '}  or  of  ^ Cyanogen  two  equiv. 

Iron  one  equiv.  3 ^ Cyanuret  of  iron  one  equiv.; 

and  the  acid  itself  consists  of  one  equivalent  of  the  radical  and  two  of 
hydrogen. 

The  salts  of  ferrocyanic  acid  were  once  called  triple prussiates,  on 
the  supposition  that  they  were  composed  of  prussic  or  hydrocyanic  acid 
in  combination  with  oxide  of  iron  and  some  other  alkaline  base.  They 
are  now  termed  ferrocyanates.  The  beautiful  dye,  Prussian  blue,  is  a 
ferrocyanate  of  the  pei’oxide  of  iron.  It  is  always  formed  when  ferro- 
cyanic acid  or  its  salts  are  mixed  in  solution  with  apersalt  of  iron;  and 
for  this  reason  the  persalts  of  iron,  provided  no  free  alkali  is  present, 
afford  a certain  and  an  extremely  delicate  test  of  the  presence  of  ferro- 
cyanic acid. 

• Sulphocyanic  Jicid, 

This  acid  was  discovered  in  the  year  1808  by  Mr.  Porrett,  who  ascer- 
tained that  it  is  a compound  of  sulphur,  carbon,  hydrogen,  and  nitro- 
gen, and  described  it  under  the  name  of  sulphuretted  chyazic  acid.  It  is 
now  more  commonly  called  acid,  and  its  salts  are  termed 

sulphocyanates. 

Sulphocyanic  acid  is  obtained  by  mixing  so  much  sulphuric  acid  with 
a concentrated  solution  of  sulphocyanate  of  potassa  as  is  sufficient  to 
neutralize  the  alkali,  and  then  distilling  the  mixture.  An  acid  liquor 
collects  in  the  recipient,  which  is  sulphocyanic  acid  dissolved  in  water, 
and  sulphate  of  potassa  remains  in  the  retort. 

Sulphocyanic  acid,  as  thus  prepared,  is  a transparent  liquid,  which  is 
either  colourless  or  has  a slight  shade  of  pink.  Its  odour  is  somewhat 
similar  to  that  of  vinegar.  I'he  strongest  solution  of  it  which  Mr.  Por- 
rett could  obtain  had  a specific  gravity  of  1.022.  It  boils  at  216.5^  F., 
and  at  54.5°  crystallizes  in  six-sided  prisms. 

Sulphocyanic  acid  reddens  litmus  paper,  and  forms  neutral  com- 
pounds with  alkalies.  Its  presence,  whether  free  or  combined,  is  easily 
detected  by  a persalt  of  iron,  with  the  oxide  of  which  it  unites,  forming 
a soluble  salt  of  a deep  blood-red  colour.  With  the  protoxide  of  cop- 
per it  yields  a white  salt,  which  is  insoluble  in  water. 

According  to  the  analysis  of  Mr.  Porrett,  (Annals  of  Philosophy,  vol. 
xiii.)  which  is  conhrmed  by  that  of  Berzelius,  (An.  de  Ch.  et  de  Ph. 
vol.  xvi.)  sulphocyanic  acid  is  composed  of 


Cyanogen 

26 

. one 

equivalent. 

Sulphur 

32 

two 

equivalents. 

Hydrogen 

1 

, one 

equivalent; 

Bisulphuret  of  cyanogen  58 

. one 

equivalent. 

Hydrogen 

1 

. one 

equivalent. 

Bisulphuret  of  Cyanogen. — Sulphocyanic  acid  may  be  regarded  as  a 
hydracid,  of  which  the  bisulphuret  of  cyanogen,  lately  described  by 
Liebig,  is  the  radical.  (An.  de  Ch.  et  de  Ph.  xli.  187.)  It  was  prepar- 
ed by  exposing  fused  sulphocyanuret  of  potassium  to  a current  of  dry 
chlorine  gas.  Reaction  readily  ensued;  and  at  first  chloride  of  sulphur 
and  bichloride  of  cyanogen  distilled  over;  but  at  length  a red  vapour 
appeared,  which  collected  as  a red  or  orange-coloured  substance  in  the 
upper  part  of  the  tube.  In  this  state  it  contained  some  free  sulphur, 
which  was  in  a great  measure  removed  by  heating  it  in  dry  chlorine 


272 


COMPOUNDS  OF  SULPHUR. 


gas;  when  it  acquired  an  orange  tint,  and  in  powder  was  yellow.  It 
had  then  so  nearly  the  constitution  of  bisulphuret  of  cyanogen,  that 
there  can  be  little  doubt  of  its  being  such.  When  heated  with  potassi- 
um the  action  is  exceedingly  violent,  and  three  compounds,  sulphocy- 
anuret,  sulphuret,  and  cyanuret  of  potassium,  are  generated. 

If  a solution  of  sulphocyanic  acid  is  exposed  to  the  air,  a yellow 
matter  gradually  collects,  which  Wohler  conceived  to  be  a compound 
of  sulphur  and  sulphocyanic  acid,  but  which  Liebig  considers  bisul- 
phuret of  cyanogen.  It  is  formed  freely  by  boiling  sulphocyanate  of 
potassa  with  dilute  nitric  acid,  the  best  proportions  being  1 part  of  the 
salt,  3 of  water,  and  2 or  2.5  of  nitric  acid;  for  if  the  nitric  acid  is  too 
strong  or  in  too  great  excess,  the  yellow  compound  will  not  be  formed. 
It  is  also  generated  by  the  action  of  chlorine  on  a strong  solution  of  the 
salt.  In  fact,  the  oxygen  of  the  air,  nitric  acid,  and  chlorine,  act  upon 
sulphocyanic  acid  in  the  same  manner  as  on  hydriodic  and  hydrosulphu- 
ric  acids.  The  yellow  matter  retains  water  with  obstinacy. 

Sulphuret  of  Cyanogen, — Another  sulphuret  of  cyanogen,  different 
from  that  just  described,  was  discovered  in  1828  by  M.  Lassaigne.  It 
was  prepared  by  the  action  of  bicyanuret  of  mercury,  in  fine  powder, 
with  half  its  weight  of  bichloride  of  sulphur,  confined  in  a small  glass 
globe,  and  exposed  for  two  or  three  weeks  to  day-light.  A small  quan- 
tity of  crystals,  biting  to  the  tongue  and  of  a penetrating  odour,  col- 
lected in  the  upper  part  of  the  vessel,  which  formed  red-coloured  com- 
pounds with  persalts  of  iron.  Its  constitution  has  not  been  accurately 
determined;  and  the  attempts  of  Liebig  to  prepare  it  were  unsuccessful. 
(An.  de  Gh.  et  de  Ph.  xxxix.) 

Seleniocyanic  Add, — This  substance  was  obtained  by  Berzelius  in  com- 
bination with  potassa,  but  he  could  not  obtain  it  in  a separate  state.  It 
may  be  regarded  as  a hydracid,  of  which  seleniuret  of  cyanogen  is  the 
radical. 


SECTION  VIL 

COMPOUNDS  OF  SULPHUR. 

Bisulphuret  of  Carbon. 

This  substance  was  discovered  accidentally  in  the  year  1796  by  Pro- 
fessor Lampadius,  who  regarded  it  as  a compound  of  sulphur  and  hy- 
drogen, and  termed  it  alcohol  of  sulphur.  Clement  and  Desormes  first 
declared  it  to  be  a sulphuret  of  carbon,  and  their  statement  was  fully 
confirmed  by  the  joint  researches  of  Berzelius  and  the  late  Dr.  Marcet. 
(Philos.  Trans,  for  1813.) 

Bisulphuret  of  carbon  may  be  obtained  by  heating  in  close  vessels  na- 
tive bisulphuret  of  iron  (iron  pyrites)  with  one-fifth  of  its  weight  of 
well  dried  charcoal;  or  by  transmitting  vapour  of  sulphui\over  frag- 
ments of  charcoal  heated  to  redness  in  a tube  of  porcelain.  The  com- 
pound, as  it  is, formed,  should  be  conducted  by  means  of  a glass  tube 
into  cold  water,  at  the  bottom  of  which  it  is  collected.  To  free  it  from 
moi.sturc  and  adhering  siilj)hur,  it  should  be  distilled  at  a low  tempera- 
ture in  contact  witli  cldoride  of  calcium. 

Bisulphuret  of  carbon  is  a transparent  colourless  liquid,  which  is  re- 


COIMPOUNDS  OF  SULPHUR. 


273 


markable  for  its  high  refractive  power.  Its  specific  gravity  is  1.  272. 
It  has  an  acid,  pungent,  and  somewhat  aromatic  taste,  and  a very  fetid 
odour.  It  is  exceedingly  volatile; — its  vapour  at  63. 5^^^  F.  supports  a 
column  of  mercury  7.36  inches  long;  and  at  110^  F.  it  enters  into  brisk 
ebullition.  From  its  great  volatility  it  may  be  employed  for  producing 
intense  cold. 

Bisulphuret  of  carbon  is  very  inflammable,  and  kindles  in  the  open 
air  at  a temperature  scarcely  exceeding  that  at  which  mercury  boils.  It 
burns  with  a pale  blue  flame.  Admitted  into  a vessel  of  oxygen  gas,  so 
much  vapour  rises  as  to  form  an  explosive  mixture;  and  when  mixed  in 
like  manner  with  deutoxide  of  nitrogen,  it  forms  a combustible  mix- 
ture, which  is  kindled  on  the  approach  of  a lighted  taper,  and  burns 
rapidlyj  with  a large  greenish-white  flame  of  dazzling  brilliancy.  It 
dissolves  readily  in  alcohol  and  ether,  and  is  precipitated  from  the  solu- 
tion by  water.  It  dissolves  sulphur,  phosphorus,  and  iodine,  and  the 
solution  of  the  latter  has  a beautiful  pink  colour.  Chlorine  decomposes 
it,  with  formation  of  chloride  of  sulphur.  The  pure  acids  have  little 
action  upon  it.  With  the  alkalies  it  unites  slowly,  forming  compounds 
which  Berzelius  calls  carhosulphurets.  It  is  converted  by  strong  nitro- 
muriatic  acid  into  a white  crystalline  substance  like  camphor,  which 
Berzelius  considers  to  be  a compound  of  muriatic,  carbonic,  and  sul- 
phurous acid  gases. 

Xanthogen  and  Hydroxanthic  Add. — M.  Zeise,  Professor  of  Chemis- 
try at  Copenhagen,  has  discovered  some  novel  and  interesting  facts,  re- 
lative to  bisulphuret  of  carbon.  When  this  fluid  is  agitated  with  a so- 
lution of  pure  potassa  in  strong  alcohol,  the  alkaline  properties  of  the 
potassa  disappear  entirely;  and  on  exposing  the  solution  to  a tempera- 
ture of  32®  F.  numerous  acicular  crystals  are  deposited.  M.  Zeise  at- 
tributes these  phenomena  to  the  formation  of  a new  acid,  the  elements 
of  which  are  derived,  in  his  opinion,  partly  from  the  alcohol  and  partly 
from  the  bisulphuret  of  carbon.  He  regards  the  acid  as  a compound  of 
carbon,  sulphur,  and  hydrogen.  He  supposes  it  to  be  a hydracid,  and 
that  its  radical  is  a sulphuret  of  carbon.  To  the  radical  of  this  hydracid 
he  applies  the  term  xanthogen  (from  |ctv^<35?/e//oi(;,and  yenocca  I gen  erate,) 
expressive  of  the  fact  that  its  combinations  with  several  metals  have  a 
yellow  colour.  The  acid  itself  is  C2\\(td  hydroxanthic  add^  and  its  salts 
hydroxanthates.  The  crystals  deposited  from  the  alcoholic  solution  are 
the  hydroxanthate  of  potassa. 

There  is  no  doubt  of  a new  acid  being  generated  under  the  circum- 
stances deseribed  by  M.  Zeise;  but  since  he  has  not  procured  xanthogen 
in  an  insulated  form,  nor  determined  with  certainty  the  constituent  prin- 
ciples of  hydroxanthic  acid,  there  exists  considerable  uncertainty  as  to 
its  real  nature.  On  tliis  account  I refer  to  the  original  essay  for  more 
ample  details  concerning  it.  (An.  de  Ch.  et  de  Ph.  vol.  xxi.;  and  An- 
nals of  Philosophy,  N.  S.  vol.  iv. ) 

Sulphuret  of  Phosphorus. — When  sulphur  and  fused  phosphorus  are 
brought  into  contact  they  unite  readily,  but  in  proportions  which  have 
not  been  precisely  determined;  and  they  frequently  react  on  each  other 
with  such  violence  as  to  cause  an  explosion.  For  this  reason  the  exper- 
iment should  be  made  with  a quantity  of  phosphorus  not  exceeding 
thirty  or  forty  grains.  I’he  phosphorus  is  placed  in  a glass  tube,  five 
or  six  inches  long,  and  about  half  an  inch  wide;  and  when  by  a gentle 
heat  it  is  liquefied,  the  sulphur  is  added  in  successive  small  portions. 
Caloric  is  evolved  at  the  moment  of  combination,  and  sulphuretted  hy- 
drogen and  phosphoric  acid,  owing  to  the  presence  of  moisture,  are 
generated.  This  compound  may  also  be  made  by  agitating  flowers  of 
sulphur  with  fused  phosphorus  under  water.  The  temperature  should 


274 


COMPOUNDS  OF  SELFNIUM. 


not  exceed  160®  F. ; for  otherwise  sulphuretted  hydrogen  and  phospho- 
ric acid  would  be  evolved  so  freely  as  to  prove  dangerous,  or  at  least 
to  interfere  with  the  success  of  the  process. 

Sulphuret  of  phosphorus,  from  the  nature  of  its  elements,  is  highly 
combustible.  It  is  much  more  fusible  than  phosphorus.  A compound 
made  by  Mr.  Faraday  with  about  five  parts  of  sulphur  and  seven  of 
phosphorus,  was  quite  fluid  at  32®  F.,  and  did  not  solidify  at  20®  F. 
(Quarterly  Journal,  vol.  iv.) 


SECTION  VIIL 

COMPOUNDS  OF  SELENIUM. 

Sulphuret  of  Selenium, 

WHEif  sulphuretted  hydrogen  gas  is  conducted  into  a solution  of 
selenic  acid,  an  orange-coloured  precipitate  subsides,  which  is  a sul- 
phuret of  selenium.  It  fuses  at  a heat  a little  above  212®  F.,  and  at  a 
still  higher  temperature  maybe  sublimed  without  change.  In  the  open 
air  it  takes  fire  when  heated,  and  sulphurous,  selenious,  and  selenic 
acids  are  the  products  of  its  combustion.  The  alkalies  and  alkaline 
hydrosulphurets  dissolve  it.  Nitric  acid  acts  upon  it  with  difficulty; 
but  the  nitro -muriatic  converts  it  into  sulphuric  and  selenious  acids. 
(Annals  of  Philosophy,  vol.  xiv.)  According  to  Berzelius,  this  sul- 
phuret is  composed  of  40  parts  or  one  proportional  of  selenium,  and  24 
parts  or  one  proportional  and  a half  of  sulphur. 

Selenium  and  sulphur  combine  readily  by  the  aid  of  heat,  but  it  is 
difficult  in  this  way  to  obtain  a definite  compound. 

Phosphuret  of  Selenium, 

Phosphuret  of  selenium  majbe  prepared  in  the  same  manner  as  sul- 
phuret of  phosphorus;  but  as  selenium  is  capable  of  uniting  with  phos- 
phorus in  several  proportions,  the  comppund  formed  by  fusing  them 
together  can  hardly  be  supposed  to  be  of  a definite  nature.  This  phos- 
phuret is  very  fusible,  sublimes  without  change  in  close  vessels,  and  is 
inflammable.  It  decomposes  water  gradually  when  digested  in  it,  giv- 
ing rise  to  seleniuretted  hydrogen,  and  one  of  the  acids  of  phosphorus, 
(Annals  of  Philosophy,  vol.  xiv. ) 


GENERAL  PROPERTIES  OF  METALS. 


275  ' 


METALS. 

GENERAL  PROPERTIES  OF  METALS. 

Metals  are  distinguished  from  other  substances  by  the  following 
properties.  They  are  all  conductors  of  electricity  and  caloric.  When 
the  compounds  which  they  form  with  oxygen,  chlorine,  iodine,  sul- 
phur, and  similar  substances,  are  submitted  to  the  action  of  galvanism, 
the  metals  always  appear  at  the  negative  side  of  the  battery,  and  are 
hence  said  to  be  positive  electrics.  They  are  quite  opake,  refusing  a 
passage  to  light,  though  reduced  to  very  thin  leaves.  They  are  in 
general  good  reflectors  of  light,  and  possess  a peculiar  lustre,  which  is 
termed  the  metallic  lustre.  Every  substance  in  which  these  characters 
reside  may  be  regarded  as  a metal. 

The  number  of  metals,  the  existence  of  which  is  admitted  by  chem- 
ists, amounts  to  forty-one.  The  following  table  contains  the  names  of 
those  tliat  have  been  procured  in  a state  of  purity,  together  with  the 
date  at  which  they  were  discovered,  and  the  names  of  the  chemists  by 
whom  the  discovery  was  made. 


Table  of  the  Discovery  of  Metals^ 


Dates  of  the 

Names  of  Metals. 

Authors  of  the  Discovery. 

Discovery, 

Gold 

Silver 

Iron 

Copper  - 
Mercury  - 
Lead 

;>Known  to  the  Ancients. 

Tin 

J 

Antimony 

Described  by  Basil  Valentine 

15th  century. 

Zinc 

Described  by  Agricola  in 

1520 

Bismuth  - 

First  mentioned  by  Paracelsus 

16th  century. 

Arsenic  - 
Cobalt  - ,- 

^ Brandt,  in 

1733 

Platinum 

Wood,  assay-master,  Jamaica, 

1741 

Nickel 

Cronstedt  - . . . 

1751 

Manganese 

Gahn  and  Scheele 

1774 

Tungsten 

MM.  D’Elhuyart 

1781 

Tellurium 

Muller  .... 

1782 

Molybdenum  - 

Hielm  - - 

1782 

Uranium  - 

Klaproth  - - . - 

1789 

Titanium 

Gregor  .... 

1791 

Chromium 

Vauquelin  - - . . 

1797 

Columbium 

Hatchett  - . - . 

1802 

Palladium 

Rhodium 

^ Dr.  Wollaston  * ’ ^ 

1803 

Iridium  - 

Descotils  and  Smithson  Tennant 

1803 

Osmium  - 

Smithson  Tennant 

1803 

Cerium  - 

Hisinger  and  Berzelius 

1804 

276 


GENERAL  PROPERTIES  OF  METALS. 


Names  of  Metals* 

Potassium 
Sodium  - 
Barium  - 
Strontium 
Calcium  - 
Cadmium 
Lithium  - 
Silicium  - 
Zirconium 
Aluminium 
Glucinium 
Yttrium  - 
Thorium 
Mag'nesium 


Authors  of  the  Discoveiy. 


3ir  H.  Davy 


Stromeyer 

Arfwedson 

- Berzelius 


-Wohler 

Berzelius 

Bussy  and  Wohler 


Dates  of  the 
Discovery. 


1807 


1818 

1818 

1824 


1828 

1829 

1829 


Most  of  the  metals  are  remarkable  for  their  great  specific  gravity; 
some  of  them,  such  as  gold  and  platinum,  which  are  the  densest  bod- 
ies known  in  nature,  being  more  than  nineteen  times  heavier  than  an 
equal  bulk  of  water.  Great  specific  gravity  was  once  supposed  to  be 
an  essential  characteristic  of  metals;  but  the  discovery  of  potassium 
and  sodium,  which  are  so  light  as  to  float  on  the  surface  of  water,  has 
shown  that  this  supposition  is  erroneous.  Some  metals  experience  an 
increase  of  density  to  a certain  extent  when  hammered,  their  particles 
being  permanently  approximated  by  the  operation.  On  this  account, 
the  specific  gravity  of  some  of  the  metals  contained  in  the  following 
table  is  represented  as  varying  between  two  extremes. 

Table  of  the  Specific  Gravity  of  Metals  at  60®  Fahr,  compared  to  Water 
as  Unity, 


Platinum 

. 

20.98 

- 

Brisson 

Gold 

- 

19.257 

- 

Do. 

Tungsten 

- 

17.6 

- 

D’Elhuyart 

Mercury 

- 

13.568 

- 

Brisson 

Palladium 

11.3  to  11.8  - 

- 

AYollaston 

Lead 

- 

11.352 

- 

Brisson 

Silver 

- 

10.474 

- 

Do. 

Bismuth 

. 

9.822 

- 

Do. 

Uranium  - 

- 

9.000 

- 

Bucholz 

Copper 

. 

8.895 

- 

Hatchett 

Cadmium  - 

- 

8.604 

- 

Stromeyer 

Cobalt 

- 

8.538 

- 

Haiiy 

Arsenic 

- 

5.8843 

- 

Turner 

Nickel 

- 

8.279 

- 

Richter 

Iron 

- 

7.783 

- 

Brisson 

Molybdenum 

- 

7.400 

- 

Hielm 

Tin 

- 

7.291 

- 

Brisson 

Zinc 

- 

6.861  to  7.1 

- 

Do. 

Manganese 

- 

6.850 

- 

Bergmann 

Antimony  - 

- 

6.702 

- 

Brisson 

Tellurium  - 

- 

6.115 

- 

Klaproth 

'ritanium  - 

- 

5.3 

- 

Wollaston 

Sodium 

- 

0.972  7 

- 

C Gay-Lussac  and 

Potassium  - 

- 

0.865  3 

- 

\ The  hard 

GENERAL  PROPERTIES  OF  METALS. 


m 


Some  metals  possess  the  property  of  malleahility^  that  is,  admit  of 
being*  beaten  into  thin  plates  or  leaves  by  hammering.  The  malleable 
metals  are  gold,  silver,  copper,  tin,  platinum,  palladium,  cadmium, 
lead,  zinc,  iron,  nickel,  potassium,  sodium,  and  frozen  mercury.  The 
other  metals  are  either  malleable  in  a very  small  degree  only,  or,  like 
antimony,  arsenic,  and  bismuth,  are  actually  brittle.  Gold  surpasses 
all  metals  in  malleability:  one  grain  of  it  may  be  extended  so  as  to  cover 
about  52  square  inches  of  surface,  and  to  have  a thickness  not  exceed- 
ing l-282020th  of  an  inch. 

Nearly  all  malleable  metals  may  be  drawn  out  into  wires,  a property 
which  is  expressed  by  the  term  ductility.  The  only  metals  which  are 
remarkable  in  this  respect  are  gold,  silver,  platinum,  iron,  and  copper. 
Dr.  Wollaston  has  described  a method  by  which  gold  wire  may  be  ob- 
tained so  fine  that  its  diameter  shall  be  only  l-5000th  of  an  inch,  and 
that  550  feet  of  it  are  required  to  weigh  one  grain.  He  obtained  a pla- 
tinum wire  so  small,  that  its  diameter  did  not  exceed  1-30, 000th  of  an 
inch.  (Philos.  Transactions  for  1813.)  It  is  singular  that  the  ductility 
and  malleability  of  the  same  metal  are  not  always  in  proportion  to  each 
other.  Iron,  for  example,  cannot  be  made  into  fine  leaves,  but  it  may 
be  drawn  into  very  small  wires. 

The  tenacity  of  metals  is  measured  by  ascertaining  the  greatest  weight 
which  a wire  of  a certain  thickness  can  support,  without  breaking. 
According  to  the  experiments  of  Guyton-Morveau,  whose  results  are 
comprised  in  the  following  table,  iron,  in  point  of  tenacity,  surpasses 


all  other  metals. 

The  diameter  of  each  wire  was  0.787th  of  a line. 

Pounds, 

Iron  wire  supports  ...  - 549.25 

Copper  - ...  - 302.278 

Platinum  .....  274.32 

Silver  .....  187.137 

Gold 150.753 

Zinc  - - ...  109. 54 

Tin  ......  34.63 

Lead  .....  27.621 


Metals  differ  also  in  hardness,  but  I am  not  aware  that  their  exact  re- 
lation to  each  other,  under  this  point  of  view,  has  been  determined  by 
experiment.  In  the  list  of  hard  metals  may  be  placed  titanium,  man- 
ganese, iron,  nickel,  copper,  zinc,  and  palladium.  Gold,  silver,  and 
platinum,  are  softer  than  these;  lead  is  softer  still,  and  potassium  and 
sodium  yield  to  the  pressure  of  the  fingers.  The  properties  of  elasti- 
city and  sonorousness  are  allied  to  that  of  hardness.  Iron  and  copper 
are  in  these  respects  the  most  conspicuous. 

Many  of  the  metals  have  a distinctly  crystalline  texture.  Iron,  for 
example,  is  fibrous;  and  zinc,  bismuth,  and  antimony  are  lamellated  ^ 
Metals  are  sometimes  obtained  also  in  crystals;  and  when  they  do  crys^ 
tallize,  they  always  assume  the  figure  of  a cube,  the  regular  octohedron, 
or  some  form  allied  to  it.  Gold,  silver,  and  copper,  occur  naturally  in 
crystals,  while  others  crystallize  when  they  pass  gradually  from  the  li- 
quid to  the  solid  condition.  Crystals  are  most  readily  procured  from 
those  metals  which  fuse  at  a low  temperature;  and  bismuth,  from  con- 
ducting caloric  less  perfectly  than  other  metals,  and  therefore  cooling 
more  slowly,  is  best  fitted  for  the  purpose.  The  process  should  be 
conducted  in  the  way  already  described  for  forming  crystals  of  sulphur* 
(Page  183.) 


24 


278 


GENERAL  PROPERTIES  OF  METALS. 


Metals,  with  the  exception  of  mercury,  are  solid  at  common  tern* 
peratures;  but  they  may  be  all  liquefied  by  heat.  The  degree  at  which 
they  fuse,  or  their  point  of  fusion,  is  very  different  for  different  me- 
tals, as  will  appear  by  inspecting  the  following  table.  (Thenard’s 
Chemistry,  vol.  i.) 

Table  of  the  Fusibility  of  different  Metals, 


red  heat. 


■"Mercury 

Fahr. 

—39° 

Potassium 

- 

136 

Sodium 

- 

190 

Tin 

- 

430 

Bismuth  - 

- 

493 

Lead 

J Tellurium— 

500 

-rather  less 

fusible  than  lead 

Arsenic — undetermined. 

Zinc 

- 

698 

Antimony — a little  be- 
low a red  heat. 
l^Cadmium 


Different  chemists. 

> Gay-Lussac  and  T! 
\ nard. 

j Newton. 

Biot. 

Klaproth. 

Brongniart. 

Stromeyer. 


Pyrometer  of  Wedgwood. 
(^Silver  - 20°  Kennedy. 

‘ Copper  - 27 

Gold  - 32 

Cobalt — rather  less  fu- 
sible than  iron. 

C130 
ll58 
160 


Iron 


^ Wedgwood. 


Wedgwood. 

Mackenzie. 


Guyton. 


Infusible  below  < 
a red  heat. 


Manganese 
Nickel — the  same  as 

Manganese  - Richter. 

Palladium 

Molybdenum')  Almostinfusible,  and  f 

Pf «“>-ed  in J the  oxy-hydro- 


Uranium 
Tungsten 
Chromium 
Titanium 
Cerium 
Osmium 
Iridium 
Rhodium 
Platinum 
J Columbium  J 


Infusible  in  the  heat  of  a smith’s  forge, 
but  fusible  before  the  oxy-hydrogen 
blowpipe. 


Metals  differ  also  in  volatility.  Some  are  readily  volatilized  by  calo- 
ric, while  others  are  of  so  fixed  a nature  that  they  may  be  exposed  to 
the  most  intense  heat  of  a wind  furnace  without  being  dissipated  in  va- 
pour. "rhere  are  seven  metals  the  volatility  of  which  has  been  ascer- 
tained with  certainty;  namely,  cadmium,  mercury,  arseniC)  tellurium, 
potassium,  sodium,  and  zinc. 

Metals  cannot  be  resolved  into  more  sim])le  parts;  and,  therefore,  in 
the  present  state  of  chemistry,  they  must  be  regarded  as  elementary 
bodies.  It  was  fonncrly  conceived  that  they  might  be  converted  into 
each  other;  and  this  notion  led  to  the  vain  attempts  of  the  alchemists 
to  convert  the  baser  metals  into  gold.  The  chemist  has  now  learned 


GENERAL  PROPERTIES  OF  METALS. 


m 

that  his  art  solely  consists  in  resolving*  compound  bodies  into  their 
elements,  and  causing  substances  to  unite  which  were  previously 
uncombined.  There  is  not  a single  fact  in  support  of  the  opinion 
that  one  elementary  principle  can  assume  the  properties  peculiar  to 
another. 

Metals  have  an  extensive  range  of  affinity,  and  on  this  account  few 
of  them  are  found  in  the  earth  native,  that  is,  in  an  uncombined  form. 
They  commonly  occur  in  combination  with  other  bodies,  especially 
with  oxygen  and  sulphur,  in  which  state  they  are  said  to  be  mineralize 
ed.  It  is  a singular  fact  in  the  chemical  history  of  the  metals,  that  they 
are  little  disposed  to  combine  in  the  metallic  state  with  compound  bo- 
dies. Chemists  are  not  acquainted  with  any  instance  of  a metal  forni- 
ing  a definite  compound  either  with  a metallic  oxide  or  with  an  acid. 
They  unite  readily,  on  the  contrary,  with  elementary  substances.  Thus, 
under  favourable  circumstances,  they  combine  with  each  other,  yield- 
ing compounds  termed  alloys,  which  possess  all  the  characteristic  phy- 
sical properties  of  pure  metals.  They  unite  likewise  with  the  simple 
substances  not  metallic,  such  as  oxygen,  chlorine,  and  sulphur,  giving 
rise  to  new  bodies  in  which  the  metallic  character  is  wholly  wanting. 
In  all  these  combinations  the  same  tendency  to  unite  in  a few  definite 
proportions  is  as  conspicuous,  as  in  that  department  of  the  science  of 
which  I have  just  completed  the  description.  The  chemical  changes 
are  regulated  by  the  same  general  laws,  and  in  describing  them  the 
same  nomenclature  is  applicable. 

The  order  which  it  is  proposed  to  follow  in  treating  the  metallic  bo- 
dies has  already  been  explained  in  the  introduction.  Before  proceed- 
ing, however,  to  describe  the  metals  individually,  some  general  obser- 
vations may  be  premised,  by  which  the  study  of  this  subject  will  be 
much  facilitated. 

Metals  are  of  a combustible  nature,  that  is,  they  are  not  only  suscep- 
tible of  slow  oxidation,  but,  under  favourable  circumstances,  they  unite 
rapidly  with  oxygen,  giving  rise  to  all  the  phenomena  of  real  combus- 
tion. Zinc  burns  with  a brilliant  flame  when  heated  to  full  redness  in 
the  open  air;  iron  emits  vivid  scintillations  on  being  inflamed  in  an  at- 
mosphere of  oxygen  gas;  and  the  least  oxidable  metals,  such  as  gold 
and  platinum,  scintillate  in  a similar  manner  when  heated  by  the  oxy? 
hydrogen  blowpipe. 

I'he  product  either  of  the  slow  or  rapid  oxidation  of  a metal,  when 
heated  in  tl\e  air,  has  an  earthy  aspect,  and  was  called  a calx  by  the 
older  chemists,  the  process  of  forming  it  being  expressed  by  the  term 
calcination.  Another  method  of  oxidizing  metals  is  by  deflagration; 
that  is,  by  mixing  them  with  nitrate  or  chlorate  of  potassa,  and  project- 
ing the  mixture  into  a red-hot  crucible.  Most  metals  may  be  oxidized 
by  digestion  in  nitric  acid;  and  nitro-muriatic  acid  is  an  oxidizing  agent 
of  still  greater  ])ower. 

Some  metals  unite  with  oxygen  in  one  proportion  only,  but  most  of 
them  have  twp  or  three  degrees  of  oxidation.  Metals  differ  remarkably 
in  their  relative  forces  of  attraction  for  oxygen.  Potassium  and  sodium, 
for  example,  are  oxidized  by  mere  exposure  to  the  air;  and  they  de- 
compose water  at  all  temperatures  the  instant  they  come  in  contact  with 
it.  Iron  and  copper  may  be  preserved  in  dry  air  witliout  change,  nor 
can  they  decompose  water  at  common  temperatures;  but  they  are  both 
slowly  oxidized  by  exposure  to  a moist  atmosphere,  and  combine  ra- 
pidly with  oxygen  wlien  heated  to  redness  in  the  open  air.  Iron  has  a 
stronger  affinity  for  oxygen  than  copper;  for  the  former  decomposes 
water  at  a red  heat,  whereas  the  latter  cannot  produce  that  effect. 
Mercury  is  less  inclined  than  copper  to  unite  with  oxygen.  Thus  it  may 


280 


GENERAL  PROPERTIES  OF  METALS. 


be  exposed  without  chang*e  to  the  infliience  of  a rhoist  atmosphere. 
At  a temperature  of  650®  or  700®  F.  it  is  oxidized;  but  at  a red  lieat  it 
is  reduced  to  tlie  metallic  state,  while  oxide  of  copper  can  sustain  the 
strong*est  heat  of  a blast  furnace  without  losing*  its  oxyg*en.  The  affi- 
nity of  silver  for  oxygen  is  still  weaker  than  that  of  mercury;  for  it 
cannot  be  oxidized  by  the  sole  agency  of  caloric  at  any  temperature. 

Metallic  oxides  suffer  reduction^  or  may  be  reduced  to  the  metallic 
state,  in  several  ways: 

1.  By  heat  alone.  By  this  method  the  oxides  of  gold,  silver,  mercu- 
ry, and  platinum  may  be  decomposed. 

2.  By  the  united  agency  of  heat  and  combustible  matter.  Thus,  by 
transmitting  a current  of  hydrogen  gas  over  the  oxides  of  copper  or 
iron,  heated  to  redness  in  a tube  of  porcelain,  water  is  generated,  and 
the  metals  are  obtained  in  a pure  form.  Carbonaceous  matters  are 
likewise  used  for  the  purpose  with  great  success.  Potassa  and  soda, 
for  example,  may  be  decomposed  by  exposing  them  to  a white  heat 
after  being  intimately  mixed  with  charcoal  in  fine  powder.  A similar 
process  is  employed  in  metallurgy  for  extracting  metals  from  their  ores, 
the  inflammable  materials  being  wood,  charcoal,  coke,  or  coal.  In  the 
more  delicate  operations  of  the  laboratory,  charcoal  and  hlach  flux  are 
p referred. 

3.  By  the  galvanic  battery.  This  is  a still  more  powerful  agent  than 
the  preceding;  since  some  oxides,  such  as  baryta  and  strontia,  which 
resist  the  united  influence  of  heat  and  charcoal,  are  reduced  by  the 
agency  of  galvanism. 

4.  By  the  action  of  deoxidizing  agents  on  metallic  solutions.  Phos- 
phorous acid,  for  example,  when  added  to  a liquid  containing  oxide  of 
mercury,  deprives  the  oxide  of  its  oxygen,  metallic  mercury  subsides, 
and  phosphoric  acid  is  generated.  In  like  manner,  one  metal  may  be 
precipitated  by  another,  provided  the  affinity  of  the  latter  for  oxygen 
exceeds  that  of  the  former.  Thus,  when  mercury  is  added  to  a solu- 
tion of  nitrate  of  the  oxide  of  silver,  metallic  silver  is  thrown  down, 
and  oxide  of  mercury  is  dissolved  by  the  nitric  acid.  On  placing  me- 
tallic copper  in  the  liquid,  pure  mercury  subsides,  and  a nitrate  of  the 
oxide  of  copper  is  formed;  and  from  this  solution  metallic  copper  may 
be  precipitated  by  means  of  iron. 

Metals,  like  the  simple  non-metallic  bodies,  may  give  rise  to  oxides 
or  acids  by  combining  with  oxygen.  The  former  are  the  most  frequent 
products.  Many  metals  which  are  not  acidified  by  oxygen  may  be 
formed  into  oxides;  whereas  one  metal  only,  arsenic,  is  capable  of 
forming  an  acid  and  not  an  oxide.  All  the  other  metals  which  are  con- 
vertible into  acids  by  oxygen,  such  as  chromium,  tungsten,  and  mo- 
lybdenum, are  also  susceptible  of  yielding  one  or  more  oxides.  In  these 
instances,  the  acids  always  contain  a larger  quantity  of  oxygen  than  the 
oxides  of  the  same  metal. 

I'he  distinguishing  feature  of  metallic  oxides  is  the  property  which 
many  possess  of  entering  into  combination  with  acids.  All  salts,  those 
of  ammonia  excepted,  are  composed  of  an  aciiHind  a metallic  oxide. 
In  some  instances  all  the  oxides  of  the  same  metal  are  capable  of  form- 
ing salts  with  acids,  as  is  exemplified  by  the  oxides  of  iron.  More  com- 
monly, however,  the  protoxide  is  the  sole  alkaline  or  sail flahk  base.  Most 
of  the  metallic  oxides  arc  Insoluble  in  water;  but  all  those  that  are  soluble 
have  the  property  of  giving  a brown  stain  to  yellow  turmeric  paper,  and 
of  restoring  the  blue  colour  of  reddened  litmus. 

Oxides  sometimes  unite  with  each  other,  and  form  definite  compounds. 
The  most  abundant  ore  of  chromium,  commonly  called  chromate  of 
iron,  is  an  instance  of  this  kind;  and  the  red  and  deutoxidc  of  manga- 


GENERAL  PROPERTIES  OF  METALS.  281 

nese,  and  the  rod  oxide  of  lead,  appear  to  belong*  to  the  same  class  of 
bodies. 

Chlorine  has  a powerful  affinity  for  metallic  substances.  It  combines 
readily  with  most  metals  at  common  temperatures,  and  the  action  is  in 
many  instances  so  violent  as  to  be  accompanied  with  the  evolution  of 
light.  For  example,  when  powdered  zinc,  arsenic,  or  antimony,  is 
thrown  into  ajar  of  chlorine  gas,  the  metal  is  instantly  inflamed.  The 
attraction  of  chlorine  for  metals  even  surpasses  that  of  oxygen.  Thus 
when  chlorine  is  brought  into  contact  at  a red  heat  with  pure  lime,  mag- 
nesia, baryta,  strontia,  potassa,  or  soda,  oxygen  is  emitted,  and  a chlo- 
ride of  the  metal  is  generated,  the  elements  of  which  are  so  strongly 
united  that  no  temperature  hitherto  tried  can  separate  them.  All  other 
metallic  oxides  are,  with  few  exceptions,  acted  on  in  the  same  manner 
by  chlorine,  and  in  some  cases  the  change  takes  place  below  the  tem- 
perature of  ignition. 

All  the  metallic  chlorides  are  solid  at  the  common  temperature,  ex- 
cept the  bichlorides  of  tin  and  arsenic,  which  are  liquid.  They  are  fu- 
sible by  heat,  assume  a crystalline  texture  in  cooling,  and  under  favour- 
able circumstances  crystallize  with  regularity.  Several  of  them,  such 
as  the  chlorides  of  tin,  arsenic,  antimony,  and  mercury,  are  volatile,  and 
may  be  sublimed  without  change.  They  are  for  the  most  part  colour- 
less, do  not  possess  the  metallic  lustre,  and  have  the  aspect  of  a salt. 
Two  of  the  chlorides  are  insoluble  in  water,  namely,  chloride  of  silver 
and  protochloride  of  mercury;  but  all  the  others  are  more  or  less  solu- 
ble in  water. 

Two  only  of  the  metallic  chlorides,  those  namely  of  gold  and  plati- 
num, are  decomposable  by  heat.  All  the  chlorides  of  the  common- 
metals  are  decomposed  at  a red  heat  by  hydrogen  gas,  muriatic  acid 
being  disengaged  while  the  metal  is  set  free.  Pure  charcoal  does  not 
effect  their  decomposition;  but  if  moisture  be  pi’esent  at  the  same  t^me, 
muriatic  and  carbonic  acid  gases  are  formed,  and  the  metal  remains. 
They  resist  the  action  of  anhydrous  sulphuric  acid;  but  all  the  chlorides, 
excepting  those  of  silver  and  mercury,  are  readily  decomposed  by  hy- 
drated sulphuric  acid,  with  disengagement  of  muriatic  acid  gas.  The 
change  is  accompanied  with  decomposition  of  water,  the  hydrogen  of 
which  combines  with  chlorine,  and  its  oxygen  with  the  metal.  All 
chlorides,  when  in  solution,  may  be  recognised  by^  yielding  with  nitrate 
of  silver  a white  precipitate,  which  is  chloride  of  silver. 

Metallic  chlorides  may  in  most  cases  be  formed  by  direct  action  of 
chlorine  on  the  pure  metals.  They  are  also  frequently  procured  by 
evaporating  a'  solution  of  the  muriate  of  a metallic  oxide  to  dryness, 
and  applying  heat  so  long  as  any  water  is  expelled.  Metallic  chlorides 
are  often  deposited  from  such  solutions  by  crystallization. 

Chlorine  manifests  a feeble  affinity  for  metallic  oxides.  No  combina- 
tion of  the  kind  occurs  at  a red  heat,  and  no  chloride  of  a metallic  oxide 
can  be  heated  to  redness  without  decomposition.  Such  compounds  can 
only  be  formed  at  low  temperatures;  and  they  are  possessed  of  little 
permanency.  It  is  well  known  that  chlorine  may  combine  under  fa- 
vourable circumstances  with  the  alkalies  and  alkaline  earths;  and  M. 
Grouvelle  has  succeeded  in  making  it  unite  with  magnesia,  and  the 
oxides  of  zinc,  copper',  andiron.  (An.  de  Ch.  etde  Ph.  vol.xvii.)  Of 
these  chlorides,  that  of  potassa  may  be  taken  as  an  example.  If  chlo- 
rine is  conducted  into  a dilute  and  cold  solution  of  pure  potassa,  the 
chloride  of  that  alkali  will  be  produced;  but  the  affinity  which  gives 
rise  to  its  formation  is  not  sufficient  for  rendering  it  permanent.  It  is 
destroyed  by  most  substances  that  act  on  either  of  its  constituents.  The 
addition  of  an  acid  produces  tliis  effect  by  combining  with  tlic  alkali, 

24* 


282 


GENERAL  PROPERTIES  OF  METALS. 


and  hence  the  chlorine  is  separated  by  the  carbonic  acid  of  the  atmos- 
phere. Animal  or  vegetable  colouring  matters  arc  fatal  to  the  com- 
pound, by  giving  chlorine  an  opportunity  to  exert  its  bleaching  power; 
and,  indeed,  the  colour  is  removed  by  the  chloride  of  potassa  almost  as 
readily  as  by  a solution  of  chlorine  in  pure  water.  It  is  also  destroyed 
by  the  action  of  heat;  nor  can  its  solution  be  concentrated  without  de- 
composition; for,  in  either  case,  muriatic  and  chloric  acids  are  genera- 
ted. (Page  206.) 

Berzelius  has  published  some  ingenious  remai’hs  in  order  to  prove 
that  chlorine  does  not  unite  with  metallic  oxides,  and  that  the  bleach- 
ing compounds,  supposed  to  be  examples  of  such  a mode  of  combina- 
tion, are  mixtures  of  a metallic  chloride  and  a chlonVe  of  an  oxide.  The 
tendency  of  the  supposed  chlorite  is  to  pass  into  a chlorate  and  chlo- 
ride, as  by  the  application  of  heat;  but  if  colouring  matter  or  an  oxida- 
ble  substance  be  present,  the  chlorous  acid  yields  its  oxygen,  and  a 
metallic  chloride  results.  The  bleaching  power  of  the  compound  is  of 
course  attributed  to  the  oxygen  which  is  set  at  liberty.  This  point  is 
powerfully  argued  by  Berzelius,  and  supported  on  well -contrived  ex- 
periments; but  since  no  decisive  proof  of  the  existence  of  such  a com- 
pound as  chlorous  acid  has  as  yet  been  given,  there  appears  to  be  no 
sufficient  reason  for  rejecting  the  explanation  generally  adopted  by 
chemists.  (An.  de  Ch.  et  de  Ph.  xxxviii.  208. ) 

Iodine  has  a strong  attraction  for  metals;  and  most  of  the  compounds 
which  it  forms  with  them  sustain  a red  heat  in  close  vessels  without  de- 
composition. But  in  the  degree  of  its  affinity  for  metallic  substances 
it  is  inferior  to  chlorine  and  oxygen.  We  have  seen  that  chlorine  has  a 
stronger  affinity  than  oxygen  for  metals,  since  it  decomposes  nearly  all 
oxides  at  high  temperatures;  and  it  separates  iodine  also  from  metals 
under  the  same  circumstances.  If  the  vapour  of  iodine  is  brought  into 
contact  with  potassa,  soda,  protoxide  of  lead,  or  oxide  of  bismuth, 
heated  to  redness,  oxygen  gas  is  evolved,  and  an  iodide  of  these  me- 
tals will  be  foi'med.  But  iodine,  so  far  as  is  known,  cannot  separate 
oxygen  from  any  other  metal;  nay,  all  the  iodides,  except  those  just 
mentioned,  are  decomposed  by  exposure  to  oxygen  gas  at  the  tempera- 
ture of  ignition.  All  the  iodides  are  decomposed  by  chlorine,  bro- 
mine, and  concentrated  sulphuric  and  nitric  acids;  and  the  iodine 
which  is  set  free  ma^  be  recognised  either  by  the  colour  of  its  vapour, 
or  by  its  action  on  starch.  (Page  221.)  The  metallic  iodides  are  gen- 
erated under  circumstances  analogous  to  those  above  mentioned  for  pro- 
curing the  chlorides. 

When  the  vapour  of  iodine  is  conducted  over  red-hot  lime,  baryta, 
or  strontia,  oxygen  is  not  disengaged,  but  an  iodide  of  those  oxides, 
according  to  Gay-Lussac,  is  generated.  The  iodides  of  these  oxides 
are,  therefore,  more  permanent  than  the  analogous  compounds  with 
chlorine.  Iodine  does  not  combine  with  any  other  oxide  under  the 
same  circumstances;  and  indeed  all  other  such  iodides,  very  few  of 
which  exist,  are,  like  the  chlorides  of  oxides,  possessed  of  little  per- 
manency, and  are  decomposed  by  a red  heat. 

The  action  of  iodine  on  metallic  oxides,  when  dissolved  or. suspended 
in  water,  is  precisely  analogous  to  that  of  chlorine.  On  adding  iodine 
to  a solution  of  the  pure  alkalies  or  alkaline  eai’ths,  water  is  decomposed, 
and  hydriodic  and  iodic  acids  are  generated. 

Bromine,  in  its  affinity  for  ^metallic  substances,  is  intermediate  be- 
tween chlorine  and  iodine;  for  while  cldorine  disengages  bromine  from 


GENERAL  PROPERTIES  OF  METALS. 


283 


its  combination  with  metals,  metallic  iodides  are  decomposed  by  bro- 
mine. The  same  phenomena  attend  the  union  of  bromine  with  metals, 
as  accompany  the  formation  of  metallic  chlorides.  Thus,  antimony  and 
tin  take  fire  by  contact  with  bromine,  and  its  action  with  potassium  is 
attended  with  a flash  of  light  and  intense  disengagement  of  caloric. 
These  compounds  have  as  yet  been  but  partially  examined.  They  may 
be  formed  either  by  the  action  of  bromine  on  the  pure  metals,  or  by 
dissolving  metallic  oxides  in  hydrobromic  acid,  and  evaporating  the  so- 
lution to  dryness.  Broniine  unites  with  potassa,  soda,  and  some  other 
oxides,  constituting  bleaching  compounds  similar  to  the  chlorides  above 
described.  Bromide  of  lime  is  obtained  by  the  action  of  bromine  on 
milk  of  lime,  a yellowish  solution  being  formed  with  water,  which 
bleaches  powerfully. 

As  fluorine  has  not  hitherto  been  obtained  in  a separate  state,  the 
nature  of  its  action  on  the  metals  is  unknown;  but  the  chief  difficulty 
of  procuring  it  in  an  insulated  form  appears  to  arise  from  its  extremely 
powerful  affinity  for  metallic  substances,  in  consequence  of  which,  at 
the  moment  of  becoming  free,  it  attacks  the  vessels  and  instruments 
employed  in  its  preparation.  The  best  mode  of  preparing  the  soluble 
fluorides,  such  as  those  of  potassium  and  sodium,  is  by  dissolving  the 
carbonates  of  the  alkalies  of  these  metals  in  hydrofluoric  acid,  and 
evaporating  the  solution  to  perfect  dryness.  The  insoluble  fluorides 
are  easily  formed  from  the  hydrofluates  of  potassa  and  soda  by  dou- 
ble decomposition.  These  compounds  are  without  exception  de- 
composed by  concentrated  sulphuric  acid  with  the  aid  of  heat;  and 
the  hydrofluoric  acid,  in  escaping,  may  easily  be  detected  by  its  action 
on  glass. 

Sulphur,  like  the  preceding  elementary  substances,  has  a strong  ten- 
dency to  unite  with  metals,  and  the  combination  may  be  effected  in 
several  ways. — 

1.  By  heating  the  metal  directly  with  sulphur.  The  metal,  in  the 
form  of  powder  or  filings,  is  mixed  with  a due  proportion  of  sulphur, 
and  the  mixture  heated  in  an  earthen  crucible,  which  is  covered  to 
prevent  the  access  of  air.  Or  if  the  metal  can  sustain  a red  heat  with- 
out fusing,  the  vapour  of  sulphur  may  be  passed  over  it  while  heated 
to  redness  in  a tube  of  porcelain.  The  act  of  combination,  which  fre- 
quently ensues  below  the  temperature  of  ignition,  is  attended  by  free 
disengagement  of  caloric;  and  in  several  instances  the  heat  evolved  is  so 
great,  that  the  whole  mass  becomes  luminous,  and  shines  with  a vivid 
light.  This  appearance  of  combustion,  which  occurs  quite  indepen- 
dently of  the  presence  of  oxygen,  is  exemplified  by  the  sulphurets  of 
potassium,  sodium,  copper,  iron,  lead,  and  bismuth. 

2.  By  igniting  a mixture  of  a metallic  oxide  and  sulphur.  The  sul- 
phurets of  the  common  metals  may  be  made  by  this  process.  The  ele- 
ments of  the  oxide  unite  with  separate  portions  of  sulphur,  forming 
sulphurous  acid  gas,  which  is  disengaged,  and  a metallic  sulphuret 
which  remains  in  the  retort. 

3.  By  depriving  the  sulphate  of  an  oxide  of  its  oxygen  by  means  of 
heat  and  combustible  matter.  Charcoal  or  hydrogen  gas  may  be  em- 
ployed for  the  purpose,  as  will  be  described  Immediately. 

4.  By  sulphuretted  hydrogen,  or  an  alkaline  hydrosulphuret.  Nearly 
all  the  salts  of  the  common  metals  are  decomposed  when  a current  of 
sulphuretted  hydrogen  gas  is  conducted  into  their  solutions.  The 
salts  of  uranium,  iron,  manganese,  cobalt,  and  nickel  are  well-known 


284 


GENERAL  PROPERTIES  OP  METALS. 


exceptions;  but  these  also  are  precipitated  by  hydrosulplmrct  of  ammo- 
nia or  potassa. 

The  sulphurets  are  ppake  brittle  solids,  many  of  which,  such  as  the 
sulphurets  of  lead,  antimony,  and  iron,  have  a metallic  lustre.  They 
are  all  fusible  by  heat,  and  commonly  assume  a crystalline  texture  in 
cooling*.  Most  of  them  are  fixed  in  the  fire;  but  the  sulphurets  of  mer- 
cury and  arsenic  are  remarkable  for  their  volatility.  All  the  sulphurets, 
excepting  those  which  are  formed  of  the  metallic  bases  of  the  alkalies 
and  earths,  are  insoluble  in  water. 

Most  of  the  protosulphurets  are  capable  of  supporting  intense  heat 
without  decomposition;  but  those  which  contain  more  than  one  equivalent 
of  sulphur,  lose  part  of  it  when  strongly  heated.  They  are  all  decom- 
posed without  exception  by  exposure  to  the  combined  agency  of  heat 
and  air  or  oxygen  gas;  and  the  products  depend  entirely  on  the  degree 
of  heat  and  the  nature  of  the  metal.  The  sulphuret  is  converted  into 
the  sulphate  of  an  oxide,  provided  the  sulphate  is  able  to  support  the 
temperature  employed  in  the  operation.  If  this  is  not  the  case,  then 
the  sulphur  is  evolved  under  the  form  of  sulphurous  acid,  and  a metal- 
lic oxide  is  left;  or  if  the  oxide  itself  is  decomposed  by  heat,  the  pure 
metal  remains.  The  action  of  heat  and  air  in  decomposing  metallic 
sulphurets  is  the  basis  of  several  metallurgic  processes.  A few  sulphu- 
rets are  decomposed  by  the  action  of  hydrogen  gas  at  a red  heat,  the 
pure  metal  being  set  free  and  sulphuretted  hydrogen  evolved.  M.  Rose 
finds  that  the  only  sulphurets  which  admit  of  being  easily  reduced  to 
the  metallic  state  in  this  way  are  those  of  antimony,  bismuth,  and  sil- 
ver. The  sulphuret  of  tin  is  decomposed  with  difficulty,  and  requires 
a very  high  temperature.  All  the  other  sulphurets  which  he  subjected 
to  this  treatment  were  either  deprived  of  a part  only  of  their  sulphur, 
such  as  bisulphuret  of  iron,  or  were  not  attacked  at  all,  as  happened 
with  the  sulphurets  of  zinc,  lead,  and  copper.  (Poggendorff  ^s  Annalen, 
iv.  109.) 

Many  of  the  metallic  sulphurets  were  formerly  thought  to  be  com- 
pounds of  sulphur  and  a metallic  oxide;  an  error  first  pointed  out  by 
Proust  in  the  essays  which  he  published  in  the  Journal  de  Physique.  In 
the  53d  volume  of  that  work,  he  demonstrated  that  sulphuret  of  iron 
(magnetic  pyrites,)  as  well  as  the  common  cubic  pyrites  or  bisulphuret, 
are  compounds  of  sulphur  and  metallic  iron  without  any  oxygen.  He 
showed  the  same  also  with  respect  to  the  sulphurets  of  other  metals, 
such  as  those  of  mercury  and  copper.  He  was  of  opinion,  however, 
that  in  some  instances  sulphur  does  unite  with  a metallic  oxide.  Thus, 
when  sulphur  and  peroxide  of  tin  are  heated  together,  sulphurous  acid 
is  disengaged,  and  the  residue,  according  to  Proust,  is  a sulphuret  of 
the  protoxide. 

It  was  the  general  belief  at  that  time,  also,  that  the  compounds  formed 
by  heating  sulphur  with  an  alkali  or  alkaline  earth  are  sulphurets  of  a 
metallic  oxide.  Thus,  the  old.  hepar  sulphuris,  sulphuretum potassse  oH 
the  Edinburgh  Pharmacopoeia,  which  is  made  by  fusing  together  a mix- 
ture of  siilphur  and  dry  carbonate  of  potassa,  was  regarded  as  a sulphu- 
ret of  potassa.  In  tlie  year  1817  M.  Vauquelln  published  an  essay  in 
the  6th  volume  of  \\\o  Annalcs  de  Chimiect  dc  Physique,  wherein  he  de- 
tailed some  experiments,  the  object  of  which  was  to  determine  tlie  state 
of  the  alkali  in  that  compound.  Tlie  late  count  Berthollet  had  observed 
that  when  hepar  sulphuris  is  dissolved  in  water,  the  solution  always  con- 
tains a considcral)le  portion  of  sulphuric  acid,  which  he  conceived  to 
be  generated  at  the  moment  of  solution.  He  su])posed  that  water  is 
then  decomposed;  and  that  its  elements  comijine  with  different  portions 
of  sulphur,  the  oxygen  giving  rise  to  the  formation  of  sulphuric  acid. 


GENERAL  PROPERTIES  OF  METALS. 


285 


and  the  hydrbg'en  to  sulphuretted  hydrog’en.  The  accuracy  of  this  ex- 
planation was  called  in  question  Vauquelin  in  the  paper  above  men- 
tioned, who  contended  that  the  sulphuric  acid  is  generated,  not  during 
the  process  of  solution,  but  by  the  action  of  heat  during  the  formation 
of  the  sulphuret.  One  portion  of  potassa,  according  to  him,  yields  its 
oxygen  at  a high  temperature  to  some  of  the  sulphur,  converting  it  in- 
to sulphuric  acid,  while  the  potassium  unites  with  pure  su'phur.  Two 
combinations,  therefore,  result — sulphuret  of  potassium  and  sulphate  of 
potassa,  which  are  mixed  together.  Though  the  experiments  adduced 
in  favour  of  this  opinion  were  not’absolutely  convincing,  yet  they  made 
it  the  more  probable  of  the  two;  and  M.  Vauquelin,  admitting  however 
the  want  of  actual  proof,  inferred  from  them  that  when  an  alkaline  ox- 
ide is  heated  to  redness  with  sulphur,  the  former  loses  oxygen,  and  a sul- 
phuret of  the  metal  itself  is  produced. 

The  sixth  volume  of  the  Annals  likewise  contains  a paper  by  Gay- 
Lussac,  who  offered  additional  arguments  in  favour  of  Vauquelin’s 
opinion,  and  1 believe  most  chemists  held  them  to  be  satisfactory.  But 
the  more  recent  labours  of  Berthier  and  Berzelius  have  given  still 
greater  insight  into  the  nature  of  these  compounds.  One  of  Vauque- 
lin’s  chief  arguments  was  drawn  from  the  action  of  charcoal  on  sulphate 
of  potassa.  When  a mixture  of  this  salt  with  powdered  charcoal  is  ig- 
nited without  exposure  to  the  air,  carbonic  oxide  and  carbonic  acid 
gases  are  formed,  and  a sulphuret  is  left,  analogous  both  in  appearance 
and  properties  to  that  which  may  be  made  by  igniting  carbonate  of  po- 
tassa  directly  with  sulphur.  They  are  both  essentially  the  same  sub- 
stance, and  Vauquelin  conceived  from  the  strong  attraction  of  carbon 
for  oxygen,  that  both  the  sulphuric  acid  and  potassa  would  be  decom- 
posed by  charcoal  at  a high  temperature;  and  that,  consequently,  the 
product  must  be^a  sulphuret  of  potassium. 

Berthier  has  proved  in  the  following  manner  that  these  changes  do 
actually  occur.  (An.  de  Ch.  et  de  Ph.  vol.  xxii.)  He  put  a known 
weight  of  sulphate  of  baryta  into  a crucible  lined  with  a mixture  of 
clay  and  charcoal,  defended  it  from  contact  with  the  air,  and  exposed  it 
to  a white  heat  for  the  space  of  two  hours.  By  this  treatment  it  suffered 
complete  decomposition,  and  it  was  found  that  in  passing  into  a sul- 
phuret, it  had  suffered  a loss  in  weight  precisely  equal  to  the  quantity 
of  ox3^gen  originally  contained  in  the  acid  and  earth.  This  circum- 
stance, coupled  with  the  fact  that  there  had  been  no  loss  of  sulphur,  is 
decisive  evidence  that  the  baryta  as  well  as  the  acid  had  lost  its  oxygen, 
and  that  a sulphuret  of  barium  had  been  formed.  He  obtained  the 
same  results  also  with  the  sulphates  of  strontia,  lime,  potassa,  and  soda; 
but  from  the  fusibility  of  the  sulphurets  of  potassium  and  sodium,  their 
loss  of  weight  could  not  be  determined  with  such  precision  as  in  the 
other  instances. 

The  experiments  of  Berzelius,  performed  about  the  same  time,  are 
exceedingly  elegant,  and  still  more  satisfactory  than  the  foregoing.  (An. 
de  Ch.  et  de  Ph.  vol.  xx.)  He  transmitted  a current  of  dry  hydrogen 
gas  over  a known  quantity  of  sulphate  of  potassa,  heated  to  redness. 
It  was  expected  from  the  strong  affinity  of  hydrogen  for  oxygen,  that 
the  sulphate  would  be  decomposed;  and,  accordingly,  a considerable 
quantity  of  water  was  formed,  which  was  carefully  collected  and 
weighed.  The  loss  of  weight  which  the  salt  had  experienced  was  pre- 
cisely equivalent  to  the  oxygen  of  the  acid  and  alkali;  and  the  oxygen 
of  the  water  was  exactly  equal  to  the  loss  in  weight.  A similar  result 
was  obtained  with  the  sulphates  of  soda,  baryta,  strontia,  and  lime. 

It  is  demonstrated,  therefore,  that  the  metallic  bases  of  the  alkalies 
and  alkaline  earths  agree  with  the  common  metals  in  their  disposition  to 


286 


GENERAL  PROPERTIES  OF  METALS. 


unite  with  sulphur.  It  is  now  certain  that,  whether  a sulphate  he  de- 
composed by  hydrogen  or  charcoal,  or  sulphur  ignited  with  an  alkali  or 
an  alkaline  earth,  a metallic  sulphuret  is  always  the  product.  Direct 
combination  between  suiphur  and  a metallic  oxide  is  a very  rare  occur- 
rence, nor  has  the  existence  of  such  a compound  been  clearly  established 
Gay-Lussac  indeed  states  that,  when  an  alkali  or  an  alkaline  earth  is 
heated  witli  sulphur  in  such  a manner  that  the  temperature  is  never  so 
high  as  a low  red  heat,  the  product  is  really  the  sulphuret  of  an  oxide. 
But  the  facts  adduced  in  favour  of  this  opinion  are  not  altogether  satis- 
factory, so  tliat  the  real  nature  of  the  product  must  be  decided  by  fu- 
ture observation. 

Several  of  the  metallic  sulphurets  occur  abundantly  in  nature.  Those 
that  are  most  frequently  met  with  are  the  sulphurets  of  lead,  antimony, 
copper,  iron,  zinc,  molybdenum,  and  silver. 

The  metallic  seleniurets  have  so  close  a resemblance  in  their  chemi- 
cal relations  to  the  sulphurets,  that  it  is  unnecessary  to  give  a separate 
description  of  them.  They  may  be  prepared  either  by  bringing  sele- 
nium in  contact  with  the  metals  at  a high  temperature,  or  by  the  action 
of  hydroselenic  acid  on  metallic  solutions. 

Cyanogen,  as  already  mentioned  at  page  260,  has  an  affinity  for  me- 
tallic substances.  Few  of  the  cyanurets,  however,  have  been  hitherto 
obtained  in  a separate  state,  excepting  those  of  potassium,  mercury, 
silver,  and  palladium.  The  three  latter  are  readily  decomposed  by  a 
red  heat. 

Cj^anogen  unites  also  with  some  of  the  metallic  oxides.  When  hy- 
drocyanic acid  vapour  is  transmitted  over  pure  baryta  contained  in  a 
porcelain  tube,  and  heated  till  it  begins  to  be  luminous,  hydrogen  gas 
IS  evolved,  and  cyanuret  of  baryta,  according  to  Gay-Lussac,  is  genera- 
ted. The  same  chemist  succeeded  in  forming  the  cyanurets  of  potassa 
and  soda  by  a similar  process.  These  compounds  exist  only  in  the  dry 
state.  A change  is  produced  in  them  by  the  action  of  water,  the  na- 
ture of  which  has  already  been  explained.  (Page  265.) 

Respecting  the  preceding  compounds  there  remains  one  subject,  the 
consideration  of  which,  as  applying  equally  to  all,  has  been  purposely 
delayed.  The  non-metallic  ingredient  of  each  of  these  compounds  is 
the  radical  of  a hydracid;  that  is,  it  has  the  property  of  forming  with 
hydrogen  an  acid,  which,  like  other  acids,  is  unable  to  unite  with  metals, 
but  appears  to  combine  readily  with  many  metallic  oxides.  Owing  to 
this  circumstance,  a difficulty  arises  in  explaining  the  action  of  such  sub- 
stances on  water.  Thus,  when  chloride  of  potassium  is  put  into  water 
it  may  dissolve  without  suffering  any  other  chemical  change,  and  the 
liquid  accordingly  contain  chloride  of  potassium  in  solution.  But  it 
is  also  possible  that  the  elements  of  this  compound  may  react  on  those 
of  watei’,  its  potassium  uniting  with  oxygen,  and  its  chlorine  with  hy- 
drogen,- and  as  the  resulting  potassa  and  muriatic  acid  have  a strong 
affinity  for  each  other,  the  solution  woidd  of  course  contain  muriate  of 
potassa.  A similar  uncertainty  attends  the  action  of  water  on  other 
metallic  chlorides,  and  on  the  compounds  of  metals  with  iodine,  bro- 
mine, sulphur,  and  similar  substances;  so  that  when  iodide,  sulphui'et, 
and  cyanuret  of  potassium  arc  put  into  water,  chemists  are  in  doubt 
whether  they  are  dissolved  as  such,  or  whether  they  may  not  be  con- 
verted, by  decomposition  of  water,  into  hydriodatc,  liydrosulphate,  and 
liydrocyanate  of  potassa.  I'liis  (picstion  would  at  once  be  decided, 
could  it  be  ascertained  whether  water  is  or  is  not  decomposed  during 


GENERAL  PROPERTIES  OF  METALS. 


287 


the  process  of  solution;  but  this  is  the  precise  point  of  difficvilty,^ since, 
from  the  operation  of  the  laws  of  chemical  union,  no  disengagement  of 
gas  does  or  can  take  place  by  which  the  occurrence  of  such  a change 
may  be  indicated.  Chemists,  accordingly,  being  ^ided  by  probabili- 
ties, are  divided  in  opinion,  and  I shall,  therefore,  give  a brief  statement 
of  both  views,  with  the  arguments  in  favour  of  each. 

According  to  one  view,  then,  chloride  of  potassium  and  all  similar 
compounds  dissolve  in  water  without  undergoing  any  other  change,  and 
are  deposited  in  their  original  state  by  crystallization.  When  any  hy- 
di’acid,  such  as  muriatic  or  hydriodic  acid,  is  mixed  with  potassa  or  any 
similar  metallic  oxide,  the  acid  and  salifiable  base  do  not  unite,  as  hap- 
pens in  other  cases;  but  the  oxygen  of  the  oxide  combines  with  the 
hydrogen  of  the  acid,  and  the  metal  itself  with  the  radical  of  the  hy- 
dracid.  This  kind  of  double  decomposition  unquestionably  takes 
place  in  some  instances,  as  when  sulphuretted  hydrogen  acts  upon  a 
salt  of  lead,  the  insoluble  sulphuret  of  lead  being  actually  precipitated; 
but  it  is  also  thought  to  occur  even  when  the  transparency  of  the  solu- 
tion is  undisturbed.  It  is  argued,  accordingly,  that  muriate  of  potassa, 
and  the  salts  of  the  hydracids  in  general,  have  no  existence.  Thus, 
when  nitrate  of  the  oxide  of  silver  is  added  to  a solution  of  chloride  or 
cyanuret  of  potassium,  metallic  silver  is  said  to  unite  with  chlorine  or 
cyanogen,  while  the  oxygen  of  the  oxide  of  silver  combines  with  po- 
tassium; so  that  nitrate  of  potassa  and  chloride  or  cyanuret  of  silver  are 
generated.  On  adding  sulphuric  acid  to  a solution  of  chloride  of  po- 
tassium, production  of  muriatic  acid  and  potassa,  which  did  not  pre- 
viously exist,  instantly  ensues,  in  consequence  of  water  being  decom- 
posed, and  yielding  its  hydrogen  to  chlorine,  and  its  oxygen  to  potas- 
sium; and  this  explanation  is  justified  by  the  circumstance,  that  the 
same  change  certainly  occurs  when  concentrated  sulphuric  acid  is 
brought  into  contact  with  solid  chloride  of  potassium.  It  is  further  be- 
lieved that  the  crystallized  muriate  of  lime,  baryta,  and  strontia,  which 
contain  water  or  its  elements,  are  metallic  chlorides  combined  with  wa- 
ter of  crystallization;  and  the  same  view  is  applied  to  all  analogous 
compounds. 

According  to  the  othr  r doctrine,  chloride  of  potassium  is  converted 
into  muriate  of  potass' , in  the  act  of  dissolving;  and  when  the  solution 
is  evaporated,  the  ek  hents  existing  in  the  salt  reunite  at  the  moment 
of  crystallization,  and  crystals  of  chloride  of  potassium  are  deposited. 
The  same  explanation  applies  in  all  cases,  when  the  salt  of  a hydracid 
crystallizes  without  retaining  the  elements  of  water.  Of  those  com- 
pounds, which  in  crystallizing  retain  water  or  its  elements  in  combina- 
tion, two  opinions  may  be  formed.  Thus  crystallized  muriate  of  baryta, 
which  consists  of  one  equivalent  of  chlorine,  one  of  barium,  two  of 
oxygen,  and  two  of  hydrogen,  may  be  regarded  as  a compound  either 
of  muriate  of  baryta  with  one  equivalent  of  water  of  crystallization,  or 
of  chloride  of  barium  with  two  equivalents  of  water.  When  exposed 
to  heat,  two  equivalents  of  water  are  expelled,  and  chloride  of  barium 
is  left.  When  nitrate  of  the  oxide  of  silver  is  mixed  in  solution  with 
muriate  of  potassa,  the  oxygen  of  the  oxide  of  silver  unites  with  the 
hydrogen  of  the  muriatic  acid;  chloride  of  silver  is  precipitated,  and 
nitrate  of  potassa  remains  in  the  liquid.  On  adding  sulphuric  acid  to  a 
muriate,  muriatic  acid  is  simply  displaced,  as  when  carbonic  acid  in 
marble  is  separated  from  lime  by  the  action  of  nitric  acid. 

On  comparing  these  opinions  it  is  manifest  that  both  are  consistent 
, with  well-known  affinities.  When,  for  example,  a metallic  chloride  is 
dissolved  in  water,  the  attraction  of  chlorine  for  the  metal,  and  that  of 
oxygen  for  hydrogen,  tend  to  prevent  chemical  change;  but  the  affini- 


288 


GENERAL  PROPERTIES  OF  METALS. 


ties  of  the  metal  for  oxyg-en,  of  chlorine  for  hydrogen,  and  of  muriatic 
acid  for  metallic  oxides,  co-operate  in  determining*  the  decomposition  of 
water,  and  the  production  of  a muriate.  Neither  view  has  materially 
the  advantag'e  in  point  of  simplicity;  for  while  some  phenomena  are 
more  simply  explained  by  one  mode  of  reasoning*,  others  are  more 
easily  explicable  according  to  the  other.  It  is  certainly  an  objection  to 
the  latter  view,  that  it  supposes  the  frequent  decomposition  and  repro- 
duction of  water,  without  there  being  any  direct  proof  of  its  occur- 
rence; for  the  solution  of  chlorides  and  similar  compounds  often  takes 
place,  even  without  disengagement  of  caloric.  The  circumstances 
which  may  be  mentioned  as  appearing  to  indicate  decomposition  of  wa- 
ter, are  the  following: — 1.  The  solutions  of  some  compounds,  such  as 
sulphuret  and  cyanuret  of  potassium,  actually  emit  an  odour  of  sul- 
phuretted hydrogen  and  hydrocyanic  acid.  2.  Other  compounds,  such 
as  the  chlorides  of  copper,  cobalt,  and  nickel,  instantly  acquire,  when 
put  into  water,  the  colour  peculiar  to  the  salts  of  the  oxides  of  those 
metals.  3.  The  solution  of  protochloride  of  iron,  like  the  protosul- 
phate, absorbs  oxygen  from  the  atmosphere;  and  this  effect  could 
scarcely  be  expected  to  occur,  unless  the  protoxide  of  iron  were  con- 
tained in  the  liquid.  4.  In  some  instances  there  is  direct  proof  of  de- 
composition of  water.  Thus  when  sulphuret  of  aluminium  is  put  into 
that  fluid,  alumina  is  generated,  and  sulphuretted  hydrogen. gas  disen- 
gaged with  effervescence.  In  like  manner  chloride  and  sulphuret  of 
silicium  are  converted  by  water  into  silica,  and  muriatic  acid  and  sul- 
phuretted hydrogen.  In  these  cases  the  want  of  affinity  between  the 
new  compounds  causes  their  separation,  and  thus  affords  direct  proof 
that  water  is  decomposed.  But  the  affinities  which  produce  this  change 
do  not  appear  so  likely  to  be  effective,  as  those  which  are  in  operation 
when  chloride  of  potassium  is  put  into  water;  especially  when  it  is 
considered  that  the  attraction  of  chlorine  for  hydrogen,  and  potassium 
for  oxygen,  is  aided  by  that  of  the  resulting  acid  and  oxide  for  each 
other. 

The  first  argument  is  not  perhaps  to  be  trusted,  because  the  produc- 
tion of  sulphuretted  hydrogen  and  hydrocyanic  acid  is  probably  occa- 
sioned by  the  carbonic  acid  of  the  atmosphere.  The  three  latter,  though 
not  amounting  to  demonstration,  give  a high  degree  of  probability  to 
the  existence  of  salts  of  muriatic  and  hydriodic  acid;  and  if  this  be  ad- 
mitted, the  same  view  may  be  extended  to  other  hydracids.  This 
opinion,  which  is  preferred  by  many  chemists,  is  adopted  in  the, pre- 
sent work.  Considering  how  much  the  affinity  of  metals  for  oxygen, 
and  that  of  the  radicals  of  the  hydracids  for  hydrogen,  differ  in  force, 
it  is  likely  that  some  of  the  chlorides  and  similar  compounds  dissolve 
without  change,  while  others  give  rise  to  decomposition  of  water.  But 
as  in  general,  chemists  possess  no  means  of  determining  the  nature  of 
the  change  in  particular  instances,  it  has  been  thought  most  consistent 
to  apply  the  same  view  to  all,  except  in  some  special  cases  when  the 
contrary  is  mentioned. 

Chemists  are  acquainted  with  several  metallic  phosphurets;  and  it  is 
probable  that  phosphorus,  like  sulphur,  is  capable  of  uniting  with  all 
the  metals.  Ifittle  attention,  however,  has  hitherto  been  devoted  to 
these  compounds;  and  for  the  greater  part  of  our  knowledge  concern- 
ing them  we  arc  indebted  to  the  researches  of  Pelletier.  (An.  de  Chi- 
mie,  vol.  i.  and  xiii.) 

The  metallic  ])h()sphurcts  may  be  prepared  in  several  ways.  The 
most  direct  method  is  by  bringing  phosphorus  in  contact  with  metals  at  . 
a high  temperature,  or  by  igniting  metals  in  contact  with  phosphoric 
acid  and  charcoal.  Several  of  the  phosphurets  may  be  formed  by  trans- 


GENERAL  PROPERTIES  METALS. 


289 


mitting’  a current  of  phosphiiretted  hydrogen  gas  over  metallic  oxides 
heated  to  redness  in  a porcelain  tube.  Water  is  generated,  and  a phosphu- 
ret  of  the  metal  remains.  By  similar  treatment  the  chlorides  and  sulphu- 
rets  of  many  metals  maybe  decomposed,  and  phosphurets  formed,  provid- 
ed the  metal  is  capable  of  retaining  phosphorus  at  a red  heat.  Accord- 
ing to  Professor  Rose  the  phosphurets  of  copper,  nickel,  cobalt,  and 
iron  are  the  only  ones  which  admit  of  being  advantageously  prepared 
by  this  method.  (Poggendorff’s  Annalen,  vi.  20.5.)  When  chlorides 
are  employed,  muriatic  acid  gas,  and  with  sulphurets  sulphuretted  hy- 
drogen gas,  is  of  course  generated. 

Phosphorus  is  said  to  unite  with  metallic  oxides.  For  example, 
phosphuret  of  lime  is  formed  by  conducting  the  vapour  of  phosphorus 
over  that  earth  at  a low  red  heat;  but  it  is  probable  that  in  this  instance, 
as  with  a mixture  of  sulphur  and  an  alkali,  part  of  the  metallic  oxide  is 
decomposed,  and  that  the  product  contains  phosphuret  of  calcium  and 
phosphate  of  lime. 

The  only  metallic  carburets  of  importance  are  those  of  iron,  which 
will  be  described  in  the  section  on  that  metal. 

Hydrogen  unites  with  few  metals.  The  only  metallic  hydrogurets 
known  are  those  of  zinc,  potassium,  arsenic,  and  tellurium.  No  com- 
pound of  nitrogen  and  a metal  has  hitherto  been  discovered. 

The  discoveries  of  modern  chemistry  have  materially  added  to  the 
number  of  the  metals,  especially  by  associating  with  them  a class  of 
bodies  which  was  formerly  believed  to  be  of  a nature  entirely  different. 
The  metallic  bases  of  the  alkalies  and  earths,  previous  to  the  year  1807, 
were  altogether  unknown;  and  before  that  date  the  list  of  metals,  with 
few  exceptions,  included  those  only  which  are  commonly  employed  in 
the  arts,  and  which  are  hence  often  called  the  common  metals.  In  con- 
sequence of  this  increase  in  number,  it  is  found  convenient  for  the  pur- 
pose of  description,  to  arrange  them  in  separate  groups;  and  as  the  al- 
kalies and  earths  differ  in  several  respects  from  the  oxides  of  other  me- 
tals, it  will  be  convenient  to  describe  them  separately.  I have  accord- 
ingly divided  the  metals  into  the  two  following  classes: — 

Class  I.  Metals  which  by  oxidation  yield  alkalies  or  earths. 

Class  II.  Metals,  the  oxides  of  which  are  neither  alkalies  nor 
earths. 

Class  I.  This  class  includes  thirteen  metals,  which  may  properly  be 
arranged  in  three  orders. 

Order  1.  Metallic  bases  of  the  alkalies.  They  are  three  in  number; 
namely. 

Potassium,  Sodium,  Lithium. 

These  metals  have  such  a powerful  attraction  for  oxygen,  that  at 
common  temperatures  they  decompose  water  at  the  moment  of  contact, 
and  are  oxidized  with  disengagement  of  hydrogen  gas.  The  resulting 
oxides  are  distinguished  by  their  causticity  and  solubility  in  watar,  and 
by  possessing  alkaline  properties  in  an  eminentdegree.  They  are  called 
alkalleSi  and  their  metallic  bases  are  sometimes  termed  alkaline  or  alkali- 
genous  metals. 

Order  2.  Metallic  bases  of  the  alkaline  earths.  These  are  four  in 
number;  namely. 

Barium,  Strontium,  Calcium,  Magnesium. 

These  metals,  like  the  preceding,  decompose  water  rapidly  at  com- 
mon temperatures.  The  resulting  oxides  are  called  alkaline  earths;  be- 
cause while  in  their  appearance  they  resemble  the  e.arths,  they  are 
similar  to  the  alkalies  in  having  a strong  alkaline  reaction  with  test 

25 


290 


GENERAL  PROPERTIES  OF  METALS. 


paper,  and  in  neutralizing*  acids.  The  three  first  are  strongly  caiistic, 
and  baryta  and  strontia  are  soluble  in  water  to  a considerable  extent. 

Order  3.  Metallic  bases  of  the  earths.  These  are  six  in  number; 
namely, 

Aluminium,  Yttrium,  Zirconium, 

Glucinium,  Thorium,  Silicium. 

The  oxides  of  these  metals  are  well  known  as  the  pure  earths.  They 
are  white  and  of  an  earthy  appearance,  in  their  ordinaiy  state  are  quite 
insoluble  in  water,  and  do  not  affect  the  colour  of  turmeric  or  litmus 
paper.  As  salifiable  bases  they  are  inferior  to  the  alkaline  earths.  Silica 
is  even  considered  by  several  chemists  as  an  acid,  and  its  chemical  rela- 
tions appear  to  justify  the  opinion.  For  reasons  to  be  afterwards  men- 
tioned, the  propriety  of  placing  silicium  among  the  metals  is  exceed- 
ingly doubtful. 


CiAss  II.  The  number  of  the  metals  included  in  this  class  amounts 
to  twenty-eight.  They  are  all  capable  of  uniting  with  oxygen,  and 
generally  in  more  than  one  proportion.  Their  protoxides  have  an  earthy 
appearance,  but  with  few  exceptions  are  coloured.  They  are  insoluble 
in  water,  and  in  general  do  not  affect  the  colour  of  test  paper.  Most 
of  them  act  as  salifiable  bases  in  uniting  with  acids,  and  forming  salts; 
but  in  this  respect  they  are  much  inferior  to  the  alkalies  arid  alkaline 
earths,  by  which  they  may  be  separated  from  their  combinations.  Sev- 
eral of  these  metals  are  capable  of  forming  with  oxygen  compounds^ 
which  possess  the  characters  of  acids.  The  metals  in  which  this  pro- 
perty has  been  noticed  are  manganese,  arsenic,  chromium,  molybde- 
num, tungsten,  columbium,  antimony,  titanium,  tellurium,  and  gold. 

The  metals  belonging  to  the  second  class  may  be  conveniently  ar- 
ranged in  the  three  following  orders: — 

Order  1.  Metals  which  decompose  water  at  a red  heat.  They  are 
seven  in  number;  namely. 

Manganese,  Cadmium,  Cobalt, 

Iron,  Tin,  Nickel. 

Zinc, 


Order  2.  Metals  which  do  not  decompose  water  at  any  tempera- 
ture, and  the  oxides  of  which  are  not  reduced  to  the  metallic  state 
by  the  sole  action  of  heat.  Of  these  there  are  thirteen  in  number; 
namely. 


Arsenic, 

Chromium, 

Molybdenumj 

Tungsten, 

Columbium, 


Antimony, 

Uranium, 

Cerium, 

Bismuth, 


Titanium, 

Tellurium, 

Copper, 

Lead. 


Order  3.  Metals,  the  oxides  of  which  are  decomposed  by  a red  heat. 
These  are 


Mercury, 

Silver, 

Gold, 


Platinum, 

Palladium, 

Rhodium, 


Osmium, 

Iridium. 


POTASSIUM. 


291 


CLASS  L 

METALS  WHICH  BY  OXIDATION  YIELD  ALKALIES  OR 
EARTHS, 

ORDER  I. 

METALLIC  BASES  OF  THE  ALKALIES. 


SECTION  1. 

POTASSIUM. 

Potassium  was  discovered  in  the  year  1807  by  Sir  H.  Davy,  and  the 
circumstances  which  led  to  the  discovery  have  already  been  described. 
(Pag’e  99.)  It  was  prepared  by  that  philosopher  by  causing*  hydrate  of 
potassa,  slig^htl}^  moistened  for  the  purpose  of  increasing*  its  conducting* 
power,  to  communicate  with  the  opposite  poles  of  a galvanic  battery 
of  200  double  plates;  when  the  oxygen  both  of  the  water  and  the  po- 
tassa, passed  over  to  the  positive  pole,  while  the  hydrogen  of  the  for- 
mer, and  the  potassium  of  the  latter,  made  their  appearance  at  the  ne- 
gative wire.  By  this  process  potassium  is  obtained  in  small  quantity 
only;  but  Gay-Lussac  and  Thenard  invented  a method  by  which  a more 
abundant  supply  may  be  procured.  (Recherches  Physico-chimiques, 
vol.  i.)  Their  process  consists  in  bringing  fused  hydrate  of  potassa  in 
contact  with  turnings  of  iron  heated  to  whiteness  in  a g*un-barrel.  The 
iron,  under  these  circumstances,  deprives  the  water  and  potassa  of 
oxygen,  hydrogen  gas  combined  with  a little  potassium  is  evolved,  and 
pure  potassium  sublimes,  and  may  be  collected  in  a cool  part  of  the 
apparatus. 

Potassium  may  also  be  prepared,  as  first  noticed  by  M.  Curaudau, 
by  mixing  dry  carbonate  of  potassa  with  half  its  weight  of  powdered 
charcoal,  and  exposing  the  mixture,  contained  in  a gun-barrel  or  sphe- 
roidal iron  bottle,  to  a strong  heat.  An  improvement  on  both  pro- 
cesses has  been  made  oy  M.  Brunner,  who  decomposes  potassa  by 
means  of  iron  and  charcoal.  From  eig’ht  ounces  of  fused  carbonate  of 
potassa,  six  ounces  of  iron  filings,  and  two  ounces  of  charcoal,  mixed 
intimately  and  heated  in  an  iron  bottle,  he  obtained  140  grains  of  po- 
tassium. (Quarterly  Journal,  xv.  279.  ) Berzelius  has  observed  that 
the  potassium  thus  made,  though  fit  for  all  the  usual  purposes  to  which 
it  is  applied,  contains  a minute  quantity  of  carbon;  and,  therefore,  if 
required  to  be  quite  pure,  must  be  rendered  so  by  distillation  in  a retort 
of  iron  or  green  glass.  A modification  of  this  process  has  been  since 
described  by  Wohler,  who  effects  the  decomposition  of  the  potassa 
solely  by  means  of  charcoal.  The  material  employed  for  the  purpose 
is  carbonate  of  potassa  prepared  by  heating  cream  of  tartar  to  redness 
in  a covered  crucible.  (Poggendoiff'^s  Annalen,  iv.  23.) 


292 


POTASSIUM. 


Potassium  is  solid  at  the  ordinary  temperature  of  the  atmosphere.  At 
70^  it  is  somewhat  fluid,  though  its  fluidity  is  not  perfect  till  it  is  heat- 
ed to  150^  F.  At  50^  it  is  soft  and  malleable,  and  yields  like  wax  to 
the  pressure  of  the  fingers;  but  it  becomes  brittle  when  cooled  to  32® 
F.  It  sublimes  at  a red  heat  without  undergoing  any  change,  provided 
atmospheric  air  be  completely  excluded.  Its  texture  is  crystalline,  as 
may  be  seen  by  breaking  it  across  while  brittle.  In  colour  and  lustre  it 
is  precisely  similar  to  mercury.  At  60®  its  density  is  0.865,  so  that  it  is 
considerably  lighter  than  water.  It  is  quite  opake,  and  is  a good  con- 
ductor of  electricity  and  caloric. 

The  most  prominent  chemical  property  of  potassium  is  its  affinity  for 
oxygen  gas.  It  oxidizes  rapidly  in  the  air,  or  by  contact  with  fluids 
which  contain  oxygen.  On  this  account  it  must  be  preserved  either  in 
glass  tubes  hermetically  sealed,  or  under  the  surface  of  liquids,  such  as 
naphtha,  of  which  oxygen  is  not  an  element.*  If  heated  in  the  open 
air,  it  takes  fire,  and  burns  with  a white  flame  and  great  evolution  of 
caloric.  It  decomposes  water  on  the  instant  of  touching  it,  and  so 
much  heat  is  disengaged,  that  the  potassium  is  inflamed,  and  burns 
vividly  while  swimming  upon  its  surface.  The  hydrogen  unites  with  a 
little  potassium  at  the  moment  of  separation;  and  this  compound 
takes  fire  as  it  escapes,  and  thus  augments  the  brilliancy  of  the 
combustion.  When  potassium  is  plunged  under  water,  yiolent  re- 
action ensues,  but  without  the  emission  of  light,  and  pure  hydrogen 
gas  is  evolved. 

Oxides  of  Potassium. 

Potassium  unites  with  oxygen  in  two  proportions.  The  protoxide, 
commonly  called  ov potassa,  is  always  formed  when  potassium  is 

put  into  water,  or  when  it  is  exposed  at  common  temperatures  to  dry 
air  or  oxygen  gas.  By  the  former  method  the  protoxide  is  obtained  in 
combination  with  water;  and  in  the  latter  it  is  anhydrous.  In  perform- 
ing the  last  mentioned  process,  the  potassium  should  be  cut  into  very 
thin  slices;  for  otherwise  the  oxidation  is  incomplete.  The  product, 
when  partially  oxidized,  was  once  suspected  to  be  a distinct  oxide;  but 
it  is  now  admitted  to  be  a mixture  of  potassa  and  potassium. 

As  potassa  is  the  protoxide  of  potassium,  it  is  supposed  to  contain 
one  atom  of  each  of  its  elements.  Its  composition  is  best  determined 
by  collecting  and  measuring  the  quantity  of  hydrogen  which  is  evolved 
when  potassium  is  plunged  under  water.  From  the  experiments  of  Sir 
H.  Davy,  and  Gay-Lussac  and  Thenard,  it  appears  that  forty  grains  of 
potassium  decompose  precisely  nine  grains  of  water;  and  that  while 
one  grain  of  hydrogen  escapes  in  the  gaseous  form,  the  corresppnding 
eight  grains  of  oxygen  combine  with  the  metal.  The  protoxide  of  po- 
tassium is,  therefore,  composed  of 

Potassium  . 40,  or  one  equivalent. 

Oxygen  . 8,  or  one  equivalent; 

and  its  equivalent  is  48. 


* Mr.  Durand,  J*harmaceutist  of  Pliiladcl|)hia,  has  ascci-tained  that 
the  essential  oil  of  copaiba  is  a good  liquid  for  tlie  preservation  of  po- 
tassium. I liavc  used  it  myself  for  this  purpose,  and  am  satisfied  that 
it  is  mud)  superior  to  tlie  ordinary  naplillia.  The  briglitness  of  the 
metal  is  but  sliglitly  impaired,  while  in  common  najilitha,  it  becomes 
covered  with  a blackish  film.  Several  chemists  have  used  this  oil  on 
the  recommendation  of  Mr.  Durand,  and  with  satisfactory  results.  B. 


POTASSIUM. 


293 


When  potassium  burns  in  the  open  air  or  in  oxygen  gas,  it  is  converted 
into  an  orange-coloured  substance,  which  is  peroxide  of  potassium.  It 
may  likewise  be  formed  by  conducting  oxygen  gas  over  potassa  at  a 
red  heat;  and  is  produced  in  small  quantity  when  potassa  is  heated  in 
the  open  air.  It  is  the  residue  of  the  decomposition  of  nitre  by  heat 
in  metallic  vessels,  provided  the  temperature  be  kept  up  for  a sufficient 
time.*  When  the  peroxide  is  put  into  water,  it  is  resolved  into  oxygen 
and  potassa,  the  former  of  which  escapes  with  effervescence,  and  the 
latter  is  dissolved.  According  to  Gay-Lussac  and  Thenard,  it  consists 
of 

Potassium  • 40,  or  one  equivalent. 

Oxygen  . 24,  or  three  equivalents. 

Anhydrous  potassa  can  only  be  prepared  by  the  slow  oxidation  of  po- 
tassium, as  already  mentioned.  In  its  pure  state,  it  is  a white  solid  sub- 
stance, highly  caustic,  which  fuses  at  a temperature  somewhat  above 
that  of  redness,  and  bears  the  strongest  heat  of  a wind  furnace  without 
being  decomposed  or  volatilized.  It  has  a powerful  affinity  for  water, 
and  intense  heat  is  disengaged  during  the  act  of  combination.  With  a 
certain  portion  of  that  liquid  it  forms  a solid  h3xlrate,  the  elements  of 
which  are  united  by  an  affinity  so  energetic,  that  no  degree  of  heat 
hitherto  employed  can  effect  their  separation.  This  substance  was 
long  regarded  as  the  pure  alkali,  but  it  is  in  reality  a hydrate  of  potassa. 
It  is  composed  of  48  parts  or  one  equivalent  of  potassa,  and  9 parts 
or  one  equivalent  of  water. 

Hydrate  of  potassa  is  solid  at  common  temperatures.  It  fuses  at  a 
heat  rather  below  redness,  and  assumes  a somewhat  crystalline  texture 
in  cooling.  It  is  highly  deliquescent,  and  requires  about  half  its  weight 
of  water  for  solution.  It  is  soluble,  likewise,  in  alcohol.  It  destroys 
all  animal  textures,  and  on  this  account  is  employed  in  surgery  as  a 
caustic.  It  was  formerly  called  lapis  causticus,  but  it  is  now  termed 
potassa  Sind  potassa  fusa  by  the  Colleges  of  Edinburgh  and  London. 
This  preparation  is  made  by  evaporating  the  aqueous  solution  of  potassa 
in  a silver  or  clean  iron  capsule  to  the  consistence  of  oil,  and  then 
pouring  it  into  moidds.  In  this  state  it  is  impure,  containing  oxide  of 
iron,  together  with  chloride  of  potassium;  and  carbonate  and  sulphate 
of  potassa.  It  is  purified  from  these  substances  by  dissolving  it  in  al- 
cohol, and  evaporating  the  solution  to  the  same  extent  as  before,  in  a 
silver  vessel.  The  operation  should  be  performed  expeditiously,  in  order 
to  prevent,  as  far  as  possible,  the  absorption  of  carbonic  acid.  When 
common  caustic  potassa  of  the  druggists  is  dissolved  in  w^ater,  a number 


* This  fact  was  ascertained  by  Dr.  Bridges  of  Philadelphia,  in  the 
spring  of  1827,  while  investigating  the  nature  of  the  gaseous  matter 
given  off,  on  tiie  addition  of  water,  from  the  residue  of  nitre,  after  ex- 
posure in  an  iron  bottle  to  a red  heat.  This  matter  proved  to  consist  of 
oxygen  nearly  pure,  and  the  residue  was  converted  into  a solution  of 
hydrate  of  potassa.  These  results  evidently  prove,  that  the  residue  in 
question  consists  of  peroxide  of  potassium.  Dr.  Bridges  suggests  that 
the  employment  of  this  residue  migiit  prove  convenient  to  the  chemist 
for  obtaining  oxygen  extemporaneously,  as  it  would  be  necessary  only 
to  add  water  in  order  to  obtain  the  gas.  North  American  Medical  and 
Surgical  Journal,  v.  241. 

About  the  same  time  that  Dr.  Bridges  made  the  above  observations, 
similar  ones  w^ere  made  by  Mr.  Phillips  in  London.  Annals  of  Philoso- 
phy, April  1827.  B. 


294 


POTASSIUM. 


of  small  bubbles  of  gas  are  disengaged,  which  is  pure  oxygen.  Mr. 
Graham  finds  its  quantity  to  be  variable  in  different  specimens,  and  to 
depend  apparently  on  the  impurity  of  the  specimen. 

The  aqueous  solution  of  potassa,  aqua  potass 35  of  the  Pharmacopoeia, 
is  prepared  by  decomposing  carbonate  of  potassa  by  lime.  "I'o  effect 
this  object  completely,  it  is  advisable  to  employ  equal  parts  of  quicklime 
and  carbonate  of  potassa.  After  slaking  the  lime  in  an  iron  vessel,  the 
carbonate  of  potassa,  dissolved  in  its  own  weight  of  hot  water,  is  added, 
and  the  mixture  boiled  briskly  for  about  ten  minutes.  The  liquid, 
after  subsiding,  is  filtered  through  a funnel,  the  throat  of  which  is  ob- 
structed by  a piece  of  clean  linen.  This  process  is  founded  on  the  fact 
that  lime  deprives  carbonate  of  potassa  of  its  acid,  forming  an  insoluble 
carbonate  of  lime,  and  setting  the  pure  alkali  at  liberty.  If  the  de- 
composition is  complete,  the  filtered  solution  should  not  effervesce 
when  neutralized  with  an  acid. 

As  pure  potassa  absorbs  carbonic  acid  I’apidly  when  freely  exposed 
to  the  atmosphere,  it  is  desirable  to  filter  its  solution  in  vessels  containing 
as  small  a quantity  of  air  as  possible.  This  is  easily  effected  by  means 
of  the  filtering  apparatus  devised  by  Mr.  Donovan.  It  consists  of  two 
vessels  A and  D,  of  equal  capacity,  and  connected  with  each  other  as 
represented  in  the  annexed  wood  cut.  The 
neck  h of  the  upper  vessel  contains  a tight  cork 
perforated  to  admit  one  end  of  the  glass  tube  c, 
and  the  lower  extremity  of  the  same  vessel  ter- 
minates in  a funnel  pipe,  which  fits  into  one  of 
the  necks  of  the  under  vessel  D by  grinding, 
luting,  or  by  a tight  cork.  The  vessel  D is  fur- 
nished with  another  neck  e,  which  receives  the 
lower  end  of  the  tube  c,  tlie  junction  being  se- 
cured by  means  of  a perforated  cork,  or  luting. 

The  throat  of  the  funnel  pipe  is  obstru9ted  by  a 
piece  of  coarse  linen  loosely  rolled  up,  and  not 
pressed  down  into  the  pipe  itself.  The  solution 
is  then  poured  in  through  the  mouth  at  b,  the 
cork  and  tube  having  been  removed;  and  the  first 
droppings,  which  are  turbid,  ai’e  not  received  in 
the  lower  vessel.  The  parts  of  the  apparatus 
are  next  joined  together,  and  the  filtration  may 
proceed  at  the  slowest  rate,  without  exposure  to 
more  air  than  was  contained  in  the  vessels  at  the 
beginning  of  the  process.  This  apparatus  should 
be  made  of  green  in  preference  to  white  glass, 
as  the  pure  alkalies  act  on  the  former  much  less 
than  on  the  latter.  (Annals  of  Philosophy,  xxvi. 

115.) 

The  mode  by  which  this  apparatus  acts  scarcely- 
needs  explanation.  In  order  that  the  liquid  should  descend  freely,  two 
conditions  arc  rccpiired: — first  that  the  air  above  the  liquid  should  have 
the  same  clastic  force,  and  therefore  exert  the  same  pressure,  as  that 
below;  and,  secondly,  as  one  means  of  securing  the  first  condition,  that 
the  air  should  liavc  free  egress  from  the  lower  vessel.  Uoth  objects, 
it  is  manifest,  are  accomplished  in  the  filtering  apparatus  of  Mr.  Dono- 
van; since  for  every  drop  of  liquid  wliich  descends  from  the  upper  to 
the  lower  vessel,  a corresponding  portion  of  air  passes  along  the  tube  c 
from  the  lower  vessel  to  tlie  upper. 

Solution  of  ])otassa  is  highly  caustic,  and  its  taste  intensely  acrid.  It 
possesses  alkaline  properties  in  an  eminent  degree,  converting  the  ve- 


J3 


POTASSIUM. 


295 


getable  blue  colours  to  green,  and  neutralizing  the  strongest  acids.  It 
absorbs  carbonic  acid  gas  rapidly,  and  is  consequently  employed  for 
withdrawing  that  substance  from  gaseous  mixtures.  For  the  same 
reason  it  should  be  preserved  in  well-closed  bottles,  that  it  may  not 
absorb  carbonic  acid  from  the  atmosphere. 

Potassa  is  employed  as  a reagent  in  detecting  the  presence  of  bodies, 
and  in  separating  them  from  each  other.  'I'he  solid  hydrate  owing  to 
its  strong  affinity  for  water,  is  used  for  depriving  gases  of  hygrometric 
moisture,  and  is  admirably  fitted  for  forming  frigorific  mixtures. 
(Page  54.) 

Potassa  may  be  distinguished  from  all  other  substances  by  the  follow- 
ing characters.  1.  If  tartaric  acid  be  added  in  excess  to  a salt  of  potassa 
dissolved  in  water,  and  the  solution  be  stirred  with  a glass  rod,  a white 
precipitate,  bitartrate  of  potassa,  soon  appears,  which  forms  peculiar 
white  streaks  upon  the  glass  by  the  pressure  of  the  rod  in  stirring.  2. 
A solution  of  muriate  of  platinum  causes  a yellow  precipitate,  muriate 
of  platinum  and  potassa.  This  is  the  most  delicate  test,  provided  the 
mixture  be  gently  evaporated  to  dryness,  and  a little  cold  water  be  after- 
wards added.  Muriate  of  platinum  and  potassa  then  remains  in  the 
form  of  small  shining  yellow  crystals.  3.  By  being  precipitated  by  no 
other  substance. 

The  following  test  has  been  recommended  by  M.  Harkort  for  distin- 
guishing between  potassa  and  soda  in  minerals.  Oxide  of  nickel,  when 
fused  by  the  blowpipe  flame  with  borax,  gives  a brown  glass;  and  this 
glass,  if  melted  with  a mineral  containing  potassa,  becomes  blue,  an 
effect  which  is  not  produced  by  the  presence  of  soda. 

Chloride  of  Potassium. — Potassium  takes  fire  spontaneously  in  an  at- 
mosphere of  chlorine,  and  burns  with  greater  brilliancy  than  in  oxygen 
gas.  This  chloride  is  also  generated  when  potassium  is  heated  in  mu- 
riatic acid  gas,  hydrogen  being  evolved  at  the  same  time.  It  is  the  re- 
sidue of  the  decomposition  of  chlorate  of  potassa  by  heat;  and  it  is  ob- 
tained in  the  form  of  colourless  cubic  crystals,  when  a solution  of  muri- 
ate of  potassa  evaporates  spontaneously. 

Chloride  of  potassium  has  a saline  and  rather  bitter  taste.  It  requires 
three  parts  of  water  at  60®  F.  for  solution,  and  is  still  more  soluble  in 
hot  water.  Its  solution  probably  contains  muriate  of  potassa.  (Page 
287-8.)  It  is  composed  of  36  parts  or  one  equivalent  of  chlorine,  and  40 
parts  or  one  equivalent  of  potassium. 

Iodide  of  Potassium. — This  compound  is  formed  with  emission  of 
light,  when  potassium  is  heated  in  contact  with  iodine.  It  may  like- 
wise be  obtained  by  moans  of  heat  from  iodate,  and  by  crystallization 
from  hydriodate  of  potassa.  It  fuses  readily  when  heated,  and  is  vola- 
tilized at  a temperature  below  redness.  It  deliquesces  in  a moist  at- 
mosphere, and  is  very  soluble  in  water.  It  dissolves  also  in  strong 
alcohol;  and  the  solution,  when  gently  evaporated,  yields  small 
colourless  cubic  crystals  of  iodide  of  potassium.  It  is  composed  of 
124  parts  or  one  equivalent  of  iodine,  and  40  parts  or  one  equivalent 
of  potassium. 

Hydrogen  and  Potassium. — These  substances  unite  in  two  propor- 
tions, forming  in  one  case  a solid,  and  in  t^ie  other  a gaseous  compound. 
I’he  latter  is  produced  when  hydrate  of  potassa  is  decomposed  by  iron 
at  a white  heat,  and  it  appears  also  to  be  generated  when  potassium 
burns  on  the  surface  of  water.  It  inflames  spontaneously  in  air  or  oxy- 
gen gas;  but  on  standing  for  some  hours  over  mercury,  the  greater  part, 
if  not  the  whole  of  the  potassium,  is  deposited. 

The  solid  hydroguret  of  potassium  was  made  by  Gay-Lussac  and 
Thenard,  by  heating  potassium  in  hydrogen  gas.  It  is  a gray  solid  sub- 


296 


SODIUM. 


stance,  which  is  readily  decomposed  by  heat  or  contact  with  water.  It 
does  not  inflame  spontaneously  in  oxygen  gas. 

Sulphuret  of  Potassium. — Sulphur  unites  readily  with  potassium  by 
the  aid  of  heat;  and  so  much  caloric  is  evolved  at  the  moment  of  com- 
bination, tliat  the  mass  becomes  incandescent.  The  best  method  of 
obtaining  a sulphuret  in  definite  proportion  is  by  decomposing  sulphate 
of  potassa  according  to  the  process  of  Berthier  or  Berzelius.  (Page 
285.)  This  sulplmret  is  composed  of  16  parts  or  one  equivalent  of 
sulphur,  and  40  parts  or  one  equivalent  of  potassium.  It  has  a red 
colour,  fuses  below  the  temperature  of  ignition,  and  assumes  a crystal- 
line texture  in  cooling.  It  is  dissolved  by  water,  being  probably  con- 
verted, with  evolution  of  caloric,  into  hydrosulphuret  of  potassa. 

Besides  this  protosulphuret,  Berzelius  has  described  four  other 
compounds,  which  he  obtained  by  igniting  carbonate  of  potassa  with 
different  proportions  of  sulphur.  Tliese  are  composed  of  one  equiv- 
alent of  potassium  with  two,  three,  four,  and  five  equivalents  of  sul- 
phur. 

PhospJiuret  of  Potassium. — This  compound  may  be  formed  by  the  ac- 
tion of  potassium  on  phosphorus  with  the  aid  of  a moderate  heat.  It  is 
converted  by  water  into  potassa  and  perphosphuretted  hydrogen  gas, 
which  inflames  at  the  moment  of  its  formation. 


SECTION  II. 

SODIUM. 

Sir  H.  Davy  made  the  discovery  of  sodium  in  the  year  1807,  a few 
days  after  he  had  discovered  potassium.  The  first  portions  of  it  were 
obtained  by  means  of  galvanism;  but  it  may  be  procured  in  much  larger 
quantity  by  chemical  processes,  precisely  similar  to  those  described  in 
the  last  section. 

Sodium  has  a strong  metallic  lustre,  and  in  colour  is  very  analogous 
to  silver.  It  is  so  soft  at  common  temperatures,  that  it  may  be  formed 
into  leaves  by  the  pressure  of  the  fingers.  It  fuses  at  200^  F.  and  rises 
in  vapour  at  a full  red  heat.  Its  specific  gravity  is  0.972. 

Sodium  soon  tarnishes  on  exposure  to  the  air,  though  less  rapidly 
than  potassium.  When  thrown  into  water  it  swims  upon  its  surface, 
occasions  violent  effervescence  and  a hissing  noise,  and  is  rapidly  oxi- 
dized; but  no  light  is  visible.  The  action  is  stronger  with  hot  water, 
and  a few  scintillations  appear;  but  still  there  is  no  flame.*  In  each  case, 
soda  is  generated,  owing  to  wliicli  the  water  acquires  an  alkaline  reac- 
tion, and  pure  hydrogen  gas  is  disengaged. 


* 'rhe  sodium  wliicli  I liave  had  occasion  to  use  uniformly  inflames 
on  boifing  water,  'flic  experiment  is  a very  beautiful  one,  aiul  deserves 
the  attention  of  chemical  lecturers.  'I'he  fact  itself  I obtained  in  con- 
versation witli  Mr.  D.  B.  Smith,  and  I do  not  recollect  to  liave  seen  it 
mentioned  in  any  cljcmical  work,  except  Professor  Silliman’s  Elements. 
It  may  be  supixjsed  that  the  inflammation  is  owing  to  the  presence  of 
potassium;  but  this  is  not  ]u*ol)able,  as  the  flame  is  of  a fine  yellow 
colour,  very  different  from  the  rose-coloured  flame  of  potassium.  B. 


SODIUM. 


29/ 


Oxides  of  Sodium. — Chemists  are  acquainted  with  two  definite  com- 
pounds only  of  sodium  and  oxyg’en.  The  protoxide,  or  soda,  is  a gray- 
white  solid,  difficult  of  fusion,  which  is  obtained  by  burning  sodium  in 
dry  atmospheric  air.  It  is  also  formed  when  sodium  is  oxidized  by  wa- 
ter; and  its  composition  may  be  determined  by  collecting  the  hydrogen 
which  is  then  disengaged.  According  to  the  experiments  of  Sir  11. 
Davy,  the  results  of  which  differ  little  from  those  of  Gay-Lussac  and 
Thenard,  soda  consists  of  24  parts  of  sodium  and  8 parts  of  oxygen. 
For  this  reason,  24  is  regarded  as  the  atomic  weight  of  sodium,  and  32 
the  combining  proportion  of  soda. 

When  sodium  is  heated  to  redness  in  excess  of  pure  oxygen,  an 
orange-coloured  substance  is  formed,  which  is  peroxide  of  sodium.  It 
is  resolved  by  water  into  oxygen  and  soda;  and  it  is  composed,  accord- 
ing to  Gay-Lussac  and  Thenard,  of  two  equivalents  of  sodium  and 
three  of  oxygen.  It  is  partially  reconverted  into  soda  by  a very  strong 
heat. 

With  water  soda  forms  a solid  hydrate,  easily  fusible  by  heat,  which 
is  very  caustic,  soluble  in  water  and  alcohol,  has  powerful  alkaline  pro- 
perties, and  in  all  its  chemical  relations  is  exceedingly  analogous  to  po- 
tassa.  It  is  prepared  from  the  solution  of  pure  soda,  exactly  in  the 
same  manner  as  the  corresponding  preparation  of  potassa.  The  solid 
hydrate  is  composed  of  32  parts  or  one  equivalent  of  soda,  and  9 parts 
or  one  equivalent  of  water. 

Soda  is  readily  distinguished  from  other  alkaline  bases  by  the  follow- 
ing characters.  1.  It  yields  with  sulphuric  acid  a salt,  which  by  its  taste 
and  form  is  easily  recognised  as  Glauber’s  salt,  or  sulphate  of  soda.  2. 
All  its  salts  are  soluble  in  water,  and  are  not  precipitated  by  any  re- 
agent. 3.  On  exposing  its  salts  by  means  of  platinum  wire  to  the  blow- 
pipe flame,  they  communicate  to  it  a rich  yellow  colour. 

Chloride  of  Sodium. — This  compound  may  be  formed  directly  by 
burning  sodium  in  chlorine,  or  by  heating  it  in  muriatic  acid  gas.  It  is 
deposited  in  crystals,  when  a solution  of  muriate  of  soda  is  evaporated; 
for  this  salt,  like  muriate  of  potassa,  exists  only  while  in  solution,  and 
is  converted  into  a chloride  during  the  act  of  crystallizing.  Hence  sea 
water,  the  chief  ingredient  of  which  is  muriate  of  soda,  yields  chlo- 
ride of  sodium  by  evaporation;  and  from  this  source  is  derived  most  of 
the  different  kinds  of  common  salt,  such  as  fishery  salt,  stoved  salt, 
and  bay  salt,  substances  essentially  the  same,  and  between  which,  the 
sole  difference  depends  on  the  mode  of  preparation.  Chloride  of  so- 
dium is  known  likewise  as  a natural  product  under  the  name  of  rock  or 
mineral  salt.  ' 

The  common  varieties  of  salt,  of  which  rock  and  bay  salt  are  the 
purest,  always  contain  small  quantities  of  sulphate  of  magnesia  and 
lime,  and  muriate  of  magnesia.  These  earths  may  be  precipitated  as 
carbonates  by  boiling  a solution  of  salt  for  a few  minutes  with  a slight 
excess  of  carbonate  of  soda,  filtering  the  liquid,  and  neutralizing  with 
muriatic  acid.  On  evaporating  this  solution  rapidly,  chloride  of  sodium 
crystallizes  in  hollow  four-sided  pyramids;  but  it  occurs  in  regular  cubic 
crystals  when  the  solution  is  allowed  to  evaporate  spontaneously.  These 
crystals  contain  no  water  of  crystallization,  but  decrepitate  remarkably 
when  heated,  owing  to  the  expansion  of  water  mechanically  confined 
within  them. 

Pure  chloride  of  sodium  has  an  agreeable  saline  taste.  It  fuses  at  a 
red  heat,  and  becomes  a transparent  brittle  mass  on  cooling.  It  deli- 
quesces slightly  In  a moist  atmosphere,  but  undergoes  no  change  when 
the  air  is  dry.  In  pure  alcohol  it  is  insoluble.  It  requires  twice  and  a 
half  its  weight  of  water  at  60°  F.  for  solution,  and  its  solubility  is  not 


298 


SODIUM. 


increased  by  heat.  Like  the  soluble  chlorides  in  g’eneral,  it  passes  into 
a muriate  while  in  the  act  of  dissolving*.  (Page  287.)  Sulphuric  acid 
decomposes  it  with  evolution  of  muriatic  acid  gas,  and  formation  of 
sulphate  of  soda.  In  com])osition  it  is  analogous  to  chloride  of  potas- 
sium, consisting  of  one  equivalent  of  chlorine  and  one  of  sodium. 

The  uses  of  chloride  of  sodium  are  well  known.  Besides  its  em- 
ployment in  seasoning  food,  and  in  preserving  meat  from  putrefaction, 
a property  which  when  pure  it  possesses  in  a high  degree,  it  is  used 
for  vai’ious  purposes  in  the  arts,  especially  in  the  formation  of  muriatic 
acid  and  chloride  of  lime. 

The  compounds  of  sodium  with  iodine,  sulphur,  and  phosphorus  are 
so  analogous  to  those  which  potassium  forms  with  the  same  elements, 
that  a particular  description  of  them  is  unnecessary.  Sodium  does  not 
unite  with  hydrogen. 

According  to  Gmelin  of  Tubingen  siilphuret  of  sodium  is  the  colour- 
ing principle  of  lapis  lazuli,  to  which  the  colour  of  ultra-marine  is  owing; 
and  he  has  succeeded  in  preparing  artificial  ultra-marine  by  heating 
sulphuret  of  sodium  with  a mixture  of  silica  and  alumina.  (An.  de  Ch. 
et  de  Ph.  xxxvii.  409.) 

Chloride  of  Soda. — This  compound  has  lately  acquired  the  attention 
of  scientific  men  under  the  name  of  Labarraque’s  disinfecting  soda  liquid^ 
which  was  announced  by  M.  Labarraque  as  a compound  of  cldorine  and 
soda,  analogous  to  the  well-known  bleaching  powder,  chloride  of  lime. 
The  nature  of  this  liquid  has  been  since  investigated  by  Mr.  Phillips  and 
Mr.  Faraday,  especially  by  the  latter;  and  it  appears  from  the  experi- 
ments of  this  chemist,  that  while  chloride  of  soda  is  the  active  ingre- 
dient, its  properties  are  considerably  modified  by  the  presence  of  car- 
bonate of  soda.  (Quarterly  Journal  of  Science,  N.  S.  ii.  84. 

Pure  chloride  of  soda  is  easily  prepared  by  transmitting  to  saturation 
a current  of  chlorine  gas  into  a cold  and  rather  dilute  solution  of  caustic 
soda.  Common  carbonate  of  soda  may  be  substituted  for  the  pure  al- 
kali; but  considerable  excess  of  chlorine  must  then  be  employed  in 
order  to  displace  the  whole  of  the  carbonic  acid.  It  may  also  be  formed 
easily,  cheaply,  and  of  uniform  strength,  by  decomposing  chloride  of 
lime  with  carbonate  of  soda,  as  proposed  by  M.  Payen.  (Quarterly 
Journal  of  Science,  N.  S.  i.  236.)  However  prepared,  its  properties  are 
the  same.  As  its  constituents  are  retained  in  combination  by  a feeble 
affinity,  the  compound  is  easily  destroyed.  It  emits  an  odour  of  chlo- 
rine, and  possesses  the  bleaching  properties  of  that  substance  in  a very 
high  degree.  When  kept  in  open  vessels,  it  is  slowly  decomposed  by 
the  carbonic  acid  of  the  atmosphere  with  evolution  of  chlorine;  and  the 
change  is  more  rapid  in  air  charged  with  putrid  effluvia,  because  the 
carbonic  acid  produced  during  putrefaction  promotes  the  decomposition 
of  the  chloride.  On  this,  as  was  proved  by  M.  Gaultier  de  Claubry, 
depends  the  efficacy  of  an  alkaline  chloride  in  purifying  air  loaded  with 
putrescent  exhalations.  When  the  solution  is  heated  to  the  boiling 
point,  or  concentrated  by  means  of  heat,  the  chloride  undergoes  a 
change  previously  explained,  (page  206)  and  is  converted  into  chlorate 
and  muriate  of  soda. 

Chloride  of  soda  may  be  employed  in  bleaching,  and  for  all  purposes 
to  which  chlorine  gas  or  its  solution  was  formerly  applied.-  It  is  now 
much  used  in  removing  the  offensive  odour  arising  from  drains,  sewers, 
or  all  kinds  of  animal  matter  in  a state  of  putrefaction.  Bodies  disin- 
terred for  the  ])urpose  of  judicial  inquiry,  or  parts  of  the  body  advanced 
in  putrefaction,  may  l)y  its  means  be  rendered  fit  for  examination;  and  it 
is  employed  in  surgical  practice  for  destroying  the  fetor  of  malignant 


SODIUM. 


299 


ulcers.  Clothes  worn  by  persons  during*  pestilential  diseases  are  disin- 
fected by  being*  washed  with  this  compound. 

It  is  also  used  in  fumigating*  the  chambers  of  the  sick;  for  the  disen- 
gagement of  chlorine  is  so  gradual,  that  it  does  not  prove  injurious  or 
annoying  to  the  patient.  In  all  these  instances  chlorine  appears  actually 
to  decompose  noxious  exhalations  by  uniting  with  the  elements  of  which 
they  consist,  and  especially  with  hydrogen. 

In  preparing  the  disinfecting  liquid  of  Labarraque,  it  is  necessary  to 
be  exact  in  the  proportion  of  the  ingredients  emplo)^ed.  The  quanti- 
ties used  by  Mr.  Faraday,  founded  on  the  directions  of  Labarraque,  are 
the  following.  He  dissolved  2800  grains  of  crystallized  carbonate  of 
soda  in  1.28  pints  of  water,  and  through  the  solution,  contained  in 
Woulfe’s  apparatus,  was  transmitted  the  chlorine  evolvedfrom  a mixture 
of  967  grains  of  sea- salt  and  750  grains  of  peroxide  of  manganese, 
when  acted  on  by  967  grains  of  sulphuric  acid,  diluted  with  750  grains 
of  water.  In  order  to  remove  any  accompanying  muriatic  acid  gas,  the 
chlorine  before  reaching  the  soda  was  conducted  through  pure  water, 
by  which  means  nearly  a third  part  was  dissolved,  but  the  remaining 
two-thirds  were  fully  sufficient  for  the  purpose.  The  gas  was  readily 
absorbed  by  the  solution,  and  from  the  beginning  to  the  end  of  the 
process,  not  a particle  of  carbonic  acid  gas  was  evolved;  whereas  by 
employing  an  excess  of  chlorine,  the  carbonic  acid  may  be  entirely  ex- 
pelled. 

The  solution  thus  prepared  has  all  the  characters  of  Labarraque^s 
soda  liquid.  Its  colour  is  pale  yellow,  and  it  has  but  a slight  odour  of 
chlorine.  Its  taste  is  at  first  sharp,  saline,  and  scarcely  at  all  alkaline; 
but  it  produces  a persisting  biting  effect  upon  the  tongue.  It  first  red- 
dens and  then  destroys  the  colour  of  turmeric  paper.  When  boiled  it 
does  not  give  out  chlorine,  nor  is  its  bleaching  power  perceptibly  im- 
paired; and  if  carefully  evaporated,  it  yields  a mass  of  damp  crystals, 
which  when  redissolved,  bleach  almost  as  powerfully  as  the  original 
liquid.  When  rapidly  evaporated  to  dryness,  the  residue  contains 
scarcely  any  chlorate  of  soda  or  chloride  of  sodium;  but  it  has  never- 
theless lost  more  than  half  of  its  bleaching  power,  and,  therefore,  chlo- 
rine must  have  been  evolved  during  the  evaporation.  The  solution 
deteriorates  gradually  by  keeping,  chloric  acid  and  chloride  of  sodium 
being  generated.  When  allowed  to  evaporate  spontaneously,  chlorine 
gas  is  gradually  evolved,  and  crystals  of  carbonate  of  soda  remain. 

In  some  respects  the  nature  of  this  liquid  is  still  obscure;  but  from 
the  preceding  facts,  drawn  from  the  essay  of  Mr.  Faraday,  two  points 
seem  to  be  established.  First,  that  the  liquid  contains  chlorine,  carbo- 
nic acid,  and  soda.  Secondly,  that  the  chlorine  is  not  simply  combined 
either  with  water  or  soda;  for  by  boiling,  the  gas  is  neither  expelled  as 
it  would  be  from  an  aqueous  solution,  nor  does  the  liquid  yield  chloric 
acid  and  chloride  of  sodium  as  when  pure  chloride  of  soda  is  heated. 
It  may  perhaps  be  regarded  as  a compound  of  chloride  and  bicarbonate 
of  soda.  Its  production  may  be  conceived  by  supposing,  that  when 
chlorine  is  introduced  in  due  quantity  into  a solution  of  carbonate  of 
soda,  it  combines  with  half  the  alkali,  while  the  remainder  with  all  the 
carbonic  acid  constitutes  bicarbonate  of  soda.  Should  this  salt  unite, 
though  by  a feeble  affinity,  with  chloride  of  soda,  both  may  thence  de- 
rive a degree  of  permanence  which  neither  singly  possesses.  During 
spontaneous  evaporation,  the  tendency  of  the  common  carbonate  to 
crystallize  may  occasion  its  reproduction,  and  the  disengagement  of 
chlorine.  These  remarks,  however,  are  merely  speculative. 


300 


LITHIUM. 


SECTION  III. 

LITHIUxM. 

In  the  year  1818  M.  Arfwedson  of  Sweden,*  in  analyzing*  the  mineral 
called  petalite,  discovered  the  existence  of  anew  alkali,  and  its  presence 
has  since  been  detected  in  spodumene,  lepidolite,  and  in  several  va- 
rieties of  mica.  Berzelius  has  found  it  also  in  the  waters  of  Carlsbad 
in  Bohemia.  From  the  circumstance  of  its  having*  been  first  obtained 
from  an  earthy  mineral,  Arfwedson  gave  it  the  name  of  lithion,  (from 
lapideus,)  a term  since  clianged  in  this  country  to  lithia.  It  has 
hitherto  been  procured  in  small  quantity  only,  because  spodumene  and 
petalite  are  rare,  and  do  not  contain  more  than  6 or  8 per  cent  of  the 
alkali.  It  is  combinec*  in  these  two  minerals  with  silica  and  alumina, 
whereas  potassa  is  likewise  present  in  lepidolite  and  lithion-mica,  and, 
therefore,  lithia  should  be  prepared  solely  from  the  former. 

The  best  process  for  preparing  lithia  is  that  which  was  suggested  by 
Berzelius.  One  part  of  petalite  or  spodumene,  inline  powder,  is  mixed 
intimately  with  two  parts  of  fluor  spar,  and  the  mixture  is  heated  with 
three  or  four  times  its  weight  of  sulphuric  acid,  as  long  as  any  acid 
vapours  are  disengaged.  'I'he  silica  of  the  mineral  is  attacked  by  hy- 
drofluonc  acid,  and  dissipated  in  the  form  of  fluosilicic  acid  gas,  while 
the  alumina  and  lithia  unite  with  sulphuric  acid.  After  dissolving  these 
salts  in  water,  the  solution  is  boiled  with  pure  ammonia  to  precipitate 
the  alumina:  it  is  then  filtered,  and  evaporated  to  dryness,  and  the  dry 
mass  heated  to  redness  to  expel  the  sulphate  of  ammonia.  The  residue 
is  pure  sulphate  of  lithia. f 

Sir  H.  Davy  succeeded,  by  means  of  galvanism,  in  obtaining  a white 
coloured  metal  like  sodium  from  lithia;  but  it  was  oxidized,  and  thus 
reconverted  into  the  alkali,  with  such  rapidity  that  it  could  not  be  col- 
lected. Lithia  may,  therefore,  be  regarded  as  the  protoxide  of  lithium; 
and,  according  to  the  analysis  of  sulphate  of  lithia  by  Stromeyer  and 
Thomson,  lithia  is  inferred  to  be  composed  of  10  parts  or  one  equivalent 
of  lithium,  and  8 parts  or  one  equivalent  of  oxygen.  Its  equivalent  is, 
therefore,  18^  but  the  accuracy  of  this  estimate  is  rendered  doubtful  by 
some  late  experiments  of  M.  Hermann,  from  whose  researches  the 
equivalent  of  lithia  may  be  estimated,  in  round  numbers,  at  14. 

Lithia  is  distinguished  from  potassa  and  soda  by  its  greater  neutraliz- 
ing power,  by  forming  sparingly  soluble  salts  with  carbonic  and  phos- 
phoric acids,  and  by  chloride  of  lithium  being  highly  deliquescent,  and 
dissolving  freely  in  strong  alcohol.  This  alcoholic  solution  burns  with 
a red  flame;  and  all  the  salts  of  lithia,  when  heated  on  platinum  wire 
before  tlie  blowpipe,  tinge  the  flame  of  a red  colour.  Further,  when 
lithia  is  fused  on  platinum  foil,  it  attacks  that  metal,  and  leaves  a dull 
yellow  trace  round  the  spot  on  which  it  lay.  (Berzelius  on  the  Blow- 
pipe. Cliildren’s  Translation.) 


* An.  dc  Ch.  ct  dc  Fh.  vol  x. 

•j-  'I'he  sulphate  of  lithia  may  be  decomposed  by  acetate  of  baryta, 
and  the  acetate  of  lithia  thus  obtained,  by  exposure  to  a red  heat,  is  con- 
verted into  the  carbonate.  The  carbonate  may  then  be  brought  to  the 
state  of  a caustic  hydrate  by  the  action  of  lime  in  the  usual  manner.  B, 


BAmUM. 


301 


Lithia  is  disting'uished  from  the  alkaline  earths  by  forming*  soluble  salts 
with  sulphuric  and  oxalic  acids;  and  by  the  circumstance  tliat  carbonate 
of  lithia,  though  sparingly  soluble  in  water,  forms  with  it  a solution 
which  gives  a brown  stain  to  turmeric  paper. 


CLASS  1. 

ORDER  II.  • 

METALLIC  BASES  OF  THE  ALKALINE  EARTHS. 


SECTION  IV. 

BARIUM. 

H.  Davy  discovered  barium,  the  metallic  base  of  baryta,  in  the 
year  1808  by  a process  suggested  by  Berzelius  and  Pontin.  It  consists 
in  forming  carbonate  of  baryta  into  a paste  with  water,  and  placing  a 
globule  of  mercury  in  a little  hollow  made  in  its  surface.  The  paste 
was  laid  upon  a platinum  tray  which  communicated  with  the  positive 
pole  of  a galvanic  battery  of  100  double  plates,  while  the  negative 
wire  was  brought  into  contact  with  the  mercury.  The  baryta  was  de- 
composed, and  its  barium  entered  into  combination  with  mercury. 
This  amalgam  w^as  'then  heated  in  a vessel  free  from  air,  by  which 
means  the  mercury  was  expelled,  and  barium  obtained  in  a pure 
form. 

Barium,  thus  procured,  is  of  a dark  gray  colour,  with  a lustre  infe- 
rior to  cast  iron.  It  is  far  denser  than  water,  for  it  sinks  rapidly  in 
strong  sulphuric  acid.  It  attracts  oxygen  with  avidity  from  the  air,  and 
in  doing  so  yields  a white  powder,  which  is  baryta.  It  effervesces 
strongly,  from  the  escape  of  hydrogen  gas,  when  thrown  into  r/ater, 
and  a solution  of  baryta  is  produced.  It  has  hitherto  been  obtained  in 
very  minute  quantities,  and  consequently  its  properties  have  not  been 
determined  with  precision. 

Oxides  of  Barium. — Barytes,  or  Baryta,  so  called  from  the  great 
density  of  its  compounds,  (from  heavy")  was  discovered  in  the 

year  1774  by  Scheele.  It  is  the  sole  product  of  the  oxidation  of  bari- 
um in  air  or  w'ater.  It  may  be  prepared  by  decomposing  nitrate  of 
baryta  at  a red  heat;  or,  as  was  ascertained  by  Dr.  Hope,  by  exposing 
carbonate  of  baryta  contained  in  a black  lead  crucible  to  an  intense 
white  heat;  a process  which  succeeds  much  better,  when  the  carbonate 
is  intimately  mixed  with  charcoal.  Baryta  is  a gray  powder,  the  spe- 
cific gravity  of  which  is  about  4.  It  requires  a very  high  temperature 
for  fusion.  It  has  a sharp  caustic  alkaline  taste,  converts  vegetable 
blue  colours  to  green,  and  neutralizes  the  strongest  acids.  Its  alkalini- 
ty, therefore,  is  equally  distinct  as  that  of  potassa  or  soda;  but  it  is 
much  less  caustic  and  less  soluble  in  water  than  those  alkalies.  In  pure 
alcohol  it  is  insoluble.  It  has  an  exceedingly  strong  affinity  for  water. 
When  mixed  with  that  liquid  it  slakes  in  the  same  manner  as  quicklime, 

26 


302 


BARIUM. 


but  with  the  evolution  of  a more  intense  h(?ht,  which,  accordinj^  to 
Dbbereiner,  sometimes  amounts  to  himinousness.  The  result  is  a white 
bulky  hydrate,  fusible  at  a red  heat,  and  which  bears  the  highest 
temperature  of  a smith’s  forge  without  parting  with  its  water.  It  is 
composed  of  78  parts  or  one  equivalent  of  baryta,  and  9 parts  or  one 
equivalent  of  water. 

Hydrate  of  baryta  dissolves  in  three  times  its  weight  of  boiling  wa- 
ter, and  in  twenty  parts  of  water  at  the  temperature  of  60®  F.  (Davy.) 
A saturated  solution  of  baryta  in  boiling  water  deposites,  in  cooling, 
transparent,  flattened,  prismatic  crystals,  which  are  composed,  accord- 
ing to  Mr.  Dalton,  of  *78  parts- or  one  equivalent  of  baryta,  and  180 
parts  or  twenty  equivalents  of  water. 

The  aqueous  solution  of  baryta  is  an  excellent  test  of  the  presence  of 
carbonic  acid  in  the  atmosphere  or  in  other  gaseous  mixtures.  The  car- 
bonic acid  unites  with  the  baryta,  and  a white  insoluble  precipitate, 
carbonate  of  baryta,  subsides. 

The  exact  combining  proportion  of  barium  is  not  known  with  cer- 
tainty; for  while  Dr.  Thomson  estimates  its  equivalent  at  70,  Berzelius 
states  it  at  68.66.  Were  1 to  venture  an  opinion  from  some  experiments 
at  present  in  progress,  and  of  which  unforeseen  hindrances  have  for 
some  time  delayed  the  conclusion,  I should  select  69  as  the  equivalent 
of  barium;  but  as  the  subject  is  still  under  investigation,  I shall  continue 
for  the  present  to  use  the  number  stated  by  Dr.  1'homson,  ‘being  that 
which  is  generally  employed  in  this  country.  Accordingly,  baryta  is 
regarded  as  a compound  of  70  parts  or  one  equivalent  of  barium,  and  8 
parts  or  one  equivalent  of  oxygen. 

Deutoxide  of  barium  may  be  formed  by  conducting  dry  oxygen  gas 
over  pure  baryta  at  a low  red  heat.  An  easier  process,  according  to 
M.  Quesneville,  junr.,  is  to  introduce  nitrate  of  baryta  into  a luted  re- 
tort of  porcelain,  to  which  is  attached  a Welter’s  safety  tube  termina- 
ting under  an  inverted  jar  full  of  water.  Heat  is  gradually  applied  to 
the  retort,  and  a red  heat  continued  as  long  as  there  is  any  disengage- 
ment of  nitric  oxide  or  nitrogen  gas.  When  these  have  ceased  and  pure 
oxygen  passes  over,  which  is  a proof  of  all  the  nitrate  being  decom- 
posed, the  process  is  discontinued.  The  peroxide  of  barium  is  then 
found  in  the  retort.  This  statement,  however,  is  declared  by  Berze- 
lius to  be  quite  inaccurate,  and  that  the  residue  is  a compound  of  baryta 
and  protoxide  of  nitrogen.  (Yahres-bericht  for  1828,  107.)  Deutoxide 
of  barium,  according  to  Thenard,  contains  twice  as  much  oxygen  as 
baryta;  oris  composed  of  one  equivalent  of  barium  and  two  equivalents 
of  oxygen.  This  is  the  substance  employed  by  Thenard  in  the  forma- 
tion of  deutoxide  of  hydrogen. 

Baryta  is  distinguished  from  all  other  substances  by  the  following 
characters.  1.  By  dissolving  in  water  and  forming  an  alkaline  solution. 
2.  By  all  its  soluble  salts  being  precipitated  as  white  carbonate  of  baryta 
by  alkaline  carbonates,  and  as  sulphate  of  baryta,  which  is  insoluble 
both  in  acid  and  alkaline  solutions,  by  sulphuric  acid  or  any  soluble  sul- 
phate. 3.  By  forming  with  muriatic  acid  a salt,  which  crystallizes  readily 
by  evaporation  in  the  form  of  four,  six,  or  eight-sided  tables,  is  insolu- 
ble in  alcoliol,  and  does  not  uiulergo  any  change  on  exposure  to  the 
air. 

'J'he  j'cadicst  method  of  forming  the  salts  of  baryta  is  by  the  action 
of  moderately  dilute  acids  on  the  native  or  artificial  carbonate. 

All  the  soluble  salts  of  l)aryta  are  poisonous.  The  carbonate,  from 
being  dissolved  by  the  juices  of  the  stomach,  likewise  acts  as  a poison. 
The  sulpliate,  from  its  perfect  insolubility,  is  inert. 

Chloride  of  Barium. — 'I'his  compound  is  generated  when  chlorine 


STRONTIUM. 


303 


gas  is  conducted  over  baryta  at  a red  heat,  and  oxygen  gas  is  disen- 
gaged. It  may  also  be  formed  by  heating  to  redness  the  crystallized 
muriate  of  baryta.  It  consists  of  one  equivalent  of  each  of  its  consti- 
tuents. It  requires  five  times  its  weight  of  water  at  60®  F.  for  solu- 
tion, and  is  much  more  soluble  in  boiling  water.  At  a strong  red  heat 
it  fuses. 

Bromide  of  Barium.— It  was  prepared  by  Mr.  Henry,  junr.,  who  j^as 
examined  it,  by  broiling  protobromide  of  iron  with  moist  carbonate  of 
baryta  in  excess,  evaporating  the  filtered  solution,  and  heating  the  re- 
sidue to  redness.  The  product  crystallizes  by  careful  evaporation  in 
white  rhombic  prisms,  which  have  a bitter  taste,  are  slightly  deliques- 
cent, and  are  soluble  in  water  and  alcohol.  It  resists  decomposition  by 
heat,  and  consists  of  one  equivalent  of  each  of  its  elements. 

Sulphur et  of  Barium. — The  protosulphuret  may  be  prepared  from 
sulphate  of  baryta  by  the  action  of  charcoal  or  hydrogen  gas  at  a high 
temperature.  (Page  283.)  It  dissolves  readily  in  hot  water,  forming 
hydrosulphuret  of  baryta.  By  means  of  this  solution  all  the  chief  salts 
of  baryta  may  be  procured.  Thus  by  adding  an  alkaline  carbonate, 
carbonate  of  baryta  is  precipitated;  and  when  muriatiai  acid  is  added, 
sulphuretted  hydrogen  is  evolved,  and  muriate  of  bm*yta  produced. 
A solution  of  pure  baryta  may  also  be  obtained  from  the  hydrosulphu- 
ret, by  boiling  it  with  peroxide  of  copper,  until  the  filtered  solution  no 
longer  gives  a dark  precipitate  with  acetate  of  lead.  The  crystallized 
hydrate  of  baryta  is  easily  prt)cured  by  means  of  this  solution. 

The  combinations  of  barium  with  the  other  non  metallic  substances 
have  not  yet  been  carefully  examined. 


SECTION  V. 

STRONTIUM. 

The  metallic  base  of  strontia,  called  strontium^  was  discovered  by 
Sir  H.  Davy  by  a process  analogous  to  that  described  in  the  last  section. 
All  that  is  known  respecting  its  properties  is,  that  it  is  a heavy  metal, 
similar  in  appearance  to  barium,  that  it  decomposes  water  with  evolu- 
tion of  hydrogen  gas,  and  oxidizes  quickly  in  the  air,  being  converted 
in  both  cases  into  strontia. 

From  the  close  resemblance  between  baryta  and  strontia,  these  sub- 
stances were  once  supposed  to  be  identical.  Dr.  Crawford,  however, 
and  M.  Sulzer  noticed  a difference  between  them;  but  the  existence  of 
strontia  was  first  established  with  certainty  in  the  year  1792  by  Dr. 
Hope,*  and  the  discovery  was  made  about  the  same  time  by  Klap- 
roth, f It  was  originally  extracted  from  strontianite,  native  carbonate 
of  strontia,  a mineral  found  at  Strontian  iji  Scotland;  and  hence  the 
origin  of  the  term,  strontites^  or  strontia^  by  which  the  earth  itself  is 
designated. 

Pure  strontia  may  be  prepared  from  nitrate  and  carbonate  of  strontia, 
in  the  same  manner  as  baryta.  It  resembles  this  earth  in  appearance, 
in  infusibility,  and  in  possessing  distinct  alkaline  properties.  It  slakes 


* Edinburgh  Philosophical  Transactions,  iv.  3, 
•j-  Klaproth’s  Contributions,  vol.  i. 


3U4 


STRONTIUM. 


when  mixed  with  water,  causing*  intense  heat,  and  forming*  a white  solid 
hydrate,  which  consists  of  32  parts  or  one  equivalent  of  strontia,  and 
9 parts  or  one  equivalent  of  water.  Hydrate  of  strontia  fuses  readily 
at  a red  heat,  but  sustains  the  strong’est  heat  of  a wind  furnace  without 
decomposition.  It  is  insoluble  in  alcohol.  Roiling*  water  dissolves  it 
freely,  and  a hot  saturated  solution,  on  cooling*,  deposites  transparent 
crystals  in  the  form  of  thin  quadrangular  tables.  These  crystals  are 
coniposed,  according  to  the  analysis  of  Dr.  Hope,  of  52  parts  or  one 
equivalent  of  strontia,  and  108  parts  or  twelve  equivalents  of  water. 
They  are^  converted  by  heat  into  the  protohydrate.  'I'hey  require  50 
times  their  weight  of  water  at  60^^  F.  for  solution,  and  twice  their  weie*!!! 
at  212^  F.  (Dalton.) 

The  solution  of  strontia  has  a caustic  taste  and  alkaline  reaction.  Like 
the  solution  of  baryta  it  is  a delicate  test  of  the  presence  of  carbonic 
acid  in  air  or  other  gaseous  mixtures,  forming  with* it  the  insoluble  car- 
bonate of  strontia. 

The  atomic  weight  of  strontia,  as  deduced  from  the  analyses  of  Ber- 
zelius, Stromeyer,  and  Thomson,  is  52;  and  consequently  strontia,  re- 
garded as  the  pi^toxide  of  strontium,  is  composed  of  44  parts  or  one 
equivalent  of  strontium,  and  one  equivalent  of  oxygen. 

Deutoxide  of  strontium  is  prepared  in  the  same  manner  as  the  cor- 
responding preparation  of  baryta.  It  may  likewise  be  formed  by 
pouring  an  aqueous  solution  of  strontia  into  deutoxide  of  hydrogen. 
According  to  Thenard,  it  contains  twice  as  much  oxygen  as  the  pro- 
toxide. 

The  soluble  salts  of  strontia,  like  those  of  baryta,  are  precipitated 
by  alkaline  carbonates,  and  by  sulphuric  acid  or  soluble  sulphates. 
Strontia  is  distinguished  from  baryta  by  forming  with  muriatic  acid  a 
salt,  which  crystallizes  in  the  form  of  slender  hexagonal  prisms,  deli- 
quesces in  a moist  atmosphere,  and  dissolves  freely  in  pure  alcohol. 
The  alcoholic  solution,  when  set  on  fire,  burns  wdth  a blood-red  flame; 
and  the  salts  of  strontia,  when  exposed  to  the  blowpipe  flame  on  pla- 
tinum wire,  impart  to  it  a red  tinge.  They  are  also  distinguished  by  a 
difference  in  the  solubility  of  their  sulphates.  On  adding  Glauber’s 
salt  in  excess  to  a soluble  salt  of  baryta,  that  base  is  so  completely  pre- 
cipitated, that  its  presence  cannot  be  afterwards  detected  in  the  solu- 
tion by  any  reagent.  But  when  a salt  of  strontia  is  thus  treated,  .so 
much  sulphate  of  strontia  remains  in  solution,  that  the  filtered  liquid 
yields  a white  precipitate  with  carbonate  of  potassa  or  soda. 

The  salts  of  strontia  are  most  conveniently  prepared  from  the  car- 
bonate. These  compounds  are  not  poisonous. 

Chloride  of  strontium  is  formed  under  precisely  the  same  circum- 
stances as  chloride  of  barium,  and  its  composition  is  analogous.  It  is 
exceedingly  soluble  in  boiling  water,  and  requires  twice  its  weight  of 
water  at  60^  F.  for  solution.  As  already  mentioned,  it  is  soluble  in 
alcoliol. 

Suljihurct  of  strontium  may  be  prepared  by  the  processes  referred 
to  in  the  last  section.  It  may  be  advantageously  employed  for  form- 
ing the  solution  and  salts  of  strontia,  in  the  same  manner  us  those  of 
baryta  are  ])repai*ed  fj*otn  sulphuret  of  barium.  It  consists  of  44  parts 
or  one  ccpiivalent  of  strontium,  and  16  jiarts  or  one  equivalent  of 
sulphur. 


CALCIUM. 


305 


SECTION  VI.^ 

CALCIUM. 

The  existence  of  calcium,  the  metallic  base  of  lime,  was  demon- 
strated by  Sir  H.  Davy  by  a process  similar  to  that  described  ^ the 
section  on  barium.  It  of  a whiter  colour  than  barium  or.  strontium, 
and  is  converted  into  lime  by  being  oxidized.  Its  other  properties  are 
unknown. 

When  carbonate  of  lime  is  exposed  to  a white  or  even  to  a very  strong 
red  heat,  carbonic  acid  is  expelled,  and  pure  lime,  commonly  called 
quicklime^  remains.  If  lime  of  great  purity  is  required,  it  should  be 
prepared  from  pure  carbonate  of  lime,  such  as  Iceland  spar  or  Carrara 
marble;  but  in  burning  lime  in  lime-kilns  for  making  mortar,  common 
lime- stone  is  employed.  The  expulsion  of  carbonic  acid  is  facilitated 
by  mixing  the  carbonate  with  combustible  substances,  in  which  case 
carbonic  oxide  is  generated.  (Page  181.) 

Lime  is  a brittle  white  earthy  solid,  the  specific  gravity  of  which  is 
about  2.3.  It  phosphoresces  powerfully  when  heated  to  full  redness, 
a property  which  it  possesses  in  common  with  strontia  and  baryta.  It  is 
one  of  the  most  infusible  bodies  known;  fusing  with  difficulty,  even 
by  the  heat  of  the  oxy-hydrogen  blowpipe.  It  has  a powerful  affinity 
for  water,  and  the  combination  is  attended  with  g'reat  increase  of  tem- 
perature, and  formation  of  a white  bulky  hydrate,  which  is  composed 
of  28  parts  or  one  equivalent  of  lime,  and  9 parts  or  one  equivalent  of 
water.  The  process  of  slaking  lime  consists  in  forming  this  hydrate, 
and  the  hydrate  itself  is  called  slaked  lime.  It  differs  from  the  hy- 
drates of  strontia  and  baryta  in  parting  with  its  water  at  a red  heat. 

Hydrate  of  lime  is  dissolved  very  sparingly  by  water,  and  it  is  a sin- 
gular fact,  first  noticed  I believe  by  Mr.  Dalton,  that  it  is  more  soluble 
in  cold  than  in  hot  water.  Thus  he  found  that  one  grain  of  lime  re- 
quires for  solution 

778  grains  of  water  . at  60°  F. 

972  ...  130° 

1270  . . . 212°. 

And,  consequently,  on  heating  a solution  of  lime,  or  lime-water^  which 
has  been  prepared  in  the  cold,  deposition  of  lime  ensues.  This  fact 
was  determined  experimentally  by  Mr.  Phillips,  who  has  likewise  ob- 
served that  water  at  32°  F.  is  capable  of  dissolving  twice  as  much  lime 
as  at  212°  F. 

Owing  to  this  circumstance  pure  lime  cannot  be  made  to  crystallize 
in  the  same  manner  as  baryta  or  strontia.  Gay-Lussac  succeeded,  how- 
ever, in  obtaining  crystals  of  lime  by  evaporating  lime-water  under  the 
exhausted  receiver  of  an  air-pump  by  means  of  sulphuric  acid,  as^  in 
Mr.  Leslie’s  process  for  freezing  water.  (Page  61.)  Small  transpai^nt 
crystals,  in  the  form  of  regular  hexahedrons,  are  deposited,  which 
consist  of  water  and  lime  in  the  same  proportion  as  in  the  hydrate  above 
mentioned. 

Lime-water  is  prepared  by  mixing  hydrate  of  lime  with  water,  agi- 
tating the  mixture  repeatedly,  and  then  setting  it  aside  in  a well- 
stopped  bottle  until  the  undissolved  parts  shall  have  subsided.  The 
substance  called  milk  or  cream  of  lime  is  made  by  mixing  hydrate  of 
lime  with  a sufficient  quantity  of  water  to  give  it  the  liquid  form; — 
it  is  merely  lime-water  in  which  hydrate  of  lime  is  mechanically  sus- 
pended. 


26* 


306 


CALCIUM. 


Lime-water  lias  a harsh  acrid  taste,  and  converts  veg’etable  blue  col- 
ours to  green.— It  agrees, therefore,  with  baryta  and  strontia  in  ])Ossess- 
ing  distinct  alkaline  properties.  Like  the  solutions  of  these  eartlis,  it 
hae  a strong  affinity  for  carbonic  acid,  and  forms  with  it  an  insoluble 
carbonate.  On  this  account  lime-water  should  be  carefully  protected 
from  the  air.  Lor  the  same  reason,  lime-water  is  rendered  turbid  by 
a solution  of  carbonic  acid;  but  on  adding  a large  quantity  of  the 
acid,  ^le  transparency  of  the  solution  is  completely  restored,  because 
carbonate  of  lime  is  soluble  in  an  excess  of  carbonic  acid.  'I'lie  ac- 
tion of  this  acid  on  the  solutions  of  baryta  and  strontia  is  precisely 
similar. 

The  atomic  weight  of  lime,  as  deduced  from  the  experiments  of  Dr. 
Thomson,  is  28;  and,  therefore,  lime,  regarded  as  the  protoxide  of 
calcium,  is  composed  of  20  parts  or  one  equivalent  of  calcium,  and  8 
parts  or  one  equivalent  of  oxygen. 

Deutoxide  of  calcium  may  be  formed  in  the  same  way  as  dcutoxide 
of  strontium.  According  to  'Lhenard  it  consists  of  one  equivalent  of 
calcium  and  two  equivalents  of  oxygen.  ^ 

The  salts  of  lime,  which  are  easily  prepared  by  the  action  of  acids  on 
pure  marble,  are  in  many  respects  similarly  affected  by  reagents,  as 
those  of  baryta  and  strontia.  They  are  precipitated,  for  example,  by 
alkaline  carbonates.  Sulphuric  acid  and  soluble  sulphates*  likewise 
precipitate  lime  from  a moderately  strong  solution.  But  sulphate  of 
lime  has  a considerable  degree  of  solubility.  Thus,  a dilute  solution  of 
a salt  of  lime  is  not  precipitated  at  all  by  sulphuric  acid,  and  when  sul- 
phate of  lime  is  separated,  it  may  be  redissolved  by  the  addition  of  ni- 
tric acid. 

The  most  delicate  test  of  the  presence  of  lime  is  oxalate  of  ammonia 
or  potassa;  for  of  all  the  salts  of  lime,  the  oxalate  is  the  most  insoluble 
in  water.  This  serves  to  distinguish  lime  from  most  substances,  though 
not  from  baryta  and  strontia;  because  the  oxalates  of  baryta  and  stron- 
tia, especially  the  latter,  are  likewise  sparingly  soluble.  All  these  oxa- 
lates dissolve  readily  in  water  acidulated  with  nitric  or  muriatic  acid. 

The  best  characters  for  distinguishing  lime  from  baryt^.'  and  strontia 
are  the  following.  Nitrate  of  lime  yields  prismalic  crystals'"  by  evapo- 
ration, is  deliquescent  in  a high  degree,  and  very  soluble  in  alcohol. 
The  nitrates  of  baryta  and  strontia  crystallize  in  regular  octohedrons  or 
segments  of  the  octohedron,  undergo  no  change  on  exposure  to  the  air, 
except  when  very  moist,  and  do  not  dissolve  in  pure  alcohol. 

The  salts  of  lime,  when  heated  before  the- blow’pipe,  or  when  their 
solutions  in  alcohol  are  set  on  fire,  communicate  to  the  flame  a dull 
brownish-red  colour. 

Chloride  of  Calcium. — This  compound  is  formed  in  the  same  manner 
as  chloride  of  strontium.  In  decomposing  muriate  of  lime  by  heat,  a 
little  muriatic  acid  is  sometimes  expelled  as  well  as  watei*.  Chloride  of 
calcium  is  soluble  in  alcohol,  and  deliquesces  rapidly  on  exposure  to 
the*atmosphere.  On  account  of  its  strong  affinity  for  water,  it  is  much 
employed  to  deprive  gases  and  other  substances  of  their  moisture.  For 
a like  reason,  it  may  be  used  for  forming  frigorific  mixtures  with  snow; 
but  foi*  this  ])urpose  crystallized  muriate  of  lime,  which  contains  six 
equivalents  of  water  of  crystallization,  is  far  preferable. 

Chloride  of  calcium  contains  one  proportional  of  each  of  its  elements. 

Chloride  of  Lime. — 'I'his  compound,  commonly  called  oxymuriate  of 
lime,  ()]•  hleacldnii;  powder,  is  prepared  by  exposing  thin  strata  of  recently 
slaked  lime  in  line  j)owdcr  to  an  atmos])here  of  chlorine.  The  gas  is 
absorbed  in  large  quantity,  and  combines  directly  with  the  lime. 

Chloride  of  lime  is  a dry  white  powder,  which  smells  faintly  of  chlo- 


CALCIUM. 


30 


rine,  and  has  a strong*  taste.  It  dissolves  partially  in  water,  and  the 
solution  possesses  powerful  bleaching*  properties,  and  contains  both 
chlorine  and  lime;  while  the  undissolved  portion  is  hydrate  of  lime,  re- 
taining* a small  quantity  of  chlorine.  The  aqueous  solution,  when  ex- 
posed to  the  atmosphere,  is  g*radually  decomposed;  chlorine  is  set  free 
and  carbonate  of  lime  generated.  On  boiling  the  liquid,  muriatic,  and 
I presume  chloric,  acid  are  formed;  and  by  long  keeping,  the  dry 
chloride  appears  to  undergo  a similar  change,  at  least  muriatic  acid  is 
produced  in  large  quantity.  Chloride  of  lime  is  also  decomposed  by  a 
strong  heat.  At  first,  chlorine  is  evolved;  but  pure  oxygen  is  afterwards 
disengaged,  and  chloride  of  calcium  remains  in  the  I’etort. 

The  composition  of  chloride  of  lime  was  first  carefully  investigated 
by  Mr.  Dalton,*  and  it  has  since  been  analyzed  by  Dr.  Thomson, -f-  M. 
Welter,  t and  Dr.  Ure.§  The  three  first  mentioned  chemists  infer  from 
their  researches  that  bleaching  powder  is  a hydrated  suhcJiloride  or  dichlo- 
ride of  lime,  in  which  36  parts  or  one  equivalent  of  chlorine  are  united 
with  56  parts  or  two  equivalents  of  lime.  They  are  also  of  opinion, 
that  on  mixing  this  sub  chloride  with  water,  a real  chloride  is  dissolved, 
and  one  equivalent  of  lime  separated  as  an  insoluble  powder.  Dr.  Ure, 
on  the  contrary,  denies  that  bleaching  powder  is  a subchloride;  and 
maintains,  according  to  the  result  of  his  own  analysis,  that  the  elements 
of  this  compound  do  not  constitute  a regular  atomic  combination.  He 
found  that  the  quantity  of  chlorine  absorbed  by  hyd]*ate  of  lime  is  variable, 
depending  not  only  on  the  pressure  and  degree  of  exposure,  but  on  the 
quantity  of  water  which  is  present.  I'he  following  is  the  result  of  his 
analysis  of  three  specimens.  No.  1 being  good  commercial  bleaching 
powder.  No.  2 made  by  himself  witli  pure  protohydrate  of  lime,  and 
No.  3 prepared  by  himself  with  lime  containing  more  water  than  in 
No.  2. 


No.  1. 

No.  2. 

No.  3. 

Chlorine 

23 

40.32 

39.5 

Lime 

46 

45.40 

39.9 

Water 

31 

14.28 

20.6 

100 

100 

100 

The  experiments  of  Dr.  Ure  appear  to  have  been  made  with  great 
care,  and  his  results  to  be  entitled  to  equal  if  not  greater  confidence 
than  those  of  the  other  chemists.  Upon  the  whole  it  is  probable,  that  com- 
mon commercial  bleaching  powder  consists  of  chloride  of  lime,  a com- 
pound of  36  parts  or  one  equivalent  of  chlorine,  and  28  parts  or  one 
equivalent  of  lime;  and  that  this,  the  essential  ingredient,  is  mixed 
with  variable  quantities  of  hydrate  of  lime. 

Several  methods  have  been  proposed  for  estimating  the  value  of  dif- 
ferent specimens  of  chloride  of  lime.  Perhaps  the  most  convenient  for 
the  artist  is  that  of  AVelter,  which  consists  in  ascertaining  the  power  of 
tlie  bleaching  liquid  to  deprive  a solution  of  indigo  of  known  strength 
of  its  colour;  and  directions  have  been  drawn  up  by  Gay-Lussac  for 
enabling  manufacturers  to  employ  this  method  with  accuracy.  (Annals 
of  Philosophy,  xxiv.  218.)  For  analytical  purposes,  the  best  method 
is  to  decompose  chloride  of  lime,  confined  in  a glass  tube  over  mercury 
by  means  of  muriatic  acid.  Muriate  of  lime  is  g*enerated,  and  the  chlo- 
rine being  set  free,  its  quantity  may  easily  be  measured. 


* Annals  of  Philosophy,  i.  15.  and  ii.  6. 
\ An.  de  Ch.  et  de  Ph.  vol.  viii. 


•j-  Ibid.  XV.  401. 

§ Quarterly  Journal,  xiii,  1. 


308 


MAGNESIUM. 


Bromide  of  Calcium.-— was  prepared  by  M.  Henry  by  tlic  action  of 
hydrate  of  lime  on  protobromide  of  iron.  It  crystallizes  in  acicular 
crystals,  which  are  very  deliquescent,  and  extremely  soluble  both  in 
water  and  alcohol.  Its  taste  resembles  that  of  chloride  of  calcium.  It 
is  partially  decomposed  by  heat,  and  consists  of  one  equivalent  of  each 
of  its  elements. 

Protosulphuret  of  calcium  is  procured  by  processes  similar  to  those  for 
forming  sulphuret  of  barium. 

The  phosphorescent  substance  called  Cantords  phosphorus,  which  is 
made  by  exposing  a mixture  of  calcined  oyster-shells  and  sulphur  to  a 
red  heat,  is  supposed  to  be  a sulphuret  of  lime;  but  its  real  composition 
has  not  been  determined. 

Phospliuret  of  Lime. — This  compound  is  formed  by  passing  the  va- 
pour of  phosphorus,  over  fragments  of  quicklime  at  a red  heat.  The 
true  nature  of  the  product  is  not  known  with  certainty.  It  is  either  a 
phosphuret  of  lime,  or  a mixture  of  phosphate  of  lime  and  phosphuret 
of  calcium.  When  it  is  put  into  water,  mutual  decomposition  ensues, 
and  phosphuretted  hydrogen,  hypophosphorous  acid,  and  phosphoric 
acid  are  generated. 


SECTION  VII. 

MAGNESIUM. 

The  galvanic  researches  of  Sir  H.  Davy  demonstrated  the  existence 
of  magnesium,  though  he  obtained  it  in  a quantity  too  minute  for  deter- 
mining its  properties.  It  has  lately  been  prepared  by  M.  Bussy  by  the 
action  of  potassium  on  chloride  of  magnesium  heated  to  redness  in  a 
tube  of  porcelain.  The  magnesium,  separated  by  washing  from  chlo- 
ride of  potassium,  had  the  appearance  of  small  bi'own  scales,  which 
when  pressed  by  a pestle  in  an  agate  mortar,  left  a metallic  trace,  the 
colour  of  which  resembled  that  of  lead.  Diluted  nitric  acid  does  not 
act  upon  it,  but  it  is  dissolved  by  muriatic  acid  and  potassa.  It  burns 
with  difficulty  even  at  a high  temperature,  and  yields  magnesia  by  the 
combustion. 

Magnesia,  the  only  known  oxide  of  magnesium,  is  obtained  by  expo- 
sing carbonate  of  magnesia  to  a very  strong  red  heat,  by  which  its  car- 
bonic acid  is  expelled.  It  is  a white  friable  powder,  of  an  earthy  ap- 
pearance; and  when  pure,  it  has  neither  taste  nor  odour.  Its  specific 
gravity  is  about  2.3,  and  it  is  exceedingly  infusible.  It  has  a weaker 
affinity  than  lime  for  water;  for  though  it  forms  a hydrate  when  mois- 
tened, the  combination  is  effected  with  hardly  any  disengagement  of 
caloric,  and  the  product  is  readily  decomposed  by  a red  heat.  There 
probably  exist  several  different  compounds  of  water  and  magnesia,  but 
llie  native  hydrate  is  the  only  one  known  with  certainty.  According  to 
tlie  analysis  of  Stromeyer,  this  liydrate  contains  one  ecpiivalent  of  each 
.of  its  constituents;  and  the  results  of  the  analysis  of  Berzelius  and  Dr. 
Fyfe  accord  very  nearly  with  this  proportion. 

Magnesia  dissolves  very  sparingly  in  water.  According  to  Dr.  Fyfe, 
it  requires  5142  times  its  weight  of  water  at  60^^,  and  36,000  of  boiling 
water  for  solution,  'flic  resulting  liejuid  does  not  change  the  colour  of 
violets;  b\it  when  pure  magnesia  is  put  upon  moistened  turmeric  pa- 
per, it  causes  a brown  stain.  From  this  there  is  no  doubt  that  the  in- 
action of  magnesia  with  respect  to  vegetable  colours,  wlien  tried  in  the 


ALUMINIUM. 


309 


# 

ordinary  mode,  is  owinp;'  to  its  insolubility.  It  possesses  the  still  more 
essential  character  of  alkalinity,  that,  namely,  of  forming*  neutral  salts 
with  acids,  in  an  eminent  degree,  it  absorbs  both  water  and  carbonic 
acid  when  exposed  to  the  atmosphere,  and,  therefore,  should  be  kept 
in  well-closed  phials. 

The  atomic  weight  of  magnesia,  as  determined  by  Ur.  Thomson,  is 
20.  Consequently  this  alkaline  base,  regarded  as  the  protoxide  of  mag- 
nesium, is  composed  of  , 

Magnesium  , 12  or  one  equivalent. 

Oxygen  . 8 or  one  equivalent. 

Magnesia  is  characterized  by  the  following  properties.  With  nitric 
and  muriatic  acids  it  forms  salts  which  are  soluble  in  alcohol,  and  ex- 
ceedingly deliquescent.  The  sulphate  of  magnesia  is  very  soluble  in 
water,  a circumstance  by  which  it  is  distinguished  from  the  other  alka- 
line earths.  Mag-nesia  is  precipitated  from  its  salts  as  a bulky  hydrate 
by  the  pure  alkalies.  It  is  precipitated  as  carbonate  of  magnesia,  by 
the  carbonates  of  potassa  and  soda;  but  the  bicarbonates,  and  the  com- 
mon carbonate  of  ammonia,  do  not  precipitate  it  in  the  cold.  If  mod- 
erately diluted,  the  salts  of  magnesia  are  not  precipitated  by  oxalate  of 
ammonia.  By  means  of  this  reagent  magnesia  may  be  both  distinguish- 
ed and  separated  from  lime. 

The  compounds  of  magnesium  with  the  other  simple  substances  have 
little  interest.  The  chloride  is  formed  by  decomposing  muriate  of 
magnesia  by  heat;  but  it  is  apt  to  lose  a portion  of  muriatic  acid  during 
the  process.  It  is  very  deliquescent,  and  is  soluble  in  alcohol.  It  is 
composed  of  36  parts  or  one  equivalent  of  chlorine,  and  12  parts  or 
one  equivalent  of  magnesium.  The  bromide  crystallizes  in  small 
acicular  prisms,  which  have  a bitter  sharp  taste,  are  deliquescent, 
and  very  soluble  in  water  and  alcohol.  It  is  decomposed  by  a strong 
heat. 


CLASS  I. 

ORDER  III. 

METALLIC  BASES  OF  THE  EARTHS. 


SECTION  VlII. 

ALUMINIUM. 

That  alumina  is  an  oxidized  body  was  proved  by  Sir  H.  Davy,  who 
found  that  potassa  is  generated  when  the  vapour  of  potassium  is  brought 
into  contact  with  pure  alumina  heated  to  whiteness;  and  it  was  inferred, 
chiefly  by  analogical  reasoning,  to  be  a metallic  oxide.  The  propriety 
of  this  inference  has  been  demonstrated  by  Wohler,  who  has  lately 
procured  aluminium^  the  metallic  base  of  alumina,  in  a pure  state. 
(Edinburgh  Journal  of  Science,  No.  xvii.  178.) 

The  preparation  of  this  metal  depends  on  the  property  which  potas- 
sium possesses,  of  decomposing  the  chloride  of  aluminium.  Decom- 


310 


% ALUMINIUM. 


position  is  cfTected  by  aid  of  a moderate  increase  of  temperature;  ])ut 
tlie  action  is. so  violent,  and  accompanied  with  siicli  intense  discng'age- 
ment  of  heat  and  light,  that  the  process  cannot  be  safely  conducted  in 
glass  vessels.  Wohler  succeeded  in  effecting  tlie  decomposition  in  a 
platinum  crucible,  retaining  the  cover  in  its  place  by  a piece  of  wire. 
The  heat  developed  during  the  action  was  so  great,  that  the  crucible, 
though  but  gently  heated  externally,  suddenly  became  red-hot.  The 
platinum  is  scarcely  attacked  during  the  process;  but  to  prevent  the 
possibility  of  error  from  this  source,  the  decomposition  was  effected 
in  a crucible  of  porcelain.  The  potassium  employed  for  the  purpose 
should  be  quite  free  from  carbon,  and  the  quantity  operated  on  at  one 
time  not  exceed  the  size  of  ten  peas.  The  heat  was  applied  by  means 
of  a spirit  lamp,  and  continued  until  the  action  was  completed.  The 
proportion  of  the  materials  requires  to  be  carefully  adjusted;  for  the 
potassium  should  be  in  such  quantity  as  to  prevent  any  chloride  of 
aluminium  from  subliming  during  the  process,  but  not  so  much  as  to 
yield  an  alkaline  solution  when  the  product  is  put  into  water.  The 
matter  contained  in  the  crucible  at  the  close  of  the  operation  is  in  gen- 
eral completely  fused,  and  of  a dark  gray  colour.  When  quite  coldy 
the  crucible  is  put  into  a large  glass  full  of  water,  in  which  the  saline 
matter  is  dissolved,  with  slight  disengagement  of  hydrogen  of  an  offen- 
sive odour;  and  a gray  powder  separates,  which  on  close  inspection, 
especially  in  sunshine,  is  found  to  consist  "solely  of  minute  scales  of 
metal.  After  being  well  washed  with  cold  water,  it  is  pure  aluminium. 
The  solution  is  neutral,  and  contains  a quantity  of  alumina,  owing  to  a 
combination  being  formed  between  chloride  of  aluminium  and  chloride 
of  potassium  during  the  action. 

Aluminium,  as  thus  formed,  is  a gray  powder,  very  similar  to  that  of 
platinum.  It  is  generally  in  small  scales  or  spangles  of  a metallic  lus- 
tre; and  sometimes  small,  slightly  coherent,  spongy  masses  are  observ- 
ed, which  in  some  places  have  the  lustre  and  white  colour  of  tin.  The 
same  appearance  is  rendered  perfectly  distinct  by  pressure  on  steel,  or 
in  an  agate  mortar;  so  that  the  lustre  of  aluminium  is  decidedly  fnetal- 
lic.  In  its  fused  state  it  is  a conductor  of  electricity,  though  it  does 
not  possess  this  property  when  in  the  form  of  powder.  This  remark, 
of  a metal  conducting  the  electric  fluid  in  one  state  and  not  in  another, 
is  very  instructive;  and  Wohler  observed  an  instance  of  ihe  same 
kind  in  iron,  which,  in  the  state  of  fine  powder,  is  a non-conductor  of 
electricity. 

Aluminium  requires  for  fusion  a temperature  higher  than  that  at 
which  cast  iron  is  liquefied.  When  heated  to  redness  in  the  open  air, 
it  takes  fire  and  burns  with  vivid  light,  yielding  aluminous  earth  of  a 
white  colour,  and  of  considerable  hardness.  Sprinkled  in  powder  in 
the  flame  of  a candle,  brilliant  sparks  are  emitted,  like  those  given  off 
during  the  combustion  of  iron  in  oxygen  gas.  When  heated  to  red- 
ness in  a vessel  of  pure  oxygen  gas,  it  burns  with  an  exceedingly  vivid 
light,  and  emission  of  intense  heat.  The  resulting  alumina  is  par- 
tially vili'ificd,  of  a yellowish  colour,  and  equal  in  hardness  to  the 
native  crystallized  aluminous  earth,  corundum.  Heated  to  near  redness 
in  an  atni()S[)here  of  chlorine,  it  takes  fire,  and  chloride  of  aluminium 
is  sublimed. 

Aluminium  is  not  oxidized  by  water  at  common  temperatures,  nor 
is  its  lustre  tarnished  by  lying  in  water  during  its  evajmration.  On  heat- 
ing the  water  to  near  its  boiling  ])oint,  oxidation  of  the  metal  com- 
mences, with  feeble  disengagement  of  hydrogen  gas,  the  evolution  of 
which  continues  even  long  after  cooling',  but  at  length  wholly  ceases. 
The  oxidation,  hovsxver,  is  very  slight;  and  even  after  continued  ebul- 


ALUMINIUM. 


311 


lition,  the  smallest  particles  of  aluminium  appear  to  have  suffered 
scarcely  any  chang’e. 

Aluminium  is  not  attacked  by  concentrated  sulphuric  or  nitric  acid 
at  common  temperatures.  In  the  former,  with  the  aid  of  heat,  it  is 
rapidly  dissolved  with  diseng'ag'ement  of  sulphurous  acid  g'as.  In  di- 
lute muriatic  and  sulphuric  acid  it  is  dissolved  with  evolution  of  hydro- 
gen gas.  It  is  easily  and  completely  dissolved  even  by  a dilute  solu- 
tion of  potassa,  hydrogen  gas  being  evolved  at  the  same  time.  Ammo- 
nia produces  a similar  effect,  and  renders  soluble  a large  quantity  of 
aluminium.  The  hydrogen  gas  which  makes  its  appearance  is  of  course 
derived  from  water,  the  oxygen  of  which  combines  with  aluminium. 

Alumina  is  one  of  the  most  abundant  productions  of  nature.  It  is 
found  in  every  region  of  the  globe,  and  in  rocks  of  all  ages,  being  a 
constituent  of  the  oldest  primary  mountains,  of  the  secondary  strata, 
and  of  the  most  recent  alluvial  depositions.  The  different  kinds  of 
clay,  of  which  bricks,  pipes,  and  earthenware  are  made,  consist  of 
hydrate  of  alumina  in  a greater  or  less  degree  of  purity.  Though  this 
earth  commonly  appears  in  rude  amorphous  masses,  it  is  sometimes 
found  beautifully  crystallized.  The  ruby  and  the  sapphire,  two  of  the 
most  beautiful  gems  with  which  we  are  acquainted,  are  composed  almost 
solely  of  alumina. 

Pure  alumina  is  prepared  from  alum,  sulphate  of  alumina  and  po- 
tassa. This  salt,  as  purchased  in  the  shops,  is  frequently  contaminated 
with  oxide  of  iron,  and  consequently  unfit  for  many  chemical  purposes; 
but  it  may  be  separated  from  this  impurity  by  repeated  crystallization. 
The  absence  of  iron  is  proved  by  the  alum  being  soluble  without  resi- 
due in  a solution  of  pure  potassa;  whereas  when  oxide  of  iron  is  pre- 
sent, it  is  either  left  undissolved  in  the  first  instance,  or  deposited  after 
a few  hours  in  yellowish-brown  flocks.  Any  quantity  of  purified  alum 
is  dissolved  in  four  or  five  times  its  weight  of  boiling  water,  a slight  ex- 
cess of  carbonate  of  potassa  added,  and  after  digesting  for  a few  min- 
utes, the  bulky  hydrate  of  alumina  is  collected  on  a filter,  and  well 
washed  with  hot  water.  It  is  necessary  in  this  operation  to  digest  and 
employ  an  excess  of  alkali;  since  otherwise  the  precipitate  would  re- 
tain some  sulphuric  acid  in  the  form  of  a subsulphate.  But  the  alumina, 
as  thus  prepared,  is  not  yet  quite  pure;  for  it  retains  some  of  the  alkali 
with  such  force,  that  it  cannot  be  separated  by  the  action  of  water. 
For  this  reason  the  precipitate  must  be  re-dissolved  in  dilute  muriatic 
acid,  and  thrown  down  by  means  of  pure  ammonia  or  its  carbonate. 
This  precipitate,  after  being  well  washed  and  exposed  to  a white  heat, 
yields  pure-  anhydrous  alumina.  Ammonia  cannot  be  employed  for 
precipitating  aluminous  earth  directly  from  alum,  because  sulphate  of 
alumina  is  not  completely  decomposed  by  this  alkali.  (Berzelius. ) An 
easier  process,  proposed  by  Gay-Lussac,  is  to  expose  sulphate  of  alu- 
mina and  ammonia  to  a strong  heat,  so  as  to  expel  the  ammonia  and 
sulphuric  acid. 

Alumina  has  neither  taste  nor  smell,  and  is  quite  insoluble  in  water. 
It  is  very  infusible,  though  less  so  than  lime  or  magnesia.  It  has  a 
powerful  affinity  for  water,  attracting  moisture  from  the  atmosphere 
with  avidity;  and  for  a like  reason,  it  adheres  tenaciously  to  the  tongue 
when  applied  to  it.  Mixed  with  a due  proportion  of  water,  it  yields  a 
soft  cohesive  mass,  susceptible  of  being  moulded  into  regular  forms,  a 
property  upon  which  depends  its  employment  in  the  art  of  pottery. 
When  once  moistened,  it  cannot  be  rendered  anhydrous,  except  by  ex- 
posure to  a full  white  heat;  and  in  proportion  as  it  parts  with  water,  its 
volume  diminishes.  (Page  40.) 

Alumina  most  probably  forms  several  different  hydrates  with  water. 


312 


ALUMINIUM. 


Dr.  Thomson  has  described  two  different  compounds  of  this  kind.  One 
is  the  bihydrate,  composed  of  one  equivalent  of  alumina  and  two  of 
water;  and  it  is  procured  by  exposing*,  for  the  space  of  two  months, 
alumina,  precipitated  by  means  of  an  alkali,  to  a dry  air,  tlie  tempera- 
ture of  which  does  not  exceed  60®  F.  The  other  compound  is  a proto- 
hydrate, obtained  by  drying*  the  bihydrate  at  a temperature  of  100®  F., 
by  which  means  half  of  its  water  is  expelled. 

Alumina,  owing  to  its  insolubility,  does  not  affect  the  blue  colour  of 
plants.  It  appears  to  possess  the  properties  both  of  an  acid  and  of  an 
alkali:— of  an  acid,  by  uniting  with  alkaline  bases,  such  as  pobissa, 
lime,  and  baryta; — and  of  an  alkali,  by  forming  salts  with  acids.  In 
neither  case,  however,  are  its  soluble  compounds  neutral  with  respect 
to  test  paper. 

Chemists  are  not  agreed  as  to  the  combining  proportion  of  alumina; 
but  Dr.  Tliomson,  after  comparing  the  results  of  a considerable  num- 
ber of  analyses,  has  fixed  upon  18  as  its  equivalent.  I'he  composition 
of  alumina  is  still  more  uncertain,  for  as  yet  no  direct  experiment  has 
been  made  on  the  subject.  Dr.  Thomson  considers  it  a compound  of 
one  proportional  of  aluminium  and  one  of  oxygen,  and  on  this  supposi- 
tion 10  is  the  equivalent  of  the  former;  but  Berzelius  believes  its  consti- 
tution to  be  analogous  to  that  of  peroxide  of  iron,  and  a strong  argu- 
ment may  be  adduced  in  favour  of  this  view. 

Alumina  is  easily  recognised  by  the  following  characters.  1.  It  is 
separated  from  acids,  as  a hydrate,  by  all  the  alkaline  carbonates, 
and  by  pure  ammonia.  2.  It  is  precipitated  by  pure  potassa  or  soda, 
but  the  precipitate  is  completely  re-dissolved  by  an  excess  of  the  alkali. 

Chloride  of  Aluminium, — This  compound^was  discovered  some  years 
ago,  by  Professor  Oersted,  by  transmitting  dry  chlorine  gas  over  a mix- 
ture of  alumina  and  charcoal  heated  to  redness.  By  acting  on  this  sub- 
stance with  an  amalgam  of  potassium  and  expelling  the  mercury  by  heat, 
he  obtained  metallic  matter,  which  he  believed  to  be  aluminium;  but 
not  having  leisure  to  pursue  the  inquiry  himself,  he  requested  Wohler 
to  investigate  the  subject.  Wohler  did  not  arrive  at  any  satisfactory 
conclusion  by  the  method  suggested  by  Oersted;  but  met  with  complete 
success  by  means  of  pure  potassium,  as  already  described. 

To  procure  chloride  of  aluminium,  Wohler  precipitated  aluminous 
earth  from  a hot  solution  of  alum  by  means  of  potassa,  and  mixed  the 
hydrate,  when  dry,  with  pulverized  charcoal,  sugar,  and  oil,  so  as  to 
form  a thick  paste,  which  was  heated  in  a covered  crucible,  until  all 
the  organic  matter  was  destroyed.  By  this  means  the  alumina  was 
brought  into  a state  of  intimate  mixture  with  finely  divided  charcoal, 
and  while  yet  hot,  was  introduced  into  a tube  of  porcelain,  fixed  in  a 
convenient  furnace.  After  expelling  atmospheric  air  from  the  interior 
of  the  apparatus  by  a current  of  dry  chlorine  gas,  the  tube  was  brought 
to  a red  heat.  I'he  formation  of  cldoride  of  aluminium  then  commen- 
ced, and  continued,  with  disengagement  of  carbonic  oxide  gas,  during 
an  hour  and  a half,  when  the  tube  became  impervious  from  sublimed 
chloride  of  aluminium  collected  within  it.  The  process  was  then  neces- 
sarily discontinued. 

As  thus  formed,  chloride  of  aluminium  is  of  a pale  gi’eenish -yellow 
colour,  partially  translucent,  and  of  a hig'hly  crystalline  lamellated 
texture,  somewhat  like  talc,  but  without  regular  crystals.  ’ On  expo- 
sure to  the  air  it  fumes  slightly,  emits  an  odour  of  muriatic  acid  gas, 
and,  delifpiescing,  yields  a clear  liquid.  When  thrown  into  water,  it 
is  speedily  dissolved  with  a hissing  noise;  and  so  much  heat  is  evolved, 
that  the  water,  if  in  small  (juantity,  is  brought  into  a state  of  brisk 
ebullition.  The  solution  is  the  common  muriate  of  alumina,  formed 


GLUCINIUM. 


313 

by  decomposition  of  water.  According  to  Oersted,  it  is  volatile  at  a 
temperature  a little  higher  than  212°,  and  fuses  nearly  at  the  same 
degree. 

Sulphuret  of  Aluminium. — Sulphur  may  be  distilled  from  aluminium 
without  combining  with  it;  but  if  a piece  of  sulphur  is  dropped  on 
aluminium  when  strongly  incandescent,  so  that  it  may  be  enveloped  in 
an  atmosphere  of  the  vapour  of  sulphur,  the  union  is  effected  with  vivid 
emission  of  light.  The  resulting  sulphuret  is  a partially  vitrified,  semi- 
metallic  mass,  which  acquires  an  iron-black  metallic  lustre  when  burn- 
ished. On  exposure  to  the  air  it  emits  a strong  odour  of  sulphuretted 
hydrogen,  swells  up  gradually,  and  falls  into  a gray  powder,  ’ sulphu- 
retted hydrogen  gas  and  alumina  being  obviously  generated  at  the  ex- 
pense of  the  watery  vapour  floating  in  the  atmosphere.  Applied  to 
the  tongue,  it  excites  a pricking  warm  taste  of  sulphuretted  hydrogen. 
When  thrown  into  pure  water  sulphuretted  hydrogen  gas  is  rapidly  dis- 
engaged, and  gray  alumina  deposited. 

Wohler  finds  that  sulphuret  of  aluminium  cannot  be  generated  by 
the  action  of  hydrogen  gas  on  sulphate  of  alumina  at  a red  heat;  for 
in  that  case  all  the  acid  is  expelled,  without  the  aluminous  earth  being 
reduced. 

Phosphuret  of  Aluminium. — When  aluminium  is  heated  to  redness  in 
contact  with  the  vapour  of  phosphorus,  it  takes  fire,  and  emits  a bril- 
liant light.  The  product  is  described  by  Wohler  as  a blackish-gray 
pulverulent  mass,  which  by  friction  acquires  a dark  gray  metallic  lus- 
tre, and  in  the  air  smells  instantly  of  phosphuretted  hydrogen.  By  the 
action  of  water  alumina  and  phosphuretted  hydrogen  gas  are  generated, 
but  the  latter  is  spontaneously  explosive.  The  effervescence  is  less 
rapid  than  with  the  sulphuret,  but  is  increased  by  heat. 

Seleniuret  of  Aluminium. — This  compound  is  formed,  with  disen- 
gagement of  heat  and  light,  by  heating  to  redness  a mixture  of  sele- 
nium and  aluminium.  The  product  is  black,  and  pulverulent,  and  as- 
sumes a dark  metallic  lustre  when  rubbed.  In  the  air  it  emits  a strong 
odour  of  seleniuretted  hydrogen;  and  this  gas  is  rapidly  disengaged  by 
the  action  of  water,  which  is  speedily  reddened  by  the  separation  of 
selenium. 


SECTION  IX. 

GLUCINIUM,  YTTRIUM,  THORIUM,  ZIRCONIUM. 

Glucinium. 

Gludna,  which  was  discovered  by  Vauquelin  in  tlie  year  1798,  has 
hitherto  been  found  only  in  three  rare  minerals,  euclase,  beryl,  and 
emerald.  It  is  the  oxide  of  a metal  which  Wohler  succeeded  in  pre- 
paring in  the  year  1828  by  a process  exactly  similar  to  that  described  in 
the  last  section.  Chloride  of  glucinium  is  readily  attacked  by  potassi- 
um when  heated  with  the  flame  of  a spirit-lamp,  and  the  decomposition 
13  attended  with  intense  heat.  After  removing  the  x^esulting  chloride  of 
potassium  by  cold  water,  the  glucinium  appears  in  the  form  of  a gray- 
ish-black powder,  which  acquires  a dark  metallic  lustre  by  burnishing. 
It  may  be  exposed  to  air  and  moisture,  or  be  even  boiled  in  water, 

27 


YTTRIUM. 


314 

without  oxidation.  When  heated  in  the  open  air,  it  takes  fire  and  bums 
with  a most  vivid  light;  and  in  oxygen  gas  the  combustion  is  attended 
with  extraordinary  splendour.  ^ The  product  in  both  cases  is  glucina, 
which  is  not  at  all  fused  by  the  intense  heat  that  accompanied  its  forma- 
tion. The  metal  is  readily  oxidized  and  dissolved  in  sulphuric,  nitric, 
or  muriatic  acid  with  the  aid  of  heat;  and  the  same  ensues  with  disen- 
gagement of  hydrogen  gas,  in  solution  of  potassa.  It  is  not  attacked, 
however,  by  pure  ammonia.  When  moderately  heated  in  chlorine  gas, 
it  burns  with  great  splendour,  and  a crystallized  chloride  sublimes. 
Similar  phenomena  ensue  in  the  vapour  of  bromine  and  iodine;  and  it 
unites  readily  with  sulphur,  selenium,  phosphorus,  and  arsenic.  (Phil. 
Mag.  and  Annals,  v.  392.) 

Glucina  is  commonly  prepared  from  beryl,  in  which  it  exists  to  the 
extent  of  about  14  per  cent,  combined  with  silica  and  alumina.  In  order 
to  procure  it  in  a separate  state,  the  mineral  is  reduced  to  an  exceedingly 
fine  powder,  mixed  with  three  times  its  weight  of  carbonate  of  potassa, 
and  exposed  to  a strong  red  heat  for  half  an  hour,  so  that  the  mixture 
may  be  fused.  The  mass  is  then  dissolved  in  dilute  muriatic  acid,  and 
the  solution  evaporated  to  perfect  dryness;  by  which  means  the  silica  is 
rendered  quite  insoluble.  The  alumina  and  glucina  are  then  redissolved 
in  water  acidulated  with  muriatic  acid,  and  thrown  down  together  by 
pure  ammonia.  The  precipitate,  after  being  well  washed,  is. macerated 
with  a large  excess  of  carbonate  of  ammonia,  by  which  glucina  is  dis- 
solved; and  on  boiling  the  filtered  liquid,  carbonate  of  glucina  subsides. 
By  means  of  a red  heat  its  carbonic  acid  is  entirely  expelled. 

Glucina  is  a white  powder,  which  has  neither  taste  nor  odour,  and  is 
quite  insoluble  in  water.  Its  specific  gravity  is  3.  Vegetable  colours 
are  not  affected  by  it.  The  salts  which  it  forms  with  acids  have  a 
sweetish  taste,  a circumstance  which  distinguishes  glucina  from  other 
earths,  and  from  which  its  name  is  derived.  {Yvom  yXvx)j^^  sweet.) 
According  to  the  analysis  of  Dr.  Thomson  and  Berzelius,  26  is  the 
atomic  weight  of  glucina;  but  the  composition  of  the  oxide  has  not  yet 
been  determined. 

Glucina  may  be  known  chemically  by  the  following  characters.  1. 
Pure  potassa  or  soda  precipitates  glucina  from  its  salts,  but  an  excess  of 
the  alkali  redissolves  it.  2.  It  is  precipitated  permanently  by  pure  am- 
monia as  hydrate,  and  by  fixed  alkaline  carbonates  as  carbonate  of  glu- 
cina. 3.  It  is  dissolved  completely  by  a cold  solution  of  carbonate  of 
ammonia,  and  is  precipitated  from  it  by  boiling.  By  means  of  this  prop- 
erty,  glucina  may  be  both  distinguished  and  separated  from  alumina. 

Yttrium. 

Yttrium  is  the  metallic  base  of  an  earth  which  was  discovered  in  the 
year  1794  by  Professor  Gadolin,  in  a mineral  found  at  Ytterby  in  Sweden, 
from  which  it  received  the  name  of  yttria.  The  metal  itself  was  pre- 
pared by  Wohler  in  1828  by  a process  similar  to  that  above  described, 
(ts  texture,  by  which  it  is  distinguished  from  glucinium  and  aluminium, 
s scaly,  its  colour  grayish-black,  and  its  lustre  perfectly  metallic.  In 
:olour  and  lustre  it  is  inferior  to  aluminium,  bearing  in  these  respects 
icarly  the  same  relation  to  that  metal,  as  iron  does  to  tin.  It  is  a brittle 
netal,  while  aluminium  is  ductile.  It  is  not  oxidized  either  in  air  or 
v^ater;  but  when  heated  to  redness,  it  burns  with  splendour  even  in 
tmosphcric  air,  and  with  far  greater  brilliancy  in  oxygen  gas.  The 
*roduct,  yttria,  is  white,  and  shows  unequivocal  marks  of  fusion.  It 
issolvcs  in  sulphuric  acid,  and  also,  though  less  readily,  in  solution  of 
)otassa;  but  it  is  not  attacked  by  ammonia.  It  combines  with  sul- 


THORIUM. 


315 


phur,  selenium,  and  phosphorus.  (Philosophical  Mag.  and  Annals,  v. 
395.) 

The  salts  of  yttria  have  in  general  a sweet  taste,  and  the  sulphate,  as 
well  as  many  of  its  salts,  has  an  amethyst  colour.  It  is  precipitated  as 
a hydrate  by  the  pure  alkalies,  and  is  not  redissolved  by  an  excess  of 
the  precipitant?  but  alkaline  carbonates,  especially  that  of  ammonia, 
dissolve  it  in  the  cold,  though  less  freely  than  glucina,  and  carbonate  of 
yttria  is  precipitated  by  boiling.  Of  all  the  earths  it  bears  the  closest 
resemblance  to  glucina?  but  it  is  readily  distinguished  from  it  by  the 
colour  of  its  sulphate,  by  its  insolubility  in  pure  potassa,  and  by  yielding 
a precipitate  with  ferrocyanate  of  potassa.  (Berzelius.)  The  equiva- 
lent of  yttria,  as  deduced  by  Dr*  Thomson  from  the  analysis  of  Berze- 
lius, is  42?  but  the  composition  of  this  earth  is  unknown. 

Thorium, 

The  earthy  substance  formerly  called  ihorina^  was  found  by  Berzelius 
to  be  phosphate  of  yttria?  but  during  last  year  he  discovered  a new 
earth,  so  similar  in  some  respects  to  what  was  formerly  called  thorina, 
that  he  applied  this  term  to  the  new  substance.  Thorina  was  procured 
from  a rare  Norwegian  mineral,  now  called  thorite^  which  was  sent  to 
Berzelius  by  M.  Esmark.  It  constitutes  57.91  per  cent  of  the  mineral, 
and  occurs  in  the  form  of  a hydrated  silicate  of  thorina.  In  order  to 
prepare  thorina,  the  mineral  is  reduced  to  powder,  and  digested  in 
muriatic  acid?  when  a gelatinous  mass  is  formed,  from  which  silica  is 
separated  by  evaporating  to  dryness,  and  dissolving  the  soluble  parts  in 
dilute  acid.  The  solution  is  then  freed  from  lead  and  tin,  which  occur 
in  thorite  along  with  several  impurities,  by  sulphuretted  hydrogen,  and 
the  earths  are  thrown  down  by  pure  ammonia.  The  precipitate,  after 
being  well  washed,  is  dissolved  in  dilute  sulphuric  acid,  and  the  solu- 
tion evaporated  at  a high  temperature  till  only  a small  quantity  of  fluid 
remains.  During  the  evaporation  the  greater  part  of  the  thorina  is 
deposited  as  a sulphate?  and  on  decanting  the  remaining  fluid,  washing 
the  residue,  and  heating  it  to  redness,  pure  thorina  remains.  (An.  de 
Ch.  et  de  Ph.  xliii.  5. ) 

The  metallic  base  of  thorina  (thorium)  was  procured  by  the  action  of 
potassium  on  chloride  of  thorium,  decomposition  being  accompanied 
with  a slight  detonation.  On  washing  the  mass,  thorium  is  left  in  the 
form  of  a heavy  metallic  powder,  of  a deep  leaden-gray  colour?  and 
when  pressed  in  an  agate  mortar,  it  acquires  metallic  lustre  and  an  iron- 
gray  tint.  Thorium  is  not  oxidized  either  by  hot  or  cold  water?  but 
when  gently  heated  in  the  open  air,  it  burns  with  great  brilliancy,  com- 
parable to  that  of  phosphorus  burning  in  oxygen.  The  resulting  tho- 
rina is  as  white  as  snow,  and  does  not  exhibit  the  least  trace  of  fusion. 
It  is  not  attacked  by  caustic  alkalies  at  a boiling  heat?  is  scarcely  at  all 
acted  on  by  nitric  acid,  and  very  slowly  by  the  sulphuric,  but  it  is  readily 
dissolved  with  disengagement  of  hydrogen  gas,  by  muriatic  acid. 

Thorina,  when  formed  by  the  oxidation  of  thorium,  or  after  being 
strongly  heated,  is  a white  earthy  substance,  of  specific  gravity  9.402, 
and  insoluble  in  all  the  acids  except  the  sulphuric?  and  it  dissolves  even 
in  that  with  difliculty.  It  is  precipitated  from  its  solutions  by  the 
caustic  alkalies  as  a hydrate,  and  in  this  state  absorbs  carbonic  acid  from 
the  atmosphere,  and  dissolves  readily  in  acids.  All  the  alkaline  car- 
bonates dissolve  the  hydrate,  carbonate,  and  sub -salts  of  thorina.  Its 
exact  composition  is  not  known?  but  its  equivalent's  about  67.6. 

Thorina  is  distinguished  from  alumina  and  glucina  by  its  insolubility 
in  pure  potassa?  from  yttria  by  forming  with  sulphate  of  potassa  a double 
salt  which  is  quite  insoluble  in  a cold  saturated  solution  of  sulphate  of 


316 


ZIRCONIUM. 


potassa;  and  from  zirconia  by  the  circumstance  that  this  earth,  after 
being*  precipitated  from  a hot  solution  of  sulphate  of  potassa,  is  almost 
insoluble  in  water  and  the  acids.  Thorina  is  precipitated,  also,  by  fer- 
rocyanate  of  potassa,  which  does  not  separate  zirconia  from  its  solutions. 
Berzelius  has  remarked  that  sulphate  of  thorina  is  much  more  soluble 
in  cold  than  in  hot  water,  so  that  a cold  saturated  solution  becomes 
turbid  when  heated,  and  in  cooling*  recovers  its  transparency. 

Chloride  of  thorium  is  readily  prepared  by'carbonizing*  an  intimate 
mixture  of  thorina  and  sugar  in  a covered  platinum  crucible,  and  then 
exposing  the  residue  at  a red  heat  in  a porcelain  tube  to  a current  of 
dry  chlorine.  The  chloride,  possessing  but  little  volatility,  collects  in 
the  tube  just  beyond  the  ignited  part  in  the  form  of  a partially  fused, 
crystalline,  white  mass.  It  is  soluble  in  water  with  considerable  rise  of 
temperature. 

When  thorium  is  heated  in  the  vapour  of  sulphur,  the  phenomena  of 
combustion  ensue  with  the  same  brilliancy  as  in  air,  and  a sulphuret 
results.  A phosphuret  may  be  formed  by  a similar  process. 

Zirconium, 

The  experiments  of  Sir  H.  Davy  proved  zirconia  to  be  an  oxidized 
body,  and  afforded  a presumption  that  its  base,  zirconiurriyis  of  a metallic 
nature.  The  decomposition  of  this  earth,  however,  had.  not  been 
effected  in  a satisfactory  manner  till  the  year  1824,  when  Berzelius 
succeeded  in  obtaining  zirconium  in  an  insulated  state. 

Zirconium  is  procured  by  heating  a mixture  of  potassium  and  hy- 
drofiuate  of  zirconia  and  potassa,  carefully  dried,  in  a tube  of  glass  or 
iron,  by  means  of  a spirit-lamp.  The  reduction  takes  place  at  a tem- 
perature below  redness,  and  without  emission  of  light.  The  mass  is 
then  washed  with  boiling  water,  and  afterwards  digested  for  some  time 
in  dilate  muriatic  acid.  The  residue  is  pure  zirconium. 

Zirconium,  thus  obtained,  is  in  the  form  of  a black  powder,  which 
may  be  boiled  in  water  without  being  oxidized,  and  is  attacked  with 
difficulty  by  sulphuric,  muriatic,  or  nitro-muriatic  acid;  but  it  is  dis- 
solved readily,  and  with  disengagement  of  hydrogen  gas,  by  hydro- 
fluoric acid.  Heated  in  the  open  air  it  takes  fire  at  a temperature  far 
below  luminousness,  burns  brightly,  and  is  converted  into  zirconia. 
Its  metallic  nature  seems  somewhat  questionable.  It  may  indeed  be 
pressed  out  into  thin  shining  scales  of  a dark  gray  colour,  and  of  a 
lustre  which  may  be  called  metallic;  but  its  particles  cohere  together 
very  feebly,  and  it  has  not  been  procured  in  a state  capable  of  conduct- 
ing electricity.  These  points,  however,  require  further  investigation 
before  a decisive  opinion  on  the  subject  can  be  adopted.* 

Zirconia  was  discovered  in  the  year  1789  by  Klaproth  in  the  jargon 
or  zircon  of  Ceylon,  and  has  since  been  found  in  tlie  hyacinth  from 
Expailly  in  France.  It  is  an  earthy  substance,  resembling  alumina  in 
appearance,  of  specific  gravity  4.3,  having  neither  taste  nor  odour,  and 
quite  insoluble  in  water.  It  is  so  liard  that  it  will  scratch  glass.  Its 
colour,  when  pure,  is  white;  but  it  has  frequently  a tinge  of  yellow, 
owing  to  the  p]*cscnce  of  iron,  from  which  it  is  separated  with  great 
difficulty.  Jt  phosphoresces  vividly  when  heated  strongly  before  the 
blowpi])e.  Us  salts  arc  distinguished  from  those  of  alumina pr  glucina 
by  being  precipitated  by  all  the  pure  alkalies,  in  an  excess  of  which  it 
is  insoluble.  The  alkaline  carbonates  precipitate  it  as  carbonate  of 


* Poggendorfi’^s  Annalen,  vol.  iv.  or  Quarterly  Journal  of  Science, 
xviii.  157, 


SILICIUM. 


317 


zirconia,  and  a small  portion  of  it  is  redissolved  by  an  excess  of  the 
precipitant,  especially  when  a bicai’bonate  is  employed.  It  differs  from 
all  the  earths,  except  thorina,  in  being*  precipitated  when  any  of  its 
neutral  salts  are  boiled  with  a saturated  solution  of  sulphate  of  potassa, 
the  zirconia  subsiding  as  a sub-salt,  and  the  potassa  remaining  in  solu- 
tion as  a bisulphate.  Zirconia  is  precipitated  from  its  salts  by  pure  am- 
monia, as  a bulky  hydrate,  which  is  readily  soluble  in  acids;  but  if  this 
hydrate  is  ignited,  dried,  or  even  washed  with  boiling  water,  it  after- 
v/ards  resists  the  action  of  tjie  acids,  and  is  dissolved  by  them  with  great 
difficulty.  Strong  sulphuric  acid  is  then  its  best  solvent.  (Berzelius.) 
When  hydrated  zirconia  is  heated  to  commencing  redness,  it  parts 
with  its  water,  and  soon  after  emits  a very  vivid  glow  for  a short  time. 
This  phenomenon  appears  to  depend  on  the  particles  of  the  zirconia 
suddenly  approaching  each  other,  and  thus  acquiring  much  greater  den- 
sity than  it  previously  possessed.  Oxide  of  chromium,  titanic  acid, 
and  several  other  compounds,  afford  instances  of  the  same  appearance; 
and  whenever  it  takes  place,  the  susceptibility  of  the  substance  to  be 
attacked  by  fluid  reagents  is  greatly  diminished,  (Berzelius.) 

The  composition  of  zirconia  has  not  yet  been  satisfactorily  determin- 
ed. From  some  analyses  by  Berzelius,  described  in  the  Essay  above 
referred  to,  it  is  probable  that  the  atomic  weight  of  this  earth  is  about 
30  or  33. 

Sulphiiret  of  Zirconium. — This  compound  may  be  prepared,  accord- 
ing to  Berzelius,  by  heating  zirconium  with  sulphur  in  an  atmosphere 
of  hydrogen  gas;  and  the  union  is  effected  with  feeble  emission'of  light. 
The  product  is  pulverulent,  a non-conductor  of  electricity,  of  a dark 
chestnut-brown  colour,  and  without  lustre.  It  is  insoluble  in  sulphuric, 
nitric,  and  muriatic  acid ; and  it  is  slowly  attacked  by  nitro-muriatic  acid, 
even  with  the  aid  of  heat.  It  is  readily  dissolved  by  hydrofluoric  acid, 
with  disengagement  of  hydrogen  gas. 


SECTION  X. 

SILICIUM. 

That  silica  or  siliceous  earth  is  composed  of  a combustible  body 
united  with  oxygen,  was  demonstrated  by  Sir  H.  Davy;  for  on  bring- 
ing the  vapour  of  potassium  in  contact  with  pure  silica  heated  to  white- 
ness, a compound  of  silica  and  potassa  resulted,  through  which  was 
diffused  the  inflammable  base  of  silica  in  the  form  of  black  particles 
like  plumbago.  To  this  substance,  on  the  supposition  of  its  being  a 
metal,  the  term  silicium  was  applied.  But  though  this  view  has  been 
adopted  by  most  chemists,  so  little  was  known  with  certainty  concern- 
ing the  real  nature  of  the  base  of  silica,  that  Dr.  Thomson  inclined  to 
the  opinion  of  its  being  a non-metallic  body,  and  accordingly  associated 
it  in  his  system  of  chemistry  with  carbon  and  boron  under  the  name  of 
silicon.  The  recent  researches  of  Berzelius  appear  almost  decisive  of 
this  question.  A substance  which  wants  the  metallic  lustre,  and  is  a 
non-conductor  of  electricity,  cannot  be  regarded  as  a metal.  It  may 
not  be  improper,  however,  to  have  the  absence  of  these  qualities  more 
completely  ascei’tained,  before  separating  silica  from  a class  of  bodies 
with  which,  in  several  respects,  it  is  so  nearly  allied. 

27* 


318 


SILICIUM. 


Pure  silicium  was  first  procured  by  Berzelius  in  the  year  1824  by  the 
action  of  potassium  on  fluosilicic  acid  gas;  but  it  is  more  conveniently 
prepared  from  the  double  hydrofluate  of  silica  and  potassa  or  soda,  pre- 
viously dried  by  a temperature  near  that  of  redness.  In  this  state  the  com- 
pound may  be  regarded  as  a double  fluoride,  in  which  neither  oxygen 
nor  hydrogen  are  present;  and  wlien  heated  in  a glass  tube  with  potas- 
sium, this  metal  unites  with  fluorine,  and  silicium  is  separated.  The 
heat  of  a spirit-lamp  is  sufficient  for  the  purpose,  and  tlie  decomposi- 
tion takes  place,  accompanied  with  feeble  detonation,  before  the  mix- 
ture becomes  red-hot.  When  the  mass  is  cold  the  soluble  parts  are  re- 
moved by  the  action  of  water;  the  first  portions  of  which  produce  dis- 
engagement of  hydrogen  gas,  owing  to  the  presence  of  some  siliciuret 
of  potassium.  The  silicium  tliiis  procured  is  chemically  united  with  a 
little  hydrogen,  and  at  a red  heat  burns  vividly  in  oxygen  gas.  In  order 
to  render  it  quite  pure,  it  should  be  first  heated  to  redness,  and  then 
digested  in  dilute  hydrofluoric  acid  to  dissolve  adherent  particles  of 
silica.  (Annals  of  Philosophy,  xxvi.  116.) 

Silicium  obtained  in  this  manner  has  a dark  nut-brown  colour,  with- 
out the  least  trace  of  metallic  lustre.  It  is  a non-conductor  of  electri- 
city. It  is  incombustible  in  air  and  in  oxygen  gas;  and  may  be  exposed 
to  the  flame  of  the  blowpipe  \tithout  fusing  or  undergoing  any  other 
change.  It  is  neither  dissolved  nor  oxidized  by  the  sulphuric,  nitric, 
muriatic,  or  hydrofluoric  acid;  but  a mixture  of  the  nitric  and  hydro- 
fluoric acids  dissolves  it  readily  even  in  the  cold.* 

Silicium  is  not  changed  by  ignition  with  chlorate  of  potassa.  In  nitre 
it  does  not  deflagrate  until  the  temperature  is  raised  so  high  that  the 
acid  is  decomposed;  and  then  the  oxidation  is  effected  by  the  affinity  of 
the  disengaged  alkali  for  silica  co-operating  with  the  attraction  of  oxy- 
gen for  silicium.  For  a similar  reason  it  burns  vividly  when  brought 
into  contact  with  carbonate  of  potassa  or  soda,  and  the  combustion  en- 
sues at  a temperature  considerably  below  that  of  redness.  It  explodes. 


* Dr.  Turner  has  not,  perhaps,  described,  in  asufficiently  distinct  man- 
ner, the  two  states  under  which  silicium  appears.  Its  characters  are  so 
much  altered  by  exposure  to  a high  temperature,  that  Berzelius  has 
deemed  it  expedient  to  give  a separate  description  of  its  properties,  as 
it  appears  before  and  after  ignition. 

Silicium  before  ignition  is  neither  dissolved  nor  oxidized  by  sulphuric, 
nitric,  or  nitro-muriatic  acid,  even  at  the  boiling  temperature;  but  it  is 
soluble  in  liquid  hydrofluoric  acid  at  common  temperatures;  and  in  a 
heated  concentrated  solution  of  caustic  potassa.  It  burns  readily  and 
vividly  in  air,  and  still  more  vividly  in  oxygen  gas.  A part  of  it  only 
undergoes  combustion,  the  remainder  being  protected  by  the  coating 
of  silica  which  becomes  formed.  In  this  state  silicium  contains  a little 
hydrogen. 

If  a portion  of  silicium  wliich  has  undergone  combustion  on  its  sur- 
face, subjected  to  the  action  of  hydrofluoric  acid,  the  silica  is  re- 
moved, and  a nucleus  of  silicium  is  obtained  in  tliat  state  in  which  it 
exists,  after  having  l)een  condensed  and  altered  in  its  properties  by  heat. 
It  is  now  perfectly  incom])Ustible,  and  is  no  longer  soluble;  in  hydro- 
fluoric acid  or  a solution  of  caustic  potassa. 

Berzelius  does  not  a]q)ear  to  attribute  the  difference  in  properties 
between  the  two  forms  of  silicium  to  the  presence  of  hydrogen  in  one  of 
them;  but  rather  to  a difference  in  the  aggregation  of  tlie  particles, 
BerzeliuSi  Traits  de  OhimiCy  i.  370.  B. 


SILICIUM. 


319 


in  consequence  of  a copious  evolution  of  hydrogen  gas,  when  it  is 
dropped  upon  the  fused  hydrate  of  potassa,  soda,  or  baryta. 

Oxide  of  Silicium  or  Silica, 

Silica  exists  in  the  earth  in  great  quantity.  It  enters  into  the  compo- 
sition of  most  of  the  earthy  minerals;  and  under  the  name  of  quartz 
rock,  forms  independent  mountainous  masses.  It  is  the  chief  ingre- 
dient in  sandstones;  and  flint,  calcedony,  rock  crystal,  and  other  ana- 
logous substances,  consist  almost  entbely  of  silica.  Siliceous  earth  of 
sufficient  purity  for  most  purposes  may,  indeed,  be  procured  by  igniting 
transparent  specimens  of  rock  crystal,  throwing  them  while  red-hot 
into  water,  and  then  reducing  them  to  powder. 

Pure  silica,  in  this  state,  is  a light  white  powder,  which  feels  rough 
and  dry  when  rubbed  between  the  fingers,  and  is  both  insipid  and  in- 
odorous. It  is  fixed  in  the  fire,  and  is  very  infusible;  but  fuses  be- 
fore the  oxy- hydrogen  blowpipe  with  greater  facility  than  lime  or 
magnesia. 

In  its  solid  form  it  is  quite  insoluble  in  water;  but  Berzelius  has 
shown  that,  when  silica  in  the  nascent  state  is  in  contact  with  that  fluid, 
it  is  dissolved  in  large  quantity.  On  evaporating  the  solution  gently,  a 
bulky  gelatinous  substance  separates,  which  is  a hydrate  of  silica.  This 
hydrate  is  partially  decomposed  by  a very  moderate  temperature;  but  a 
red  heat  is  required  for  expelling  the  whole  of  the  water.  According' 
to  Dr.  Thomson,  silica  unites  with  watei;  in  several  proportions.  (First 
Principles,  vol.  i.  p.l91.) 

Silica,  most  likffiy  from  its  insolubility,  does  not  change  the  blue  vege- 
table colours.  It  appears  to  possess  the  properties  of  an  acid  rather 
than  of  an  alkali.  Thus,  no  acid  acts  upon  silica  except  hydrofluoric 
acid;  whereas  it  is  dissolved  by  solutions  of  the  fixed  alkalies,  and  com- 
bines with  many  of  the  metallic  oxides.  On  this  account  silica  is  term- 
ed silicic  acid  by  some  chemists,  and  its  compounds  with  alkaline  bases 
silicates.  The  compound  earthy  minerals  that  contain  silica  may  be  re- 
garded as  native  silicates. 

The  combination  of  silica  with  the  fixed  alkalies  is  best  effected  by 
mixing  pure  sand  with  carbonate  of  potassa  or  soda,  and  heating  the 
mixture  to  redness.  During  the  process,  carbonic  acid  is  expelled, 
and  a silicate  of  the  alkali  is  generated.  The  nature  of  the  product 
depends  upon  the  proportions  which  are  employed.  On  igniting  one 
part  of  silica  with  three  of  carbonate  of  potassa,  a vitreous  mass  is 
formed,  which  is  deliquescent,  and  may  be  dissolved  completely  in  wa- 
ter. This  solution,  which  was  formerly  called  liquor  silicum,  has  an 
alkaline  reaction,  and  absorbs  carbonic  acid  on  exposure  to  the  atmos- 
phere, by  which  it  is  partially  decomposed.  Concentrated  acids  preci- 
pitate the  silica  as  a gelatinous  hydrate;  but  if  a considerable  quantity 
of  water  is  present,  and  the  acid  is  added  gradually,  the  alkali  may  be 
perfectly  neutralized  without  any  separation  of  silica.  When  a solution 
of  this  kind  is  evaporated  to  dryness,  the  silica  is  rendered  quite  inso- 
luble, and  may  thus  be  obtained  in  a pure  form. 

But  if  the  proportion  of  silica  and  alkali  be  reversed,  a transparent 
brittle  compound  results,  which  is  insoluble  in  water,  is  attacked  by 
none  of  the  acids  excepting  the  hydrofluoric,  and  possesses  the  well- 
known  properties  of  glass.  Every  kind  of  glass  is  composed  of  silica 
and  an  alkali,  and  all  its  varieties  are  owing  to  differences  in  the  pro- 
portion of  the  constituents,  to  the  nature  of  the  alkali,  or  to  the  pre- 
sence of  foreign  matters.  Thus,  green  bottle  glass  is  made  of  impure 
materials,  such  as  river  sand,  which  contains  iron,  and  the  most  common 
kind  of  kelp  or  pearlashes.  Crown  glass  for  windows  is  made  of  a 


320 


SILICIUM. 


purer  alkali,  and  sand  which  is  free  from  iron.  Plate  glass,  for  looking, 
glasses,  is  composed  of  sand  and  alkali  in  their  purest  state;  and  in  the 
formation  of  flint  glass,  besides  these  pure  ingredients,  a considerable 
quantity  of  litharge  or  red  lead  is  employed.  A small  portion  of  perox- 
ide of  manganese  is  also  used,  in  order  to  oxidize  carbonaceous  matters 
contained  in  the  materials  of  the  glass;  and  nitre  is  sometimes  added 
with  the  same  intention. 

Berzelius  ascertained  the  composition  of  silica  by  oxidizing  a known 
quantity  of  silicium,  and  weighing  the  product  carefully;  and  accord- 
ing to  this  synthetic  experiment,  100  parts  of  silica  are  composed  of  48 
parts  of  silicium  and  52  parts  of  oxygen.  The  atomic  weight  of  silica, 
deduced  apparently  with  great  care  by  Dr.  Thomson,  is  precisely  16. 
Chemists  are  not  agreed  about  the  atomic  constitution  of  silica.  Ber- 
zelius considers  it  a compound  of  one  atom  of  silicium  and  three  atoms 
of  oxygen;  but  the  opinion  of  Dr.  Thomson,  that  it  is  composed  of  an 
atom  of  each  element,  is  both  more  simple  and  agrees  better  with  the 
combining  proportion  of  silica.  According  to  this  view,  and  adopting 
16  as  the  equivalent  of  silica,  8 is  of  course  the  equivalent  of  silicium, 
an  inference  which  accords  very  nearly  with  the  experimental  result  of 
Berzelius. 

Chloride  of  Silicium. — When  silicium  is  heated  in  a current  of  chlo- 
rine gas,  it  takes  fire,  and  is  rapidly  volatilized.  The  product  of  the 
combustion  condenses  into  a liquid,  which  appears  to  be  naturally 
colourless,  but  to  which  an  excess  of  chlorine  communicates  a yellow 
tint.  This  fluid  is  very  limpid  and  volatile,  and  evaporates  almost  in- 
stantaneously in  open  vessels  in  the  form  of  a white  vapour.  It  has  a 
suffocating  odour  not  unlike  that  of  cyanogen,  and  when  put  into  water 
is  converted  into  muriatic  acid  and  silica,  the  latter  being  easily  obtained 
in  the  gelatinous  form.  (Berzelius.) 

Sulphuret  of  Silicium.’ — This  compound  is  formed  by  heating  silicium 
in  the  vapour  of  sulphur,  and  the  union  is  attended  with  the  phenomena 
of  combustion.  The  product  is  a white  earthy-looking  substance, 
which  is  instantly  converted  by  the  action  of  water  into  sulphuretted 
hydrogen  and  silica;  and  while  the  former  escapes  with  effervescence, 
the  latter  is  dissolved  in  large  quantity.  In  open  vessels,  owing  to  the 
moisture  of  the  atmosphere,  it  undergoes  a similar  change;  but  in  dry 
air  it  may  be  kept  unaltered. 

Fluosilicic  Acid  Gas, 

This  gas  is  formed  whenever  hydrofluoric  acid  comes  in  contact  with 
siliceous  earth;  and  this  is  the  reason  why  pure  hydrofluoi’ic  acid  can 
be  prepared  in  metallic  vessels  only,  and  with  fluor  spar  that  is  free 
from  rock  crystal.  The  most  convenient  method  of  procuring  the  gas 
is  to  mix  in  a retort  one  part  of  pulverized  fluor  spar  with  its  own 
weight  of  sand  or  pounded  glass,  and  two  parts  of  strong  sulphuric 
acid.  On  applying  a gentle  heat,  fluosilicic  acid  gas  is  disengaged  with 
effervescence,  and  may  be  collected  over  mercury. 

The  cliemical  changes  attending  this  process  are  differently  explained 
according  to  the  view  which  is  taken  concerning  the  nature  of  the 
product.  In  regarding  fluor  spar  as  a compound  of  fluoric  acid  and 
lime,  the  former  at  the  moment  of  being  set  free  is  thought  to  unite 
directly  with  silica;  so  that  tlic  resulting  compound  consists  of  silica 
and  fluoric  acid.  But  for  reasons  already  stated,  (page  234)  fluor  spar 
is  here  not  considered  as  fluate  of  lime;  and,  therefore,  this  view  cannot 
be  admitted.  It  is  inferred,  on  the  contrary,  that  when,  by  the  action 
of  sulphuric  acid  on  fluoride  of  calcium,  hydrofluoric  acid  is  generated, 
the  elements  of  this  acid  react  on  tliose  of  silica,  and  give  rise  to  the 


SILICIUM. 


321 


production  of  water  and  fluosilicic  acid  gas.  This  gas  is,  therefore,  a 
fluoride  of  silicium;  and  though  in  compliance  with  the  usage  of  other 
chemists,  I liave  retained  its  ordinary  name,  its  title  to  be  considered  an 
acid  is  questionable.  It  may  occur  to  some  whether  hydrofluoric  acid 
does  not  unite  directly  with  silica;  but  this  idea  is  inconsistent  with  the 
proportion  in  which  the  elements  of  the  gas  are  found  to  be  united. 

This  compound  is  a colourless  gas,  which  extinguishes  flame,  destroys 
animals  that  are  immersed  in  it,  and  irritates  the  respiratory  organs 
powerfully.  It  does  not  corrode  glass  vessels  provided  they  are  quite 
dry.’  When  mixed  with  atmospheric  air  it  forms  a white  cloud,  owing 
to  the  presence  of  watery  vapour.  Its  specific  gravity,  according  to 
Dr.  Thomson,  is  3.6111;  and  100  cubic  inches  of  it,  at  60^  F.  and  when 
the  barometer  stands  at  30  inches,  weigh  110.138  grains. 

Water  acts  powerfully  on  fluosilicic  acid  gas,  of  which  it  condenses, 
according  to  Dr.  John  Davy,  365  times  its  volume.  (Philos.  Trans, 
for  1812.)  The  gas  suflers  decomposition  at  the  moment  of  contact 
with  water,  depositing  part  of  its  silica  in  the  form  of  a gelatinous 
hydrate,  which  when  well  washed  is  quite  pure.  The  liquid,  which  has  a 
sour  taste  and  reddens  litmus  paper,  contains  the  whole  of  the  hydro- 
fluoric acid,  together  with  two  thirds  of  the  silica  which  was  originally 
present  in  the  gas.  (Berzelius.)  By  conducting  fluosilicic  acid  gas 
into  a solution  of  ammonia,  complete  decomposition  ensues; — hydro- 
fluoric acid  unites  with  the  alkali,  forming  hydrofluate  of  ammonia,  and 
all  the  silica  is  deposited.  On  this  fact  is  founded  the  mode  of  analy- 
zing fluosilicic  acid  gas,  adopted  by  Dr.  Davy  and  Dr.  Thomson.  Ac- 
cording to  the  results  obtained  by  Dr.  Thomson,  which  appear  more  cor- 
rect than  those  of  Dr.  Davy,  this  gas  is  composed  of  18.86  parts  or  one 
equivalent  of  fluorine,  and  8 parts  or  one  equivalent  of  silicium.  Con- 
sidered as  a compound  of  fluoric  acid  and  silica,  it  consists  of  10.86 
parts  or  one  equivalent  of  fluoric  acid,  and  16  parts  or  one  equivalent 
of  silica. 

The  solution  which  is  formed  by  fully  saturating  water  with  fluosilicic 
acid  gas  is  powerfully  acid,  and  emits  fumes  on  exposure  to  the  air.  It 
is  commonly  known  by  the  name  of  silicated  fluoric  acid;  but  a more 
appropriate  term  is  silico-Jiy dr o fluoric  acid.  According  to  the  experi- 
ments of  Berzelius,  it  appears  to  be  a definite  compound  of  hydrofluoric 
acid  and  silica  in  the  ratio  of  three  equivalents  of  the  former  to  two  of 
the  latter.  If  evaporated  before  separation  from  the  silica  deposited  by 
the  action  of  water  on  fluosilicic  acid  gas,  this  compound  is  reproduced. 
But  if  the  solution  is  poured  off  from  the  silica  thus  deposited,  and  then 
evaporated,  fluosilicic  acid  gas  is  at  first  evolved,  and  subsequently 
hydrofluoric  acid  and  water  are  expelled.  The  evaporation  of  silico- 
hydrofiuoric  acid  in  vacuo  is  attended  by  a similar  change,  so  that  this 
acid  cannot  be  obtained  free  fi’om  water.  It  does  not  corrode  glass; 
but  when  evaporated  in  glass  vessels,  the  production  of  free  hydrofluo- 
ric acid  of  course  gives  rise  to  corrosion. 

On  neutralizing  silico-hydrofluoi’ic  acid  with  ammonia,  and  gently 
evaporating  to  dryness,  all  the  silica  is  rendered  insoluble.  By  exactly 
neutralizing  with  carbonate  of  potassa,  nearly  all  the  silica  and  acid  are 
precipited  in  the  form  of  a sparingly  soluble  double  hydrofluate  of  silica 
and  potassa;  and  a still  more  complete  precipitation  is  effected  by 
muriate  of  baryta  in  excess,  when  hydrofluate  of  silica  and  baryta  is 
generated.  A variety  of  similar  compounds  may  be  obtained  either  by 
double  decomposition,  or  by  the  action  of  silico-hydrofluoric  acid  on 
metallic  oxides.  Most  of  these  salts  are  soluble  in  water,  those  of 
potassa,  soda,  lime,  baryta,  and  yttria,  being  the  only  sparingly  soluble 
ones  noticed  by  Berzelius.  They  have  in  general  a sour  bitter  taste. 


322 


MANGANESE. 


redden  litmus  paper,  and  are  decomposed  at  a high  temperature  with 
disengagement  of  fluosilicic  acid  gas.  These  salts  were  formerly 
known  by  the  name  of  fluosilicatesy  in  which  silica  and  fluoric  acid  were 
thought  to  act  the  part  of  a compound  acid;  but  Berzelius  has  shown 
that  this  view  is  inaccurate,  and  that  they  may  be  regarded  as  double 
salts,  consisting  of  two  proportionals  of  hydrofluate  of  silica,  and  one 
proportional  of  a hydrofluate  of  some  other  base. 

Most  of  the  facts  contained  in  the  preceding  account  of  silico-hydro- 
fluoric  acid  are  drawn  in  part  from  an  essay  of  Berzelius  in  the  Annals 
of  Philosophy,  xxiv.  450,  but  chiefly  from  his  Lehrbuch  der  Qhemity  i. 
631. 


CLASS  11. 

METALS,  THE  OXIDES  OF  WHICH  ARE  NEITHER  ALKALIES 
NOR  EARTHS. 

ORDER  I. 

METALS  WHICH  DECOMPOSE  WATER  AT  A RED  HEAT. 


SECTION  IX, 

MANGANESE. 

The  black  oxide  of  manganese  was  described  in  the  year  1774  by 
Scheele  as  a peculiar  earth,  and  Gahn  subsequently  showed  that  it  con- 
tained a new  metal,  to  which  he  gave  the  name  of  magnesium ^ a term 
since  applied  to  the  metallic  base  of  magnesia,  and  for  which  the  words 
manganesium  and  manganium  have  been  substituted.  This  metal, 
owing  doubtless  to  its  strong  affinity  for  oxygen,  has  never  been  found 
in  an  uncombined  state  in  the  earth;  but  its  oxides  are  very  abundant. 
The  metal  may  be  obtained  by  forming  finely  powdered  oxide  of  man- 
ganese into  a paste  with  oil,  laying  the  mass  in  a Hessian  crucible  lined 
with  charcoal,  luting  down  a cover  carefully,  and  exposing  it  during  an 
hour  and  a half,  or  two  hours,  to  the  strongest  heat  of  a smith’s  forge. 

Manganese  is  a hard  brittle  metal,  of  a grayish-white  colour,  and 
granular  texture.  Its  specific  gravity,  according  to  John,  is  8.013. 
When  pure  it  is  not  attracted  by  the  magnet. 

It  is  exceedingly  infusible,  requiring  a heat  of  160^  Wedgwood  for 
fusion.  It  soon  tarnishes  on  exposure  to  the  air,  and  absorbs  oxygen 
with  rapidity  when  heated  to  redness  in  open  vessels.  It  is  said  to  de- 
comjiose  water  at  common  temperatures  with  disengagement  of  hydro- 
gen gas,  though  the  process  is  exceedingly  slow;  but  at  a red  heat 
decomposition  is  rapid,  and  protoxide  of  manganese  is  generated.  De- 
composition of  water  is  likewise  occasioned  by  dilute  muriatic  or  sul- 


MANGANESE. 


S23 


phuric  acid,  and  the  muriate  or  sulphate  of  protoxide  of  manganese  is 
the  product. 

Oxides  of  Manganese. 

In  studying  metallic  oxides,  it  is  necessary  to  distinguish  oxides  formed 
by  the  direct  union  of  oxygen  and  a metal,  from  those  that  consist  of 
two  other  oxides  united  with  each  other,  and  which,  therefore,  in  com- 
position, partake  of  the  patiire  of  a salt  rather  than  of  an  oxide.  An 
instance  of  this  kind  of  combination  is  supplied  by  the  black  oxide  of 
iron;  and  it  is  probable  that  two,  if  not  three,  of  the  five  compounds 
enumerated  as  oxides  of  manganese,  have  a similar  constitution.  The 
composition  of  these  oxides  has  been  particularly  investigated  by  Ber- 
zelius, Dr.  Thomson,  (First  Pi’inciples,  i.)  M.  Arfwedson,*  M.  Berthier,f 
and  myself.i:  The  following  table,  drawn  up  by  Mr.  Phillips,  correctly 
represents  the  relative  quantities  of  oxygen  and  manganese  contained 
in  these  oxides. 


Protoxide 

Mang, 
28  H 

Oxy, 

p 8 or 

Mang, 
one  + 

Oxy. 

one  equivalent. 

Deutoxide 

28  ^ 

- 12 

two  + 

three 

Peroxide 

28  + 16 

• one  + 

two 

Red  oxide 

28  -f  10.66 

three  + 

four 

Varvicite 

28  4-  14 

four  -[- 

seven 

Peroxide, — This  is  the  well  known  ore  commonly  called  from  its  co- 
lour black  oxide  of  manganese.  It  generally  occurs  massive  of  an  earthy 
appearance,  and  mixed  with  other  substances,  such  as  siliceous  and  alu- 
minous earths,  oxide  of  iron,  and  carbonate  of  lime.  It  is  sometimes 
found,  on  the  contrary,  in  the  form  of  minute  prisms  grouped  together, 
and  radiating  from  a common  centre.  In  these  states  it  is  anhydrous; 
but  the  essential  ingredient  of  one  variety  of  the  earthy  mineral  called 
wad  is  hydrated  peroxide  of  manganese,  consisting  of  one  equivalent 
of  water  and  two  of  the  oxide.  The  peroxide  may  be  made  artificially 
by  exposing  nitrate  of  manganese  to  a commencing  red  heat,  until  the 
whole  of  the  nitric  acid  is  expelled;  but  I have  never  succeeded  in 
procuring  it  quite  pure  by  this  process,  because  the  heat  required  to  drive 
oif  the  last  traces  of  acid,  likewise  expels  some  oxygen  from  the  peroxide. 

Peroxide  of  manganese  undergoes  no  change  on  exposure  to  the  air. 
It  is  insoluble  in  water,  and  does  not  unite  either  with  acids  or  alkalies. 
When  boiled  with  sulphuric  acid,  it  yields  oxygen  gas,  and  a sulphate 
of  the  protoxide  is  formed.  (Page  141.)  With  muriatic  acid,  a mu- 
riate of  the  protoxide  is  generated,  and  chlorine  is  evolved.  (Page  204.) 
The  solution  in  both  cases  is  of  a deep-red  colour,  provided  undissolved 
oxide  is  present;  but  if  separated  from  the  undissolved  portions,  it  is 
readily  rendered  colourless  by  heat.  The  colour  seems  owing  to  a small 
quantity  of  deutoxide  of  manganese  held  in  solution  by  a large  excess 
of  free  sulphuric  acid.  The  action  of  sulphuric  acid  in  the  cold  is  ex- 
ceedingly tardy  and  feeble,  a minute  quantity  of  oxygen  gas  is  slowly 
disengaged,  and  the  acid  acquires  an  amethyst-red  tint.  On  exposure . 
to  a red  heat,  it  is  converted,  with  evolution  of  oxygen  gas,  into  deu- 
toxide of  manganese.  (Page  140.) 

Peroxide  of  manganese  is  employed  in  the  arts,  in  the  manufacture  of 
glass,  and  in  preparing  chlorine  for  bleaching.  In  the  laboratory  it  is 


* Letter  from  Berzelius  in  the  An.  de  Ch.  et  de  Ph.  vi. 

■}■  Ibid.  XX. 

t Philos.  Trans,  of  Edin.  for  1828;  or  Phil.  Mag.  and  Annals,  iv. 


S24  MANGANESE. 

used  for  procuring*  chlorine  and  oxygen  gases,  and  in  the  preparation  of 
the  salts  of  manganese. 

Deutoxide. — This  oxide  occurs  nearly  pure  in  nature,  and  as  a hy- 
drate it  is  found  abundantly,  often  in  large  prismatic  crystals,  at 
Jhlefeld  in  the  Hartz.  It  may  be  formed  artificially  by  exposing  per- 
oxide of  manganese  for  a considerable  time  to  a moderate  red  heat, 
and,  therefore,  is  the  chief  residue  of  the  usual  process  for  procuring 
a supply  of  oxygen  gas;  but  it  is  difficult  so  to  regulate  the  degree  and 
duration  of  the  heat,  that  the  resulting  oxide  shall  be  quite  pure. 

The  colour  of  the  deutoxide  of  manganese  varies  with  the  source 
from  which  it  is  derived.  That  which  is  procured  by  means  of  heat 
from  the  native  peroxide  or  hydrated  deutoxide,  has  a brown  tint;  but 
when  prepared  from  nitrate  of  manganese,  it  is  nearly  as  black  as  the 
peroxide,  and  the  native  deutoxide  is  of  the  same  colour.  AVith  sul- 
phuric and  muriatic  acids,  it  gives  rise  to  tlie  same  phenomenon  as  the 
peroxide,  but  of  course  yields  a smaller  proportional  quantity  of  oxy- 
gen and  chlorine  gases.  It  is  more  easily  attacked  than  the  peroxide 
by  cold  sulphuric  acid.  With  strong  nitric  acid  it  yields  a soluble  pro- 
tonitrate and  the  peroxide,  as  observed  by  Berthier;  and  when  boiled 
witli  dilute  sulphuric  acid,  it  undergoes  a similar  change.  From  the 
proportion  of  oxygen  and  manganese  in  this  oxide,  it  may  be  regarded 
as  a compound  of  44  parts  or  one  equivalent  of  peroxide,  aud  36  parts 
or  one  equivalent  of  protoxide  of  manganese. 

Protoxide. — By  this  term  is  meant  that  oxide  of  manganese  which  is 
a strong  salifiable  base,  is  contained  in  all  the  ordinary  salts  of  this  me- 
tal, and  which  appears  to  be  its  lowest  degree  of  oxidation.  This 
oxide  may  be  formed,  as  was  shown  by  Berthier,  by  exposing  the  per- 
oxide, deutoxide,  or  red  oxide  of  manganese  to  the  combined  agency 
of  charcoal  and  a white  heat;  and  Dr.  Forchhammer,  in  the  Annals  of 
Philosophy,  xvii.  52,  has  described  an  elegant  mode  of  preparation, 
by  exposing  either  of  the  oxides  of  manganese  contained  in  a tube  of 
glass,  porcelain,  or  iron,  to  a current  of  hydrogen  gas  at  an  elevated 
temperature.  The  best  material  for  this  purpose  is  the  red  oxide  pre- 
pared from  nitrate  of  manganese;  for  some  of  the  oxides,  especially 
the  peroxide,  are  fully  reduced  to  the  state  of  protoxide  by  hydrogen 
with  difficulty.  The  reduction  commences  at  a low  red  heat;  but  to 
decompose  all  the  red  oxide,  a full  red  heat  is  required.  The  same 
compound  is  formed  by  the  action  of  hydrogen  gas  at  an  intense  white 
heat- 

Protoxide  of  manganese,  when  pure,  is  of  a light-green  colour,  very 
near  the  mountain  green.  According  to  Forchhammer,  it  attracts  oxy- 
gen rapidly  from  the  air;  but  in  my  experiments  it  was  very  permanent, 
undergoing  no  change  either  in  weight  or  appearance  during  the  space 
of  nineteen  days.  At  600®  F.  it  is  oxidized  with  considerable  rapidity, 
and  at  a low  red  heat  is  converted  in  an  instant  into  red  oxide.  It  some- 
times takes  fire  when  thus  heated;  but  this  phenomenon  is  by  no  means 
constant.  It  unites  readily  with  acids  without  effervescence,  producing 
the  same  salts  as  when  the  same  acids  act  on  carbonate  of  manganese. 
When  it  comes  in  contact  with  concentrated  sulphuric  acid,  intense 
heat  is  instantly  evolved;  and  the  same  phenomenon  is  produced, 
though  in  a less  degree,  by  strong  muriatic  acid.  The  resulting  salt 
is  the  same  as  when  tliesc  acids  arc  heated  with  cither  of  the  other 
oxides  of  manganese.  If  quite  pure,  the  protoxide  should  readily  and 
completely  dissolve  in  cold  dilute  sulphuric  acid,  and  yield  a colourless 
solution. 

Ill  order  to  prepare  a pure  salt  of  manganese  from  the  common  per- 
oxide of  commerce,  either  of  the  following  processes  should  be.  em- 


MANGANESE. 


325 


ployed.  The  impure  deutoxide  left  in  the  process  for  procuring*  oxy- 
g*en  gas  from  the  peroxide  by  means  of  heat,  is  mixed  with  a sixth  of 
its  weight  of  charcoal  in  powder,  and  exposed  to  a white  heat  for  half 
an  hour  in  a covered  crucible.  The  protoxide  thus  formed  is  to  be  dis- 
solved in  muriatic  acid,  the  solution  evaporated  to  dryness,  and  the  re- 
sidue kept  for  a quarter  of  an  hour  in  perfect  fusion;  being  protected 
as  much  as  possible  from  the  air.  By  this  means  the  chlorides  of  iron, 
calcium,  and  other  metals  are  decomposed.  The  fused  chloride  of 
manganese  is  then  poured  out  on  a clean  sandstone,  dissolved  in  water, 
and  the  solution  separated  from  insoluble  matters  by  filtration.  If  free 
from  iron,  it  will  give  a white  precipitate  with  ferrocyanate  of  potassa, 
without  any  appearance  of  green  or  blue,  and  a flesh-coloured  precipi- 
tate with  hydrosulphuret  of  ammonia.  The  manganese  is  then  thrown 
down  as  a white  carbonate  of  potassa  or  soda;  and  from  this  salt,  after 
being  well  washed,  all  the  other  salts  of  manganese  may  be  prepared. 
The  other  method  of  forming  a pure  muriate  was  suggested  by  Mr. 
Faraday,  and  consists  of  heating  to  redness  a mixture  of  peroxide  of 
manganese  with  half  its  weight  of  muriate  of  ammonia.  Owing  to  the 
volatility  of  the  sal  ammoniac  it  is  necessary  to  apply  the  required  heat 
as  rapidly  as  possible,  and  this  is  best  done  by  projecting  the  mixture 
in  small  portions  at  a time  into  a crucible  kept  red-hot.  In  this  process 
the  chlorine  of  the  muriatic  acid  unites  with  the  metal  of  the  oxide  to 
the  exclusion  of  every  other  substance,  provided  an  excess  of  manga- 
nese be  present.  The  resulting  chloride  is  then  dissolved  in  water,  and 
the  insoluble  matters  separated  by  filtration.  (Faraday,  in  Quarterly 
Journal,  vol.  vi.) 

In  preparing  manganese  of  great  purity,  the  operator  should  bear  in 
mind  that  the  precipitated  carbonate  sometimes  contains  muriatic  acid, 
retained  probably  in  the  form  of  submuriate.  It  may  likewise  contain 
- traces  of  lime;  for  oxalate  of  lime,  insoluble  as  it  is  in  pure  water,  does 
not  completely  subside  from  a strong  solution  of  chloride  of  manganese, 
and,  therefore,  a small  quantity  of  that  earth  may  be  present,  although 
not  indicated  by  oxalate  of  ammonia. 

The  salts  of  manganese  are  in  general  colourless  if  quite  pure;  but 
more  frequently  they  have  a shade  of  pink,  owing  to  the  presence  of  a 
little  red  oxide.  The  protoxide  is  precipitated  from  its  solutions,  as  a 
white  hydrate  by  ammonia,  or  the  pure  fixed  alkalies;  as  white  carbo- 
Jiate  of  manganese  by  alkaline  carbonates  and  bicarbonates;  and  as 
white  ferrocyanate  of  manganese  by  ferrocyanate  of  potassa,  a charac- 
ter by  which  the  absence  of  iron  may  be  demonstrated.  I'hese  white 
precipitates,  with  the  exception  of  that  obtained  by  means  of  a bicar- 
bonate, very  soon  become  brown  from  the  absorption  of  oxygen.  None 
of  the  salts  of  manganese  which  contain  a strong  acid,  such  as  the  ni- 
tric, muriatic,  or  sulphuric,  are  precipitated  by  sulphuretted  hydrogen. 
With  an  alkaline  hydrosulphuret,  on  the  contrary,  a flesh-coloured  pre- 
cipitate is  formed,  which  is  either  a hydrosulphuret  of  the  protoxide, 
or  a hydrated  protosulphuret  of  metallic  manganese.  When  heated 
in  close  vessels,  it  yields  a dark-coloured  sulphuret,  and  water  is 
evolved. 

Red  Oxide, — The  substance  called  red  ojTide  of  manganese,  oxidum 
manganoso-manganicum  of  Arfvvedson,  occurs  as  a natural  production, 
and  may  be  formed  artificially  by  exposing  the  peroxide  or  deutoxide 
to  a white  heat  either  in  close  or  open  vessels.  It  is  also  produced  by 
absorption  of  oxygen  from  the  atmosphere,  when  the  protoxide  is  pre- 
cipitated from  its  salts  by  pure  alkalies,  or  when  the  anhydrous  pro- 
toxide or  carbonate  is  heated  to  redness.  It  is  very  permanent  in  the 
air,  not  passing  to  a higher  stage  of  oxidation  at  any  temperature.  Its 

28 


326 


MANGANESE. 


colour  when  rubbed  to  the  same  deg'ree  of  fineness  Is  brownisb-red 
when  cold,  and  nearly  black  wlfile  warm.  Fused  witli  borax  or  ^dasa, 
it  communicates  a beautiful  violet  tint,  a character  by  which  mang’aneso 
may  be  easily  detected  before  the  blowpipe;  and  it  is  the  cause  of  the 
ricb^  colour  of  the  amethyst.  It  is  acted  on  by  strong*  sulphuric  and 
muriatic  acids,  with  the  aid  of  beat,  in  the  same  manner  as  the  ])erox- 
ide  and  deutoxide,  but  of  course  yields  proportionally  a smaller  quan- 
tity of  oxygen  and  chlorine  gases,  liy  cobl  concentrated  suljdiuric  acid 
it  is  dissolved  in  small  quantity,  without  appreciable  disengagement  of 
oxygen  gas,  and  the  solution  is  promoted  by  a slight  increase  of  tem- 
perature. The  liquid  has  an  amethyst  tint,  wdiich  disappears  when 
heat  is  applied,  or  by  the  action  of  deoxidizing  substances,  such  as 
protomuriate  of  tin,  or  sulphurous  and  phosphorous  acids,  protosul- 
phate of  manganese  being  generated.  The  pink  colour  which  the 
salts  of  mang'anese  generally  possess,  is  owing  to  the  presence  of  a 
small  quantity  of  red  oxide.  By  strong  nitric  acid,  or  when  boiled 
with  dilute  sulphuric  acid,  it  undergoes  the  same  kind  of  change  as  the 
deutoxide. 

The  red  oxide  of  manganese  contains  more  oxygen  than  the  protox- 
ide and  less  than  the  deutoxide.  Its  elements  are  in  such  proportion, 
that  it  may  be  regarded  as  a compound  either  of 

Deutoxide  80  or  two  equiv.  ? qj.  5 Peroxide  44  or  one  equiv. 

Protoxide  36  or  one  equiv.  5 ^protoxide  72  or  two  equiv. 

116  116 

It  contains  27.586  per  cent,  of  oxygen,  and  loses  6.896  percent,  of 
oxygen,  when  converted  into  the  g’reen  oxide. 

Varmcife. — This  compound  is  known  only  as  a natural  production, 
having  been  first  noticed  a year  or  two  ago,  by  Mr.  Phillips,  among 
some  ores  of  manganese  found  in  Warwickshire.  The  locality  of  the 
mineral  suggested  its  name;  but  I have  also  detected  it  as  the  constitu- 
ent of  an  ore  of  manganese  from  Jhlefeld,  sent  me  during  last  winter 
by  Professor  Stromeyer.  Varvicite  was  at  first  mistaken  for  peroxide 
of  manganese,  to  which  both  in  the  colour  of  its  powder  and  its  de- 
gree of  hardness  it  bears  considerable  resemblance;  but  it  is  readily 
distinguished  from  that  ore  by  its  stronger  lustre,  its  highly  lamellated 
texture,  which  is  very  similar  to  that  of  manganite,  and  by  yielding 
water  freely  when  heated  to  redness.  Its  specific  gravity  is  4.531..  It 
has  not  been  found  regularly  crystallized;  but  my  specimen  from  Jhle- 
feld is  in  <z//er-cr^57f//5,  possessing  the  form  of  the  six-sided  pyramid  of 
calcareous  spar.  When  strongly  heated  it  is  converted  into  red  oxide, 
losing  5.725  per  cent,  of  water,  and  7,385  of  oxygen.  It  is  probably, 
like  the  red  oxide,  a compound  of  two  other  oxides;  and  the  propor- 
tions just  stated  justify  the  supposition  that  it  consists  of  one  equivalent 
of  peroxide  and  one  of  deutoxide  of  manganese,  united  in  the  mineral 
witli  haif  an  ecpiivalent  of  water.  (Phil.  Mag.  and  Annals,  v.  209,  vi. 
281,  and  vii.  284.) 

It  has  been  inferred  from  some  experiments  of  Berzelius  and  Johii^ 
that  there  are  two  other  o^dcs  of  manganese,  which  contain  less  oxygen 
than  the  green  or  ])r()toxi(U'^  Wc  have  no  proof,  however,  of  the  ex- 
istence of  such  compounds. 

Manganese  is  one  of  those  metals  which  is  capable  of  forming  an  acid 
with  oxygen.  When  peroxide  of  manganese  is  mixed  with  an  equal 
weight  of  nitre  or  cariionate  of  ])otassa,  and  the  mixture  is  exposed  to 
a red  heat,  a green-coloured  fused  mass  is  formed,  which  has  been  long 
known  under  llie  name  of  mineral  chamdeon.  On  putting  this  substance 


MANGANESE. 


32/ 


into  water,  a green  solution  is  obtained,  the  colour  of  which  soon  passes 
into  blue,  purple,  and  red;  and  ultimately,  a brown  flocculent  matter, 
red  oxide  of  mang’anese,  subsides,  and  the  liquid  becomes  colourless. 
I’hese  cbang-es  take  place  more  rapidly  by  dilution,  or  by  employing 
hot  water.  We  are  indebted  to  MM.  Chevillot  and  Edwards  for  a con- 
sistent explanation  of  these  phenomena.*  They  demonstrated  that 
peroxide  of  manganese,  when  fused  with  potassa,  absorbs  oxygen  from 
the  atmosphere,  and  is  the,reby  converted  into  an  acid,  the  manganesic, 
which  unites  with  the  alkali.  They  attributed  the  different  changes  of 
colour  above  mentioned  to  the  combination  of  this  acid  with  different 
proportions  of  potassa.  By  evaporating  the  red  solution  rapidly,  they 
succeeded  in  obtaining  a manganesiate  of  potassa  in  the  form  of  small 
prismatic  crystals  of  a purple  colour.  This  salt  yields  oxygen  to  com- 
bustible substances  with  great  facility,  and  detonates  powerfully  with 
phosphorus.  It  is  decomposed  when  in  solution  by  very  slight  causes, 
being  converted  into  red  oxide  of  manganese. 

The  subsequent  researches  of  Dr.  Forchhammer  render  it  probable 
that  the  green  and  red  colours  are  produced  by  two  distinct  acids,  the 
manganeseous  and  manganesic,  the  former  giving  rise  to  the  green,  and 
the  latter  to  the  red  tint.  He  succeeded  in  forming  a solution  of  man- 
ganesic acid  in  the  following  manner.  By  heating  a mixture  of  nitrate 
of  baryta  with  peroxide  of  manganese,  manganesite  of  baryta  was  gen- 
erated; and  to  this  salt,  after  having  been  well  washed  with  water,  a 
quantity  of  dilute  sulphuric  acid  was  added,  precisely  sufficient  for 
combining  with  its  base.  The  manganeseous  acid,  at  the  moment  of 
being  set  free,  resolved  itself  into  deutoxide  of  manganese  and  manga- 
nesic acid;  and  the  latter,  dissolving  in  the  w^ater,  formed  a beautiful 
red  solution.  Dr.  Forchhammer  infers  from  his  analysis  of  these  com- 
pounds, that  manganeseous  acid  contains  three  and  mangamesic  four 
atoms  of  oxygen  united  with  one  atom  of  manganese.  (Annals  of  Phi- 
losophy, vol.  xvi.) 

Chloride  of  Manganese. — This  compound  is  best  prepared  by  evapo- 
rating a solution  of  muriate  of  manganese  to  dryness  by  a gentle  heat, 
and  heating  the  residue  to  redness  in  a glass  tube,  while  a current  of 
muriatic  acid  gas  is  transmitted  through  it.  The  heat  of  a spirit-lamp 
is  sufficient  for  the  purpose.  It  fuses  readily  at  a red  heat,  and  forms 
a pink-coloured  lamellated  mass  on  cooling.  It  is  deliquescent,  and  of 
course  very  soluble  in  w\ater,  being  converted  by  that  fluid,  with  evo- 
lution of  caloric,  into  muriate  of  manganese.  It  is  composed  of  28 
parts  or  one  equivalent  of  manganese,  and  36  paids  or  one  equivalent 
of  chlorine. 

A new  chloride  of  manganese,  remarkable  for  its  volatilit}^  has  been 
described  by  M.  Dumas.  (Edinburgh  Journal  of  Science,  viii.  1/9. ) Itis 
readily  formed  by  putting  a solution  of  manganesic  into  strong  sulphuric 
acid,  and  then  adding  fused  sea-salt.  The  muriatic  and  manganesic 
acids  mutually  decompose  each  other;  water  and  perchloride  of  manga- 
nese are  generated,  and  the  latter  escapes  in  the  form  of  vapour.  The 
best  mode  of  preparation  is  to  form  the  green  mineral  chameleon,  and 
convert  it  into  red  by  means  of  sulphuric  acid.  The  solution,  when  eva- 
porated, leaves  a residue  of  sulphate  and  nf.^|j^anesiate  of  potassa.  This 
mixture,  treated  by  strong  sulphuric  acid,  yields  a solution  of  manga- 
nesic acid,  into  which  are  added  small  fragments  of  sea-salt,  as  long  as 
coloured  vapour  continues  to  be  evolved. 

The  new  chloride,  when  first  formed,  appears  as  a vapour  of  a cop- 


* An.  de  Ch.  et  de  Ph.  vol.  viii. 


328 


IRON. 


per  or  greenish  colour;  but  on  traversing  a glass  tube  cooled  to  5®  or 
— 4®  F.,  it  is  condensed  into  a greenish-brown  coloured  liquid.  When 
generated  in  a capacious  tube,  its  vapour  gradually  displaces  the  air, 
and  soon  fills  the  tube.  If  it  is  then  poured  into  a large  flask,  the  sides 
of  which  are  moist,  the  colour  of  the  vapour  changes  instantly  on  com- 
ing into  contact  with  the  moisture,  a dense  smoke  of  a pretty  rose  tint 
appears,  and  muriatic  and  manganesic  acids  are  generated.  From  this 
it  is  manifest,  that  the  new  chloride  is  proportional  to  manganesic  acid; 
tliat  is,  when  its  chlorine  unites  with  hydrogen,  the  oxygen  required  to 
constitute  water  with  that  hydrogen  exactly  suffices  for  forming  manga- 
nesic acid  with  the  manganese.  It  is  hence  supposed  to  consist  of  28 
parts  or  one  equivalent  of  manganese,  and  144  parts  or  four  equivalents 
of  chlorine. 

Fluoride  of  Manganese, — A gaseous  compound  of  fluorine  and  man- 
ganese has  been  discovered  by  M.  Dumas  and  Dr.  AVbliler.  (fhlinburgh 
Journal  of  Science,  ix.)  It  is  best  formed  by  mixing  common  mineral 
chameleon  with  half  its  weight  of  fluor  spar,  and  decomposing  the 
mixture  in  a platinum  vessel  by  fuming  sulphuric  acid.  'I'he  fluoride  is 
then  disengaged  in  the  form  of  a greenish-yellow  gas  or  vapour,  of  a 
more  intensely  yellow  tint  than  chlorine.  When  mixed  with  atmosphe-t 
ric  air,  it  instantly  acquires  a beautiful  purple-red  colour;  and  it  is  freely 
absorbed  by  water,  yielding  a solution  of  the  same  red  tint..  It  acts  in- 
stantly on  glass,  with  formation  of  fluosilicic  acid  gas,  a brown  matter 
being  at  the  same  time  deposited,  which  becomes  of  a deep  purple-red 
tint  on  the  addition  of  water. 

It  may  be  inferred  from  the  experiments  of  Wohler  that  this  yellow 
gas  is  a fluoride  of  manganese;  that  when  mixed  with  water  both  com- 
pounds are  decomposed,  and  hydrofluoric  and  manganesic  acids  gene- 
rated, which  are  dissolved;  that  a similar  formation  of  the  two  acids 
ensues  from  the  admixture  of  the  yellow  gas  with  atmospheric  air, 
owing  to  the  moisture  contained  in  the  latter;  and  that  by  contact  with 
glass,  fluosilicic  acid  gas  is  produced,  and  anhydrous  manganesic  acid 
deposited.  In  consequence  of  its  acting  so  powerfully  on  glass,  its 
other  properties  have  not  been  ascertained;  but  from  those  above  men- 
tioned, its  composition  i&obviously  similar  to  that  of  the  gaseous  chloride 
of  manganese.  It  hence  consists  of  one  equivalent  of  manganese,  and 
four  equivalents  of  fluorine. 

The  protosulphuret  of  manganese  may  be  procured  by  igniting  the 
sulphate  with  one-sixth  of  its  weight  of  charcoal  in  powder.  (Berthier.) 
It  is  also  formed  by  the  action  of  sulphuretted  hydrogen  on  the  proto- 
sulphate at  a red  heat.  (Arfwedson  in  An.  of  Phil.  vol.  vii.  N.  S.)  It 
occurs  native  in  Cornwall  and  at  Nagyag  in  Transylvania.  It  dissolves 
completely  in  dilute  sulphuric  or  muriatic  acid,  with  disengagement  of 
very  pure  sulphuretted  hydrogen  gas. 


ACTION  XII.  " 

IRON. 


Iiiox  has  a pccidiar  gray  colour,  and  strong  metallic  lustre,  which  is 
Buscc])tible  of  being  heiglitcncd  by  polishing.  In  ductility  and  mal- 
leability it  is  inferior  to  several  metals,  but  exceeds  them  all  in  tenacity. 


IRON. 


329 


(Pao'e  277.)  At  common  temperatures  it  is  very  hard  and  unyielding’, 
audits  hardness  may  be  increased  by  being  heated  and  then  suddenly 
cooled;  but  it  is  at  the  same  time  rendered  brittle.  When  heated  to 
redness  it  is  remarkably  soft  and  pliable,  so  that  it  may  be  beaten  into 
any  form,  or  be  intimately  incorporated  or  welded  with  another  piece  of 
red-hot  iron  by  hammering.  Its  texture  is  fibrous.  Its  specific  gravity 
may  be  estimated  at  7.7;  but  it  varies  slightly  according  to  the  degree/ 
with  which  it  has  been  rolled,  hammered,  or  drawn,  and  it  is  increased 
by  fusion.  In  its  pure  state  it  is  exceedingly  infusible,  requiring  for 
fusion  a temperature  of  158*^  of  Wedgwood’s  pyrometer.  It  is  at.- 
Iracted  by  the  magnet,  and  may  itself  be  rendered  permanently  mag- 
netic by  several  processes;  a property  of  great  interest  and  importance, 
and  which  is  possessed  by  no  other  metal  excepting  cobalt  and  nickel. 

The  occurrence  of  native  iron,  except  that  of  meteoric  origin,  which 
always  contains  nickel  and  cobalt,  is  exceedingly  rare;  and  few  of  the 
specimens  said  to  be  such  have  been  well  attested.  In  combination, 
however,  especially  with  oxygen  and  sulphur,  it  is  abundant;  being 
contained  in  animals  and  plants,  and  being  dlflVised  so  universally  in  the 
earth,  that  there  are  few  mineral  substances  in  which  its  presence  may 
not  be  detected.  Minerals  which  contain  iron  in  such  form,  and  in  such 
quantity,  as  to  be  employed  in  the  preparation  of  the  metal,  are  called 
ores  of  iron;  and  of  these  the  principal  are  the  following.  The  red 
oxides  of  iron  included  under  the  name  of  red  haematite;  the  brown 
haematite  of  mineralogists,  consisting  of  hydrated  peroxide  of  iron;  the 
black  oxide,  or  magnetic  iron  ore;  and  protocarbonate  of  iron,  either 
pure,  or  in  the  form  of  clay  iron  ore,  when  it  is  mixed  with  siliceous, 
aluminous,  and  other  foreign  sy.bstances.  The  three  former  occur  most 
abundantly  in  primary  districts,  and  supply  the  finest  kinds  of  iron,  as 
those  of  Sweden  and  India;  while  clay-iron  stone,  from  which  most  of 
the  English  iron  is  extracted,  occurs  in  secondary  deposites,  and  chiefly 
in  the  coal  formation. 

The  extraction-ofiiron  from  its  ores  is  effected  by  exposing  the  ore, 
previoiisly  roasted  ahd  reduc'ed  to  a coarse  powder,  to  the  action  of 
charcoal,  or  coke,  and  lime  at  a high  temperature.  The  action  of  car- 
bonaceous matter  in  depriving  the  ore  of  its  oxygen  is  obvious;  and  the 
lime  plays  a part  equally  important.  It  acts  as  a flux  by  combining 
with  all  the  impurities  of  the  ore,  and  forming  a fusible  compound 
called  a sla^.  The  whole  mass  being  thus  in  a fused  state,  the  particles 
of  reduced  metal  descend  by  reason  of  their  greater  density,  and  col- 
lect at  the  bottom;  while  the  slag  forms  a stratum  above,  protecting  the 
melted  metal  from  the  action  of  the  air.  The  latter,  as  it  collects,  runs 
out  at  an  aperture  in  the  side  of  the  furnace;  and  the  fused  iron  is  let 
oft'  by  a hole  in  the  bottom,  which  was  previously  filled  with  sand.  The 
process  is  never  successful  unless  the  flux,  together  with  the  impurities 
of  the  ore,  are  in  such  proportion  as  to  constitute  a fusible  compound. 
The  mode  of  accomplishing  this  object  is  learned  only  by  experience; 
and  as  different  ores  commonly  differ  in  the  nature  or  quantity  of  their 
impurities,  the  workman  is  obliged  to  vary  his  flux  according  to  the 
composition  of  the  ore  with  which  he  operates.  Thus  if  the  ore  is 
deficient  in  siliceous  matter,  sand  must  be  added;  and  if  it  contain  a 
large  quantity  of  lime,  ])roportionally  less  of  that  earth  will  be  required. 
Much  is  often  accomplished  by  the  admixture  of  different  ores  with  each 
other.  The  slag  consists  of  a compound  of  earthy  salts,  similar  to 
some  siliceous  minerals,  in  which  silica  acts  the  part  of  an  acid,  and 
lime,  alumina,  protoxide  of  manganese,  and  sometimes  oxide  of  iron, 
act  as  bases.  The  most  usual  combination,  according  to  Mitscherlich, 
l»  bisilicate  of  lime  and  magnesia,  sometimes  with  a little  bisilicate  qf 

28* 


330 


IRON. 


the  black  oxide  of  iron;  a compound  wliich  he  lias  obtained  in  crystals 
having  the  precise  form  of  pyroxen.  Artificial  minerals  may  in  fact  by 
such  processes  be  procured,  similar  in  form  and  composition  to  those 
which  occur  in  the  earth.  We  are  indebted  to  IVlitschcrlich  for  some 
valuable  facts  on  this  subject.  (An.  de  Ch.  et  de  Ph.  xxiv.  355.) 

The  iron  obtained  by  this  process  is  the  cast  iron  of  commerce,  and 
contains  a considerable  quantity  of  carbon,  unreduced  ore,  and  earthy 
substances.  It  is  converted  into  soft  or  malleable  iron  by  exposure  to  a 
strong  heat  while  a current  of  air  plays  upon  its  surface,  lly  this  means 
any  undecomposed  ore  is  reduced,  earthy  impurities  rise  to  tlic  surface 
as  slag,  and  carbonaceous  matter  is  burned.  I'he  exposed  iron  is  also 
more  or  less  oxidized  at  its  surfiice,  and  the  resulting  oxide,  being 
stirred  with  the  fused  metal  below,  facilitates  the  oxidation  of  the  car- 
bon. As  the  purity  of  the  iron  increases,  its  fusibility  diminishes,  until 
at  length,  though  the  temperature  remains  the  same,  the  iron  becomes 
solid.  It  is  then  subjected,  while  still  hot,  to  the  operation  of  rolling 
or  hammering,  by  which  its  particles  are  approximated,  and  its  tenacity 
greatly  increased.  It  is  then  the  malleable  iron  of  commerce.  It  is  not 
however,  absolutely  pure;  for  Berzelius  has  detected  in  it  about  one 
half  per  cent  of  carbon,  and  it  likewise  contains  traces  of  silicium.  The 
carbonaceous  matter  may  be  removed  by  mixing  iron  filings  with  a 
quarter  of  its  weight  of  black  oxide  of  iron,  and  fusing  the  mixture, 
confined  in  a covered  Hessian  crucible,  by  means  of  a blast  furnace.  A 
little  powdered  green  glass  should  be  laid  on  the  mixture,  in  order  that 
the  iron  may  be  completely  protected  from  the  air  by  a covering  of 
melted  glass,  and  any  unreduced  oxide  dissolved.  But  the  best  and 
readiest  mode  of  procuring  iron  in  a state  of  perfect  purity,  is  by  trans- 
mitting hydrogen  gas  over  the  pure  oxide,  heated  to  redness  in  a tube 
of  porcelain.  The  oxygen  of  the  oxide  unites  with  hydrogen,  and  the 
metal  is  left  in  the  form  of  a porous  spongy  mass.  M.  Magnus  has 
observed  that  the  reduction  takes  ]:)lace  at  a heat  considerably  below 
that  of  r.edness;  and  when  the  iron,  thus  reduced,  is  exposed  to  the  air, 
it  takes  fire  spontaneously,  and  the  oxide  is  instantly  reproduced.  This 
singular  property,  which  Magnus  has  also  remarked  in  nickel  and  cobalt 
prepared  in  a similar  manner,  appears  to  depend  on  the  extremely 
divided  and  expanded  state  of  the  metallic  mass;  for  when  the  reduction 
is  effected  at  a reel  heat,  which  enables  the  metal  to  acquire  its  natural 
degree  of  compactness,  the  phenomenon  is  not  observed.  If  the  oxide 
is  mixed  with  a little  alumina,  and  then  reduced  at  a red  heat,  the  pre- 
sence of  tlie  earth  prevents  that  contraction  which  would  otherwise 
ensue:  the  metal  is  in  the  same  mechanical  condition  as  when  it  is 
deoxidized  at  a low  temperature,  and  its  spontaneous  combustibility  is 
preserved. 

But  iron,  in  its  ordinary  state,  has  a strong  affinity  for  oxygen.  In  a 
perfectly  dry  atmosphere  it  undergoes  no  change;  but  when  moisture  is 
likewise  present,  its  oxidation,  or  rustings  is  rapid.  The  first  part  of  the 
change  appears  to  consist  in  the  formation  of  protocarbonate  of  iron; 
but  the  protoxide  gradually  passes  into  hydrated  ])eroxide,  and  the  car- 
bonic acid  at  the  same  tiiiK*  is  evolved.  Rust  of  iron  always  contains 
ammonia,  a circumstance  which  indicates  tliat  the  oxidation  is  probably 
accompanied  by  decompositioji  of  water;  and  M.  Clievallier  has  observed 
that  ammonia  is  also  ])r(‘scnt  in  llie  native  oxides  of  iron.  Heated  to 
redness  in  the  open  air,  iron  abs.orbs  oxygen  rapidly,  and  is  converted 
into  black  scales,  called  the  hldck  oxide  of  iron;  and  in  an  atmosphere  of 
oxygen  gas  it  burns  with  vivid  scintillations.  It  decomposes  the  vapour 
of  water,  by  uniting  with  its  oxygen,  at  all  tcmj)eratures,  from  a dull 
red  to  u white  heat;  a singular  fact  when  it  is  considered,  that  at  the 


IRON. 


33 


very  same  temperatures  the  oxides  of  iron  are  reduced  to  the  metallic 
state  by  hydrogen  gas.  (Gay-Lussac  in  An.  de  Oh.  et  de  Physique,  i. 
36. ) These  opposite  effects,  various  instances  of  which  are  known  to 
chemists,  are  accounted  for  by  a mode  of  reasoning  similar  to  that 
explained  on  a former  occasion.  (Page  J 16-17.) 

Oxides  of  Iron- 

Iron  combines  with  oxygen  in  two  proportions  only,  forming  the  blue 
or  protoxide,  and  the  red  or  peroxide  of  iron.  Both  these  compounds 
are  capable  of  yielding  regular  crystallizable  salts  with  acids. 

Protoxide. — This  oxide  is  the  base  of  the  native  carbonate  of  iron, 
and  of  the  green  vitriol  of  commerce.  Its  existence  was  inferred  some 
years  ago  by  Gay-Lussac ; (An.  de  Ch.  vol.  Ixxx.)  but  Stromeyer  first 
obtained  it  in  an  insulated  form  by  transmitting  dry  hydrogen  gas  over 
peroxide  of  iron  at  a very  low  temperature.  (Edinburgh  Journal  of 
Science,  No.  x.) 

Protoxide  of  iron  has  a dark-blue  colour,  and  when  melted  with  vit- 
reous substances  communicates  to  them  a tint  of  blue.  It  is  attracted 
by  the  magnet,  though  less  powerfully  than  metallic  iron.  It  is  ex- 
ceedingly combustible;  for  when  fully  exposed  to  air  at  common  tem- 
peratures, it  suddenly  takes  fire  and  burns  vividly,  being  reconverted 
into  the  peroxide.  Its  salts,  particularly  when  in  solution,  absorb  oxy- 
gen from  the  atmosphere  with  such  rapidity  that  they  may  even  be  em- 
ployed in  eudiometry.  This  protoxide  is  always  formed  with  evolution 
of  hydrogen  gas  when  metallic  iron  is  put  into  dilute  sulphuric  or  mu- 
riatic acid;  and  its  composition  may  be  determined  by  collecting  and^ 
measuring  the  gas  which  is  disengaged.  According  to  Gay-Lussac  it  is 
composed  of  8 parts  of  oxygen,  and  28.3  parts  of  iron;  but  Dr.  Thom- 
son infers  from  an  analysis  of  protosulphate  of  iron,  that  the  quantity  of 
iron  united  with  8 parts  of  oxygen  is  28  precisely.  The  atomic  weight 
of  the  protoxide  is,  therefore,  36. 

Protoxide  of  iron  is  precipitated  from  its  salts  as  a white  hydrate  by 
pure  alkalies,  as  a white  carbonate  by  alkaline  carbonates,  and  as  a 
white  ferrocyanate  by  ferrocyanate  of  potassa.  The  two  former  preci- 
pitates become  first  green  and  then  red,  and  the  latter,  green  and  blue 
by  exposure  to  the  air.  J'he  solution  of  gall-nuts  produces  no  change 
of  colour.  Sulphuretted  hydrogen  does  not  act  if  the  protoxide  is 
united  with  any  of.  the  stronger  acids;  but  alkaline  hydrosulphurets 
cause  a black  precipitate,  protosulphuret  of  iron. 

Peroxide. — The  red  or  peroxide  is  a natural  product,  known  to  min- 
eralogists under  the.  name  of  red  hsematite.'  It  sometimes  occurs  mas- 
sive, at  other  times  fibrous,  and  occasionally  in  the  form  of  beautiful 
rhomboidal  crystals.  It  may  be  made  chemically  by  dissolving  iron  in 
nitro-muriatic  acid,  and  adding  an  alkali.  The  hydrate  of  the  red 
oxide  of  a brownish-red  colour  subsides,  which  is  identical  in  composi- 
tion with  the  mineral  called  brown  haematite,  and  consists  of  40  parts 
or  one  equivalent  of  the  peroxide,  and  9 parts  or  one  equivalent  of 
water. 

Peroxide  of  iron  is  not  attracted  by  the  magnet.  Fused  with  vitreous 
substances  it  communicates  to  them  a red  or  yellow  colour.  It  com- 
bines with  most  of  the  acids,  forming  salts,  the  greater  number  of 
which  are  red.  Its  presence  may  be  detected  by  very  decisive  tests. 
The  pure  alkalies,  fixed  or  volatile,  precipitate  it  as  the  hydrate.  Al- 
kaline carbonates  have  a similar  effect,  peroxide  of  iron  not  forming  a 
permanent  salt  with  carbonic  acid.  With  ferrocyanate  of  potassa  it 
forms  Prussian  blue,  ferrocyanate  of  the  peroxide  of  iron.  Sulphocy- 
anate  of  potassa  causes  a deep  blood-red,  and  infusion  of  gall-nuts,  a 


332 


IRON. 


black  colour.  Sulpluirettecl  hyclrog-en  converts  the  peroxide  into  pro- 
toxide of  iron,  and  deposition  of  sulpluir  takes  place  at  tlic  same  time. 
These  reagents,  and  especially  ferrocyanate  and  sulphocyanate  of  po- 
tassa,  afford  an  unerring  test  of  the  presence  of  minute  quantities  of 
peroxide  of  iron.  On  this  account  it  is  customary,  in  testing  for 
iron,  to  convert  it  into  the  peroxide,  an  object  which  is  easily  ac- 
complished by  boiling  the  solution  with  a small  quantity  of  nitric 
acid. 

The  researches  of  several  chemists,  such  as  Gay-Lussac,  Berzelius, 
Bucholz,  and  Thomson,  leave  no  doubt  that  the  oxygen  contained  in 
the  blue  and  red  oxides  of  iron  is  in  tlie  ratio  of  one  to  one  and  a half. 
Consequently,  the  peroxide  consists  of  28  parts  or  one  equivalent  of 
iron,  and  12  parts  or  an  equivalent  and  a half  of  oxygen. 

Black  Oxide. — This  substance,  long  supposed  to  be  protoxide  of 
iron,  contains  more  oxygen  than  the  blue,  and  less  than  the  red  oxide. 
It  cannot  be  regarded  as  a definite  compound  of  iron  and  oxt  gen;  but 
it  is  composed  of  the  two  real  oxides  united  in  a proportion  which  is 
by  no  means  constant.  It  occurs  native,  frequently  crystallized  in  the 
form  of  a regular  octohedron;  and  it  is  not  only  attracted  by  the  mag- 
net, but  is  itself  sometimes  magnetic.  It  is  always  formed  when  iron 
is  heated  to  redness  in  the  open  air;  and  is  likewise  generated  by  the 
contact  of  watery  vapour  with  iron  at  elevated  temperatures.  I'he 
composition  of  the  ])roduct,  however,  varies  with  the  duration  of  the 
process  and  the  temperature  which  is  employed.  Thus,  according  to 
Bucholz,  Berzelius,  and  Thomson,  100  parts  of  iron,  when  oxidized 
by  steam,  unite  with  nearly  30  of  oxygen;  whereas  in  a similar  experi- 
ment performed  by  Gay-Lussac,  37.8  parts  of  oxygen  were  absorbed. 
The  oxide  of  Gay-Lussac  may  be  regarded  as  a compound  of  one  equiv- 
alent of  the  protoxide  and  two  equivalents  of  the  peroxide,  and  Ber- 
zelius is  of  opinion  that  the  composition  of  magnetic  iron  ore  is  similar. 
M.  Mosander  states,  that  on  heating  a bar  of  iron  in  the  open  air,  the 
outer  layer  of  the  scales  contains  a greater  quantity  of  peroxide  than 
the  inner  layer.  The  former  consists  of  one  equivalent  of  peroxide  to 
two  of  the  protoxide,  and  in  the  latter  are  contained  one  equivalent  of 
peroxide  to  three  equivalents  of  protoxide.  The  inner  layer  seems 
uniform  in  composition;  but  the  outer  is  variable,  its  more  exposed 
parts  being  richer  in  oxygen. 

The  nature  of  the  black  oxide  is  further  elucidated  by  the  action  of 
acids.  On  digesting  the  black  oxide  in  sulphuric  acid,  an  olive-colour- 
ed solution  is  formed,  containing  two  salts,  sulphate  of  the  peroxide 
and  protoxide,  which  may  be  separated  from  each  other  by  means 
of  alcohol.  (Proust  and  Gay-Lussac.)  These  mixed  salts  give  green 
precipitates  with  alkalies,  and  a very  deep-blue  ink  with  infusion  of 
gall-nuts.  The  black  oxide  of  iron  is  the  cause  of  the  dull-green  col- 
our of  bottle  glass. 

Chlorides  of  Iron. — Chlorine  unites  in  two  proportions  with  iron, 
forming  compounds  which  were  described  in  1812  by  Dr.  John  Davy. 
The  protochloridc  is  made  by  evajmrating  a solution  of  the  protomu- 
riatc  to  dryness,  and  heating  it  to  redness  in  a glass  tube  from  which 
the  air  is  excluded.  'J’he  resulting  chloride  has  a gray  colour,  a lam. 
ellated  texture,  and  metallic  lustre.  St  is  composed  of  one  propor- 
tional of  each  element,  and  is  converted  by  water  into  protomuriate  of 
iron. 

The  pcrchloride  is  formed  hy  burning  iron  wire  in  an  atmosphere  of 
chlorine.  It  is  of  a l)right  yellowish-brown  colour,  crystallizes  in  small 
iridescent  plates,  and  is  volatile  at  a temperature  a little  above  212^  F. 
It  consists  of  one  equivalent  of  iron  and  an  equivalent  and  a half  of 


IRON. 


333 


chlorine,  and  forms  with  water  a red-coloured  solution,  which  is  per- 
muriate  of  iron. 

Bromides  of  Iron. — Into  a porcelain  capsule  put  any  quantity  of  bro- 
mine with  about  twenty  times  its  weight  of  water,  and  add  iron  filings 
as  long  as  any  action  continues,  promoting  union  by  gentle  heat  and 
agitation.  If  the  solution  is  made  and  evaporated  to  dryness  in  close 
vessels,  a protobromide  is  obtained;  but  if  freely  exposed  to  the  air, 
the  perbromide  is  left.  In  order  to  obtain  it  pure,  it  should  be  redis- 
solved in  water,  filtered  to  remove  a little  peroxide,  and  again  evapor- 
ated. A red  perbromide  remains,  which  is  deliquescent,  soluble  in 
water  and  alcohol,  and,  according  to  M.  Henry,  consists  of  one  equiv- 
alent of  iron  and  two  of  bromine.  The  accuracy  of  this  estimate  is 
surely  very  doubtful. 

By  exactly  decomposing  a solution  of  perbromide  of  iron  by  means 
of  alkalies  or  alkaline  earths,  the  hydrobromates  of  those  bases  are 
easily  prepared. 

Iodide  of  iron  may  be  formed  by  heating  the  metal  in  the  vapour  of 
iodine,  or  by  evaporating  a solution  of  the  hydriodate  prepared  as  in 
the  process  just  described  for  procuring  bromide  of  iron. 

Sulphurets  of  Iron. — There  are  two  compounds  of  iron  and  sulphur, 
both  of  which  are  natural  products.  The  protosulphuret  is  the  mag- 
netic iron  pyrites  of  mineralogists.  It  is  a brittle  yellow  substance,  of 
a metallic  lustre,  and  is  feebly  attracted  by  the  magnet.  By  exposure 
to  air  and  moisture,  it  is  gradually  converted  into  protosulphate  of  iron. 
It  may  be  made  artificially  by  igniting  protosulphate  of  iron  with  char- 
coal; or  still  more  conveniently  by  heating  a mixture  of  iron  filings  and 
sulphur.  (Page  252.)  It  is  dissolved  completely  and  readily  by  dilute 
sulphuric  and  muriatic  acid,  with  disengagement  of  sulphureUed  hydro- 
gen. It  is  composed  of  28  parts  or  one  equivalent  of  iron,  and  16  parts 
or  one  equivalent  of  sulphur. 

The  bisulphuret,  which  contains  two  equivalents  of  sulphur,  is  com- 
mon iron  pyrites.  When  heated  to  redness,  it  loses  half  its  sulphur, 
and  is  converted  into  the  protosulphuret.  It  is  insoluble  in  sulphuric 
and  muriatic  acid. 

Fhosphuret  of  Iron. — This  compound  may  be  formed  by  heating  phos- 
phate of  iron  with  charcoal.  It  is  sometimes  contained  in  metallic  iron, 
to  the  properties  of  which  it  is  exceedingly  injurious  by  causing  it  to 
be  brittle  at  common  temperatures. 

Carburets  of  Iron.— -C2ivhoi\  and  iron  unite  in  very  various  proportions; 
but  there  ara  three  compounds  very  distinct  from  each  other — namely, 
graphite,  cast  or  pig  iron,  and  steel. 

Graphite,  also  known  under  the  names  of  plumbago  and  black  lead, 
occurs  not  unfrequently  as  a mineral  production,  and  is  found  in  great 
purity  at  Borrowdale  in  Cumberland.  It  may  be  made  artificially  by 
exposing  iron  with  excess  of  charcoal  to  a violent  and  long-continued 
heat;  and  it  is  commonly  generated  in  small  quantity  during  the  prepa- 
ration of  cast  iron.  Pure  specimens  contain  about  four  or  five  per  cent, 
of  iron,  but  sometimes  its  quantity  amounts  to  10  per  cent.  Most  chemists 
believe  the  iron  to  be  chemically  united  with  the  charcoal;  but  accord- 
ing to  the  researches  of  Dr.  Karsten  of  Berlin,  native  graphite  is  only 
a mechanical  mixture  of  charcoal  and  iron,  while  artificial  graphite  is  a 
real  carburet. 

Graphite  is  exceedingly  unchangeable  in  the  air,  and  like  charcoal  is 
attacked  with  difficulty  by  chemical  reagents.  It  may  be  heated  to  any 
extent  in  close  vessels  without  change;  but  if  exposed  at  the  same  time 
to  the  air,  its  carbon  is  entirely  consumed,  and  oxide  of  iron  re- 
mains. It  has  an  iron-gray  colour,  metallic  lustre,  and  granular  tex- 


334 


IRON. 


ture;  and  it  is  soft  and  unctuous  to  the  touch.  Its  chief  use  is  in  the 
inanufacture  of  pencils  and  crucibles;  and  in  burnisliing*  iron  to  protect 
it  from  rust. 

Cast  iron  is  the  product  of  the  process  for  extractinp;’  iron  from  its 
ores,  and  is  commonly  regarded  as  a real  compound  of  iron  and  cliar- 
coal.  It  always  contains  impurities,  such  as  charcoal,  undecomposed 
ore,  and  eartliy  matters,  which  are  often  visible  by  mere  inspection; 
and  sometimes  traces  of  chromium,  manganese,  sulphur,  phosphorus, 
and  arsenic  are  present.  It  fuses  readily  at  a full  red  heat,  and  in  cool- 
ing acquires  a crystalline  granular  texture.  The  quality  of  different 
specimens  is  by  no  means  uniform;  and  two  kinds,  white  and  gray  cast 
iron,  are  in  particular  distinguished  from  each  other.  'I’he  former  is 
exceedingly  hard  and  brittle,  sometimes  breaking  like  glass  from  sud- 
den change  of  temperature;  while  the  latter  is  softer  and  much  more 
tenacious.  This  difference  appears  owing  to  the  mode  of  combination, 
rather  than  to  a difference  in  the  proportion  of  carbon;  for  the  white 
variety  may  be  converted  into  the  g'ray  by  exposure  to  a strong  heat 
and  cooling  slowly,  and  the  gray  may  be  changed  into  the  white  by  be- 
ing heated  and  rapidly  cooled.  According  to  Karsten  the  carbon  of  the 
latter  is  combined  with  the  whole  mass  of  Iron,  and  amounts  as  a maxi- 
mum to  5.25  per  cent.;  but  in  some  specimens  its  proportion  is  consi- 
derably less.  I'he  former,  on  the  contrary,  contains  from  3.15  to  4.65 
per  cent,  of  carbon,  of  which  about  three-fourths  are  in  the  state  of 
graphite,  and  are  left  as  such  after  the  iron  is  dissolved  by  acids;  while 
the  remaining  fourth  is  in  combination  with  the  whole  mass  of  metal, 
constituting  a carburet  which  is  very  similar  to  steel.  Gray  cast  iron 
may  hence  be  regarded  as  a kind  of  steel,  in  which  graphite  is  mechani- 
cally mixed. 

Steel  is  commonlj^  prepared  in  this  country  by  the  process  of  cement- 
ation, which  consists  in  filling  a large  furnace  with  alternate  strata  of 
bars  of  the  purest  malleable  iron  and  powdered  charcoal,  closing  every 
aperture  so  as  perfectly  to  exclude  atmospheric  air,  and  keeping  the 
whole  during  several  days  at  a red  heat.  By  this  treatment  tlie  iron 
gradually  combines  with  from  1.3  to  1.75  per  cent,  of  carbon,  its  texture 
is  greatly  changed,  and  its  sui-face  is  blistered.  It  is  subsequently 
hammered  at  a red  heat  into  small  bars,  and  may  be  w'elded  either  with 
other  bars  of  steel  or  with  malleable  iron.  Mr.  Mackintosh  of  Glasgow 
has  introduced  an  elegant  process  of  forming  steel  by  exposing  heated 
iron  to  a current  of  coal  gas,  when  carburetted  hydrogen  is  decompos- 
ed, its  carbon  enters  into  combination  with  iron,  and  hydrogen  gas  is 
evolved. 

In  ductility  and  malleability  it  is  fiir  inferior  to  iron;  but  exceeds  it 
greatly  in  hardness,  sonorousness,  and  elasticity.  Its  texture  is  also 
more  compact,  and  it  is  susceptible  of  a higher  polish.  It  sustains  a 
full  red  heat  without  fusing’,  and  is,  therefore,  less  fusible  than  cast 
iron;  but  it  is  much  more  so  than  malleable  iron.  By  fusion  it  forms 
cast  steel,  which  is  more  uniform  in  composition  and  texture,  and  pos- 
(3CSSCS  a closer  grain,  than  ordiiuuy  steel, 


ZINC 


335 


SECTION  XIIL 

ZINC.— CADMIUM. 

Zinc. 

The  zinc  of  commerce,  sometimes  called  speller^  is  obtained  either 
from  calamine,  native  carbonate  of  zinc,  or  from  the  native  sulphuret, 
zinc  blende  of  mineralog’ists.  It  is  procured  from  the  former  by  heat 
arid  carbonaceous  matters;  and  from  the  latter  by  a similar  process  after 
the  ore  has  been  previously  oxidized  by  roasting,  that  is,  by  exposure 
to  the  air  at  a low  red  heat.  Its  preparation  affords  an  instance  of  what 
is  called  distillation  by  descent.  The  furnace  or  crucible  for  reducing* 
the  ore  is  closed  above,  and  in  its  bottom  is  fixed  an  iron  tube,  the  up- 
per aperture  of  which  is  in  the  interior  of  the  crucible,  and  its  lower 
terminates  just  above  a vessel  of  water.  The  vapour  of  zinc,  together 
with  all  the  gaseous  products,  passes  through  this  tube,  and  the  zinc  is 
condensed.  The  first  portions  are  commonly  very  impure,  containing 
cadmium  and  arsenic,  the  period  of  their  disengagement  being  indica- 
ted by  what  the  workmen  call  the  brown  blaze;  but  when  the  blue  blaze 
begins,  that  is,  when  the  metallic  vapour  burns  with  a bluish-white 
flame,  the  zinc  is  collected.  As  thus  obtained,  it  is  never  quite  pure: 
it  frequently  contains  traces  of  charcoal,  sulphur,  cadmium,  arsenic, 
lead,  and  copper;  and  iron  is  always  present.  It  may  be  freed  from 
these  impurities  by  distillation,  by, exposing  it  to  a white  heat  in  an 
earthen  retort,  to  which  a receiver  full  of  water  is  a(!apted;  but  the  first 
portions,  as  liable  to  contain  arsenic  and  cadmium,  should  be  re- 
jected. 

Zinc  has  a strong  metallic  lustre,  and  a bluish-white  colour.  Its 
texture  is  lamellated,  ,and  its  density  about  7.  It  is  a hard  metal,  being 
acted  on  by  the  file  with  difficulty.  At  low  or  high  degrees  of  heat  it 
is  brittle;  but  at  a temperature  between  210®  and  300®  F.  it  is  both 
malleable  and  ductile,  a property  which  enables  zinc  to  be  rolled  or 
hammered  into  sheets  of  considerable  thinness.  Its  malleability  is  con- 
siderably diminished  by  the  impurities  which  the  zinc  of  commerce 
contains.  It  fuses  at  680®  F.,  and  when  slowly  cooled  crystallizes  in 
four  or  six-sided  prisms.  Exposed  in  close  vessels  to  a white  heat,  it 
sublimes  unchan,ged. 

Zinc  undergoes  little  change  by  the  action  of  air  and  moisture.  When 
fused  in  open  vessels  it  absorbs  oxygen,  and  forms  the  white  oxide, 
called  flowers  of  zinc.  Heated  to  full  redness  in  a covered  crucible,  it 
bursts  into  flame  as  soon  as  the  cover  is  removed,  and  burns  with  a 
'brilliant  white  light.  I'he  combustion  ensues  with  such  violence,  that 
the  oxide  as  it  is  formed  is  mechanically  carried  up  into  the  air.  Zinc 
is  readily  oxidized  by  dilute  sulphuric  or  muriatic  acid,  and  the  hydro- 
gen which  is  evolved  contains  a small  quantity  of  metallic  zinc  in  com- 
bination. 

Oxides  of  Zinc. — Chemists  are  not  agreed  as  to  the  number  of  the 
oxides  of  zinc;  but  tliere  is  certainly  only  one  oxide  of  importance, 
that,  namely,  which  is  formed  under  the  circumstances  above  mention- 
ed, and  which  is  the  base  of  the  salts  of  zinc.  At  common  tempera- 
tures it  is  white;  but  when  heated  to  low  redness,  it  assumes  a yellow 
colour,  which  gradually  disappears  on  cooling.  It  is  quite  fixed  in  the 
fire.  It  is  insoluble  in  water,  and,  therefore,  docs  not  affect  the  blue 


336 


CADMIUM. 


colour  of  plants;  but  it  is  a stront^  salifiable  base,  forming*  reg*ular  salts 
with  acids,  most  of  which  are  colourless.  It  combines  also  with  some 
of  the  alkalies.  According  to  the  experiments  of  Berzelius  and  'I'liom- 
son,  42  is  its  equivalent;  and  it  may  be  regarded  as  a compound  of 
34  parts  or  one  equivalent  of  zinc,  and  8 parts  or  one  equivalent  of 
oxygen. 

The  presence  of  zinc  is  easily  recognized  by  the  following  cliaracters. 
The  oxide  is  precipitated  from  its  solutions  as  a white  hydrate  by  pure 
potassa  or  ammonia,  and  as  carbonate  by  carbonate  of  ammonia,  but  is 
completely  redissolved  by  an  excess  of  the  precipitant.  The  fixed  al 
kaline  carbonates  precipitate  it  permanently  as  white  carbonate  of 
zinc.  Hydrosulphuret  of  ammonia  causes  a white  precipitate,  which 
is  either  a hydrosulphuret  of  the  oxide  of  zinc,  or  a hydrated  sulphuret 
of  the  metal.  Sulphuretted  hydrogen  acts  in  a similar  manner,  if  the 
solution  is  quite  neutral;  but  it  has  no  effect  if  an  excess  of  any  strong 
acid  is  present. 

When  metallic  zinc  is  exposed  for  some  time  to  air  and  moisture,  or 
is  kept  under  water,  it  acquires  a superficial  coating  of  a gray  matter, 
which  Berzelius  describes  as  a suboxide.  It  is  probably  a mixture  of 
metallic  zinc  and  the  white  oxide,  into  which  it  is  resolved  by  the  ac- 
tion of  acids.  The  superoxide  is  prepared,  according  to  Thenard,  by 
acting  on  hydrated  white  oxide  of  zinc  with  peroxide  of  hydrogen  di- 
luted with  water.  It  resolves  itself  so  readily  into  oxygen  and  the  ox- 
ide already  described,  that  it  cannot  be  preserved  even  under  the  sur- 
face of  water,  and  its  composition  is  quite  unknown. 

Chloride  of  Zinc. — This  compound,  called  butter  of  zinc  from  its  soft 
consistence,  is  formed,  with  evolution  of  heat  and  light,  when  zinc 
filings  are  introduced  into  chlorine  gas.  It  was  prepared  by  Dr.  John 
Davy  by  evaporating  muriate  of  zinc  to  dryness,  and  heating  the  residue 
to  redness  in  a glass  tube.  It  deliquesces  on  exposure  to  the  air,  being 
reconverted  into  a muriate.  It  consists  of  one  equivalent  of  each  of  its 
elements. 

Bromide  and  iodide  of  zinc  may  be  formed  by  processes  similar  to 
those  for  preparing  the  analogous  compounds  of  iron.  (Page  333.) 

Native  sulphuret  of  zinc,  or  zinc  blende,  is  frequently  found  in  do- 
decahedral crystals,  or  in  forms  allied  to  the  dodecahedron.  Its  struc- 
ture is  lamellated,  its  lustre  adamantine,  and  its  colour  variable,  being 
sometimes  yellow,  red,  brown,  or  black.  It  may  be  made  artificially 
by  heating  to  redness  a mixture  of  oxide  of  zinc  and  sulphur,  by  de- 
composing sulphate  of  zinc  by  charcoal,  or  by  drying  the  white  pre- 
cipitate obtained  on  adding  hydrosulphuret  of  ammonia  to  a salt  of 
zinc. 

Sulphuret  of  zinc  is  composed  of  one  proportional  of  each  of  its  con- 
stituents, and  is  dissolved  with  disengagement  of  sulphuretted  hydrogen 
gas  by  dilute  muriatic  or  sulphuric  acid. 

Cadmium. 

Cadmium  was  discovered  in  the  year  1817  by  Stromeyer  in  an  oxide 
of  zinc  which  had  been  ])rcparcd  for  medical  purposes;*  and  he  has 
since  found  it  in  several  of  the  ores  of  that  metal,  especially  in  a radi- 
ated blende  fiom  Bohemia  which  contains  about  five  per  Cent,  of  cad- 
mium. The  late  Dr.  (Jarkc  detected  its  existence  in  some  of  the  zinc 
ores  of  Derbyshire,  and  in  the  common  zinc  of  commerce.  Mr.  H era- 
path  has  found  it  in  considerable  (piantity  in  the  zinc  works  near  Bris- 


Annals  of  Philosophy,  vol,  xiy. 


CADMIUM. 


337 


tol.^  During  the  reduction  of  calamine  by  coal,  the  cadmium,  which 
is  very  volatile,  flies  off  in  vapour,  mixed  with  soot  and  some  oxide  of 
zinc,  and  collects  in  the  roof  of  the  vault,  just  above  the  tube  leading 
from  the  crucible.  Some  portions  of  this  substance  yielded  from  twelve 
to  twenty  per  cent,  of  cadmium. 

The  process  by  which  Stromeyer  separates  cadmium  from  zinc  or 
other  metals  is  the  following.  The  ore  of  cadmium  is  dissolved  in  di- 
lute sulphuric  or  muriatic  acid,  and  after  adding  a portion  of  free  acid, 
a current  of  sulphuretted  hydrogen  gas  is  transmitted  through  the  liquid, 
by  means  of  which  the  cadmium  is  precipitated  as  sulphuret,  while  the 
zinc  continues  in  solution.  The  sulphuret  of  cadmium  is  then  decom- 
posed by  nitric  acid,  and  the  solution  evaporated  to  dryness.  The  dry 
nitote  of  cadmium  is  dissolved  in  water,  and  an  excess  of  carbonate  of 
ammonia  added.  The  white  carbonate  of  cadmium  subsides,  which, 
when  heated  to  redness,  yields  a pure  oxide.  By  mixing  this  oxide 
with  charcoal,  and  exposing  the  mixture  to  a red  heat,  metallic  cadmium 
is  sublimed. 

A very  elegant  process  for  separating  zinc  from  cadmium  was  pro- 
posed by  Dr.  Wollaston.  The  solution  of  the  mixed  metals  is  put  into 
a platinum  capsule,  and  a piece  of  metallic  zinc  is  placed  in  it.  If 
cadmium  is  present,  it  is  reduced,  and  adheres  so  tenaciously  to  the 
capsule,  that  it  may  be  washed  with  water  without  danger  of  being 
lost.  It  may  then  be  dissolved  either  by  nitric  or  dilute  muriatic 
acid. 

Cadmium,  in  colour  and  lustre,  has  a strong  resemblance  to  tin,  but 
is  somewhat  harder  and  more  tenacious.  It  is  very  ductile  and  mallea- 
ble. Its  specific  gravity  is  8.604  before  being  hammered,  and  8.694  after- 
wards. It  melts  at  about  the  same  temperature  as  tin,  and  is  nearly  as 
volatile  as  mercury,  condensing*  like  it  into  globules  which  have  a me- 
tallic lustre.  Its  vapour  has  no  odour. 

When  heated  in  the  open  air,  it  absorbs  oxygen,  and  is  converted 
into  an  oxide.  Cadmium  is  readily  oxidized  and  dissolved  by  nitric  acid, 
which  is  its  proper  solvent.  Sulphuric  and  muriatic  acids  act  upon  it 
less  easily,  and  the  oxygen  is  then  derived  from  water. 

Cadmium  combines  with  oxygen,  so  far  as  is  yet  known,  in  one  pro- 
portion only;  and  this  oxide  is  conveniently  procured  in  a separate  state 
by  igniting  the  carbonate.  It  has  an  orange  colour,  and  is  fixed  in  the 
fire.  It  is  insoluble  in  water,  and  does  not  change  the  colour  of  violets; 
but  it  is  a powerful  salifiable  base,  forming  neutral  salts  with  acids.  This 
oxide,  according  to  the  analysis  of  Stromeyer,  is  composed  of  56  parts 
of  cadmium  and  8 parts  of  oxygen.  It  is  of  course  regarded  as  a com- 
pound of  one  equivalent  of  each  element,  and  consequently  56  is  the 
equivalent  of  cadmium. 

Oxide  of  cadmium  is  precipitated  as  a white  hydrate  by  pure  ammo- 
nia, but  is  redissolved  by  excess  of  the  alkali.  It  is  precipitated  per- 
manently by  pure  potassa  as  a hydrate,  and  by  all  the  alkaline  carbo- 
* nates  as  carbonate  of  cadmium. 

Sulphuret  of  cadmium,  which  occurs  native  in  some  kinds  of  zinc 
blende,  is  easily  procured  by  the  action  of  sulphuretted  hydrogen  on  a 
salt  of  cadmium.  It  has  a yellowish-orange  colour,  and  is  distinguished 
from  sulphuret  of  arsenic  by  being  insoluble  in  pure  potassa,  and  by 
sustaining  a white  heat  without  subliming.  It  is  composed  of  56  parts 
or  one  equivalent  of  cadmium,  and  16  parts  or  one  equivalent  of  sul- 
phur. (Stromeyer.) 


* Annals  of  Philosophy,  N.  S.  vol.  iii. 
29 


338 


TIN. 


Chloride  of  cadmium  may  be  prepared  by  decomposing*  the  muriate 
by  heat. 


SECTION  XIV. 

TIN. 

The  tin  of  commerce,  known  by  the  name  of  block  and  tin,  is 
procured  from  the  native  oxide  by  means  of  heat  and  charcoal.  In 
Cornwall,  which  has  been  celebrated  for  its  tin  mines  during*  many 
centuries,  the  ore  is  both  extracted  from  veins,  and  found  in  tlie  form 
of  rounded  grains  among  beds  of  rolled  materials,  which  have  been 
deposited  by  the  action  of  water.  These  grains,  commonly  called 
stream  tin,  contain  a very  pure  oxide,  and  yield  the  purest  kind  of 
grain  tin.  An  inferior  sort  is  prepared  by  heating  bars  of  tin,  extract- 
ed from  the  common  ore,  to  very  near  their  point  of  fusion,  when  the 
more  fusible  parts,  which  are  the  purest,  flow  out;  and  the  less  fusi- 
ble portions  constitute  block  tin.  The  usual  impui’ities  are  iron,  cop- 
per, and  arsenic. 

Tin  has  a white  colour,  and  a lustre  resembling  that  of  silver.  The 
brilliancy  of  its  surface  is  soon  impaired  by  exposure  to  the  atmosphere, 
though  it  is  not  oxidized  even  by  the  combined  agency  of  air  and  mois- 
ture. Its  malleability  is  very  considerable;  for  the  thickness  of  common 
tin-foil  does  not  exceed  1 -1000th  of  an  inch.  In  ductility  and  tenacity 
it  is  inferior  to  several  metals.  It  is  soft  and  inelastic,  and  when  bent 
backwards  and  forwards,  emits  a peculiar  crackling  noise.  Its  speciflc 
gravity  is  about  7.9.  At  442^  F.  it  fuses,  and  if  exposed  at  the  same 
time  to  the  air,  its  surface  tarnishes,  and  a gray  powder  is  formed. 
When  heated  to  whiteness,  it  takes  fire  and  burns  with  a white  flame, 
being  converted  into  peroxide  of  tin. 

Oxides  of  Tin. — Tin  is  susceptible  of  two  degrees  of  oxidation.  Both 
the  oxides  of  tin  form  salts  by  uniting  with  acids;  but  they  are  likewise 
capable  of  combining  with  alkalies.  From  data  furnished  by  the  ex- 
periments of  Berzelius,  Gay-Lussac,  and  Thomson,  these  oxides  are 
inferred  to  be  thus  constituted: — 

Tin,  Oxygen, 

Protoxide  58  or  one  equivalent.  8 or  one  equivalent. 

Peroxide  58  16  or  two  equivalents. 

The  protoxide  is  of  a gray  colour,  and  is  formed  when  tin  is  kept  for 
some  time  in  a state  of  fusion  in  an  open  vessel.  It  may  also  be  pro- 
cured by  precipitation  from  protomuriate  of  tin.  This  salt  is  made  by 
boiling  tin  in  strong  muriatic  acid,  when  the  metal  is  oxidized  by  decom- 
position of  water;  and  if  atmospheric  air  be  carefully  excluded,  a pure 
protomuriate  results.  From  this  solution  the  hydrated  protoxide  may 
be  preci[)ilatcd  citlier  by  ])ure  potassa  or  its  carbonate;  but  an  excess 
of  tlie  foi'iner  must  be  cai*efully  avoided,  as  otherwise  the  precipitate 
would  be  redissolved.  It  is  essential  likewise  to  the  success  of  the 
process  that  the  ])rotoxidc  should  be  both  washed  and  dried  without 
exposure  to  the  air. 

Protoxide  of  tin  is  remarkable  for  its  powerful  affinity  for  oxygen. 
When  heated  in  open  vessels,  it  is  converted  into  peroxide  with  evolu- 


TIN. 


339 


tion  of  heat  and  light.  Its  salts  not  only  attract  oxygen  from  the  air, 
but  act  as  powerful  deoxidizing  agents.  Thus,  protomuriate  of  tin 
converts  the  peroxide  of  copper  or  iron  into  protoxides,  and  precipi- 
tates silver,  mercury,  and  platinum  from  their  solutions  in  the  metallic 
state.  Added  to  a solution  of  gold,  it  occasions  a purple  coloured  pre- 
cipitate, the  purple  of  Cassius^  which  appears  to  be  a compound  of 
peroxide  of  tin  and  protoxide  of  gold.  By  this  character  protoxide  of 
tin  is  recognized  with  certainty.  It  is  thrown  down  by  sulphuretted 
hydrogen  as  black  protosulphuret  of  tin. 

Peroxide  of  tin  is  most  conveniently  prepared  by  the  action  of  nitric 
acid  on  metallic  tin.  Nitric  acid,  in  its  most  concentrated  state,  does 
not  act  easily  upon  tin;  but  when  a small  quantity  of  water  is  added, 
violent  effervescence  takes  place,  owing  to  the  evolution  of  nitrous 
acid  and  deutoxide  of  nitrogen,  and  a white  powder,  the  hydrated 
peroxide,  is  produced.  On  edulcorating  this  substance,  and  heating  it 
to  redness,  watery  vapour  is  expelled,  and  the  pure  peroxide,  of  a straw 
yellow  colour,  remains.  In  this  process  ammonia  is  generated,  a cir- 
cumstance which  proves  water  as  well  as  nitric  acid  to  have  been 
decomposed. 

Peroxide  of  tin  acts  the  part  of  a weak  acid,  uniting  with  alkalies, 
and  forming  soluble  compounds  with  them.  Its  affinity  for  acids  is 
feeble.  As  prepared  by  the  preceding  method  it  is  insoluble  in  acids; 
but  if  precipitated  from  permuriate  of  tin  by  a pure  alkali,  when  the 
oxide  falls  as  a gelatinous  hydrate,  it  is  readily  dissolved  by  muriatic  and 
sulphuric  acid. 

Peroxide  of  tin  is  separated  from  its  solution  in  muriatic  acid  as  a 
bulky  hydrate  by  potassa,  ammonia,  or  the  alkaline  carbonates,  and  the 
precipitate  is  easily  and  completely  redissolved  by  the  pure  fixed  alka- 
li in  excess.  Sulphuretted  hydrogen  occasions  a yellow  precipitate, 
which  is  either  hydrosulphuret  of  peroxide  of  tin,  or  bisulphuret  of  the 
metal. 

Peroxide  of  tin,  when  melted  with  glass,  forms  white  enamel. 

Chlorides  of  Tin. — Tin  unites  in  two  proportions  with,  chlorine,  and 
the  researches  of  Dr.  Davy  leave  no  doubt  of  these  compounds  being 
analogous  in  composition  to  the  oxides  of  tin. 

The  protochloride,  which  consists  of  one  equivalent  of  tin  and  one 
equivalent  of  chlorine,  may  be  made  either  by  evaporating  the  muriate 
of  the  protoxide  to  dryness  and  fusing  the  residue  in  a close  vessel,  or 
by  heating  an  amalgam  of  tin  with  calomel.  (Dr.  Davy.)  It  is  a gray 
solid  substance,  of  a resinous  lustre,  which  fuses  at  a heat  below  red- 
ness, and  when  heated  in  chlorine  gas  is  converted  into  the  bichloride. 

The  bichloride,  composed  of  one  equivalent  of  tin  and  two  equiva- 
lents of  chlorine,  may  be  prepared  either  by  lieating  metallic  tin  or  the 
protochloride  in  an  atmosphere  of  chlorine,  or  by  distilling  a mixture  of 
eight  parts  of  tin  in  powder  wiih  twenty-four  of  corrosive  sublimate. 
It  is  a colourless  volatile  liquid,  which  emits  copious  white  fumes  when 
exposed  to  the  atmosphere.  It  has  a very  strong  attraction  for  water, 
and  is  converted  by  that  fluid  into  the  permuriate.  It  was  formerly 
called  \\\Q  fuming  liquor  of  Lihavius. 

Sulphurets  of  Tin. — The  protosulphuret  is  best  formed  by  heating 
sulphur  with  metallic  tin.  A brittle  compound  of  a bluish-gray  colour 
and  metallic  lustre  results,  which  is  fusible  at  a red  heat,  and  assumes  a 
lamellated  structure  in  cooling.  It  is  dissolved  by  muriatic  acid,  with 
disengagement  of  sulphuretted  hydrogen.  According  to  the  analysis 
of  Dr.  Davy  and  Berzelius,  it  is  composed  of  one  equivalent  of  tin  and 
one  equivalent  of  sulphur. 

The  bisulphuret,  formerly  called  aurum  musivumi  has  a golden  yellow 


340 


COBALT. 


colour,  and  is  made  by  heating  a mixture  of  sulpluir  and  peroxide  of 
tin  in  close  vessels.  The  elements  of  the  latter  unite  with  separate 
portions  of  sulpluir,  forming  sulphurous  acid  and  bisulphuret  of  tin. 
This  compound  was  supposed  by  Proust  to  be  the  hydrosulpliuret  of 
the  peroxide  of  tin,  and  its  real  nature  was  first  made  known  by  Dr. 
Davy.  (Philos. Trans,  for  1812,  page  198.)  It  consists  of  one  equiva- 
lent of  tin  and  two  equivalents  of  sulphur. 

By  exposing  a mixture  of  sulphur  and  protosulphuret  of  tin  to  a low 
red  heat,  Berzelius  obtained  a compound  consisting  of  58  parts  or  one 
equivalent  of  tin,  and  24  parts  or  one  equivalent  and  a half  of  sulphur. 
If  it  is  really  a definite  compound,  it  should  be  termed  a sesquisul- 
pliuret. 


SECTION  XV. 

COBALT,— NICKEL. 

Cobalt, 

This  metal  is  met  with  in  the  earth  chiefly  in  combination  with 
arsenic,  constituting  an  ore  from  which  all  the  cobalt  of  commerce  is 
derived.  It  is  a constant  ingredient  of  meteoric  iron;  at  least  Professor 
Stromeyer  informs  me  that  he  has  analysed  several  varieties,  in  every 
one  of  which  he  has  detected  the  presence  of  cobalt. 

When  native  arseniuret  of  cobalt  is  broken  into  small  pieces,  and 
exposed  in  a reverberatory  furnace  to  the  united  action  of  heat  and  air, 
its  elements  are  oxidized,  most  of  the  arsenious  acid  is  expelled  in  the 
form  of  vapour,  and  an  impure  oxide  of  cobalt,  called  zaffre^  remains. 
On  heating  this  substance  with  a mixture  of  sand  and  potassa,  a beauti- 
ful blue-coloured  glass  is  obtained,  which,  when  reduced  to  powder,  is 
known  by  the  name  of  smalt. 

Metallic  cobalt  may  be  obtained  by  dissolving  zaffre  in  muriatic  acid, 
and  transmitting  through  the  solution  a current  of  sulphuretted  hydro- 
gen gas  until  the  arsenious  acid  is  completely  separated  in  the  form  of 
sulphuret  of  arsenic.  The  filtered  liquid  is  then  boiled  with  a little 
nitric  acid,  in  order  to  convert  the  protoxide  into  peroxide  of  iron,  and 
an  excess  of  carbonate  of  potassa  is  added.  The  precipitate  consisting 
of  peroxide  of  iron  and  carbonate  of  cobalt,  after  being  well  washed 
with  water,  is  digested  in  a solution  of  oxalic  acid,  which  dissolves  the 
iron  and  leaves  the  cobalt  in  the  form  of  an  insoluble  oxalate.  (Laugier.) 
On  heating  the  oxalate  of  cobalt  in  a retort  from  which  atmospheric  air 
is  excluded,  a larg'c  quantity  of  carbonic  acid  is  evolved,  and  a black 
powder,  metallic  cobalt,  is  left.  (I'homson  in  Annals  of  Philosophy,  N. 
S.  i.)  'rhe  jnire  metal  is  easily  procured  also  by  passing  a current  of 
dry  hydrogen  gas  over  oxide  of  cobalt  heated  to  redness  in  a tube  of 
]iorcelain.  In  tliis  slate  it  is  jiorous,  and  if  formed  at  a lo\v  temperature 
it  inflames  spontaneously,  as  stated  in  the  section  on  iron  (page  330). 

A solution  of*  cobalt  may  also  be  made  by  acting  on  the  native 
arseniuret  with  sulphuric  mixed  with  a fourth  part  of  nitric  acid,  sepa- 
rating as  much  arseniovis  acid  as  possible  by  cvajioration,  and  conducting 
the  remainder  of  the  process  as  above  described.  The  arseniuret  from 


COBALT. 


341 


TUnaber^  should  be  preferred  for  this  purpose,  as  it  is  in  g'eneral  free 
from  nickel,  which  always  accompanies  the  cobalt  ores  of  Germany. 

Cobalt  is  a brittle  metal,  of  a reddish-gray  colour,  and  weak  metallic 
lustre.  Its  density,  according  to  my  observation,  is  7.834.  It  fuses  at 
about  130^  of  Wedgwood,  and  when  slowly  cooled  it  crystallizes.  It  is 
atti’acted  by  the  magnet,  and  is  susceptible  of  being  rendered  perma- 
nently magnetic.  It  undergoes  little  change  in  the  air,  but  absorbs 
oxygen  when  heated  in  open  vessels.  It  is  attacked  with  difficulty  by 
sulphuric  or  muriatic  acid,  but  is  readily  oxidized  by  means  of  nitric 
acid.  Like  iron  and  the  other  metals  of  this  order,  it  decomposes  water 
at  a red  heat  with  disengagement  of  hydrogen  gas.  (Despretz.) 

Oxides  of  Cohalt. — Chemists  are  acquainted  with  two  oxides  of  cobalt. 
According  to  tlie  experiments  of  Ilothoff,*  the  protoxide  is  composed 
of  29.5  parts  of  cobalt  and  8 parts  of  oxygen,  so  that  the  atomic  weight 
of  cobalt  is  29.5.  Dr.  Thomson,  on  the  contrary,  infers  from  his  analy- 
sis of  sulphate  of  cobalt,  that  26  is  the  equivalent  of  this  metal.  From 
this  discordance  it  may  be  doubted  if  the  atomic  weight  of  cobalt  is 
known  with  certainty.  According  to  Rothoff,  the  oxygen  contained  in 
the  two  oxides 'is  as  1 to  1.5. 

The  protoxide  is  of  an  ash-gray  colour,  and  is  the  basis  of  the  salts  of 
cobalt,  most  of  which  are  of  a pink  hue.  When  heated  to  redness  in 
open  vessels  it  absorbs  oxygen,  and  is  converted  into  the  peroxide.  It 
may  be  prepared  by  decomposing  carbonate  of  cobalt  by  heat  in  a ves- 
sel from  which  atmospheric  air  is  excluded.  It  is  easily  recognized  by 
giving  a blue  tint  to  borax  when  melted  with  it;  and  is  employed  in  the 
arts,  in  the  form  of  smalt,  for  communicating  a similar  colour  to  glass 
earthenware,  and  porcelain. 

Protoxide  of  cobalt  is  precipitated  from  its  salts  by  pure  potassa  as  a 
blue  hydrate,  which  absorbs  oxygen  from  the  air,  and  gradually  becomes 
black.  Pure  ammonia  likewise  causes  a blue  precipitate,  which  is 
redissolved  by  the  alkali  if  in  excess.  It  is  thrown  down  as  a pale  pink 
carbonate  by  carbonate  of  potassa,  soda,  or  ammonia;  but  an  excess  of 
the  last  redissolves  it  with  facility.  Sulphuretted  hydrogen  produces 
no  change,  unless  the  solution  is  quite  neutral,  or  the  oxide  is  combined 
with  a weak  acid.  Alkaline  hydrosulphurets  always  precipitate  it  as 
black  sulphuret  of  cobalt. 

MujL’iate  of  cobalt  is  celebrated  as  a sympathetic  ink.  When  diluted 
with  water  so  as  to  form  a pale  pink  solution,  and  then  employed  as  ink, 
the  letters,  which  are  invisible  in  the  cold,  become  blue  if  gently  heated. 

Peroxide, of  cobalt  is  of  a black  colour,  and  is  easily  formed  from  the 
protoxide  in  the  way  already  mentioned.  It  does  not  unite  with  acids; 
and  when  digested  in  muriatic  acic],  the  protomuriate  of  cobalt  is 
generated  with  disengagement  of  chlorine.  Wlien  strongly  heated  in 
close  vessels,  it  gives  oh*  oxygen,  and  is  converted  into  the  protoxide. 

When  a salt  of  cobalt  is  treated  with  pure  ammonia  in  close  vessels, 
part  of  the  cobalt  is  dissolved,  and  part  subsides  in  form  of  a blue 
powder.  On  admitting  atmospheric  air,  this  substance  passes  to  a 
higher  state  of  oxidation,  and  is  gradually  dissolved.  If  nitrate  of 
cobalt  is  used,  a double  salt  maybe  obtained  in  crystals  which  L.  Gmelin, 
to  whom  we  are  indebted  for  these  remarks,  believes  to  consist  of  nitrate 
and  cohaltute  of  ammonia.  The  existence  of'this  acid,  however,  has 
not  yet  been  satisfactorily  established. 

Cobalt  appears  to  unite  with  sulphur  in  three  proportions;  the  first 
being  a protosulphuret,  the  second  a sesquisulphuret,  and  the  third  a 


* Annals  of  Philosophy,  vol.  iii*  p.  356. 
29* 


342 


NICKEL. 


deutosulpliuret.  The  protosulphuret  has  a g*ray  colour,  a metallic 
lustre,  and  a crystalline  texture.  It  may  be  formed  in  tlie  dry  way 
either  by  throwing  fragments  of  sulphur  on  red-hot  cobalt,  or  by  igniting 
oxide  of  cobalt  with  sulphur;  and  it  is  thrown  down  as  a black  precipi- 
tate from  the  salts  of  cobalt  by  alkaline  hydrosulphurets,  or  even  liy 
sulphuretted  hydrogen  gas  if  the  salt  is  quite  neutral,  or  the  oxide 
united  with  any  of  the  feebler  acids. 

Arfwedson  has  observed  that  when  hydrogen  gas  is  transmitted  over 
sulphate  of  cobalt  heated  to  redness,  water  and  sulphurous  acid  are 
evolved,  and  a compound  remains,  called  an  oxisiilphuret,  consisting  of 
oxide  of  cobalt  united  with  sulphuret  of  cobalt.  When  this  substance 
is  exposed  to  sulphuretted  hydrogen  gas  at  a red  heat,  the  oxide  is 
decomposed,  and  the  sesquisulphuret  is  formed. 

The  deutosulpliuret  is  prepared,  according  to  Setterberg,  by  heating 
carbonate  of  cobalt  in  a state  of  intimate  mixture  with  one  and  a half  of 
its  weight  of  sulphur.  The  process  is  conducted  in  a glass  retort,  and 
the  heat  continued  as  long  as  sulphur  is  expelled;  but  the  temperature 
should  not  be  suffered  to  reach  that  of  redness. 

The  compounds  of  cobalt  with  the  other  non-metallic  bodies  have 
hitherto  been  little  examined. 

Nickel. 

Nickel  is  a constituent  of  meteoric  iron.  It  occurs  likewise  in  the 
copper-coloured  mineral  of  Westphalia,  termed  copper-nickel^  a native 
arseniuret  of  nickel,  which  in  addition  to  its  chief  constituents  contains 
sulphur,  iron,  cobalt,  and  copper.  The  preparations  of  nickel  may 
either  be  made  from  this  mineral  or  from  the  artificial  arseniuret  called 
speiss,  a metallurgic  production  obtained  in  forming  smalt  from  the 
roasted  ores  of  cobalt.  Various  processes  have  been  devised  for  pro- 
curing a pure  salt  of  nickel,  but  the  following  appears  to  me  as  simple 
and  perhaps 'as  successful  as  any.  After  reducing  speiss  to  fine  powder 
it  is  digested  in  sulphuric  acid,  to  which  a fourth  part  of  nitric  acid  is 
added;  and  when  the  solution  is  saturated  with  nickel,  it  is  set  aside  for 
several  hours  in  order  that  arsenious  acid  may  separate,  and  is  then  fil- 
tered. I'he  clear  liquid  is  subsequently  mixed  with  a solution  of  sul- 
phate of  potassa,  and  set  aside  to  crystallize  spontaneously;  when  a 
double  salt,  sulphate  of  nickel  and  potassa,  is  deposited.  Dr.  Thom- 
son, who  proposed  this  process,  states  that  the  crystals  thus  obtained 
are  quite  free  from  arsenic  and  iron,  and  contain  no  impurities  except 
copper  and  cobalt.  The  former  is  easily  precipitated  as  sulphuret  by  a 
current  of  sulphuretted  hydrogen  gas,  a little  free  sulphuric  acid  being 
previously  added;  and  at  the  same  time  any  traces  of  arsenic,  if  present, 
would  likewise  subside  as  orpiment.  The  filtered  liquid  is  then  heated 
to  expel  free  sulphuretted  liydrogen,  and  the  oxides  of  nickel  and 
cobalt  precipitated  by  carbonate  of  potassa.  The  separation  of  these 
oxides  may  tlicn  be  effected  by  the  method  siigg’ested  b}^  M.  Berthier. 
2’he  mixed  liydrates,  after  being  well  washed,  are  suspended  in  water 
through  wbicli  clilorine  is  transmitted  to  saturation.  All  the  cobalt, 
and  generally  some  nickel,  is  converted  into  peroxide  and  thus  ren- 
dered insoluble;  while  the  greater  part  of  the  nickel  is  dissolved  in  the 
form  of  muriate,  and  may  be  removed  from  the  insoluble  peroxides 
by  filtration. 

Metallic  nickel,  which  may  be  prepared  either  by  heating  the  oxalate 
in  close  vessels,  or  by  the  combined  action  of  heat  and  charcoal  or  hy- 
drogen on  oxide  of  nickel,  is  of  a white  colour,  intermediate  between 
that  of  tin  and  silver.  It  has  a strong  metallic  lustre,  and  is  both  duc- 
tile and  malleable.  It  is  attracted  by  the  magnet,  and  like  iron  and  co- 


NICKEL. 


343 


bait  maybe  rendered  magnetic.  Its  specific  gravity  after  fusion  is  about 
8.279,  and  is  increased  to  near  9.0  by  hammering. 

Nickel  is  very  infusible,  but  less  so,  according  to  my  obsei’vation, 
than  pure  iron.  It  suffers  no  change  at  common  temperatures  by  ex- 
posure to  air  and  moisture;  but  it  absorbs  oxygen  at  a red  heat,  though 
not  rapidly,  and  is  partially  oxidized.  It  decomposes  water  at  the  same 
tempex'ature.  Muriatic  and  sulphuric  acids  act  upon  it  with  difficulty; 
but  by  nitric  acid  it  is  readily  oxidized,  and  forms  a nitrate  of  the  pro- 
toxide of  nickel. 

Nickel  is  susceptible  of  two  stages  of  oxidation.  According  to  the 
experiments  of  Berzelius,  Berthier,  and  Thomson,  the  combining  pro- 
portion of  nickel  is  26,  and  that  of  its  protoxide  34.  The  protoxide 
may  hence  be  regarded  as  a compound  of  one  equivalent  of  each  ele- 
ment. (Edinburgh  Journal  of  Science,  No.  xiii.  157.)  Peroxide  of 
nickel  has  been  less  fully  examined  than  the  protoxide;  but  from 
some  experiments  of  Rothoff,  it  appears  to  consist  of  26  parts  or 
one  equivalent  of  nickel,  and  12  parts  or  one  equivalent  and  a half  of 
oxygen. 

Protoxide  of  nickel  may  be  formed  by  heating  the  carbonate,  oxalate, 
or  nitrate  to  redness  in  an  open  vessel,  and  is  then  of  an  ash-gray  col- 
our; but  after  being  heated  to  whiteness,  its  colour  is  a dull  olive-green. 
It  is  said  to  be  reducible  by  heat  unaided  by  combustible  matter;  but  I 
have  exposed  it  to  intense  heat  in  a wind  furnace,  without  its  reduction 
being  effected.  It  is  not  attracted  by  the  magnet.  It  is  a strong  alka- 
line base,  and  nearly  all  its  salts  have  a green  tint.  It  is  precipitated  as 
a hydrate  of  a pale -green  colour  by  the  pure  alkalies,  but  it  is  redissolv- 
ed by  ammonia  in  excess;  as  a pale-green  carbonate  by  alkaline  carbo- 
nates, but  is  dissolved  by  an  excess  of  carbonate  of  ammonia;  and  as  a 
black  sulphuret  by  alkaline  hydrosulphurets.  Sulphuretted  hydrogen 
occasions  no  precipitate,  unless  the  solution  is  quite  neutral,  or  the 
oxide  combined  with  a weak  acid. 

Peroxide  of  nickel  has  a black  colour,  and  is  formed  by  transmitting 
chlorine  gas  through  water  in  which  the  hydrate  of  the  protoxide  is  sus- 
pended. The  peroxide  does  not  unite  with  acids,  is  decomposed  by  a 
red  heat,  and  with  hot  muriatic  acid  forms  a protomuriate  with  disen- 
gagement of  chlorine  gas. 

Thenard  succeeded  in  preparing  a peroxide  by  the  action  of  peroxide 
of  hydrogen  on  hydrated  protoxide  of  nickel;  but  it  is  uncertain  whe- 
ther the  composition  of  this  peroxide  is  identical  with  that  above  de- 
scribed, or  different.  Two  suboxides  have  likewise  been  enumerated; 
but  their  existence  is  exceedingly  problematical. 

Protosulphuret  of  nickel  is  formed  by  processes  similar  to  those  de- 
scribed for  preparing  protosulphuret  of  cobalt.  The  precipitated  sul- 
phuret is  dark  brown  or  nearly  black,  and  is  dissolved  by  muriatic  acid 
with  evolution  of  sulphuretted  hydrogen;  while  that  procured  in  the 
dry  way  is  of  a grayish-yellow  colour,  and  requires  for  solution  nitric  or 
nitro-muriatic  acid.  It  occurs  as  a natural  production  in  very  delicate 
acicular  crystals,  the  haarkies  of  the  Germans. 

Arfwedson  obtained  another  sulphuret  by  transmitting  hydrogen  gas 
over  sulphate  of  nickel  at  a red  heat.  It  is  of  a lighter  yellow  and 
more  fusible  than  the  former,  and  appears  to  be  a disulphuret,  consist- 
ing of  one  equivalent  of  sulphur  and  two  of  nickel. 

Phosphorus  unites  readily  with  nickel,  forming  a white  fusible  phos- 
phuret.  When  nickel  and  charcoal  are  heated  together,  and  the  un- 
combined metal  removed  by  muriatic  acid,  a carburet  of  nickel  remains, 
similar  in  appearance  to  graphite.  (Berzelius.) 


344 


ARSENIC. 


CLASS  II. 


ORDER  II. 


METALS  M TllCH  DO  NOT  DECOMPOSE  WATER  AT  ANY 
TEMPERATURE,  AND  THE  OXIDES  OF  M HICII  ARE  NOT 
REDUCED  TO  THE  METALLIC  STATE  BY  THE  SOLE 
ACTION  OF  HEAT. 


SECTION  XVI. 

ARSENIC. 

Metallic  arsenic  sometimes  occurs  native,  but  more  frequently  it  is 
found  in  combination  with  other  metals,  and  especially  with  cobalt  and 
iron.  On  roasting-  these  arsenical  ores  in  a reverberatory  furnace,  the 
arsenic,  from  its  volatility,  is  expelled,  combines  with  oxyg*en  as  it 
rises,  and  condenses  into  thick  cakes  on  the  roof  of  the  chimney.  The 
sublimed  mass,  after  being-  purified  by  a second  sublimation,  is  the  vir- 
ulent poison  known  by  the  name  of  arsenic  or  white  oxide  of  arsenic. 
From  this  substance  the  metal  itself  is  procured  by  heating-  it  with 
charcoal.  The  most  convenient  process  is  to  mix  the  white  oxide  with 
about  twice  its  weight  of  black  flux,  and  expose  the  mixture  to  a red 
heat  in  a Hessian  crucible,  over  which  is  luted  an  empty  crucible  for 
I’eceiving  the  metal.  The  reduction  is  easily  effected,  and  metallic 
arsenic  collects  in  the  upper  crucible,  which  should  be  kept  cool  for 
the  purpose  of  condensing  the  vapour. 

Arsenic  is  an  exceedingly  brittle  metal,  of  a strong  metallic  lustre, 
and  white  colour,  running  into  steel-gray.  Its  structure  is  crystalline, 
and  its  density,  according  to  my  observation,  is  5.8843.  When  heated 
to  356^  F.  it  sublimes  without  previously  liquefying;  for  its  point  of  fu- 
sion is  far  above  that  of  its  sublimation,  and  has  not  hitherto  been  de- 
termined. Its  vapour  has  a strong  odour  of  garlic,  a property  which 
affords  a distinguishing  character  for  metallic  arsenic,  as  it  is  not  pos- 
sessed by  any  other  metal,  with  tlie  exception  perhaps  of  zinc,  which 
is  said  to  emit  a similar  odour  when  thrown  in  powder  on  burning  char- 
coal. In  close  vessels  it  may  be  sublimed  without  change,  but  if  at- 
mospheric air  ])e  admitted  it  is  rapidly  converted  into  the  white  oxide. 
According  to  Hah.neman  it  is  slowly  oxidized  and  dissolved  by  being 
boiled  in  watex*.  In  general  it  speedily  tarnishes  by  exposure  to  air  and 
moisture,  acquiring  upon  its  surface  a dark  film,  which  is  extremely 
superficial;  but  Berzelius  remarks  that  he  has  kept  some  specimens  in 
open  vessels  for  years  without  loss  of  lustre,  while  others  are  oxidized 
through  their  whole  substance,  and  fall  into  powder.  The  product  of 
this  spontaneous  oxidation,  which  is  known  abroad  under  the  name  of 
Jly-powder,  is  supposed  by  Berzelius  to  be  an  oxide;  but  it  is  moi’e  gen- 
erally regarded  as  a mixture  of  white  oxide  and  metallic  arsenic.  (Lehr- 
buch  der  Chemie,  ii.  32.) 


ARSENIC. 


345 


Compounds  of  Arsenic  and  Oxygen* 

Chemists  are  acquainted  with  two  compounds  of  arsenic  and  oxygen; 
and  as  they  both  possess  the  properties  of  an  acid,  the  terms  arsenious 
and  arsenic  acid  have  been  properly  applied  to  them.  Considerable 
difference  of  opinion  exists  as  to  their  composition.  Dr.  Thomson  be- 
lieves 38  to  be  the  combining  proportion  of  metallic  arsenic,  and  that 
arsenious  acid  consists  of  one  atom  of  metal  to  two  atoms  of  oxygen, 
and  arsenic  acid  of  one  atom  of  metal  to  three  atoms  of  oxygen.  Ac- 
cording to  Berzelius,  37.627  is  the  equivalent  of  the  metal,  and  the 
oxygen  in  the  two  acids  is  in  the  ratio  of  3 to  5.  Arsenious  acid  is 
stated  by  the  former  to  contain  29.63,  and  by  the  latter  24.18  per  cent, 
of  oxygen,  a difference  which  is  very  considerable.  The  results  of 
Dr.  Thomson  are  commonly  adopted  in  this  country;  but  as  several  cir- 
cumstances induce  me  to  suspect  their  accuracy,  I shall  employ  those 
of  Berzelius  by  preference.  As  the  atomic  weight  of  metallic  arsenic 
was  found  nearly  the  same  by  both  chemists,  38  may  be  adopted  as  the 
most  convenient.  The  composition  of  the  two  acids  of  arsenic  may  ac- 
cordingly be  thus  stated; — 

Arsenic*  Oxygen* 

Arsenious  acid  38  or  one  equiv.  12  or  one  and  a half  equiv. 

Arsenic  acid  38  or  one  equiv.  20  or  two  and  a half  equiv. 

Arsenious  Acid. — This  compound,  frequently  called  white  oxide  of 
arsenic,  is  always  generated  when  arsenic  is  heated  in  open  vessels,  and 
may  be  prepared  by  digesting  the  metal  in  dilute  nitric  acid.  The 
white  arsenic  of  commerce  is  derived  from  the  native  arseniurets  of  co- 
balt, being  sublimed  during  the  roasting  of  these  ores  for  the  prepara- 
tion of  zaffre,  and  it  is  purified  by  a second  sublimation  in  iron  vessels. 
It  is  commonly  sold  in  the  state  of  a fine  white  powder;  but  when  first 
sublimed,  it  is  in  the  form  of  brittle  masses,  more  or  less  transparent, 
colourless,  of  a vitreous  lustre,  and  conchoidal  fracture.  This  glass, 
which  may  also  be  obtained  by  fusion,  preserves  its  transparency  in  a 
perfectly  dry  atmosphere,  but  in  ordinary  states  of  the  air  gradually 
becomes  opake  and  white.  Its  specific  gravity  is  3.7.  At  380^^  F.  it  is 
volatilized,  yielding  vapours  which  do  not  possess  the  odour  of  garlic, 
and  which  condense  unchanged  on  cold  surfaces.  If  the  sublimation  is 
slowly  conducted,  the  vapour  collects  in  the  form  of  distinct  octohedral 
crystals  of  adamantine  lustre  and  perfectly  transparent.  Its  point  of 
fusion  is  rather  higher  than  that  at  which  it  sublimes;  and,  therefore,  in 
order  to  be  vitrified,  it  must  either  be  heated  underpressure,  or  the 
temperature  ra])idly  raised  beyond  380^. 

The  taste  of  arsenious  acid  is  stated  differently  by  different  persons. 
It  is  prevalently  thought  to  be  acrid;  but  I am  satisfied  from  personal 
observation  that  it  may  be  deliberately  tasted  witliout  exciting  more 
than  a very  faint  impression  of  sweetness,  and  perhaps  of  acidity.  The 
acrid  taste  ascribed  to  .it  has  probably  been  confounded  with  the  local 
inflammation,  by  which  its  application,  if  of  some  continuance,  is  fol- 
lowed. (Dr.  Christison  on  the  Taste  of  Arsenic  in  the  Edinburgh  Med- 
ical and  Surgical  Journal  for  July,  1827.)  It  reddens  vegetable  blue 
colours  feebly,  an  effect  which  is  best  shown  by  placing  the  acid  in 
powder  on  moistened  litmus  paper.  It  combines  with  salifiable  bases, 
forming  salts  which  are  termed  arsenites* 

According  to  the  experhuents  of  Klaproth  and  Bucholz,  1000  parts 
of  boiling  water  dissolve  77.75  of  arsenious  acid;  and  the  solution,  after 
having  cooled  to  60?  F.,  contains  only  30  parts.  The  same  quantity  of 


346 


ARSENIC. 


water  at  60^,  when  mixed  with  the  acid  in  powder,  dissolves  only  two 
parts  and  a half.  Guibourt  has  lately  observed  that  the  transparent  and 
opake  varieties  of  arsenic  differ  in  solubility.  He  found  that  1000  parts 
of  temperate  water  dissolve,  during*  36  hours,  9.6  of  tlie  transparent, 
and  12.5  of  the  opake  variety;  that  the  same  quantity  of  boiling*  water 
dissolves  97  parts  of  the  transparent  variety,  retaining*  18  when  cold, 
but  takes  up  115  of  the  opake  variety,  and  retains  29  on  cooling*.  Ry 
the  presence  of  organic  substances,  such  as  milk  or  tea,  its  solubility  is 
materially  impaired.  (Christison  on  Poisons,  177.) 

When  metallic  arsenic  is  sharply  heated  with  hydrate  of  potassa,  pure 
hydrogen  gas  is  evolved;  and  a mass  is  left  consisting  of  arseniuret  of 
potassium  and  arsenite  of  potassa;  facts,  which  prove  that  a portion  of 
arsenic  is  oxidized,  and  derives  its  oxygen  partly  from  water  and  partly 
from  potassa.  If  the  heat  is  raised  to  redness,  the  arsenious  acid  is 
resolved  into  arsenic  acid  and  metal,  the  former  remaining  as  an 
arseniate,  while  the  latter  is  expelled.  Similar  phenomena  ensue 
with  hydrates  of  soda,  baryta,  and  lime;  except  that  with  the  two 
latter  no  arsenic  acid  is  produced.  (Soubeiran  in  An.  de  Ch.  et  de  Ph. 
lliii.  410.) 

The  tests  commonly  recommended  for  detecting  the  presence  of 
arsenious  acid  are  four  in  number;  namely,  lime-water,  ammoniacal 
nitrate  of  silver,  ammoniacal  sulphate  of  copper,  and  sulphuretted  hy- 
drogen. 

1.  When  lime-water  is  added  in  excess  to  a solution  of  arsenious 
acid,  a white  precipitate  subsides,  which  is  arsenite  of  lime.  On  dry- 
ing this  salt,  mixing  it  with  powdered  charcoal  or  black  flux,  and  heat- 
ing the  mixture  contained  in  a glass  tube  to  redness  by  means  of  a spirit- 
lamp,  the  arsenic  is  reduced,  sublimes,  and  condenses  in  a cool  part  of 
the  tube.  The  process  of  reduction  is  absolutely  necessary,  since  sev- 
eral other  acids  as  well  as  the  arsenious,  such  as  carbonic,  phosphoric, 
oxalic,  and  tartaric  acid,  yield  white  precipitates  with  lime-water. 
Arsenite  of  lime  is  soluble  in  all  acids  which  are  capable  of  dissolving 
lime  itself;  and  indeed  all  the  arsenites  are  dissolved  by  those  acids  with 
which  their  bases  do  not  form  insoluble  compounds. 

Lime-water  is  of  little  service  for  discovering  arsenious  acid  in  mixed 
fluids;  for  arsenite  of  lime  is  so  light  a powder,  that  when  formed  in 
gelatinous  or  oleaginous  solutions,  such  as  in  broth,  or  tea  made  with 
milk,  it  remains  suspended  in  the  liquid,  and  cannot  be  separated 
from  it. 

2.  Arsenious  acid  is  not  precipitated  by  nitrate  of  silver,  unless  an 
alkali  is  present  to  neutralize  the  nitric  acid.  Ammonia  is  commonly 
employed  for  the  purpose;  but  as  arsenite  of  silver  is  very  soluble  in 
ammonia,  an  excess  of  the  alkali  would  retain  tlie  arsenite  in  solution. 
To  remedy  this  inconvenience,  Mr.  Hume  pi’oposes  to  employ  the  am- 
moniacal nitrate  of  silver,  which  is  made  by  dropping  ammonia  into  a 
solution  of  lunar  caustic  till  the  oxide  of  silver  at  first  thrown  down^  is 
nearly  all  dissolved.  I'he  li(piid  thus  pre])ared  contains  the  precise 
quantity  of  ammonia  which  is  required;  ancl  when  mixed  with  arsenious 
acid,  two  neutral  salts  result,  the  soluble  nitrate  of  ammonia,  and  the 
insoluble  yellow  arsenite  of  silver.  Ammoniacal  nitrate  of  silver  like- 
wise diminisli(*s  the  risk  of  fallacy  thatmig'ht  arise  from  the  presence  of 
pliosphoric  acid.  Ifliosphate  of  silver  is  so  very  soluble  in  ammonia, 
that  when  a neutral  ]>hosj)batc  is  mixed  witli  the  ammoniacal  nitrate  of 
silver,  the  resulting  j>bospbate  of  silver  is  held  almost  entirely  in  solu- 
tion by  the  free  anynonia. 

'JMie  te.stof  nitrate  of  silver,  however,  even  in  its  improved  state,  is 
still  liable  to  objection.  Tor  when  arsenious  acid  in  small  proportion  is 


ARSENIC. 


347 


mixed  with  salts  of  muriatic  acid,  or  animal  and  vegetable  infusions, 
tlie  arsenite  of  silver  either  does  not  subside  at  all,  or  is  precipitated  in 
so  impure  a state  that  its  characteristic  colour  cannot  be  distinguished. 
Several  methods  have  been  proposed  for  obviating  this  source  of  falla- 
cy; but  Dr.  Christison  has  shown,  as  I conceive  quite  satisfactorily,  that 
this  test  cannot  be  relied  on  in  practice. 

3.  Ammoniacal  sulphate  of  copper,  which  is  made  by  adding  am- 
monia to  a solution  of  sulphate  of  copper  until  the  precipitate  at  first 
thrown  down  is  nearly  all  redissolved,  occasions  with  arsenious  acid  a 
green  precipitate,  which  has  been  long  used  as  a pigment  under  the 
name  of  Schede^s  green.  This  test,  though  well  adapted  for  detecting 
arsenious  acid  dissolved  in  pure  water,  is  very  fallacious  when  applied 
to  mixed  fluids.  Dr.  Christison  has  proved  that  ammoniacal  sulphate 
of  copper  produces  in  some  animal  and  vegetable  infusions,  containing 
no  arsenic,  a greenish  precipitate,  which  may  be  mistaken  for  Scheele’s 
green;  whereas,  in  other  mixed  fluids,  such  as  tea  and  porter,  to 
which  arsenic  has  been  previously  added,  it  occasions  none  at  all,  if 
the  arsenious  acid  is  in  small  quantity.  In  some  of  these  liquids,  a free 
vegetable  acid  is  doubtless  the  solvent;  but  arsenite  of  copper  is  also 
dissolved  by  tannin  and  perhaps  by  other  vegetable  as  well  as  some 
animal  principles. 

4.  When  a current  of  sulphuretted  hydrogen  gas  is  conducted  through 
a solution  of  arsenious  acid,  the  fluid  immediately  acquires  a yellow 
colour,  and  in  a short  time  becomes  turbid,  owing  to  the  formation  of 
orpiment,  yellow  sulphuret  of  arsenic.  The  precipitate  is  at  first  par- 
tially suspended  in  the  liquid;  but  as  soon  as  free  sulphuretted  hydro- 
gen is  expelled  by  boiling,  it  subsides  perfectly,  and  may  easily  be  col- 
lected on  a filter.  One  condition,  however,  must  be  observed  in  order 
to  ensure  success,  namely,  that  the  liquid  does  not  contain  a free  alkali; 
for  sulphuret  of  arsenic  is  dissolved  with  remarkable  facility  by  pure 
potassa  or  ammonia.  To  avoid  this  source  of  fallacy,  it  is  necessary  to 
acidulate  the  solution  with  a little  acetic  or  muriatic  acid.  Sulphuretted 
hydrogen  likewise  acts  on  arsenic  in  all  vegetable  and  animal  fluids  if 
previously  boiled,  filtered,  and  acidulated. 

But  it  does  not  necessarily  follow,  because  sulphuretted  hydrogen 
causes  a yellow  precipitate,  that  arsenic  is  present;  for  there  are  not 
less  than  four  other  substances,  namely,  selenium,  cadmium,  tin,  and 
antimony,  the  sulphurets  of  which,  judging  from  their  colour  alone, 
might  be  mistaken  for  orpiment.  From  these  and  all  other  substances 
w^hatever,  the  sulphuret  of  arsenic  may  be  thus  distinguished. — When 
heated  with  black  flux  in  the  manner  described  for  reducing  arsenite  of 
lime,  a metallic  crust  of  an  iron-gray  colour  externally,  and  crystalline 
on  its  inner  surface,  is  deposited  on  the  cool  part  of  the  tube.  This 
character  alone  is  quite  satisfactory;  but  it  is  easy  to  procure  additional 
evidence,  by  reconverting  the  metal  into  arsenious  acid,  so  as  to  obtain 
it  in  the  form  of  resplendent  octohedral  crystals.  This  is  done  by  hold- 
ing that  part  of  the  tube  to  which  the  arsenic  adheres  about  three- 
fourths  of  an  inch  above  a very  small  spirit-lamp  flame,  so  that  the 
metal  may  be  slowly  sublimed.  As  it  rises  in  vapour  it  combines  with 
oxygen,  and  is  deposited  in  crystals  within  the  tube.  The  character  of 
these  crystals  with  respect  to  volatility,  lustre,  transparency,  and  form, 
is  so  exceedingly  well  marked,  that  a practised  eye  may  safely  identify 
them,  though  their  weight  should  not  exceed  the  100th  part  of  a grain. 
This  experiment  does  not  succeed  unless  the  tube  be  quite  clean  and 
dry. 

The  only  circumstance  which  occasions  a difficulty  in  the  preceding 
process,  is  the  presence  of  organic  substances,  which  cause  the  preci- 


348 


ARSENIC. 


pitate  to  subside  Imperfectly,  render  filtration  tedious,  and  froth  Up  in- 
conveniently during-  tlie  reduction.  Hence  if  abundant,  they  sJiould  be 
removed  before  sulphuretted  hydrog-en  is  employed;  and  this  object  is 
accomplished  by  sliglitly  acidulating-  the  solution  with  nitric  acid,  ad- 
ding nitrate  of  silver  as  long  as  a precipitate  appears,  filtering,  removing 
excess  of  silver  by  muriate  of  soda,  neutralizing  the  filtered  solution 
with  an  alkali,  and  lastly,  acidulating  as  usual  with  acetic  acid.  I’he 
object  of  these  directions  will  readily  appear.  The  organic  substances 
form  an  insoluble  compound  with  oxide  of  silver,  while  the  arsenic, 
excess  of  nitrate  of  silver,  and  tlie  acid  of  the  decomposed  nitrate,  remain 
in  the  liquid.  Now  silver  and  free  nitric  acid  would  interfere  with  the  ac- 
tion of  sulpliuretted  hydrogen.  The  former  is  precipitated  as  a black  sul- 
phuret  by  this  reagent;  while  free  nitric  acid  decomposes  the  gas,  and 
throws  down  sulphur,  which,  if  mixed  in  any  quantity  with  sulphuret 
of  arsenic,  prevents  its  reduction.  (Christison  on  Poisons,  199.) 

It  hence  appears,  that  of  the  various  tests  for  arsenic,  the  only  one 
which  gives  uniform  results,  and  is  applicable  to  every  case,  is  sulphu- 
retted hydrogen:— all  the  rest  may  be  dispensed  with.  For  this  great 
improvement  in  the  mode  of  testing  for  arsenious  acid,  we  are  indebted 
to  Dr.  Christison.  By  this  process  he  discovered  the  presence  of  arse- 
nious acid  when  mixed  with  complex  fluids,  such  as  tea,  porter,  and 
the  like,  in  the  proportion  of  one-fourth  of  a grain  to  an  ounce;  and 
more  recently  he  has  twice  obtained  so  small  a quantity  as  the  20th  of  a 
grain  from  the  stomachs  of  people  who  had  been  poisoned  with  arsenic. 
(Edinburgh  Medical  and  Surgical  Journal  for  October,  1824;  and  second 
volume  of  the  Transactions  of  the  Medico-chirurgical  Society  of  Edin- 
burgh.) 

The  black  flux  employed  in  the  processes  for  reducing  arsenic,  is 
prepared  by  deflagrating  a mixture  of  bitartrate  of  potassa  with  half 
its  weight  of  nitre.  The  nitric  and  tartaric  acid  undergo  decomposition, 
and  the  solid  product  is  charcoal  derived  from  tartaric  acid,  and  pure 
carbonate  of  potassa.  When  this  substance  is  employed  in  the  reduction 
of  arsenious  acid  or  its  salts,  the  charcoal  is  of  course  the  decomposing 
agent;  but  the  alkali  is  of  use  in  retaining  the  arsenious  acid  until  the 
temperature  is  sufficiently  high  for  its  , decomposition.  With  sulphuret 
of  arsenic,  on  tlie  contrary,  the  alkali  is  the  active  principle,  the  potas- 
sium of  which  unites  with  sulphur  and  liberates  the  arsenic;  but  the 
charcoal  operates  usefully  by  facilitating  the  decomposition  of  the 
alkaline  carbonate. 

Arsenic  Acid. — This  compound  is  made  by  dissolving  arsenious  acid  in 
concentrated  nitric,  mixed  with  a little  muriatic  acid,  and  distilling  the 
solution  to  perfect  dryness.  The  acid  thus  prepared  has  a sour  metallic 
taste,  reddens  vegetable  blue  colours,  and  with  alkalies  forms  neutral 
salts,  which  are  termed  arseniates.  It  is  much  more  soluble  in  water 
than  arsenious  acid,  dissolving  in  five  or  six  times  its  weight  of  cold,  and 
in  a still  smaller  quantity  of  hot  water.  It  forms  irregular  grains 
when  its  solution  is  evaporated,  but  does  not  crystallize.  If  strongly 
lieatcd  it  fusej}  into  a glass  which  is  deliquescent.  Wlien  urged  by  a 
vciy  strong  red  heat  it  is  resolved  into  oxygen  and  arsenious  acid.  It  is 
an  active  jioison. 

Arsenic  acidi.s  decomposed  by  sulphuretted  hydrogen  gas,, and  yields 
a sulphuret  of  arsenic  very  like  orpiment  in  colour,  but  containing  a 
greater  projioi-tional  quantity  of  sulphur.  The  soluble  arseniates,  when 
mixed  with  the  nitrati-s  of  lead  or  silver,  form  insoluble  arseniates,  the 
former  of  wlfich  has  a wliite,  and  the  latter  a brick-red  colour.  They 
dissolve  readily  in  dilute  nitric  acid,  and  when  heated  with  charcoal 
yield  metallic  arsenic. 


ARSENIC. 


SA9 


Chloride  of  Jlrsenic. — When  arsenic  in  powder  is  thrown  into  a jar 
full  of  dry  chlorine  gas,  it  takes  fire,  and  a cliloride  of  arsenic  is  gene- 
rated; and  the  same  compound  may  be  formed  by  distilling  a mixture 
of  six  parts  of  corrosive  sublimate  with  one  of  arsenic.  It  is  a colour- 
less volatile  liquid,  which  fumes  strongly  on  exposure  to  the  air,  hence 
called liquor  of  arsenic^  and  is  resolved  by  water  into  muriatic 
and  arsenious  acids.  According  to  Dr.  J.  Davy  it  is  composed  of  60.48 
parts  of  chlorine  and  39.^2  of  arsenic,  a proportion  which  does  not 
correspond  with  the  laws  of  combination,  and,  therefore,  is  doubtless 
inexact. 

The  following  process  has  been  lately  proposed  by  M.  Dumas.  Into 
a tubulated  retort  is  introduced  a mixture  of  arsenious  acid  with  ten 
times  its  weight  of  concentrated  sulphuric  acid;  and  after  raising  its 
temperature  to  near  212®  fragments  of  sea-salt  are  thrown  in  by 
the  tubular.  If  the  salt  is  added  in  successive  small  portions,  scarcely 
any  muriatic  acid  gas  is  evolved,  and  the  pure  chloride  may  be 
collected  in  cooled  vessels.  Towards  the  end  of  the  process  a little 
water  frequently  passes  over  with  the  chloride;  but  this  hydrated  por- 
tion does  not  mix  with  the  anhydrous  chloride,  but  swims  on  its  surface. 
The  h}'drate  may  be  decomposed,  and  a pure  chloride  obtained,  by 
distilling  the  mixture  from  a sufficient  quantity  of  concentrated  sul- 
phuric acid.  M.  Dumas  considers  this  compound  a protochloride  of 
arsenic,  so  that  it  is  probably  different  from  that  obtained  by  means  of 
corrosive  sublimate.  (Quarterly  Journal  of  Science,  N.  S.  i.  235.) 

Iodide  of  arsenic  is  formed  by  bringing  its  elements  into  contact,  and 
promoting  union  by  gentle  heat.  They  form  a deep-red  compound, 
which  is  resolved  into  arsenic  and  hydriodic  acids  by  the  action  of  water. 
(Plisson  in  An.  de  Ch.  et  de  Ph,  xxxix.  266.) 

Bromide  of  Arsenic. — The  elements  of  this  compound  unite  at  the 
moment  of  contact,  with  vivid  evolution  of  heat  and  light.  Serullas 
prepared  it  by  adding  dry  arsenic  to  bromine  as  long  as  light  was 
emitted,  the  former  being  added  in  successive  small  quantities,  to  pre- 
vent the  temperature  from  rising  too  high.  The  bromide  is  then  dis- 
tilled, and  collected  in  a cool  receiver.  (An.  de  Ch.  et  de  Ph.  xxxviii. 
318.) 

This  compound  is  solid  at  or  below  68®  F.,  liquefies  between  68®  and 
77®,  and  boils  at  428®.  As  a liquid  it  is  transparent  and  slightly  yellow, 
and  yields  long  prisms  by  evaporation.  It  is  composed  of  one  equiva- 
lent of  arsenic  and  one  and  a half  of  bromine;  and  by  contact  with 
water  it  is  converted  into  arsenious  and  hydrobromic  acids. 

Arseniuretted' Hydrogen. — 'This  gas,  which  was  discovered  by  Scheele, 
has  been  studied  by  Proust,  Trommsdorf,  and  others,  but  especially  by 
Stromeyer.  It  is  generally  made  by  digesting  an  alloy  of  tin  and 
arsenic  in  muriatic  acid;  but  as  thus  prepared  it  is  always  mixed  with 
free  hydrogen.  M.  Soubeiran,  who  has  lately  written  on  this  compound, 
generated  it  by  fusing  arsenic  with  its  own  weight  of  granulated  zinc, 
and  decomposing  the  alloy  with  strong  muriatic  acid.  The  gas,  thus 
developed,  is  quite  free  from  hydrogen,  being  absorbed  without  residue 
by  a saturated  solution  of  sulpliate  of  copper.  Its  specific  gravity, 
calculated  by  Soubeiran,  is  4.1828.  It  is  colourless,  and  has  a fetid 
odour  like  that  of  garlic.  It  extinguishes  bodies  in  combustion,  but  is 
itself  kindled  by  them,  and  burns  with  a blue  flame.  It  instantly 
destroys  small  animals  that  are  immersed  in  it,  and  is  poisonous  to 
man  in  a high  degree,  having  proved  fatal  to  a German  philosopiier,  the 
late  M.  Gehlen.  Water  absorbs  one-fifth  of  its  volume,  and  acquires 
the  odour  of  the  gas.  It  wants  altogether  the  propei  ties  of  an  acid. 

Arseniuretted  hydrogen  is  decomposed  by  various  agents.  It  suflers 

30 


350 


ARSENIC. 


gradual  decomposition  when  mixed  with  atmospheric  air,  water  being 
formed,  and  metallic  arsenic,  together  with  a little  oxide,  deposited. 
With  nitric  acid,  water  is  generated,  and  a deposite  of  metal  takes  place, 
which  is  subsequently  oxidized.  Chlorine  decomposes  it  instantly  with 
disengagement  of  heat  and  light,  muriatic  acid  being  generated,  and 
the  metal  set  free.  With  iodine  it  yields  hydriodic  acid  gas  and  iodide 
of  arsenic,  and  sulphur  and  phosphorus  produce  analogous  changes. 
By  its  action  on  salts  of  the  easily  reducible  metals,  such  as  silver  and 
gold,  the  metal  is  revived,  and  its  oxygen  uniting  with  the  elements  of 
the  gas  constitutes  arsenious  acid  and  water.  A\dth  salts  of  copper  the 
products  are  water  and  arseniuret  of  copper;  and  with  several  other 
metallic  salts  its  action  is  similar. 

M.  Soubeiran  observed  that  arseniuretted  hydrogen  in  a glass  tube  is 
completely  decomposed  by  the  heat  of  a spirit-lamp,  and  tliat  its  hy- 
drogen occupies  one  and  a half  as  much  space  as  when  in  combination. 
He  has  also  confirmed  the  observation  of  Humas  that  when  mixed  with 
oxygen,  and  detonated  by  the  electric  spark,  each  volume  of  the  gas, 
in  forming  water  and  arsenious  acid,  requires  one  and  a half  its  volume 
of  oxygen  gas.  The  oxygen,  therefore,  is  equally  divided  between 
the  arsenic  and  hydrogen;  and  arseniuretted  hydrogen  consists  of  one 
equivalent  of  arsenic  and  one  and  a half  of  hydrogen.  By  volume,  it 
is  composed  of  half  a volume  of  the  vapour  of  arsenic,  and  one  and  a 
half  of  hydrogen,  condensed  into  one  measure.*  (An.  de  Ch.  et  de 
Ph.  xliii.  407.) 

A solid  compound  of  arsenic  and  hydrogen,  of  a brown  colour,  was 
discovered  by  Sir  H.  Davy,  and  Gay-Lussac  and  Thenard.  The  former 
prepared  it  by  attaching  a piece  of  arsenic  to  the  negative  Avire  during 
the  decomposition  of  water  by  galvanism;  and  the  French  chemists,  by 
the  action  of  water  on  an  alloy  of  potassium  and  arsenic.  M.  Soubeiran, 
in  his  late  experiments,  succeeded  in  forming  it  by  the  latter  process, 
but  not  by  that  of  l)avy.  It  appears  to  be  a compound  of  one  equiv- 
alent of  arsenic  and  one  of  hydrogen. 

Sulphurets  of  Arsenic. — Sulphur  unites  with  arsenic  in  at  least  three 
proportions,  forming  compounds,  two  of  which  occur  in  the  mineral 
kingdom,  and  are  well  known  by  the  names  of  realgar  and  orpiment. 
Realgar  or  the  protosulphuret  may  be  formed  artificially  by  heating  ar- 
senious acid  with  about  half  its  weight  of  sulphur,  until  the  mixture  is 
brought  into  a state  of  perfect  fusion.  The  cooled  mass  is  crystalline, 
transparent,  and  of  a ruby-red  colour;  and  may  be  sublimed  in  close 
vessels  without  change.  It  is  composed  of  38  parts  or  one  equivalent 
of  arsenic,  and  16  parts  or  one  equivalent  of  sulphur. 

Orpiment,  or  sesquisulphuret  of  arsenic,  may  be  prepared  by  fusing 
together  equal  parts  of  arsenious  acid  and  sulphur;  but  the  best  mode 
of  obtaining  it  quite  pure  is  by  transmitting  a current  of  sulphuretted 

* In  this  statement  Dr.  Turner  has  departed  from  the  general  princi- 
ple, wliich  he  has  uniformly  adopted  elsewhere,  that  equivalent  quan- 
tities of  the  different  simple  gases  and  vapours,  except  oxygen,  occu- 
py tlie  same  volume.  A more  consistent  view,  therefore,  of  the  com- 
position of  arseniuretted  liydrogen,  would  be  to  consider  it  as  composed 
of  o??e  volume  of  tl»e  vapour  of  arsenic  united  to  one  and  a half  volumes  of 
hydrogen,  condensed  into  one  volume.  Its  composition  as  stated  by 
Dr.  "J'urner,  makes  the  coml)ining  volume  of  arsenic  vapour  the  same  as 
that  of  oxygen,  instead  of  causing  it  to  coincide  with  the  combining 
volume  of  tlie  vapours  of  iodine,  carbon,  plmsphorus,  and  sulphur, 
whicli  Dr.  Turner  has  uniformly  and  very  properly  represented  by  an 
cn/ire  volume.  B. 


CHROMIUM. 


351 


hydrogen  gas  through  a solution  of  arsenious  acid.  Orpiment  has  a 
rich  yellow  colour,  fuses  readily  when  heated,  and  becomes  crystalline 
on  cooling,  and  in  close  vessels  may  be  sublimed  without  change.  It  is 
dissolved  with  great  ficility  by  the  pure  alkalies,  and  yields  colourless 
solutions.  In  composition  it  is  proportional  to  arsenious  acid;  that  is, 
it  consists  of  38  parts  or  one  equivalent  of  arsenic,  and  24  parts  or  one 
equivalent  and  a half  of  sulphur. 

Orpiment  is  employed  ;is  a pigment,  and  is  the  colouring  principle  of 
the  paint  called  King^s  yellow.  M.  Braconnot  has  proposed  it  likewise 
for  dyeing  silk,  woollen,  or  cotton  stuffs  of  a y ellow  colour.  For  this 
purpose  the  cloth  is  soaked  in  a solution  of  orpiment  in  ammonia,  and 
then  suspended  in  a warm  apartment.  The  alkali  evaporates,  and  leaves 
the  orpiment  permanently  attached  to  the  fibres  of  the  cloth.  (An.  de 
Ch.  et  de  Ph.  vol.  xii.) 

Persulphuret  of  arsenic  is  prepared  by  transmitting  sulphuretted  hy- 
drogen gas  through  a moderately  strong  solution  of  arsenic  acid;  or  by 
saturating  a solution  of  arseniate  of  potassa  or  soda  with  the  same  gas, 
and  acidulating  with  muriatic  or  acetic  acid.  The  oxygen  of  the  acid 
unites  with  the  hydrogen  of  the  gas,  and  persulphuret  of  arsenic  sub- 
sides. In  colour  it  is  very  similar  to  orpiment,  is  dissolved  by  pure 
alkalies,  fuses  by  heat,  and  may  be  sublimed  in  close  vessels  without 
decomposition.  It  is  proportional,  in  composition,  to  arsenic  acid;  that 
is,  it  consists  of  one  equivalent  of  arsenic  and  two  equivalents  and  a 
half  of  sulphur. 

The  experiments  of  Orfila  have  proved  that  the  sulphurets  of  arsenic 
are  poisonous,  though  in  a much  less  degree  than  arsenious  acid.  The 
precipitated  sulphuret  is  more  injurious  than  native  orpiment. 


SECTION  XVII. 

CHROMIUM.— MOLYBDENUM.— TUNGSTEN.— COLUMBIUM. 

Chromium. 

Chromium*  was  discovered  in  the  year  1797  by  Vauquelin  in  a beau- 
tiful red  mineral,  the  native  dichromate  of  lead.  (An.  de  Ch.  xxv.  and 
Ixx.)  It  has  since  been  detected  in  the  mineral  called  chromate  of  iron, 
a compound  of  the  oxides  of  chromium  and  iron,  which  occurs  abun- 
dantly in  several  parts  of  the  continent,  in  America,  and  at  Unst  in  Shet- 
land. (Hibbert.) 

Chromium,  which  has  hitherto  been  procured  in  very  small  quantity, 
owing  to  its  powerful  attraction  for  oxygen,  may  be  obtained  by  expos- 
ing the  oxide  of  chromium  mixed  with  charcoal  to  the  most  intense 
heat  of  a smith’s  forge.  Its  colour  is  white  with  a sliade  of  yellow, 
and  distinct  metallic  lustre.  It  is  a brittle  metal,  very  infusible,  and 
with  difficulty  attacked  by  acids,  even  by  the  nitro-muriatic.  Its  spe- 
cific gravity  has  been  stated  at  5.9;  but  Ur.  Thomson  found  it  a little 
above  5.  When  fused  with  nitre  it  is  oxidized,  and  converted  into 
chromic  acid. 


* From  colour,  indicative  of  its  remarkable  tendency  to  form 

coloured  compounds. 


352 


CHROMIUM. 


Chromium  unites  with  oxygen  in  two  proportions,  forming  tlie  green 
oxide,  and  cliromic  acid.  Dr.  Thomson  some  years  ago  ascertained 
that  the  combining  proportion  of  chromic  acid  is  52;  and  according  to 
the  results  of  an  elaborate  investigation,  published  in  the  Philosophical 
Transactions  for  1827,  the  oxide  and  acid  are  thus  constituted:— 
Chromium.  Oxygen.. 

Green  oxide  32  or  one  equivalent  8 or  one  equivalent. 

Chromic  acid  32  . . 20  or  two  and  a half  equivalents. 

Protoxide. — This  oxide  is  easily  prepared  by  dissolving  chromate  of 
potassa  in  water,  and  mixing  it  with  a solution  of  protonitrate  of  mer- 
cury, when  an  orange-coloured  precipitate,  protochromate  of  mercury, 
subsides.  ^ On  heating*  this  salt  to  redness  in  an  earthen  crucible,  tlie 
mercury  is  dissipated  in  vapour,  and  the  chromic  acid  is  resolved  into 
oxygen  and  protoxide  of  chromium. 

Protoxide  of  chromium  is  of  a green  colour,  exceedingly  infusible, 
and  sufiers  no  change  by  heat.  It  is  insoluble  in  water,  and  after  being 
strongly  heated,  resists  the  action  of  the  most  powerful  acids.  Defla- 
grated with  nitre,  it  is  oxidized  to  its  maximum,  and  is  thus  reconvert- 
ed into  chromic  acid.  Fused  with  borax  or  vitreous  substances,  it  com- 
municates to  them  a beautiful  green  colour,  a property  which  affords 
an  excellent  test  of  its  presence,  and  renders  it  exceedingly  useful 
in  the  arts.  The  emerald  owes  its  colour  to  the  presence  of  this 
Qxide. 

Protoxide  of  chromium  is  a salifiable  base,  and  its  salts,  which  have 
a green  colour,  may  be  easily  prepared  in  the  following  manner.  To  a 
boiling  solution  of  chromate  of  potassa  in  water,  equal  measures  of 
strong  muriatic  acid  and  alcohol  are  added  in  successive  small  portions, 
until  the  red  tint  of  the  chromic  acid  disappears  entirely,  and  the  li- 
quid acquires  a pure  green  colour.  On  pouring  an  excess  of  pure 
ammonia  into  this  solution,  a pale  green  bulky  hydrate  subsides,  which 
consists  of  one  equivalent  of  the  protoxide  and  twenty-six  equivalents 
of  water.  (Thomson.)  The  oxide,  in  this  state,  is  readily  dissolved  by 
acids. 

The  anhy^drous  oxide  is  formed  when  bichromate  of  potassa  is  brisk- 
ly boiled  with  sugar  and  a little  muriatic  acid.  At  first  a brown  matter 
falls,  consisting  of  the  acid  and  oxide  of  chromium;  but  subsequently 
the  green  oxide  appears  in  the  form  of  a finely  divided  powder.  If  the 
bichromate  and  sugar  are  employed  without  muriatic  acid,  the  brown 
matter  is  the  only  solid  product,  and  on  boiling  this  compound  with  a 
little  carbonate  of  potassa,  a blue  carbonate  of  chromium,  of  a very 
fine  colour,  is  obtained.  For  this  mode  of  preparation  I am  indebted 
to  my  late  pupil,  Mr.  Thomas  Thomson,  of  Clitheroe,  near  Man- 
chester. 

Chromic  Jlcid. — This  acid  is  prepared  by  digesting  chromate  of  baryta, 
precij)itated  from  a mixture  of  nitrate  of  barytii  and  chromate  of  po- 
tassa, in  a (piantity  of  dilute  sulphuric  acid  exactly  sufficient  for  com- 
bining with  the  baryta.  'I'he  sulphate  of  baryta  subsides,  and  a solu- 
ti'in  of  ehromic  acid  is  obtained.  Another  metliod  has  been  lately  pro- 
posed by  M.  Arnold  Mans,  which  consists  in  decomposing  a hot  con- 
ca  i.trated  solution  of  bichromate  of  potassa  by  silicated  hydrofluoric 
acid.  'I'lie  chromic  aciil,  after  being  separated  from  the  s])aringly  solu- 
ble bydrofluate  of  silicii  and  potassa,  is  evajiorated  to  dryness  in  a pla- 
tinum cupside;  and  then  redissolved  in  the  smallest  ])ossible  quantit}^  of 
watei*.  liy  this  means  the  hist  portions  of  the  double  salt  are  rendered 
insoluble,  and  the  ])ure  chromic  acid  may  be  se])arated  by  decantation. 
The  acid  must  not  be  filtered  in  this  concentrated  state;  as  it  then  cox'- 


CHROMIUM. 


353 


rodes  paper  like  sulphuric  acid,  and  is  converted  into  chromate  of  the 
green  oxide  of  chromium.  When  it  is  wished  to  prepare  a large  quan- 
tity of  chromic  acid  by  this  process,  porcelain  vessels  may  be  safely 
employed  in  the  first  part  of  the  operation,  provided  care  is  taken 
to  add  a quantity  of  silicated  hydrofluoric  acid  not  quite  sufflcient  for 
precipitating  the  whole  of  the  potassa.  (Edinburgh  Journal  of  Science, 
viii.  175.) 

Chromic  acid  has  a dark  ruby-red  colour,  and  forms  irregular  crystals 
when  its  solution  is  concentrated.  It  is  very  soluble  in  water,  has  a 
sour  taste,  and  possesses  all  the  properties  of  an  acid.  It  is  converted 
into  the  green  oxide,  with  evolution  of  oxygen,  by  exposure  to  a strong 
heat.  It  yields  a muriate  of  the  protoxide  when  boiled  with  muriatic 
acid  and  alcohol,  and  the  direct  solar  rays  have  a similar  effect  when 
muriatic  acid  is  present.  With  sulphurous  acid  it  forms  a sulphate  of 
the  protoxide;  and  it  is  more  or  less  completely  converted  into  protox- 
ide by  being  boiled  with  sugar,  starch,  or  various  other  organic  princi- 
ples. It  destroys  the  colour  of  indig'o,  and  of  most  vegetable  and  ani- 
mal colouring*  matters;  a property  advantageously  employed  in  calico- 
printing,  and  which  manifestly  depends  on  the  facility  with  which  it  is 
deprived  of  oxyg'en. 

Chromic  acid  is  characterized  by  its  colour,  and  by  forming  coloured 
salts  with  alkaline  bases.  The  most  important  of  these  salts  is  chromate 
of  lead,  which  is  found  native  in  small  quantity,  and  is  easily  prepared 
by  mixing  chromate  of  potassa  with  a soluble  salt  of  lead.  It  is  of  a 
rich  yellow  colour,  and  is  employed  in  the  arts  of  painting  and  dyeing 
to  great  extent. 

When  sulphurous  acid  gas  is  transmitted  into  a solution  of  chromate 
or  bichromate  of  potassa,  a brown  precipitate  subsides,  which  was  long 
regarded  as  a distinct  ox’de  of  chromium;  but  Dr.  Thomson,  in  the 
essay  above  cited,  has  proved  that  it  is  the  green  oxide  combined  with 
a little  chromic  acid.  The  acid  may  in  a great  measure  be  washed  away 
by  means  of  water,  and  by  ammonia  it  is  entirely  removed;  but  the 
best  method  of  separating  it,  is  to  dissolve  the  brown  matter  with 
muriatic  acid,  and  then  precipitate  the  green  oxide  by  ammonia.  The 
brown  compound  may  be  formed  by  boiling  a solution  of  bichromate  of 
potassa  with  alcohol;  and  it  is  also  rapidly  generated,  when  bichromate 
of  potassa  is  gently  boiled  with  sugar  and  a little  muriatic  acid. 

Fluodiromic  Acid  Gas, — When  a mixture  of  fluor  spar  and  chrom.ate 
of  lead  is  distilled  with  fuming  or  even  common  sulphuric  acid  in  a 
leaden  retort,  a red-coloured  g'as  is  disengag’ed.  This  gas  acts  rapidly 
upon  glass,  with  deposition  of  chromic  acid  and  formation  of  fluosilicii 
acid  gas.  It  is  absorbed  by  water,  and  the  solution  is  found  to  contain 
a mixture  of  hydrofluoric  and  chromic  acids.  The  watery  vapour  of 
the  atmosphere  effects  its  decomposition,  so  that  when  mixed  with  air, 
red  fumes  appear,  owing*  to  the  separation  of  minute  crystals  of  chro- 
mic acid.  This  gas  may  be  regarded  as  a compound  eitlier  of  fluorine 
and  chromium,  or  of  hydrofluoric  and  chromic  acids;  but  from  the  cir- 
cum.stance  of  its  being  decomposed  so  readily  by  moisture,  the  first 
view  is  tlie  more  probable. 

Chlorochromic  Acid  Gas. — This  compound  is  formed  by  the  action  of 
fuming  sulphuric  acid  on  a mixture  of  chromate  of  lead  and  chloride  of 
sodium.  It  is  a red-coloured  gas  which  may  he  collected  in  glass  ves- 
sels over  mercury.  It  is  decomposed  instantly  by  water,  and  yields  a 
solution  of  muriatic  and  chromic  acids.  It  may  be  regarded  either  as  a 
compound  of  muriatic  and  chromic  acids,  or  of  chlorine  and  chromium. 

'I'liese  gases  were  discovered  in  the  year  1825  by  M.  Unverdorben. 
(Edinburgh  Journal  of  Science,  No.  vii.  129.) 

30* 


354 


MOLYBDENUM. 


Dr.  Thomson,  in  the  essay  already  referred  to,  has  described  a red- 
coloured  liquid  under  the  name  of  chlorochromic  acid,  wliich  he  ob- 
tained by  the  action  of  concentrated  sulphuric  acid  on  a mixture  of  dry 
bichromate  of  potassa  and  sea-salt.  It  obviously  contains  chromic  acid 
and  chlorine;  but  its  exact  nature  has  not  been  satisfactorily  establislied, 
and  according  to  Dr.  Tliomson’s  description,  it  can  scarcely  be  reg’arded 
as  a definite  compound. 

F rotochloride  of  Chromium. — This  compound  is  best  prepared,  accord- 
ing* to  the  method  of  forming  chlorides  suggested  by  Oersted,  by  trans- 
mitting dry  chlorine  over  a mixture  of  protoxide  of  chromium  and 
charcoal  heated  to  redness  in  a tube  of  porcelain.  The  chloride 
gradually  collects  as  a crystalline  sublimate  of  a purple  colour,  which  is 
transparent  in  thin  layers,  but  when  in  thicker  masses  is  opake.  It  is 
slowly  dissolved  by  water,  yielding  a green  solution,  possessed  of  all 
the  properties  of  the  protomuriate. 

Sulpkuret  of  chromium  may  be  formed  by  transmitting  the  vapour  of 
bisulphuret  of  carbon  over  protoxide  of  chromium  at  a white  heat;  by 
heating  in  close  vessels  an  intimate  mixture  of  sulphur  and  hydrated 
protoxide;  or  by  fusing  the  protoxide  with  a persulphuret  of  potassium, 
and  dissolving  the  soluble  parts  in  water.  It  cannot  be  prepared  in  the 
moist  way.  It  is  of  a dark-gray  colour,  and  acquires  metallic  lustre  by 
friction  in  a mortar.  It  is  readily  oxidized  when  heated  in  the  open  air, 
and  is  dissolved  by  nitric  or  niti’O-muriatic  acid.  It  consists  of  an  equiva- 
lent of  each  of  its  elements. 

Phosphuret  of  Chromium. — This  compound  is  best  prepared  by  ex- 
posing phosphate  of  chromium  in  a covered  crucible  lined  with  charcoal 
to  a strong  heat.  It  is  a porous  friable  substance  of  a light-gray  colour, 
undergoes  little  change  in  the  open  fire,  and  is  very  slightly  affected 
even  by  nitro-muriatic  acid. 

Molybdenum, 

When  native  sulphuret  of  molybdenum,  in  fine  powder,  is  digested 
in  nitro-muriatic  acid  until  the  ore  is  completely  decomposed,  and  the 
residue  is  briskly  heated  in  order  to  expel  sulphuric  acid,  molybdic  acid 
remains  in  the  form  of  a white  heavy  powder.  From  this  acid  metallic 
molybdenum  may  be  obtained  by  exposing  it  with  charcoal  to  the 
strongest  heat  of  a smith’s  forge;  or  by  conducting  over  it  a current  of 
hydrogen  gas  while  strongly  heated  in  a tube  of  porcelain.  (Berzelius.) 
The  sulphuret,  which  was  long  mistaken  for  graphite,  was  distinguished 
in  the  year  1778  by  Scheele;  but  the  metal  was  first  obtained  in  a sepa- 
rate state  by  Hjelm,  It  hkewise  occurs  in  nature  in  the  form  of  mo- 
lybdate of  lead. 

Molybdenum  is  a brittle  metal,  of  a white  colour,  and  so  very  Infusible 
that  hitherto  it  has  only  been  obtained  in  a state  of  semi-fusion.  In  this 
form  it  has  a specific  gravity  varying  between  8.615  to  8.636.  When 
heated  in  open  vessels  it  absorbs  oxyg'en,  and  is  converted  into  molybdic 
acid;  and  the  same  compound  is  generated  by  the  action  of  chlorine  or 
niti*o-muriatic  acid.  It  has  three  degrees  of  oxidation,  forming  two 
oxides  and  one  acid.  The  molybdic  acid,  according  to  Bucholz,  is 
composed  of  48  parts  of  molybdenum  and  24  ])arts  of  oxygen;  and 
consecpiently  on  tlie  supposition  tb.at  this  acid  contains  thrc<j  atoms  of 
oxygen,  48  is  the  atomic  weight  of  tlie  metal  itself. 

Molybdic  acid  is  a wliite  ])owder,  of  specific  gravity  3.4.  It  has  a 
sliarp  metallic  taste,  reddens  litmus  pa])er,  and  forms  salts  with  alkaline 
bases.  It  is  very  s])aringly  soluble  in  water;  but  the  molybdates  of  po- 
tassa, soda,  and  ammonia,  dissolve  in  that  lluid,  and  the  molybdic  acid 
is  precipitated  from  the  solutions  by  any  of  the  strong  acids. 


TUNGSTEN. 


355 


Berzelius  has  lately  described  the  two  oxides  of  molybdenum.  (Edin- 
burg^h  Journal  of  Science,  iv.  133.)  The  protoxide  is  black,  and  con- 
sists of  one  equivalent  of  oxygen  and  one  equivalent  of  molydenum. 
The  deutoxide  is  brown,  and  contains  twice  as  much  oxygen  as  the 
protoxide.  I'hey  both  form  salts  with  acids.  Berzelius  states  that  the 
blue  molyhdous  acid  of  Bucholz  is  a bimolybdate  of  the  deutoxide  of 
molybdenum. 

Berzelius  has  likewise  succeeded  in  forming  three  chlorides  of  molyb- 
denum, the  composition  of  which  is  analogous  to  the  compounds  of 
this  metal  with  oxygen. 

The  native  sulphuret  of  molybdenum,  according  to  the  analysis  of 
Bucholz,  is  composed  of  48  parts  or  one  equivalent  of  molybdenum, 
and  32  parts  or  two  equivalents  of  sulphur.  Berzelius  has  lately  dis- 
covered another  sulphuret,  of  a ruby-red  colour,  transparent,  and 
crystallized.  It  is  proportional  to  the  molybdic  acid;  that  is,  contains 
three  equivalents  of  sulphur  to  one  equivalent  of  the  metal. 

Tungsten. 

Tungsten  maybe  procured  in  the  metallic  state  by  exposing  tungstic 
acid  to  the  action  of  charcoal  or  dry  hydrogen  gas  at  a red  heat;  but 
though  the  reduction  is  easily  effected,  an  exceedingly  intense  tempera- 
ture is  required  for  fusing  the  metal.  I'ungsten  has  a grayish- white 
colour,  and  considerable  lustre.  It  is  brittle,  nearly  as  hard  as  steel, 
and  less  fusible  than  manganese.  Its  specific  gravity  is  near  17.4. 
When  heated  to  redness  in  the  open  air  it  takes  fire,  and  is  converted 
into  tungstic  acid;  and  it  undergoes  the  same  change  by  the  action  of 
nitric  acid.  Digested  with  a concentrated  solution  of  pure  potassa,  it 
is  dissolved  with  disengagement  of  hydrogen  gas,  and  tungstate  of 
potassa  is  generated. 

Chemists  are  acquainted  with  two  compounds  of  this  metal  and  oxy- 
gen, namely,  the  dark-brown  oxide,  and  the  yellow  acid  of  tungsten; 
and  according  to  the  analyses  of  Berzelius,  (An.  de  Ch.  et  de  Ph.  xvii.) 
the  oxygen  of  the  former  is  to  that  of  the  latter  in  the  ratio  of  two  to 
three.  It  is  hence  inferred,  that  the  real  protoxide  of  tungsten  is  yet 
unknown,  and  that  tungstic  acid  contains  three  atoms  of  oxygen  to  one 
atom  of  the  metal.  Now,  Bucholz  ascertained  that  this  acid  consists  of 
96  parts  of  tungsten  and  24  parts  of  oxygen,  and  consequently  96  is  the 
atomic  weight  of  tungsten,  and  120  the  equivalent  of  its  acid.  The 
brown  oxide  is  composed  of  96  parts  or  one  equivalent  of  metal,  and  16 
parts  or  tvi^o  equivalents  of  oxygen. 

A convenient  method  of  preyiaring  tungstic  acid  is  by  digesting  na- 
tive tungstate  of  lime,  very  finely  levigated,  in  nitric  acid;  by  which 
means  nitrate  of  lime  is  formed,  and  tungstic  acid  separated  in  the  form 
of  a yellow  powder.  Long  digestion  is  required  before  all  the  lime  is 
removed;  but  the  process  is  facilitated  by  acting  upon  the  mineral  alter- 
nately by  nitric  acid  and  ammonia.  The  tungstic  acid  is  dissolved  readi- 
ly by  that  alkali,  and  may  be  obtained  in  a separate  state  by  heating  the 
tungstate  of  ammonia  to  redness.  Tungstic  acid  may  also  be  prepared 
by  the  action  of  muriatic  acid  on  tvolfram,  native  tungstate  of  iron  and 
manganese.  It  is  also  obtained  by  heating  the  brown  oxide  to  redness 
in  open  vessels. 

Tungstic  acid  is  of  a yellow  colour,  is  insoluble  in  water,  and  has  no 
action  on  litmus  paper.  Witli  alkaline  bases  it  forms  salts  called  tung- 
states, which  are  decomposed  by  the  stronger  acids,  tlie  tungstic  acid 
in  general  falling  combined  with  the  acid  by  which  it  is  precipitated. 
When  strongly  heated  in  open  vessels,  it  acquires  a green  colour,  and 
becomes  blue  when  exposed  to  the  action  of  hydrogen  gas  at  a tern- 


356 


TUNGSTEN. 


perature  of  500®  or  600®  E.  The  blue  compound,  according-  to  Hcr- 
zclius,  i3  a tungstate  of  the  oxide  of  tungsten;  and  the  green  colour 
is  probably  produced  by  an  admixture  of  this  compound  with  the  yel- 
low acid. 

The  oxide  of  tungsten  is  formed  by  the  action  of  hydrogen  gas  on 
tungstic  acid  at  a low  I’ed  heat;  but  the  best  mode  of  procuring  it  both 
pure  and  in  quantity,  is  that  recommended  by  AA'ohler.  (Uuarterly 
Journal  of  Science,  xx.  177.)  This  process  consists  in  mixing  wolfram 
in  fine  powder  with  twice  its  weight  of  carbonate  of  potassa,  and  fusing 
the  mixture  in  a platinum  crucible.  The  resulting  tungstate  of  potassa 
is  dissolved  in  hot  water,  mixed  with  about  half  its  weight  of  muriate 
of  ammonia  in  solution,  evaporated  to  dryness,  and  exposed  in  a Hes- 
sian crucible  to  a red  heat.  The  mass  is  well  washed  with  boiling  wa- 
ter, and  the  insoluble  matter  digested  in  dilute  potassa  to  remove  any 
tungstic  acid.  The  residue  is  oxide  of  tungsten.  It  appears  that  in 
this  process  the  tungstate  of  potassa  and  muriate  of  ammonia  mutually 
decompose  each  other,  so  that  the  dry  mass  consists  of  chloride  of  po- 
tassium and  tungstate  of  ammonia.  The  elements  of  the  latter  react 
on  each  other  at  a red  heat,  giving  rise  to  water,  nitrogen  gas,  and 
oxide  of  tungsten;  and  this  compound  is  protected  from  oxidation  by 
the  fused  chloride  of  potassium  with  which  it  is  enveloped.  I'his  oxide 
is  also  formed  by  puttiiig  tungstic  acid  in  contact  with  zinc,  in  dilute 
muriatic  acid.  The  tungstic  acid  first  becomes  blue  and  then  assumes  a 
copper  colour;  but  the  oxide  in  this  state  can  with  difficulty  be  pre- 
served, as  by  exposure  to  the  air,  and  even  under  the  surface  of  water, 
it  absorbs  oxyg-en,  and  is  reconverted  into  tungstic  acid. 

Oxide  of  tungsten,  when  prepared  by  means  of  hydrogen  gas,  has  a 
brown  colour,  and  when  polished  acquires  the  colour  of  copper;  but 
when  procured  by  Wohler’s  process,  it  is  nearly  black.  It  does  not 
unite,  so  far  as  is  known,  with  acids;  and  when  heated  to  near  redness, 
it  takes  fire  and  yields  tungstic  acid. 

Chlorides  of  Tungsien. — According  to  Wohler  tungsten  and  chlorine 
unite  in  three  proportions.  The  perchloride  is  generated  by  heating 
the  oxide  of  tungsten  in  chlorine  gas.  The  action  is  attended  with  the 
appearance  of  combustion,  dense  fumes  arise,  and  a thick  sublimate  is 
obtained  in  the  form  of  white  scales,  like  native  boracic  acid.  It  is 
volatile  at  a low  temperature  without  previous  fusion.  It  is  converted 
by  the  action  of  water  into  tungstic  and  muriatic  acids,  and  must  there- 
fore, in  composition,  be  proportional  to  tungstic  acid;  that  is,  it  consists 
of  96  parts  or  one  equivalent  of  tungsten,  and  108  parts  or  three  equiv- 
alents of  chlorine. 

When  metallic  tungsten  is  heated  in  chlorine  gas,'  it  takes  fire,  and 
yields  the  deutochloride.  The  compound  appears  in  the  form  of  deli- 
cate fine  needles,  of  a deep-red  colour  resembling  wool,  but  more  fre- 
quently as  a deep-red  fused  mass  which  has  the  brilliant  fracture  of  cin- 
nabar. When  heated,  it  fuses,  boils,  and  yields  a red  vapour.  By 
water  it  is  changed  into  muriatic  acid  and  oxide  of  tungsten.  It  is  en- 
tirely dissolved  by  solution  of  pure  potassa,  with  disengagement  of  hy- 
drogen gas,  yielding  muriate  and  tungstate  of  potassa.  A similar  change 
is  produced  by  ammonia,  exce])t  that  some  oxide  of  tungsten  is  left 
undissolved. 

Another  chloride  has  been  described  by  W^ohler.  It  is  formed  at  the 
same  time  as  the  first;  and  though  it  is  converted  into  muriatic  and 
tungstic  acids  by  the  a6tion  of  water,  and  would  thus  seem  identical 
with  the  perchloride  in  the  ])ro|)ortio]i  of  its  elements,  its  other  pro- 
perties are  nevertheless  difi'erent.  It  is  the  most  beautiful  of  all  these 
compounds,  existing  in  long  transparent  crystals  of  a fine  red  colour. 


COLUMBIUM. 


357 


It  is  very  fusible  and  volatile,  and  Its  vapour  is  red  like  that  of  nitrous 
acid.  The  difference  between  this  compound  and  the  chloride  first  de- 
scribed has  not  yet  been  discovered. 

The  compounds  of  tung'sten  with  the  other  simple  substances  have 
been  very  little  or  not  at  all  examined. 

Cohtmbium, 

This  metal  was  discovered  in  1801  by  Mr.  Hatchett,  who  detected  it 
in  a black  mineral  belonging  to  the  British  Museum,  supposed  to  have 
come  from  Massachusetts  in  North  America;  and,  from  this  circum- 
stance, applied  to  it  the  name  of  columblum.  About  two  years  after, 
M.  Ekeberg,  a Swedish  chemist,  extracted  the  same  substance  from 
tantalite  and  yttro-tantallte;  and,  on  the  supposition  of  its  being  differ- 
ent from,  columbium,  described  it  under  the  name  of  tantalum.  The 
identity  of  these  metals,  however,  was  established  in  the  year  1809  by 
Dr.  Wollaston. 

Columbic  acid  is  with  difficulty  reduced  to  the  metallic  state  by  the 
action  of  heat  and  cliarcoal;  but  Berzelius  succeeded  in  obtaining  this 
metal  by  the  same  process  which  he  employed  in  the  preparation  of 
zirconium  and  silicium,  namely,  by  heating  potassium  with  the  double 
fluoride  of  potassium  and  columbium.  {Lehrhuch  der  Chemie^  ii.  120.) 
On  washing  the  reduced  mass  with  hot  water,  in  order  to  remove  the 
fluoride  of  potassium,  columbium  is  left  in  the  form  of  a black  pow- 
der. In  this  state  it  does  not  conduct  electricity;  but  in  a denser  state 
it  is  a perfect  conductor.  By  pressure  it  acquires  metallic  lustre,  and 
has  an  iron-gray  colour.  It  is  not  fusible  at  the  temperature  at  which 
glass  is  fused.  When  heated  in  the  open  air  it  takes  fire  considerably 
below  the  temperature  of  ignition,  and  glows  with  a vivid  light,  yield- 
ing columbic  acid.  It  is  scarcely  at  all  acted  on  by  the  sulphuric,  mu- 
riatic, or  nitro-muriatic  acid;  whereas  it  is  dissolved  with  heat  and  dis- 
engagement of  hydrogen  gas  by  hydrofluoric  acid,  and  still  more  easily 
by  a mixture  of  nitric  and  hydrofluoric  acids.  It  is  also  converted  into 
columbic  acid  by  fusion  with  hydrate  of  potassa,  the  hydrogen  gas  of 
the  water  being  evolved. 

Columbium  unites  with  oxygen  in  two  proportions,  giving  rise  to  an 
oxide  and  an  acid.  The  oxygen  in  these  compounds  is  in  the  ratio  of 
2 to  3,  and  the  experiments  of  Berzelius  lead  to  the  inference  that  the 
oxide  is  formed  of  185  parts  or  one  equivalent  of  columbium,  united 
with  16  parts  or  two  equivalents  of  oxygen;  and  the  acid  of  one  equiv- 
alent of  the  metal  and  three  of  oxygen.  But  the  combining  proportion 
of  the  acid  is  not  known  with  such  certainty  as  altogether  to  establish 
the  accuracy  of  this  opinion. 

The  oxide  of  columbium  is  generated  by  placing  columbic  acid  in  a 
crucible  lined  with  charcoal,  luting  carefully  to  exclude  atmospheric 
air,  and  exposing  it  for  an  hour  and  a half  to  intense  heat.  The  acid, 
where  in  direct  contact  with  charcoal,  is  entirely  reduced;  but  the  film 
of  metal  is  very  thin.  The  interior  portions  are  pure  oxide  of  a dark- 
gray  colour,  very  hard  and  coherent.  When  reduced  to  pow'der,  its 
colour  is  dark  brown.  It  is  not  attacked  by  any  acid,  even  by  nitro- 
hydrofluoric  acid;  but  it  is  converted  into  columbic  acid  either  by  fu- 
sion with  hydrate  of  potassa,  or  deflagration  with  nitre.  When  heated 
to  low  redness  it  takes  fire,  and  glows,  yielding  a light-gray  powder;  but 
in  this  way  it  is  never  completely  oxidized.  Berzelius  states  that  this 
oxide,  in  union  with  protoxide  of  iron  and  a little  protoxide  of  manga- 
nese, occurs  at  Kirnito  in  Finland,  and  may  be  distinguished  from  the 
other  ores  of  columbium  by  yielding  a chestnut-brown  pow'der. 

Columbium  exists  in  most  of  its  ores  as  an  acid,  united  either  with 


358 


ANTIMONY. 


the  oxides  of  Iron  and  mang’anese,  as  in  tantalite,  or  with  the  earth 
yttria,  as  in  the  yttro-tantalite.  Tiiis  acid  is  obtained  by  fusing*  its  ore 
with  tliree  or  four  times  its  weight  of  carbonate  of  potassa,  when  a so- 
luble columbate  of  that  alkali  results,  from  which  columbic  acid  is  pre- 
cipitated as  a white  hydrate  by  acids.  Berzelius  also  prepares  it  by  fu- 
sion with  bisulphate  of  potassa. 

Hydrated  columbic  acid  is  tasteless,  and  insoluble  in  water;  but  when 
placed  on  moistened  litmus  paper,  it  communicates  a red  tinge.  It  is 
dissolved  by  the  sulphuric,  muriatic,  and  some  vegetable  acids;  but  it 
does  not  diminish  their  acidity,  or  appear  to  form  definite  compounds 
with  them.  With  alkalies  it  unites  readily;  and  though  it  does  not  neu- 
tralize their  properties  completely,  crystallized  salts  may  be  obtained  by 
evaporation.  When  the  hydrated  acid  is  heated  to  redness,  water  is 
expelled,  and  the  anhydrous  columbic  acid  remains.  In  this  state  it  is 
attacked  by  alkalies  only. 

Chloride  of  Columhium. — When  columbium  is  heated  in  chlorine  gas, 
it  takes  fire  and  burns  actively,  yielding  a yellow  vapour,  which  con- 
denses in  the  cold  parts  of  the  apparatus  in  the  form  of  a white  powder 
with  a tint  of  yellow.  Its  texture  is  not  in  the  least  crystalline.  By 
contact  with  water,  it  is  converted,  with  a hissing  noise  and  increase  of 
temperature,  into  columbic  and  muriatic  acids. 

Sulphuretof  Columhium. — This  compound,  first  prepared-by  Rosc,as 
generated,  with  the  phenomena  of  combustion,  when  columbium  is 
heated  to  commencing  redness  in  the  vapour  of  sulphur,  or  by  trans- 
mitting the  vapour  of  bisulphuret  of  carbon  over  columbic  acid  in  a 
porcelain  tube  at  a white  heat,  carbonic  oxide  being  also  evolved. 

Berzelius  has  also  described  a compound  of  columbium  and  fluorine. 
The  other  compounds  of  columbium  have  been  scarcely  or  not  at  all 
examined. 


SECTION  XVIII. 


ANTIMONY. 

Axttmoxy  sometimes  occurs  native;  but  its  only  ore  which  is  abun- 
dant, and  from  which  the  antimony  of  commerce  is  derived,  is  the  sul- 
phuret.  This  sulphuret  was  long  regarded  as  the  metal  itself,  and  was 
called  antimony i or  crude  antimony while  the  pure  metal  was  termed 
the  regulus  of  antimony. 

Metallic  antimony  may  be  obtained  either  by  heating  the  native  sul- 
phurct  in  a covered  crucible  with  half  its  weig'ht  of  iron  filings;  or  by 
mixing  it  with  two-tliirds  of  its  weight  of  cream  of  tartar  and  one-third 
of  nitre,  and  throwing  the  mixture,  in  small  successive  portions,  into  a 
red-hot  crucil)le.  By  the  first  process  the  sulphur  unites  with  iron,  and 
in  the  second  it  is  expelled  in  tlic  form  of  sulpliurous  acid;  while  the 
fused  antimony,  wliicli  in  both  cases  collects  at  the  bottom  of  the  cru- 
cible, may  be  drawn  ofl  and  received  in  moulds,  dhe  antimony,  thus 
obtained,  is  not  absolutely  pure;  and,  therefore,  for  chemical  purposes, 
sliould  be  procured  by  heating  tlie  oxide  with  an  equal  weight  of  cream 
of  tartar.  . . , . . . 

Antimony  is  a brittle  metal,  of  a white  colour  running  into  bluish- 
gray,  and  is  possessed  of  considerable  lustre.  Its  density  is  about  6.7. 
At  810''  T.  it  fuses;  and  when  slowly  cooled,  sometimes  crystallizes  in 


ANTIMONY, 


359 


octohedral  or  dodecahedral  crystals.  Its  structure  is  highly  lamellated.  It 
has  the  character  of  being  a volatile  metal;  but  Thenard  found  that  it 
bears  an  intense  white  heat  without  subliming,  provided  atmospheric  air 
be  perfectly  excluded,  and  no  gaseous  matters,  such  as  carbonic  acid  or 
watery  vapour,  be  disengaged  during  the  process.  Its  surface  tarnishes 
by  exposure  to  the  atmosphere;  and  by  the  continued  action  of  air  and 
moisture,  a dark  matter  is  formed,  which  Berzelius  regards  as  a definite 
compound.  It  appears,  however,  to  be  merely  a mixture  of  the  real 
protoxide  and  metallic  antimony.  Heated  to  a white  or  even  full-red 
heat  in  a covered  crucible,  and  then  suddenly  exposed  to  the  air,  it  in- 
flames, and  burns  with  a white  light. 

During  the  combustion  a white  vapour  rises,  which  condenses  on 
cool  surfaces,  frequently  in  the  form  of  small  shining  needles  of  silvery 
whiteness.  These  crystals  were  formerly  called  argentine  flowers  of  an- 
timony, and  in  chemical  works  are  generally  described  as  deutoxide  of 
antimony;  but  according  to  Berzelius  they  are  protoxide,  an  opinion 
which  I believe  to  be, correct. 

The  chemists  who  have  paid  most  attention  to  the  oxides  of  antimony 
are  Thenard,*  Proust, | Berzelius,^  and  Thomson. § The  former  main- 
tained the  existence  of  six,  the  second  of  two,  the  third  of  four,  and 
the  last  of  three  oxides  of  antimony.  The  opinion  of  Dr.  Thomson  is 
now  admitted  by  most  chemists;  and  there  is  reason  to  believe  that 
the  proportions  which  he  has  assigned  to  these  oxides  are  very  near  the 
truth. 


Protoxide 

Deutoxide 

Peroxide 


Antimony. 

44  or  one  equivalent. 

44  . . . 

44  . . . 


Oxygen. 

8 = 52 
12  = 56 
16  = 60 


Protoxide. — When  muriate  of  the  protoxide  of  antimony,  made  by 
boiling  the  sulphuret  in  muriatic  acid,  (page  252,)  is  poured  into  water, 
a white  curdy  precipitate,  formerly  called  powder  of  Algaroth,  sub- 
sides, which  is  a submuriate  of  the  protoxide.  H On  digesting  this  salt 
in  a solution  of  carbonate  of  potassa,  and  then  edulcorating  it  with 
water,  the  protoxide  is  obtained  in  a state  of  purity.  It  may  also  be 
procured  directly  by  adding  carbonate  of  potassa  or  soda  to  a solution 
of  tartar  emetic.  It  is  also  generated  during  the  combustion  of  metallic 
antimony;  but  as  thus  formed,  I apprehend  it  is  not  quite  pure. 

Protoxide  of  antimony,  when  prepared  in  the  moist  way,  is  a white 
powder  with  a somewhat  dirty  appearance.  When  heated  it  acquires  a 
yellow  tint,  and  at  a dull-red  heat  in  close  vessels  it  is  fused,  yielding 
a yellow  fluid,  which  becomes  an  opake  grayish  crystalline  mass  on 
cooling.  It  is  very  v61atile,  and  if  protected  from  atmospheric  air  may 


* An.  de  Chimie,  vol.  xxxii.  f Journal  de  Physique,  vol.  Iv. 

t An.  de  Chimie,  vol.  Ixxxiii,  and  An.  de  Ch.  et  de  Ph.  vol.  xvii, 

§ First  Principles,  vol.  ii. 

H As  there  is  no  instance  known  of  an  insoluble  muriate,  it  is  not 
probable  that  the  powder  of  Algaroth  is  a submuriate  of  the  protoxide 
of  antimony.  Dr.  Duncan  suggests  that  this  preparation  is  probably 
Dr.  Thomson’s  dichloride  of  antimony,  consisting  of  one  equivalent  of 
chlorine  and  two  equivalents  of  antimony;  but  this  is  not  likely,  as  Dr. 
Thomson  states  that  the  dichloride  is  partially  soluble  in  water.  Upon 
the  whole,  it  seems  most  probable,  that  the  powder  of  Algaroth  is  es- 
sentially the  protoxide  of  antimony  merely  contaminated  with  a small 
portion  of  muriatic  acid.  B. 


360 


ANFIMONY. 


be  sublimed  completely  without  chang’e.  When  heated  in  open  vessels 
it  absorbs  oxyg-en;  and  when  the  temperature  is  suddenly  ruisc-d,  and 
the  oxide  is  porous,  it  takes  fire  and  burns.  In  both  cases  the  deutox- 
ide  is  g’enerated.  It  is  the  only  oxide  of  antimony  which  forms  regular 
salts  with  acids,  and  is  the  base  of  the  medicinal  preparation  tartar 
emetic,  the  tartrate  of  antimony  and  potassa.  Most  of  its  salts,  how- 
ever, are  either  insoluble  in  water,  or,  like  muriate  of  antimony,  are 
decomposed  by  it,  owing  to  the  affinity  of  that  fluid  for  the  acid  being 
greater  than  that  of  the  acid  for  oxide  of  antimony.  This  oxide  is, 
therefore,  a feeble  base;  and,  indeed,  possesses  the  property  of  unit- 
ing with  alkalies.  To  the  foi-egoing  remark,  however,  tartrate  of  an- 
timony and  potassa  is  an  exception;  for  it  dissolves  readily  in  water 
without  change.  By  excess  of  tartaric  or  muriatic  acid,  the  insoluble 
salts  of  antimony  may  be  rendered  soluble  in  water. 

The  presence  of  antimony  in  solution  is  easily  detected  by  sulphu- 
retted hydrogen.  I'his  gas  occasions  an  orang'e-coloured  precipitate, 
hydrated  protosulphuret  of  antimony,  which  is  soluble  in  pure  potassa, 
and  is  dissolved  by  disengagement  of  sulphuretted  hydrogen  gas  by  hot 
muriatic  acid,  forming  a solution  from  which  the  white  submuriate  is 
precipitated  by  water.* 

Deutoxide. — When  metallic  antimony  is  digested  in  strong  nitric  acid, 
the  metal  is  oxidized  at  the  expense  of  the  acid,  and  a white. hydrate  of 
the  peroxide  is  formed;  and  on  exposing  this  substance  to  a red  heat,  it 
gives  out  water  and  oxygen  gas,  and  is  converted  into  the  deutoxide. 
It  is  also  generated  when  the  protoxide  is  exposed  to  heat  in  open  ves- 
sels. Thus,  on  heating  sulphuret  of  antimony  with  free  exposure  to 
the  air,  sulphurous  acid  and  protoxide  of  antimony  are  generated;  but 
on  continuing  the  roasting  until  all  the  sulphur  is  burned,  the  protoxide 
gradually  absorbs  oxygen  and  passes  into  the  deutoxide.  Hence  this 
oxide  is  formed  in  the  process  for  preparing  the  pulvis  antimonialis  of 
the  pharmacopoeia. 

Deutoxide  of  antimony  is  white,  infusible,  and  fixed  in  the  fire,  two 
characters  by  which  it  is  readily  distinguished  from  the  protoxide.  It  is 
insoluble  in  water,  and  likewise  in  acids  after  being  heated  to  redness. 
It  combines  with  alkalies,  and  for  this  reason  it  has  been  called  antimo- 
nious  acid,  and  its  salts  antimonites,  by  Berzelius.  Antimonious  acid  is 
precipitated  from  these  salts  by  acids  as  a hydrate,  which  reddens  litmus 
paper,  and  is  dissolved  by  muriatic  and  tartaric  acids,  though  without 
appearing  to  form  with  them  definite  compounds. 

Peroxide  of  antimony,  or  antimonic  acid.,  is  obtained  as  a white  hy- 
drate, either  by  digesting  the  metal  in  strong  nitric  acid  or  by  dissolving 
it  in  nitro-muriatic  acid,  concentrating  by  heat  to  expel  excess  of  acid, 
and  throwing  the  solution  into  water.  When  recently  precipitated  it 
reddens  litmus  paper,  and  may  then  be  dissolved  in  water  by  means  of 
muriatic  or  tartaric  acid.  It  does  not  enter  into  definite  combination 
with  acids,  but  with  alkalies  forms  salts,  which  are  called  antimoniates. 
When  the  hydrated  peroxide  is  cxj)Osed  to  a temperature  of  500®  or 
600®  F.  the  water  is  evolved,  and  the  pure  peroxide  of  a yellow  colour 
remains.  Jn  this  state  it  resists  the  action  of  muriatic  acid.  Wdien 
exposed  to  a red  heat,  it  parts  with  oxygen,  and  is  converted  into  the 
deutoxide. 

Ckloridca  of  Jlntirnony.  — When  antimony  in  powder  is  thrown  into  a 


• For  an  account  of  the  means  of  detecting  antimony  in  mixed  fluids, 
for  the  purpose  of  judicial  iiujuiry,  the  reader  may  consult  an  essay  on 
that  subject  in  the  Medical  and  Surgical  Journal  for  1827. 


ANTIMONY. 


361 


jar  of  chlorine  gas,  combustion  ensues,  and  the  protochloride  of  anti- 
mony is  generated.  The  same  compound  may  be  formed  by  distilling 
a mixture  of  antimony  with  about  twice  and  a half  its  weight  of  corro- 
sive sublimate,  when  the  volatile  chloride  of  antimony  passes  over  into 
the  recipient,  and  metallic  mercury  remains  in  the  retort.  At  common 
temperatures  it  is  a soft  solid,  thence  called  hutter  of  antimony ^ which 
is  liquefied  by  gentle  heat,' and  crystallizes  on  cooling.  It  deliquesces 
on  exposure  to  the  air;  and  when  mixed  with  water,  is  converted  into 
muriatic  acid  and  protoxide  of  antimony.  If  a large  quantity  of  water 
is  employed,  the  whole  of  the  oxide  subsides  as  the  sub  muriate. 

The  bichloride  is  generated  by  passing  dry  chlorine  gas  over  heated 
metallic  antimony.  It  is  a transparent  volatile  liquid,  which  emits 
fumes  on  exposure  to  the  air.  Mixed  with  water,  it  is  converted  into 
muriatic  acid  and  the  hydrated  peroxide,  which  subsides.  It  contains 
twice  as  much  chlorine  as  the  protochloride,  or  is  composed  of  one 
equivalent  of  antimony,  and  two  equivalents  of  chlorine.  (Rose  in  the 
Annals  of  Philosophy,  N.  S.  x.) 

Dr.  Thomson,  in  his  “First  Principles,^’  has  described  another  chlo- 
ride of  antimony,  composed  of  one  equivalent  of  chlorine  and  two 
equivalents  of  the  metal.  It  is,  therefore,  a dichloride. 

Bromide  of  Antimony. — The  union  of  bromine  and  antimony  is 
attended  with  disengagement  of  heat  and  light,  and  the  compound  is 
readily  obtained  by  distillation,  as  in  the  process  for  preparing  bromide 
of  arsenic.  It  is  solid  at  common  temperatures,  is  fused  at  206®  F., 
and  boils  at  518®  F.  It  is  colourlessj  and  crystallizes  in  needles;  it  at- 
tracts moisture  from  the  air,  and  is  decomposed  by  water. 

Sulphurets  of  Antimony. — The  native  sulphuret  of  antimony  is  of  a 
lead-gray  colour,  and  though  generally  compact,  sometimes  occurs  in 
acicular  crystals,  or  in  rhombic  prisms.  When  heated  in  close  vessels, 
it  enters  into  fusion  without  undergoing  any  other  chang'e.  Boiled  in 
hot  muriatic  acid,  it  is  dissolved  with  disengagement  of  sulphuretted 
hydrogen,  llie  experiments  of  Berzelius,  Dr.  Davy,  and  Thomson, 
leave  no  doubt  of  its  being  analogous  in  composition  to  the  protoxide  of 
antimony,  that  is,  consisting  of  one  equivalent  of  each  of  its  elements. 
It  may  be  formed  artificially  by  fusing  together  antimony  and  sulphur, 
or  by  transmitting  a current  of  sulphux’etted  hydrogen  gas  through  a 
solution  of  tartar  emetic.  The  orange  precipitate,  which  subsides  in 
the  last  mentioned  process,  is  commonly  regarded  as  hydrosulphuret  of 
the  oxide  of  antimony.  In  my  opinion  it  is  a hydrated  sulphuret  of  the 
metal;  for  when,  well  washed  and  treated  by  sulphuric  acid,  it  does  not 
yield  a trace  of  sulphuretted  hydrogen.  The  accuracy  of  this  view  has 
been  lately  confirmed  by  Gay  Lussac.  (An.  de  Ch.  et  de  Ph.  xlii.  87.) 

The  sesquisulphuret  is  formed,  according  to  Rose,  by  tranvSmitting 
sulphuretted  hydrogen  gas  through  a solution  of  deutoxide  of  antimony 
in  dilute  muriatic  acid.  (An.  of  Phil.  N.  S.  x ) 

Rose  formed  the  hisulphurety  consisting  of  one  equivalent  of  antimo- 
ny and  two  of  sulphur,  by  the  action  of  sulphuretted  hydrogen  on  a 
solution  of  the  peroxide.  The  golden  sulphuret,  prepared  by  boiling 
sulphuret  of  antimony  and  sulphur  in  solution  of  potassa,  a process 
which  is  not  adopted  by  either  of  our  colleges,  is  a bisulphuret. 

M.  Rose  has  likewise  demonstrated  that  the  red  antimony  of  miner- 
alogists {rothspiesghnzers)  is  a compound  of  one  equivalent  of  the  pro- 
toxide combined  with  two  equivalents  of  the  protosulphuret  of  anti- 
mony; and  it  may  hence  be  called  an  oxy -sulphuret.  The  pharmaceu- 
tic preparations  known  by  the  terms  of  glass,  liver,  and  crocus  of  anti- 
mony, are  of  a similar  nature,  though  less  definite  in  composition,  owing 
to  the  mode  by  which  they  are  prepared.  They  are  made  by  roasting 


362 


URANIUM. 


the  native  siilphuret,  so  as  to  form  sulphurous  acid  and  oxide  of  antimo- 
ny, and  then  vitrifying*  the  oxide  together  with  the  undecomposed  ore, 
by  means  of  a strong  heat.  The  product  will  of  course  differ  according 
as  more  or  less  of  the  siilphuret  escapes  oxidation  during  the  process. 

When  siilphuret  of  antimony  is  boiled  in  a solution  of  potassa  or  soda, 
a liquid  is  obtained,  from,  which,  on  cooling,  an  orange -red  matter  called 
kermes  mineral  is  deposited;  and  on  subsequently  neutralizing  the  cold 
solution  with  an  acid,  an  additional  quantity  of  a similar  substance,  the 
golden  siilphuret  of  the  Pharmacopoeia,  subsides.  These  compounds 
may  also  be  obtained  by  igniting  sulphuret  of  antimony  with  an  alkaline 
carbonate,  and  treating  the  product  with  hot  water;  or  by  boiling  the 
mineral  in  a solution  of  carbonate  of  soda  or  potassa.  The  finest  kermes 
is  obtained,  according  to  M.  Cluzel,  from  a mixture  of  4 parts  of  sul- 
phuret of  antimony,  90  of  crystallized  carbonate  of  soda,  and  1000  of 
w'ater.  Tiiese  materials  are  boiled  for  half  or  three-quarters  of  an  hour; 
the  hot  solution  is  filtered  into  a warm  vessel,  in  order  that  it  may  cool 
slowly;  and  after  twenty-four  hours,  the  deposite  is  collected  on  a filter 
moderately  washed  with  cold  water,  and  dried  at  a temperature  of  70^ 
or  80^  p.  Kermes  is  considered  by  Berzelius  and  Rose  as  a hydrated 
protosulphuret,  and  it  was  described  as  such  in  the  last  edition  of  this 
work;  but  from  the  observations  lately  published  by  Gay-Lussac,  it  ap- 
pears to  be  ahydi'ated  oxy-sulphuret,  identical,  when  deprivedof  its  water, 
with  the  red  antimony  above  referred  to.  When  digested  in  a solution 
of  cream  of  tartar  or  tartaric  acid,  oxide  of  antimony  is  dissolved,  and 
a pure  sulphuret  remains;  and  on  reducing  it  by  means  of  heat  and 
hydrogen  gas,  sulphuretted  hydrogen  and  water  are  generated.  I'he 
golden  sulphuret  has  a similar  constitution;  but  its  colour  inclines  more 
to  the  orange,  and  it  commonly  contains  a little  free  sulphur. 

The  theory  of  the  formation  of  kermes,  as  given  by  Gay-Lussac,  is 
the  following.  A portion  of  potassa  and  sulphuret  of  antimony  ex- 
change elements  with  each  other,  yielding  sulphuret  of  potassium  and 
oxide  of  antimony:  the  latter,  combining  with  undecomposed  sulphuret 
of  antimony,  constitutes  the  oxy-sulphuret,  which  is  freely  dissolved 
by  the  hot  alkaline  solution,  and  is  deposited  as  it  cools.  The  addition 
of  an  acid  throws  down  an  additional  quantity  of  the  same  substance, 
accompanied  with  evolution  of  sulphuretted  hydrogen,  arising  from  de- 
composed sulphuret  of  potassium.  Of  course  the  oxygen  which  unites 
with  antimony,  and  which  Gay-Lussac  derives  from  potassa,  may  be 
ascribed  to  decomposition  of  water,  the  hydrogen  of  which  gives  rise  to 
sulphuretted  hydrogen. 


SECTION  XIX. 


URANIUM— CERIUM. 

Uranium. 

UuANiuTvi  was  iliscovcrcd  in  the  year  1789  by  Klaproth  in  a mineral  of 
Saxony,  called  from  its  black  colom'  pi tchhlende, yh\ch  consists  of  pro- 
toxide of  uranium  and  oxide  of  iron.  Ivrom  this  ore  the  uranium  may 
be  conveniently  extracted  by  the  following  process.  After  heating  the 
mineral  to  redness,  and  reducing  it  to  fine  powder,  it  is  digested  in  pure 


URANIUM. 


363 


nitric  acid  diluted  with  three  or  four  parts  of  water,  taking  the  precau- 
tion to  employ  a larger  quantity  of  the  mineral  than  the  nitric  acid 
present  can  dissolve.  By  this  mode  of  operating,  the  protoxide  is  con- 
verted into  peroxide  of  uranium,  which  unites  with  the  nitric  acid  almost 
to  the  total  exclusion  of  the  iron.  A current  of  sulphuretted  hydrogen 
gas  is  then  transmitted  through  the  solution,  in  order  to  separate  lead 
and  copper,  the  sulphurets  of  which  are  always  mixed  with  pitchblende. 
The  solution  is  boiled  to  expel  free  sulphuretted  hydrogen,  and  after 
being  concentrated  by  evaporation,  is  set  aside  to  crystallize.  The  ni- 
trate of  uranium  is  gradually  deposited  in  flattened  four-sided  prisms  of 
a beautiful  lemon-yellow  colour. 

The  properties  of  metallic  uranium  are  as  yet  known  imperfectly. 
It  was  prepared  by  Arfwedson  by  conducting  hydrogen  gas  over  the 
protoxide  of  uranium  heated  in  a glass  tube.  The  substance  obtained 
by  this  process  was  crystalline,  of  a metallic  lustre,  and  of  a reddish- 
brown  colour.  It  suffered  no  change  on  exposure  to  air  at  common 
temperatures;  but  when  heated  in  open  vessels  it  absorbed  oxygen,  and 
was  reconverted  into  the  protoxide.  From  its  lustre  it  was  inferred  to 
be  metallic  uranium. 

Chemists  are  acquainted  with  two  compounds  of  uranium  and  oxygen, 
the  composition  of  which  has  been  minutely  studied  by  Arfwedson^  and 
Thomson.  (First  Principles,  ii.)  According  to  the  chemist  last  men- 
tioned, whose  experiments  are  the  most  recent,  the  equivalent  of  ura- 
nium is  208,  and  its  oxides  are  composed  of 

Uranium,  Oxygen, 

Protoxide  . 208  . 8 « 216 

Peroxide  . 208  . 16  =x=  224 

According  to  the  analyses  of  Arfwedson,  216  is  the  atomic  weight  of 
uranium,  and  the  oxygen  in  its  two  oxides  is  in  the  ratio  of  1 to  1.5; 
and  Berzelius,  from  the  composition  of  three  salts  of  uranium,  has  ar- 
rived at  a similar  conclusion. 

The  protoxide  of  uranium  is  of  a very  dark-green  colour,  and  is  ob- 
tained by  decomposing  nitrate  of  the  peroxide  by  heat.  It  is  exceed- 
ingly infusible,  and  bears  any  temperature  hitherto  tried  without 
change.  It  unites  with  acids,  forming  salts  of  a green  colour.  It  is 
readily  oxidized  by  nitric  acid,  and  yields  a yellow  solution  which  is  a 
pernitrate.  The  protoxide  is  employed  in  the  arts  for  giving  a black 
colour  to  porcelain. 

Peroxide  of  uranium  is  of  a yellow  or  orange  colour,  and  most  of  its 
salts  have  a similar  tint.  It  not  only  combines  with  acids,  but  likewise 
unites  with  alkaline  bases,  a property  which  was  first  noticed  by  Arf- 
wedson. It  is  precipitated  from  acids  as  a yellow  hydrate  by  pure  al- 
kalies, fixed  or  volatile;  but  retains  a portion  of  these  bases  in  combi- 
nation. It  is  thrown  down  as  a carbonate  by  carbonate  of  potassa;  but 
it  is  not  precipitated  at  all  by  the  carbonates  of  soda  or  ammonia,  a cir- 
cumstance which  affords  an  easy  method  of  separating  uranium  from 
iron.  It  is  not  precipitated  by  sulphuretted  hydrogen.  With  ferrocy- 
anate  of  potassa  it  gives  a brownish-red  precipitate,  not  unlike  ferro- 
cyanate  of  the  peroxide  of  copper. 

Peroxide  of  uranium  is  decomposed  by  a strong  heat,  and  converted 
into  the  protoxide.  From  its  affinity  for  alkalies,  it  is  difficult  to  obtain 
it  in  a state  of  perfect  purity.  It  is  employed  in  the  arts  for  giving  an 
orange  colour  to  porcelain. 


♦ Annals  of  Philosophy,  N.  S.  vii. 


364 


CERIUM. 


^ Sulphxiret  of  uranhim  may  be  formed  by  transmitting*  the  vapour  of 
bisulphuret  of  carbon  over  protoxide  of  aranium  stro'ng*ly  licated  in  a 
tube  of  porcelain.  (Rose.)  It  is  of  a dark-gray  or  nearly  black  colour, 
is  converted  into  protoxide  when  heated  in  the  open  air,  and  is  readily 
dissolved  by  nitric  acid.  Muriatic  acid  attacks  it  feebly. 

Cerium, 

Cerium  was  discovered  in  the  year  1803  by  MM.  Hisinger  and  Berze- 
lius, in  a rare  Swedish  mineral  known  by  the  name  of  cerite,  and  its 
existence  was  recognized  about  the  same  time  by  Klaproth.  Ur.  Thom- 
son has  since  found  it  to  the  extent  of  thirty-four  per  cent,  in  a mineral 
from  Greenland,  called  Allanite,  in  honour  of  Mr.  Allan,  who  first  dis- 
tinguished it  as  a distinct  species. 

The  properties  of  cerium  are  in  a great  measure  unknown.  It  ap- 
pears from  the  experience  of  Vauquelin,  who  obtained  it  in  minute 
buttons  not  larger  than  the  head  of  a pin,  that  it  is  a white  brittle 
metal,  which  resists  the  action  of  nitric,  but  is  dissolved  by  nitro-mu- 
riatic  acid.  According  to  an  experiment  made  by  Mr.  Children  and  Dr. 
Thomson,  metallic  cerium  is  volatile  in  very  intense  degrees  of  heat. 
(Annals  of  Philosophy,  vol.  ii.) 

Oxides  of  Cerium, — Cerium  unites  with  oxygen  in  two  proportions, 
and  the  composition  of  the  resulting  oxides  has  been  particularly  stu- 
died by  M.  Hisinger.  (An.  of  Phil,  iv.)  Dr.  Thomson  has  likewise 
made  experiments  on  the  subject,  and  infers  from  data  furnished 
partly  by  himself  and  partly  by  M.  Hisinger,  that  50  is  the  atomic 
weight  of  cerium,  and  that  its  oxides  are  thus  constituted.  (First  Prin- 
ciples, i.): — 

Cerium,  Oxygen, 

Protoxide  . 50  . 8 = 58 

Deutoxide  . 50  . 12  ==  62 

Protoxide  of  cerium  is  a white  powder,  which  is  insoluble  in  water, 

and  forms  salts  with  acids,  all  of  which,  if  soluble,  have  an  acid  re- 
action. Exposed  to  the  air  at  common  temperatures  it  suffers  no 
change;  but  if  heated  in  open  vessels,  it  absorbs  oxygen  and  is  con- 
verted into  the ‘peroxide.  It  is  precipitated  from  its  salts  as  a white  hy- 
drate by  pure  alkalies;  as  a w^hite  carbonate  by  alkaline  carbonates,  but 
is  redissolved  by  the  precipitant  in  excess;  and  as  a white  oxalate  by 
oxalate  of  ammonia. 

Peroxide  of  cerium  is  of  a fawn-red  colour.  It  is  dissolved  by  several 
of  the  acids,  but  is  a weaker  base  than  the  protoxide.  Digested  in 
muriatic  acid,  chlorine  is  disengaged  and  a protomuriate  results. 

Tlie  most  convenient  method  of  extracting  pure  oxide  of  cerium  from 
cerite  is  by  the  process  of  Laugier.  After  reducing  cerite  to  powder, 
it  is  dissolved  by  nitro-muriatic  acid,  and  the  solution  is  evaporated  to 
perfect  dryness,  ’'fhe  soluble  parts  are  then  redissolved  by  water,  and 
an  excess  of  ammonia  is  added.  The  precipitate  thus  formed,  consist- 
ing of  the  oxides  of  iron  and  cerium,  is  well  washed  and  afterwards  di- 
gested in  a solution  of  oxalic  acid,  which  dissolves  the  iron,  and  forms 
an  insoluble*  oxalate  with  tlic  cerium.  By  heating  this  oxalate  to  redness 
in  an  open  fire,  the  acid  is  decomposed,  and  the  peroxide  of  cerium  is 
obtained  in  a pure  state. 

Sulphur  el  of  Cerium. — Dr.  Mosander  has  succeeded  in  forming  this 
compound  by  two  different  processes.  The  first  method  is  by  trans- 
mitting tlie  vaj)Our  of  sul[)huret  of  carbon  over  carbonate  of  cerium  at 
a red  heat;  and  tlie  second  is  by  fusing  oxide  of  cerium  at  a white  heat 
>vith  a large  excess  of  sulphuret  of  potassium  {Jicpwr  sulpliuris,)  and 


BISMUTH. 


365 


afterwards  removing  the  soluble  parts  by  water.  The  product  of  the 
first  operation  is  porous,  light,  and  of  a red  colour  like  red  lead;  and 
that  of  the  second  is  in  small  brilliant  scales,  and  of  a yellow  colour, 
like  aicrum  musivum.  These  sulphurets,  though  different  in  appear- 
ance, are  similar  in  point  of  composition,  containing  26  per  cent,  of 
sulphur.  They  are  insoluble  in  water,  but  are  dissolved  in  acids  with 
evolution  of  sulphuretted  hydrogen  gas,  without  any  residuum  of  sul- 
phur. (Philos.  Mag.  and  Annals,  i.  71.) 


SECTION  XX. 

BISMUTH.— TITANIUM.— TELLURIUM. 

Bismuth, 

Bismuth  is  found  in  the  earth  both  native  and  in  combination  with 
other  substances,  such  as  sulphur,  oxygen,  and  arsenic.  That  which 
is  employed  in  the  arts  is  derived  chiefly  from  native  bismuth,  and  com- 
monly contains  small  quantities  of  sulphur,  iron,  and  copper.  It  may 
be  obtained  pure  for  chemical  purposes  by  heating  the  oxide  or  subni- 
trate to  redness  along  with  charcoal. 

Bismuth  has  a reddish-white  colour  and  considerable  lustre.  Its  struc- 
ture is  highly  lamellated,  and  when  slowly  cooled,  it  crystallizes  in 
octohedrons.  Its  density  is  about  10.  It  is  brittle  when  cold,  but  may 
be  hammered  into  plates  while  warm.  At  476^  F.  it  fuses,  and  sub- 
limes in  close  vessels  at  about  30®  Wedgwood.  It  is  a less  perfect 
conductor  of  caloric  than  most  other  metals. 

Bismuth  undergoes  little  change  by  exposure  to  air  at  common  tem- 
peratures. When  fused  in  open  vessels,  its  surface  becomes  covered 
with  a gray  film,  which  is  a mixture  of  metallic  bismuth  with  the  oxide 
of  the  metal.  Heated  to  its  subliming  point  it  burns  with  a bluish-vrliite 
flame,  and  emits  copious  fumes  of  oxide  of  bismuth.  The  metal  is  at- 
tacked with  difficulty  by  muriatic  or  sulphuric  acid,  but  it  is  readily 
oxidized  and  dissolved  by  nitric  acid. 

Oxide  of  Bismuth,— TWis  metal  unites  with  oxygen  in  one  proportion 
only,  forming  a yellow-coloured  oxide,  which  may  be  easily  procured 
by  heating  the  subnitrate  to  redness.  At  a full  red  heat  it  is  fused,  and 
yields  a transparent  yellow  glass.  At  a still  higher  temperature  it  is 
sublimed.  It  unites  with  acids,  and  most  of  its  salts  are  white.  Ac- 
cording to  the  experiments  of  Dr.  J.  Davy,^  it  is  composed  of  72  parts 
of  bismuth,  and  8 parts  of  oxygen;  and  therefore  72  is  the  atomic 
weight  of  bismuth,  and  80  the  equivalent  of  its  oxide.  This  result  is 
confirmed  by  the  researches  of  Dr.  Thomson,  f 

When  nitrate  of  bismuth,  either  in  solution  or  in  crystals,  is  put  into 
water,  a copious  precipitate,  the  subnitrate,  of  a beautifully  white  col- 
our subsides,  which  was  formerly  called  the  magistery  of  bismuth.  From 
its  whiteness  it  is  sometimes  employed  as  a paint  for  improving  the  com- 


* Philosophical  Transactions  for  1812.  f First  Principles,  vol.  i. 

31* 


366 


TH'ANIUM. 


plexion;  but  It  is  an  inconvenient  pigment,  owing  to  the  facility  with 
which  it  is  blackened  by  sulphuretted  hydrogen.  If  tlie  nitrate  witli 
which  it  is  made  contains  no  excess  of  acid,  and  a large  quantity  of 
water  is  employed,  the  whole  of  tlie  bismuth  is  separated  as  a subni- 
trate. By  this  cliaracter  bismuth  may  be  both  distinguished  and  sepa- 
rated from  other  metals. 

Chloride  of  Bismuth. — When  bismuth  inline  powder  is  introduced 
into  chlorine  gas,  it  takes  fire,  burns  with  a pale-blue  light,  and  is  con- 
verted into  a chloride,  formerly  termed  hiUter  of  bismuth.  It  may  be 
prepared  conveniently  by  heating  two  parts  of  corrosive  sublimate  with 
one  of  bismuth,  and  afterwards  expelling  the  excess  of  the  former, 
together  with  tlie  metallic  mercury,  by  heat. 

Chloride  of  bismuth  is  of  a grayish-white  colour,  opake,  and  of  a 
gTanular  texture.  ^ It  fuses  at  a temperature  a little  above  that  at  which 
the  metal  itself  is  liquefied,  and  bears  a red  heat  in  close  vessels 
without  subliming.  (Dr.  Davy.)  From  the  experiments  of  Drs.  Davy 
and  Thomson,  it  appears  to  consist  of  one  equivalent  of  each  of  its 
elements. 

Bromide  of  bismuth  is  prepared  by  heating  the  metal  with  a large 
excess  of  bromine  in  along  tube;  when  a gray-coloured  bromide  re- 
sidts,  similar  in  its  aspect  to  fused  iodine.  At  392'^  F.  it  enters  into  fu- 
sion, and  at  alow  red  heat  sublimes.  With  water  it  is  converted  into 
oxide  of  bismuth  and  hydrobromic  acid,  the  former  of  which  combines 
with  some  undecomposed  bromide  of  bismuth  as  an  oxy-bromide. 
(Serullas.) 

Sulphurei  of  Bismuth. — This  sulphuret  is  found  native,  and  may  be 
formed  artificially  by  fusing  bismuth  with  sulphur.  It  is  of  a lead-gray 
colour,  and  metallic  lustre.  The  experiments  of  Dr.  Davy,  Thomson, 
and  Lagerhielm^  leave  no  doubt  of  its  being  composed  of  one  equiva- 
lent of  bismuth  and  one  equivalent  of  sulphur.  I apprehend  the  dark- 
brown  precipitate  caused  by  the  action  of  sulphuretted  hydrogen  on  the 
salts  of  bismuth  is  likewise  a protosulphuret. 

Titanium, 

Titanium  was  first  recognized  as  a new  substance  by  Mr.  Gregor  of 
Cornwall,  and  its  existence  was  afterwards  established  by  Klaproth. -j- 
But  the  properties  of  the  metal  were  not  ascertained  in  a satisfactory  man- 
ner until  the  year  1822,  when  Dr.  Wollastont  was  led  to  examine  some 
minute  crystals  which  were  found  in  a slag  at  the  bottom  of  a smelting 
furnace  at  the  great  iron  works  at  Merthyr  Tydvil  in  Wales,  and  pre- 
sented to  him  by  the  Rev.  Dr,  Buckland.  These  crystals,  which  have 
since  been  found  at  other  iron  works,  are  of  a cubic  form,  and  in  col- 
our and  lustre  resemble  burnished  copper.  They  conduct  electricity, 
and  are  attracted  slightly  by  the  magnet,  a property  which  seems  ow- 
ing to  the  presence  of  a minute  quantity  of  iron.  Their  specific  gravity 
is  5.3;  and  tlicir  hardness  is  so  great,  that  they  scratch  a polished  sur- 
face of  rock  crystal.  They  are  exceedingly  infusible;  but  when  ex- 
posed to  the  united  action  of  heat  and  air,  tlieir  surface  becomes  cover- 
ed with  a purple-coloured  film  which  is  an  oxide.  They  resist  the 
action  of  nitric  and  nitro-muriatic  acids,  but  arc  completely  oxidized  by 
being  strongly  heated  with  nitre.  They  are  then  converted  Into  a white 
substance,  which  possesses  all  the  properties  of  peroxide  of  titanium. 
By  this  character  they  arc  proved  to  be  metallic  titanium. 


* Annals  of  iMiilosophy,  vol.  iv.  + Contributions,  vol.  i. 

\ Bhilosophical  'J'ransactions  for  the  year  1^3. 


TITANIUM. 


367 


Oxides  of  Titanium. — This  metal  has  probably  two  degrees  of  oxida- 
tion. The  protoxide  is  of  a purple  colour,  and  is  supposed  to  exist 
pure  in  the  mineral  called  anatase;  but  its  composition  and  chemical 
properties  are  unknown.  The  peroxide  exists  in  a nearly  pure  state  in 
titanite  or  rutile.  Menaccanite,  in  which  titanium  was  originally  dis- 
covered by  Mr.  Gregor,  is  a compound  of  the  oxides  of  titanium,  iron, 
and  manganese.  This  oxide  is  best  prepared  from  rutile.  The  mineral, 
after  being  reduced  to  an  exceedingly  fine  powder,  is  fused  in  a plati- 
num crucible  with  three  times  its  weight  of  carbonate  of  potassa,  and 
the  mass  afterwards  washed  with  water  to  remove  the  excess  of  alkali, 
A gray  mass  remains,  which  consists  of  potassa  and  oxide  of  titanium. 
This  compound  is  dissolved  in  concentrated  muriatic  acid;  and  on  dilut- 
ing with  water,  and  boiling  the  solution,  the  greater  part  of  the  oxide 
of  titanium  is  thrown  down.  It  is  then  collected  on  a filter,  and  well 
washed  with  water  acidulated  with  muriatic  acid.  In  this  state,  the 
oxide  is  not  quite  pure;  but  contains  a little  oxide  of  manganese  and 
iron,  derived  from  the  rutile.  The  best  mode  of  separating  these  im- 
purities is  to  digest  the  precipitate,  while  still  moist,  with  hydrosul- 
phuret  of  ammonia,  which  converts  the  oxides  of  iron  and  manganese 
into  sulphurets,  but  does  not  act  on  the  oxide  of  titanium.  The  two 
sulphurets  are  readily  dissolved  by  dilute  muriatic  acid;  and  the  oxide 
of  titanium,  after  being  collected  on  a filter  and  well  washed,  as  before, 
may  be  dried  and  heated  to  redness.  This  method  was  proposed  by 
Professor  Kose  of  Berlin.  (An.  de  Ch.  et  de  Physique,  xxiii.) 

Rose  has  since  simplified  the  process  in  the  following  manner.  Either 
rutile  or  titaniferous  iron,  after  being  pulverized  and  washed,  is  ex- 
posed in  a porcelain  tube,  at  a very  strong  red  heat,  to  a current  of 
sulphuretted  hydrogen  gas,  which  acts  upon  the  oxide  of  iron,  giving 
rise  to  water  and  sulphuret  of  iron.  As  soon  as  water  ceases  to  ap- 
pear, the  process  is  discontinued,  the  mass  digested  in  muriatic  acid  to 
remove  the  iron,  and  the  oxide  of  titanium  separated  from  adhering 
sulphur  by  heat.  A little  iron  is  still  usually  retained;  but  the  whole 
may  be  removed  by  a repetition  of  the  same  process.  An.  de  Ch.  et  de 
Ph.  xxxviii.  131.) 

Peroxide  of  titanium,  when  pure,  is  quite  white.  It  is  exceedingly 
infusible  and  difficult  of  reduction;  and  after  being  once  ignited,  it 
ceases  to  be  soluble  in  acids.  M.  Rose  has  observed  that,  like  silica,  it 
possesses  weak  acid  properties.  Thus  he  finds  that  it  unites  readily  with 
alkalies,  and  denies  its  power  of  acting  as  an  alkaline  base.  On  this 
account  he  proposes  for  it  the  name  of  titanic  acid.  In  the  state  of 
hydrate,  as  when  precipitated  from  muriatic  acid  by  boiling,  or  when 
combined  with  an  alkali  after  fusion,  it  has  a singular  tendency  to  pass 
through  the  pores  of  a filter  when  washed  with  pure  water;  but  the 
presence  of  a little  acid,  alkali,  or  a salt,  prevents  this  inconvenience. 
After  exposure  to  a red  heat  it  is  not  attacked  by  acids,  except  by  the 
hydrofluoric. 

If  previously  ignited  with  carbonate  of  potassa,  oxide  of  titanium  is 
soluble  in  dilute  muriatic  acid;  but  it  is  retained  in  solution  by  so  feeble 
an  attraction,  that  it  is  precipitated  merely  by  boiling.  It  is  likewise 
thrown  down  by  the  pure  and  carbonated  alkalies,  both  fixed  and  vola- 
tile. A solution  of  gall-nuts  causes  an  orange-red  colour,  which  is 
very  characteristic  of  the  presence  of  titanium;  an  effect  which  ap- 
pears owing  to  tannin  and  not  to  gallic  acid.  When  a rod  of  zinc  is 
suspended  in  the  solution,  a purple-coloured  powder,  probably  the 
protoxide,  is  precipitated,  which  is  gradually  reconverted  into  the  per- 
oxide. 

The  atomic  weight  of  titanium,  as  deduced  by  Dr.  Thomson  from 


368 


TELLURIUM. 


experiments  made  by  Rose  and  by  himself,  is  32.  ■ Titanic  acid  is  infer- 
red, from  the  same  data,  to  be  composed  of  32  parts  or  one  equivalent 
of  titanium,  and  16  parts  or  two  equivalents  of  oxygen.  The  equiva- 
lent of  peroxide  of  titanium,  and  its  chemical  constitution,  have  not, 
however,  been  ascertained  with  certainty. 

Chloride  of  Titanium. — This  substance  was  first  prepared  in  the  year 
1824  by  Mr.  George  of  Leeds,  by  transmitting  dry  chlorine  gas  over 
metallic  titanium  at  a red  heat.  At  common  temperatures  it  is  a trans- 
parent colourless  fluid,  of  considerable  specific  gravity,  boils  violently 
at  a temperature  a little  above  212°  F.,  and  condenses  again  without 
change.  In  open  vessels  it  is  attacked  by  the  moisture  of  the  atmos- 
phere, and  emits  dense  white  fumes  of  a pungent  odour  similar  to  that 
of  chlorine,  but  not  so  offensive.  On  adding  a few  drops  of  water  to  a 
few  drops  of  the  liquid,  a very  rapid,  almost  explosive,  disengagement 
of  chlorine  gas  ensues,  attended  with  considerable  increase  of  tempe- 
rature; and  if  the  water  is  not  in  excess,  a solid  residue  is  obtained. 
This  substance  is  deliquescent,  and  soluble  in  water;  and  its  solution 
possesses  all  the  characters  of  muriate  of  titanium. 

The  composition  of  this  chloride  has  not  been  satisfactorily  establish- 
ed; but  it  contains  more  chlorine  than  is  capable  of  uniting  with  the 
hydrogen  derived  from  water,  when  the  oxygen  of  that  fluid  converts 
titanium  into  the  peroxide. 

Sulphuret  of  Titanium. — This  compound  was  discovered  by  Rose, 
who  prepared  it  by  transmitting  the  vapour  of  bisulphuret  of  carbon 
over  peroxide  of  titanium  heated  to  whiteness  in  a tube  of  porcelain. 
It  occurs  in  thick  green  masses,  which  by  the  least  friction  acquire  a 
dark-yellow  colour  and  metallic  lustre.  When  heated  in  the  open  air 
it  is  converted  into  sulphurous  acid  and  oxide  of  titanium.  By  acids  it 
is  slowly  decomposed,  and  is  dissolved  by  muriatic  acid  with  disengage- 
ment of  sulphuretted  hydrogen  gas.  According  to  the  experiments  of 
Rose  it  is  proportional  to  peroxide  of  titanium,  consisting  of  32  parts  or 
one  equivalent  of  titanium,  and  32  parts  or  two  equivalents  of  sulphur. 

Tellurium. 

Tellurium  is  a rare  metal,  hitherto  found  only  in  the  gold  mines  of 
Transylvania,  and  even  there  in  very  small  quantity.  Its  existence  was 
inferred  by  Muller  in  the  year  1782,  and  fully  established  in  1798  by 
Klaproth.*  It  occurs  in  the  metallic  state,  chiefly  in  combination  with 
gold  and  silver. 

Tellurium  has  a tin-white  colour  running  into  lead- gray,  a strong 
metallic  lustre,  and  lamellated  texture.  It  is  very  brittle,  and  its  density 
is  6.115.  It  fuses  at  a temperature  below  redness,  and  at  a red  heat  is 
volatile.  When  heated  before  the  blowpipe,  it  takes  fire,  bui*ns  rapid- 
ly with  a blue  flame  bordered  with  green,  and  is  dissipated  in  gray- 
coloured  pungent  inodorous  fumes.  The  odour  of  decayed  horse-radish 
is  sometimes  emitted  during  the  combustion,  and  was  thought  by  Klap- 
roth to  ])e  peculiar  to  tellurium;  but  Berzelius  ascribes  it  solely  to  the 
presence  of  selenium. 

Oxide  of  Tellurium. — Tellurium  is  rapidly  oxidized  by  nitric  acid, 
and  a soluble  nitrate  of  tlie  oxide  results.  The  oxide  is  likewise  formed 
during  tlie  combustion  of  tlic  metal.  It  is  of  a gray  colour,  fuses  at  a 
red  heat,  and  at  a temperature  still  higher  sublimes.  When  heated 
before  the  blowpipe  on  cliarcoal  it  is  decomposed  with  violence.  It  has 
the  property  of  forming  salts  both  witli  acids  and  alkalies.  It  is  precipi- 


* Contributions,  vol.  iii. 


COPPER. 


369 


tated  from  its  solution  in  acids,  as  a hydrate,  by  all  the  alkalies  both 
pure  and  carbonated;  but  it  is  redissolved  by  an  excess  of  the  precipi- 
tant. Alkaline  hydrosulphurets  occasion  a black  precipitate,  which  is 
probably  a sulphuret  of  tellurium.  It  is  reduced  to  the  metallic  state, 
and  thrown  down  as  a black  powder,  by  insertion  of  a rod  of  zinc,  tin, 
antimony,  or  iron. 

According  to  Berzelius  oxide  of  tellurium  is  composed  of  nearly  32 
parts  of  the  metal,  and  8 parts  of  oxygen;  so  that  32  may  be  regarded 
as  the  atomic  weight  of  tellurium,  and  40  of  its  oxide.  This  result, 
however,  differs  considerably  from  that  of  Klaproth,  and,  therefore, 
requires  confirmation. 

Tellurium  unites  in  one  proportion  with  chlorine,  and  in  two  propor- 
tions with  hydrogen.  The  most  interesting  of  these  compounds  is  tel- 
luretted  hydrogen  gas,  discovered  in  the  year  1809  by  Sir  H.  Davy. 
This  gas  is  colourless,  has  an  odour  similar  to  that  of  sulphuretted  hydro- 
gen, and  is  absorbed  by  water,  forming  a claret-coloured  solution.  As 
it  unites  with  alkalies,  it  may  be  regarded  as  a feeble  acid.  It  reddens 
litmus  paper  at  first;  but  loses  this  property  after  being  washed  with 
water. 


SECTION  XXL 

COPPER. 

Native  copper  is  by  no  means  uncommon.  It  occurs  in  large  amor- 
phous masses  in  some  parts  of  America,  and  is  sometimes  found  in  octo- 
hedral  crystals,  or  in  forms  allied  to  the  octohedron.  The  metallic  cop- 
per of  commerce  is  extracted  chiefly  from  the  native  sulphuret;  espe- 
cially from  copper  pyrites,  a double  sulphuret  of  iron  and  copper.  The 
first  part  of  the  process  consists  in  roasting  the  ore,  so  as  to  burn  off 
some  of  the  sulphur,  and  leave  the  remainder  as  a subsulphate  of  the 
oxide  of  iron  and  copper.  The  mass  is  next  heated  with  some  un- 
roasted ore  and  siliceous  substances,  by  which  means  much  of  the  iron 
unites  in  the  state  of  black  oxide  with  silica,  and  rises  as  a fusible  slag 
to  the  surface;  while  most  of  the  copper  returns  to  the  state  of  sul- 
phuret. It  is  then  subjected  to  long-continued  roasting,  when  the 
greater  part  of  the  sulphur  escapes  as  sulphurous  acid,  and  the  metal 
is  oxidized;  after  which  it  is  reduced  by  charcoal,  and  more  of  the  iron 
separated  as  a silicate  by  the  addition  of  sand.  Lastly,  the  metal  is 
strongly  heated  while  a current  of  air  plays  upon  its  surface;  the  impu- 
rities, chiefly  sulphur  and  iron,  being  more  oxidable  than  copper,  com- 
bine with  oxygen  by  preference,  and  the  copper  is  at  length  left  in  a 
state  of  purity  sufficient  for  the  purposes  of  commerce. 

Copper  is  distinguished  from  all  other  metals,  titanium  excepted,  by 
having  a red  colour.  It  receives  a considerable  lustre  by  polishing.  Its 
density,  when  fused,  is  8.667,  and  it  is  increased  by  hammering.  It  is 
both  ductile  and  malleable,  and  in  tenacity  is  inferior  only  to  iron.  It  is 
hard  and  elastic,  and  consequently  sonorous.  In  fusibility  it  stands 
between  silver  and  gold. 

Copper  undergoes  little  change  in  a perfectly  dry  atmosphere,  but  is 
rusted  in  a short  time  by  exposure  to  air  and  moisture,  being  converted 
into  a green  substance,  carbonate  of  the  peroxide  of  copper.  At  a red 
heat  it  absorbs  oxygen,  and  is  converted  into  the  peroxide,  which  ap- 


370 


COPPER. 


pears  in  the  form  of  black  scales.  It  is  attacked  with  difficulty  by  mu- 
riatic and  sulphuric  acids,  and  not  at  all  by  the  vegetable  acids,  if 
atmospheric  air  be  excluded^  but  if  air  has  free  access,  the  metal  ab- 
sorbs oxygen  with  rapidity,  the  attraction  of  the  acid  for  the  oxide  of 
copper  co-operating  with  that  of  the  copper  for  oxygen.  Nitric  acid 
acts  with  violence  on  copper,  forming  a nitrate  of  the  peroxide. 

Oxides  of  Copper.  'I'lie  oxides  of  this  metal  have  been  studied  by 
Proust,  Chenevix,  I3r.  Davy,  and  Berzelius,  and  especially  the  former.* 
From  the  labours  of  these  chemists,  it  appears  that  there  are  but  two 
oxides  of  copper,  and  that  they  are  thus  constituted: — 

Copper.  Oxygen. 

Protoxide  . 64  . . 8 = 72 

Peroxide  - . 64  . . 16  = 80 

Consequently,  if  the  first  be  regarded  as  a compound  of  one  equiva- 
lent of  each  element,  64  is  the  atomic  weight  of  copper. 

The  red  or  protoxide  occurs  native  in  the  form  of  octohedral  crystals, 
and  is  found  of  peculiar  beauty  in  the  mines  of  Cornwall.  It  may  be 
prepared  artificially  by  mixing  64  parts  of  metallic  copper,  in  a state  of 
fine  division,  with  80  parts  of  the  peroxide,  and  heating  tlie  mixture  to 
redness  in  a close  vessel^  or  by  boiling  a solution  of  acetate  of  copper 
with  sugar,  when  the  peroxide  is  partially  deoxidized,  and. subsides  as 
a red  powder. 

Protoxide  of  copper  combines  with  the  muriatic,  sulphuric,  and  pro- 
bably with  several  other  acids,  forming  salts,  most  of  which  are  colour- 
less, and  from  which  the  protoxide  is  precipitated  as  an  orange-coloured 
hydrate  by  alkalies.  They  attract  oxygen  rapidly  from  the  atmosphere, 
by  which  they  are  converted  into  persalts.  The  protomuriate  is  easily 
formed  by  putting  a solution  of  the  permuriate  with  free  muriatic  acid 
and  copper  filings  into  a well-closed  glass  phial.  The  protoxide  of  cop- 
per is  soluble  in  ammonia,  and  the  solution  is  quite  colourless;  but  it 
becomes  blue  with  surprising  rapidity  by  free  exposure  to  air,  owing  to 
the  formation  of  the  peroxide. 

Peroxide  of  copper,  copper  black  of  mineralogists,  is  sometimes  found 
native,  being  formed  by  the  spontaneous  oxidation  of  other  ores  of 
copper.  It  may  be  prepared  artificially  by  calcining  metallic  copper, 
by  precipitation  from  the  persalts  of  copper  by  means  of  pure  potassa, 
and.  by  heating  nitrate  of  copper  to  redness. 

Peroxide  of  copper  varies  in  colour  from  a dark  brown  to  a bluish- 
black,  according  to  the  mode  of  formation.  It  undergoes  no  change 
by  heat  alone,  but  is  readily  reduced  to  the  metallic  state  by  heat  and 
combustible  matter.  It  is  insoluble  in  water,  and  does  not  affect  the 
vegetable  blue  colours.  It  combines  with  nearly  all  the  acids,  and  most 
of  its  salts  have  a green  or  blue  tint.  It  is  soluble  likewise  in  ammonia, 
forming  with  it  a deep-blue  solution,  a property  by  which  the  peroxide 
of  copper  is  distinguished  from  all  other  substances. 

Peroxide  of  copper  is  precipitated  by  pure  potassa  as  a blue  hy- 
drate, which  is  rendered  black  by  boiling,  the  hydrate  being  decom- 
posed at  that  temperature.  Pure  ammonia  at  first  throws  down  a green- 
ish-blue insoluble  subsulphatef,  which  is  rcdissolved  by  the  precipitant  in 


• Journal  de  Physique,  vol.  lix. 

f Dr.  'ruriTcr  lias  here  taken  it  for  granted  that  the  ammonia  is  added 
to  a solution  of  tlie  sulpliate  of  copper.  I'hc  sentence,  to  make  it  intel- 
ligible to  tlie  student,  ought  to  read  thus:  “From  the  sulphate  of  cop- 
per, pure  ammonia  at  first  throws  down,”  &c.  B. 


COPPER, 


371 


excess,  and  forms  the  deep-blue  ammoniacal  sulphate  of  copper.  Alkaline 
carbonates  cause  a bluish-green  precipitate,  carbonate  of  copper,  which 
is  redissolved  by  an  excess  of  carbonate  of  ammonia.  It  is  precipitated  as  a 
dark-brown  bisulphuret  by  sulphuretted  hydrogen,  and  as  a reddish- 
brown  ferrocyanate  by  ferrocyanate  of  potassa.  It  is  thrown  down  of  a 
yellowish- white  colour  by  albumen,  and  M.  Orfila  has  proved  that  this 
compound  is  inert,  so  that  albumen  is  an  antidote  to  poisoning  by  copper. 

Copper  is  separated  in  the  metallic  state  by  a rod  of  iron  or  zinc. 
The  copper  thus  obtained,  after  being  digested  in  a dilute  solution  of 
muriatic  acid,  is  chemically  pure. 

The  best  mode  of  detecting  copper,  when  supposed  to  be  present  in 
mixed  fluids,  is  by  sulphuretted  hydrogen.  The  sulphuret,  after  being 
collected,  and  heated  to  redness  in  order  to  char  any  organic  substances, 
should  be  placed  on  a piece  of  porcelain,  and  be  digested  in  a few 
drops  of  nitric  acid.  Sulphate  of  copper  is  formed,  which,  when  eva- 
porated to  dryness,  strikes  the  characteristic  deep  blue  on  the  addition 
of  ammonia. 

The  red  oxide  of  copper  is  by  some  chemists  supposed  to  be  a sub- 
oxide, or  a compound  of  two  atoms  of  copper  and  one  atom  of  oxygen; 
while  the  elements  of  the  black  oxide  are  thought  to  be  in  the  ratio  of 
one  atom  of  each.  According  to  this  view  the  atomic  weight  of  cop- 
per is  32  or  half  that  above  stated.  This  opinion,  which  is  adopted  by 
Dr.  Thomson,  is  certainly  supported  by  the  tendency  of  the  red  oxide 
to  absorb  oxygen  and  pass  into  the  state  of  black  oxide;  and  other  ar- 
guments may  be  adduced  in  its  favour.  But,  nevertheless,  as  the  red 
oxide  is  unquestionably  a definite  compound,  capable  of  uniting  with 
acids,  and  proportional  to  several  other  compounds,  such  as  the  proto- 
sulphuret  and  protochloride  of  copper,  it  appears  to  me  more  consistent 
to  consider  it  as  the  real  protoxide,  composed  of  one  atom  of  each  of 
its  elements. 

Some  chemists  admit  the  existence  of  a third  oxide,  which  Thenard 
prepared  by  the  action  of  peroxide  of  hydrogen  diluted  with  water  on 
the  hydrated  black  oxide.  It  suffers  spontaneous  decomposition  under 
water;  but  it  may  be  dried  in  vacuo  by  means  of  sulphuric  acid.  It  is 
s^d  to  contain  twice  as  much  oxygen  as  the  black  oxide;  but  as  the 
latter  is  so  commonly  known  by  the  term  peroxide,  the  former  may 
be  conveniently  distinguished  by  the  name  of  superoxide.  This  is 
the  more  necessary,  as  its  existence  is  by  no  means  unequivocally  estab- 
lished. 

Chlorides  of  Copper, — The  chlorides  of  copper  have  been  minutely 
studied  by  Proust  and  Dr.  Davy.  From  the  able  researches  of  these 
chemists,  and  especially  of  the  latter,  there  is  no  doubt  that  the  two 
chlorides  are  proportional  to  the  two  oxides  of  copper,  or  that  they  are 
composed  of 

Copper,  Chlorine,, 

Protochloride  - - 64  - - 36 

Per  chloride  - - 64  - - 72 

When  copper  filings  are  introduced  into  ^an  atmosphere  of  chlorine 
gas,  the  metal  takes  fire  spontaneously,  and  both  the  chlorides  are  gen- 
erated. 

The  protochhride  may  be  conveniently  prepared  by  heating  copper 
filings  with  twice  their  weight  of  corrosive  sublimate.  In  this  way  it 
was  originally  made  by  Mr.  Boyle,  who  termed  it  resin  of  copper,  from 
its  resemblance  to  common  resin.  Proust  procured  it  by  the  action 
of  protomuriate  of  tin  on  permuriate  of  copper;  and  also  by  decom- 


372 


LEAD. 


posing'  the  pei-muriate  by  heat.  He  gave  it  the  name  of  tvkife  muriate 
of  copper. 

Protochloride  of  copper  is  fusible  at  a heat  just  below  redness,  and 
bears  a red  heat  in  close  vessels  without  subliming.  It  is  insoluble  in 
water,  but  dissolves  in  muriatic  acid,  and  is  precipitated  unchanged  by 
water  as  a white  powder.  Its  colour  varies  with  the  mode  of  prepara- 
tion, being  white,  yellow,  or  dark  brown. 

The  percliloride  is  best  formed  by  exposing  permuriate  of  copper 
to  a temperature  not  exceeding  400®  F.  (Dr.  Davy.)  It  is  a pulveru- 
lent substance  of  a yellow  colour,  deliquesces  on  exposure  to  air, 
and  is  reconverted  by  water  into  the  permuriate.  It  parts  with 
half  its  chlorine  when  strongly  heated,  and  protochloride  of  copper  is 
generated. 

Sulphurets  of  Copper. — The  protosulphuret  is  a natural  production, 
well  known  to  mineralogists  under  the  name  of  copper  glance;  and  in 
combination  with  sulphuret  of  iron,  it  is  a constituent  of  variegated 
copper  ore.  It  is  formed  artificially  by  heating  copper  filings  with  a 
third  of  their  weight  of  sulphur,  the  combination  being  attended 
with  such  free  disengagementof  caloric,  that  the  mass  becomes  vividly 
luminous.  According  to  the  analysis  of  Berzelius,  it  is  composed  of  64 
parts  or  one  equivalent  of  copper,  and  16  parts  or  one  equivalent  of 
sulphur. 

Bisulphuret  of  copper  is  a constituent  of  copper  pyrites,  in  which  it 
is  combined  with  protosulphuret  of  iron.  It  may  be  formed  artificially 
by  the  action  of  sulphuretted  hydrogen  on  a persult  of  copper.  When 
exposed  to  a red  heat  in  a close  vessel,  it  loses  half  of  its  sulphur,  and 
is  converted  into  the  protosulphuret. 

Phosphuret  of  copper  may  be  formed  by  the  contact  of  heated  me- 
tallic copper  and  vapour  of  phosphorus,  by  transmitting  perphosphu- 
retted  hydrogen  over  chloride  or  sulphuret  of  copper  with  the  aid  of 
heat,  or  by  the  action  of  the  same  gas  on  salts  of  copper.  It  is  proba- 
ble that  there  are  several  different  phosphurets  of  copper;  but  their 
composition  has  not  been  fully  determined. 


SECTION  XXII. 


LEAD. 

Native  lead  is  an  exceedingly  rare  production;  but  in  combination, 
especially  with  sulphur,  it  occurs  in  large  quantity.  All  tlie  metallic 
lead  of  commerce  is  extracted  from  the  native  sulphuret,  the  galena  of 
mineralogists.  This  ore,  in  the  state  of  a coarse  powder,  is  heated  in 
a reverberatory  furnace;  when  part  of  it  is  oxidized,  yielding  sulphate 
of  lead,  sulpluirous  acid,  which  is  evolved,  and  free  oxide  of  lead. 
Hiese  oxidized  portions  then  react  on  sulphuret  of  lead:  hy  the  reac- 
tion of  two  cipilvalents  of  oxide  of  lead  and  one  of  the  sulphuret,  three 
equivalents  of  metallic  lead  and  one  of  sulphurous  acid  result;  while 
one  equivalent  of  the  sulpluiret  and  one  of  sulphate  of  lead  mutually 
decompose  each  other,  giving  rise  to  two  equivalents  of  sulphurous 
acid  and  two  of  metallic  lead.  The  slag  which  collects  on  the  surface 
of  the  fused  lead  contains  a large  quantity  of  sulphate  of  lead,  and  is 


LEAD. 


373 


decomposed  by  the  addition  of  quicklime,  the  oxide  so  separated  re- 
acting as  before  on  sulphuret  of  lead.  The  lead  of  commerce  com- 
monly contains  silver,  iron,  and  copper. 

Lead  has  a bluish-gray  colour,  and  when  recently  cut,  a strong  me- 
tallic lustre;  but  it  soon  tarnishes  by  exposure  to  the  air,  acquiring  a 
superficial  coating  of  carbonate  of  lead.  (Christison.)  Its  density  is 
11.358.  It  is  soft,  flexible,  and  inelastic.  It  is  both  malleable  and  duc- 
tile, possessing  the  former  property  in  particular  to  a considerable  ex- 
tent. In  tenacity,  it  is  inferior  to  all  ductile  metals.  It  fuses  at  about 
612®  F.,  and  when  slowly  cooled  forms  octohedral  crystals.  It  may  be 
heated  to  whiteness  in  close  vessels  without  subliming.  Most  of  the 
compounds  of  lead  are  poisonous. 

Lead  absorbs  oxygen  quickly  at  high  temperatures.  When  fused  in 
open  vessels,  a gray  film  is  formed  upon  its  surface,  which  is  a mixture 
of  metallic  lead  and  protoxide;  and  when  strongly  heated,  it  is  dissi- 
pated in  fumes  of  the  yellow  oxide  of  lead.  In  distilled  water,  pre- 
viously boiled  and  preserved  in  close  vessels,  it  undergoes  no  change; 
but  in  open  vessels  it  is  oxidized  with  considerable  rapidity,  yielding 
minute,  shining,  brilliantly  white,  crystalline  scales  of  carbonate  of 
lead,  the  oxygen  and  carbonic  acid  being  derived  from  the  air.  The 
presence  of  saline  matter  in  water  retards  the  oxidation  of  the  lead;  and 
some  salts,  even  in  very  minute  quantity,  prevent  it  altogether.  1'he 
protecting  influence,  exerted  by  certain  substances,  was  first  noticed  by 
Guyton  Morveau;  but  it  has  lately  been  minutely  investigated  by  Dr. 
Christison  of  Edinburgh,  who  has  discussed  the  subject  in  his  excellent 
Treatise  on  Poisons.  He  finds  that  the  preservative  power  of  neutral 
salts  is  materially  connected  with  the  insolubility  of  the  compound 
which  their  acid  is  capable  of  forming  with  lead.  Thus,  phosphates, 
hydriodates,  muriates,  and  sulphates  are  highly  preservative ; so  small 
a quantity  as  1-30, 000th  part  of  phosphate  of  soda  or  hydriodate  of  po- 
tassa  in  distilled  water  preventing  the  corrosion  of  lead.  In  a preserv- 
ative solution  the  metal  gains  weight  during  some  weeks,  in  consequence 
of  its  surface  gradually  acquiring  a superficial  coating  of  carbonate, 
which  is  slowly  decomposed  by  the  saline  matter  of  the  solution.  The 
metallic  surface  being  thus  covered  with  an  insoluble  film,  which  ad- 
heres tenaciously,  all  further  change  ceases.  Many  kinds  of  spring 
water,  owing  to  the  salts  which  they  contain,  do  not  corrode  -lead;  and 
hence,  though  intended  for  drinking,  may  be  safely  collected  in 
leaden  cisterns.  Of  this,  the  water  of  Edinburgh  is  a remarkable 
instance. 

Lead  is  not  attacked  by  the  muriatic  or  the  vegetable  acids,  though 
their  presence,  at  least  in  some  instances,  accelerates  the  absorption  of 
oxygen  from  the  atmosphere  in  the  same  manner  as  with  copper.  Cold 
sulphuric  acid  does  not  act  upon  it;  but  when  boiled  in  that  liquid,  the 
lead  is  slowly  oxidized  at  the  expense  of  the  acid.  The  only  proper 
solvent  for  lead  is  nitric  acid.  This  reagent  oxidizes  it  rapidly,  and 
forms  with  its  oxide  a salt  which  crystallizes  in  opake  octohedrons  by 
evaporation. 

Oxides  of  Lead, — Lead  has  three  degrees  of  oxidation;  and  the  com- 
position of  its  oxides,  as  determined  with  great  care  by  Berzelius,  is  as 
follows  (An.  of  Phil,  xv.): — 


Lead. 

Oxygen, 

Protoxide 

104 

8 

112 

Deutoxide 

104 

12 

B=a  116 

Peroxide 

104 

16 

=>  120 

Protoxide, — This  oxide  is  prepared  on  a large  scale  by  coUacting  the 

32 


374 


LEAD. 


gray  film  which  forms  on  the  surface  of  melted  lead,  and  exposing  it 
to  heat  and  air  until  it  accjuires  a uniform  yellow  colour.  In  this  state 
it  is  the  massicot  of  commerce;  and  when  partially  fused  by  heat,  the 
tenn  litharge  is^  applied  to  it.  As  thus  procured  it  is  always  'mixed 
with  the  deutoxide.  It  may  be  obtained  pure  by  heating  the  carbonate 
or  nitrate  to  low  redness  in  a vessel  from  which  atmospheric  air  is  ex- 
“^cluded. 

Protoxide  of  lead  has  a yellow  colour,  is  insoluble  in  water,  fuses  at 
a red  heat,  and  in  close  vessels  is  fixed  and  unchangeable  in  the  fire. 
Heated  with  combustible  matters  it  parts  with  oxygen  and  is  reduced. 
From  its  insolubility  it  does  not  change  the  vegetable  colours  under 
common  circumstances;  but  when  rendered  soluble  by  a small  quan- 
tity of  acetic  acid,  it  has  a distinct  alkaline  reaction.  It  unites  with 
acids,  and  is  the  base  of  all  the  salts  of  lead,  most  of  which  are  of  a 
white  colour. 

Protoxide  of  lead  is  precipitated  from  its  solutions  by  pure  alkalies 
as  a white  hydrate,  which  is  redissolved  by  potassa  in  excess;  as  a white 
carbonate,  which  is  the  well-known  pigment  white  leadj  by  alkaline 
carbonates;  as  a white  sulphate  by  soluble  sulphates;  as  a dark-browm 
sulphuret  by  sulphuretted  hydrogen;  and  as  yellow  iodide  of  lead  by 
hydriodic  acid  or  hydriodate  of  potassa. 

M.  Orfila  has  proved  experimentally  that  sulphate  of  lead,  owing 
to  its  insolubility,  is  not  poisonous;  and,  therefore,  sulphate  of  mag- 
nesia, or  any  soluble  sulphate,  renders  the  soluble  poisonous  salts  of 
lead  inert. 

The  best  method  of  detecting  the  presence  of  lead  in  wine  or  other 
suspected  mixed  fluids  is  by  means  of  sulphuretted  hydrogen.  The 
sulphuret  of  lead,  after  being  collected  on  a filter  and  washed,  is  to 
be  digested  in  nitric  acid  diluted  with  twice  its  weight  of  water,  untfl 
the  dark  colour  of  the  sulphuret  disappears.  The  solution  of  nitrate 
of  lead  should  then  be  brought  to  perfect  dryness  on  a watch-glass, 
in  order  to  expel  the  excess  of  nitric  acid,  and  the  residue  be  redissolv- 
ed in  a small  quantity  of  cold  water.  On  dropping  a particle  of  hydri- 
odate of  potassa  into  a portion  of  this  liquid,  yellow  iodide  of  lead  will 
instantly  appear. 

Protoxide  of  lead  unites  readily  with  earthy  substances,  forming  with 
them  a transparent  colourless  glass.  Owing  to  this  property  it  is  much 
employed  for  glazing  earthenware  and  porcelain.  It  enters  in  large 
quantity  into  the  composition  of  flint  glass,  which  it  renders  more  fusi- 
ble, transparent,  and  uniform. 

Lead  is  separated  from  its  salts  in  the  metallic  state  by  iron  or  zinc. 
The  best  way  of  demonstrating  this  fact  is  by  dissolving  one  part  of 
acetate  of  lead  in  twenty-four  of  water,  and  suspending  a piece  of 
zinc  in  tlie  solution  by  means  of  a thread.  The  lead  is  deposited  upon 
the  zinc  in  a peculiar  arborescent  form,  giving  rise  to  the  appearance 
called  arhor  katurni.  This  is  a convenient  method  of  obtaining  very 
pure  metallic  lead. 

Deutoxide. — Deutoxide  of  lead  is  the  minmrn  ovred  lead  of  commerce, 
which  is  employed  as  a pigment,  and  in  the  manufacture  of  flint  glass. 
It  is  formed  by  heating  litharge  in  open  vessels,  while  a current  of  air 
is  made  to  ])layupon  its  surface. 

''rhis  oxide  docs  not  unite  with  acids.  When  heated  to  redness  it 
gives  off  pure  oxygen  gas,  and  is  reconverted  into  the  protoxide.  When 
digested  in  nitric  acid  it  is  resolved  into  protoxide  and  peroxide  of  lead, 
llic  former  of  which  unites  with  the  acid,  while  the  latter  remains  as  an 
insoluble  ])owder. 

Dcroxidc, — This  oxide  may  be  obtained  by  the  action  of  nitric  acid  on 


LEAD. 


3/5 


minliim,  as  just  mentioned;  but  the  most  convenient  method  of  pre- 
paring’ it  is  by  transmitting  a,  current  of  chlorine  gas  through  a solution 
of  acetate  of  lead.  In  this  process  water  is  decomposed; — its  hydrogen 
uniting  with  chlorine,  and  its  oxygen  with  protoxide  of  lead,  gives  rise 
to  muriatic  acid  and  peroxide  of  lead. 

Peroxide  of  lead  is  of  a puce  colour,  and  does  not  unite  with  acids. 
It  is  resolved  by  a red  heat  into  the  protoxide  and  oxygen  gas. 

Chloride  of  Lead. — This  compound,  sometimes  called  horn  lead  or 
plumbum  corneum,  is  slowly  formed  by  the  action  of  chlorine  gas  on 
thin  plates  of  lead,  and  may  be  obtained  more  easily  by  adding  muriatic 
acid  or  a solution  of  sea-salt  to  acetate  or  nitrate  of  lead  dissolved  in 
water.  This  chloride  dissolves  to  a considerable  extent  in  hot  water, 
especially  when  acidulated  with  muriatic  acid.  In  solution  it  is  proba- 
bly a muriate  of  the  protoxide  of  lead;  but  in  cooling,  the  chloride  sep- 
arates in  the  form  of  small  acicular  crystals  of  a white  colour.  It  fuses  at  a 
temperature  below  redness,  and  forms  as  it  cools  a semi-transparent 
horny  mass.  It  bears  a full  red  heat  in  close  vessels  without  subliming. 
According  to  the  analysis  of  Dr.  Davy,  it  is  composed  of  one  equivalent 
of  lead  and  one  equivalent  of  chlorine. 

The  pigment  called  mineral  or  patent  yellow  is  a compound  of  chlo- 
ride and  protoxide  of  lead.  It  is  prepared  for  the  purposes  of  the  arts 
by  the  action  of  moistened  sea-salt  on  litharge,  by  which  means  a 
portion  of  the  protoxide  is  converted  into  chloride  of  lead,  and  then 
fusing  the  mixture.  Soda  is  set  free  during'  this  process,  and  is  con- 
verted into  a carbonate  by  absorbing  carbonic  acid  from  the  atmosphere. 

Iodide  of  lead  is  easily  formed  by  mixing  a solution  of  hydriodic  acid 
or  hydriodate  of  potassa  with  acetate  or  nitrate  of  lead  dissolved  in 
water;  and  it  is  of  a rich  yellow  colour.  It  is  dissolved  by  boiling  wa- 
ter, forming  a colourless  solution,  and  is  deposited  on  cooling  in  yellow 
crystalline  scales  of  a brilliant  lustre.  It  is  composed  of  one  equivalent 
of  iodine  and  one  equivalent  of  lead. 

Sulphuretof  lead  may  be  made  artificially,  either  by  heating  together 
lead  and  sulphur,  or  by  the  action  of  sulphuretted  ^drogen  on  a salt 
of  lead.  It  is  an  abundant  natural  product,  well  known  by  the  name 
of  galena.  It  consists  of  one  equivalent  of  lead  and  one  equivalent  of 
sulphur. 

Phosphuret  of  lead  has  been  little  examined.  It  may  be  formed  by 
heating  phosphate  of  lead  with  charcoal,  by  mixing  a solution  of  phos- 
phorus in  alcohol  or  ether  with  a solution  of  a salt  of  lead,  or  by  the 
action  of  phosphuretted  hydrogen  on  a similar  solution. 

Carburet  of  lead  may  be  obtained  by  reducing  oxide  of  lead  in  a state 
of  fine  division  and  intimate  admixture  with  charcoal.  It  is  also  gen- 
erated when  salts  of  lead,  which  contain  vegetable  acid,  are  decompo- 
sed by  heat  in  close  vessels.  (Berzelius.) 


376 


MERCURY. 


CLASS  11. 

ORDER  III. 

METALS,  THE  OXIDES  OF  WHICH  ARE  REDUCED  TO  THE 
METALLIC  STATE  BY  A RED  HEAT. 


SECTION  XXIII. 

MERCURY  OR  QUICKSILVER. 

Mercuut  is  found  in  the  native  state,  but  it  occurs  more  commonly 
in  combination  with  sulphur  as  cinnabar.  From  this  ore  the  mercury 
of  commerce  may  be  extracted  by  heating  it  with  lime  or  iron  filings, 
by  which  means  the  mercury  is  volatilized  and  the  sulphur  retained. 
As  prepared  on  a large  scale  it  is  usually  mixed  in  small  quantity  with 
other  metals,  from  which  it  may  be  purified  by  cautious  distillation. 

Mercury  is  distinguished  from  all  other  metals  by  being  fluid  at  com- 
mon temperatures.  It  has  a tin-white  colour  and  strong  metallic  lustre. 
It  becomes  solid  at  a temperature  which  is  39  or  40  degrees  below  zero; 
and  in  congealing,  evinces  a strong  tendency  to  crystallize  in  octohe- 
drons.  It  contracts  greatly  at  the  moment  of  congelation;  for  while  ics 
density  at  47®  F.  is  13.545,  the  specific  gravity  of  frozen  mercury  is 
15.612.  When  solid  it  is  malleable,  and  may  be  cut  with  a knife.  At 
680®*  F.,  or  near  that  degree,  it  enters  into  ebullition,  and  condenses 
again  on  cool  surfaces  into  metallic  globules. 

Mercury,  if  quite  pure,  is  not  tarnished  in  the  cold  by  exposure  to 
air  and  moisture;  but  if  it  contain  other  metals,  the  amalgam  of  those 
metals  oxidizes  readily,  and  collects  as  a film  upon  its  surface.  Mercu- 


* At  page  36,  Dr.  Turner  has  quoted  a table  from  the  memoir  of 
MM.  Dulong  and  Petit,  giving  the  boiling  point  of  mercury  at  680®  F., 
and  the  same  number  is  repeated  in  this  place.  If  I understand  the 
subject  correctly,  this  number  of  Dulong  and  Petit  is  the  apparent 
boiling  point  of  mercury,  measured  by  that  metal  in  glass,  both  heated 
to  the  boiling  point  of  the  former.  Wlien,  however,  its  boiling  point 
is  determined  by  an  air  thermometer,  wliich  is  generally  admitted  to 
fiirnisli  true  indications,  the  French  experimenters  make  it  662®.  Ac- 
cording to  Mr.  Crighton,  the  boiling  ])oint  of  mercury,  as-  ascertained 
by  a good  mercurial  thermometer,  making  no  correction  for  the  ex- 
pansion of  tile  glass,  or  the  increasing  rate  of  expansion  of  the  mercury 
itself,  is  656®.  Tliis  number  does  not  dificr  much  from  the  corrected 
number  of  Dulong  and  J*ctit;  and  the  near  coincidence  seems  to  show 
tliat  there  is  a pretty  accurate  compensation  between  the  causes  in- 
fluencing the  correctness  of  the  mercurial  thermometer,  inconsequence 
of  whicli  its  general  indications  vary  but  little  from  the  truth.  B. 


MiiRCtJRY. 


377 


vy  is  said  to  be  oxidized  by  long*  agitation  in  a bottle  half  full  of  air,  and 
the  oxide  so  formed  Was  called  by  Boerhaave  etidops  per  se;  but  it  is  very 
probable  that  the  oxidation  of  mercury  observed  under  these  circum- 
stances was  solely  owing  to  the  presence  of  other  metals.  When  mer- 
cury is  exposed  to  the  air  or  oxygen  gas,  while  in  the  form  of  vapour, 
it  slowly  absorbs  oxygen,  and  is  converted  into  peroxide  of  mercury. 

The  only  acids  that  act  on  mercury  are  the  sulphuric  and  nitric  acids. 
The  former  has  no  action  whatever  in  the  cold;  but  on  the  application 
of  heat,  the  mercury  is  oxidized  at  the  expense  of  the  acid,  pure  sul- 
phurous acid  gas  is  disengaged,  and  a sulphate  of  mercury  is  generated. 
Nitric  acid  acts  energetically  upon  mercury  both  with  and  without  the 
aid  of  heat,  oxidizing  and  issolving  it  with  evolution  of  deutoxide  of 
nitrogen. 

Oxides  of  Mercuxy. 

Mercury  is  susceptible  of  two  stages  of  oxidation,  and  both  its  oxides 
are  capable  of  forming  salts  with  acids.  It  appears  from  the  researches 
of  Donovan*  and  Sefstrom,-]- whose  results  are  confirmed  by  the  ex- 
periments of  Dr.  Thomson,  that  these  oxides  are  formed  in  the  follow- 
ing propoi’tions; — 

JHercury.  Oxygen, 

Protoxide  200  or  one  equivalent  . 8 = 208 

Peroxide  200  . . . , 16  = 216 

Protoxide, — This  oxide,  which  is  a black  powder,  insoluble  in  water, 
is  best  prepared  by  the  process  recommended  by  Donovan.  This  con- 
sists in  mixing  calomel  briskly  in  a mortar  with  pure  potassa  in  excess 
so  as  to  effect  its  decomposition  as  rapidly  as  possible.  The  protoxide 
is  then  to  be  washed  with  cold  water,  and  dried  spontaneously  in  a dark 
place.  These  precautions  are  rendered  necessary  by  the  tendency  of 
the  protoxide  to  resolve  itself  into  the  peroxide  and  metallic  mercury, 
a change  which  is  easily  effected  by  heat,  by  the  direct  solar  rays,  and 
even  by  daylight.  It  is  on  this  account  very  difficult  to  procui^e  pro- 
toxide of  mercury  in  a state  of  absolute  purity. 

This  oxide  is  precipitated  from  its  salts,  of  which  the  nitrate  is  the 
most  interesting,  as  the  black  protoxide  by  pure  alkalies;  as  a white 
carbonate,  which  soon  becomes  dark  from  the  loss  of  carbonic  acid,  by 
alkaline  carbonates;  as  calomel  by  muriatic  acid  or  any  soluble  muriate 
and  as  the  black  protosulphuret  by  sulphuretted  hydrogen.  Of  these 
tests  the  action  of  muriatic  acid  is  the  most  characteristic.  The  oxide 
is  reduced  to  the  metallic  state  by  copper,  phosphorous  acid,  or  proto- 
muriate of  tin. 

Peroxide. — This  oxide  may  be  formed  either  by  the  combined  agency 
of  heat  and  air,  as  already  mentioned,  or  by  dissolving  mercury  in  nitric 
acid,  and  exposing  the  nitrate  so  formed  to  a temperature  just  sufficient 
for  expelling  the  whole  of  the  nitric  acid.  It  is  commonly  known  by 
the  name  of  red  precipitate. 

Peroxide  of  mercury,  thus  prepared,  is  commonly  in  the  form  of 
shining  crystalline  scales  of  a red  colour.  It  is  soluble  to  a small  extend 
in  water,  forming  a solution  which  has  an  acrid  metallic  taste,  and  com- 
municates a green  colour  to  the  blue  infusion  of  violets.  When  heated 
to  redness,  it  is  converted  into  metallic  mercury  and  oxygen.  Long 
exposure  to  light  has  a similar  effect.  (Guibourt.) 

Some  of  the  neutral  salts  of  this  oxide,  such  as  the  nitrate  and  sul- 


* Annals  of  Philosophy,  vol.  xiv. 

32* 


-j-  Ibid.  vol.  iii.  p.  355. 


MERCURY. 


378 


phate,  are  converted  by  water,  especially  at  a boiling  temperature,  into 
insoluble  yellow  subsalts,  and  into  soluble  colourless  supersalts.  The 
oxide  is  separated  from  all  acids  as  a red,  or  when  hydratic  as  a yellow 
precipitate,  by  the  pure  and  carbonated  fixed  alkalies.  Ammonia  and 
its  carbonate  cause  a white  precipitate,  which  is  a double  salt,  consisting 
of  one  equivalent  of  the  acid,  one  equivalent  of  the  peroxide,  and  one 
equivalent  of  ammonia.  The  oxide  is  readily  reduced  to  the  metallic 
state  by  metallic  copper.  Sulphuretted  hydrogen,  phosphorous  acid, 
and  protomuriate  of  tin,  reduce  the  peroxide  into  the  protoxide;  and 
when  added  in  larger  quantity  the  first  throws  down  a black  sulpliuret 
and  the  two  latter  metallic  mercury.  The  action  of  sulphuretted  hy- 
di'ogen  on  a solution  of  corrosive  sublimate  is,  however,  peculiar;  for 
at  first  it  occasions  a white  precipitate,  which  according  to  Rose,  is  a 
com])ound  of  two  equivalents  of  bisulphuret  to  one  of  bichloride  of 
mercury.  This  gas  acts  on  bibromide  and  biniodide  of  mercury  in  a 
similar  manner.  (An.  de  Ch.  et  de  Ph.  xl.  46.) 


Chlorides  of  Mercury, 

Mercury  unites  with  chlorine  in  two  proportions;  and  the  researches 
of  Sir  H.  Davy  and  Mi*.  Chenevix  leave  no  doubt  that  these  compounds 
are  analogous  in  composition  to  the  oxides  of  mercury,  that  is,  are  com- 


posed  of 

Mercury. 

Chlorine. 

Protochloride 

200 

36 

236 

Bichloride 

200 

72 

= 272 

Btchloride. — When  mercury  is  heated  in  chlorine  gas,  it  takes  fire, 
and  burns  with  a pale-red  flame,  forming  the  well  known  medicinal 
preparation  and  virulent  poison  corrosive  sublimate  or  bichloride  of  mer- 
cury. It  is  prepared  for  medicinal  purposes  by  subliming  a mixture 
of  bisulphate  of  peroxide  of  mercury,  with  chloride  of  sodium  or  sea- 
salt.  The  exact  quantities  required  for  mutual  decomposition  are  296 
parts  or  one  equivalent  of  the  bisulphate,  to  120  pai’ts  or  two  equiva- 
lents of  the  chloride.  Thus, 


One  equiv.  of  bisulphate  of  mercury 
consists  of 

Sulphuric  acid  . 80  or  two  equiv. 

Peroxide  of  mercury  216  or  one  equiv. 


Two  equivalents  of  chloride 
of  sodium  consist  of 
72  or  two  equiv.  of  chlorine. 
48  or  two  equiv.  of  sodium. 


296 


120 


And  the  products  are. 

One  equiv.  of  bichloride  of 
mercury  consisting  of 
Mercury  . 200  or  one  equiv. 

Chlorine  . 72  or  two  equiv. 


Two  equivalents  of  sulphate  of  soda 
consisting  of 

Sulphuric  acid  80  or  two  equivalents. 
Soda  . . 64  or  two  equivalents. 


272  144 

Ificbloride  of  mercuiy,  when  obtained  by  sublimation,  is  a semi- 
ti-ansparent  colourless  substance,  of  a crystalline  texture.  . It  has  an 
acrid  burning  tastc,and  leaves  a nauseous  metallic  flavour  on  the  tongue. 
Its  specific  gravity  is  5.2.  It  sublimes  at  a red  heat  without  change. 
It  requires  twenty  himes  Its  weight  of  cold,  and  only  twice  its  weight  of 
boiling  water  for  solution,  and  is  deposited  from  tlie  latter,  as  it  cools, 
in  the  form  of  prismatic  crystals.  Sti’ong  alcohol  and  ether  dissolves  it 
in  the  same  proportion  as  boiling  water;  and  it  is  soluble  in  half  its 


MERCURY. 


379 


weight  of  concentrated  muriatic  acid  at  the  temperature  of  70®  Fahr. 
With  the  muriates  of  ammonia,  potassa,  soda,  and  several  other  bases, 
it  enters  into  combination,  forming  double  salts,  which  are  more  soluble 
than  the  chloride  itself. 

Bichloride  of  mercury  is  probably  converted  at  the  moment  of  solu- 
tion into  a bimuriate  of  the  peroxide;  at  least  this  view  may  safely  be 
admitted,  since  alkalies  and  other  reagents  act  upon  it  precisely  in  the 
same  manner  as  on  other  persalts  of  mercury.  Its  aqueous  solution  is 
gradually  decomposed  by  light,  calomel  being  deposited. 

The  presence  of  mercury  in  a fluid  supposed  to  contain  corrosive 
sublimate  may  be  detected  by  concentrating  and  digesting  it  with  an 
excess  of  pure  potassa.  Oxide  of  mercury,  which  subsides,  is  then 
sublimed  in  a small  glass  tube  by  means  of  a spirit-lamp,  and  obtained 
in  the  form  of  metallic  globules.  But  in  cases  of  poisoning,  when  the 
bichloride  is  mixed  with  organic  substances.  Dr.  Christison  recommends 
that  the  liquid,  without  previous  filtration,  be  agitated  with  a fourth  of 
its  volume  of  ether,  which  separates  the  poison  from  the  aqueous  part, 
and  rises  to  the  surface.  The  ethereal  solution  is  then  evaporated  on  a 
watch-glass,  the  i-esidue  dissolved  in  hot  water,  and  the  mercury  preci- 
pitated in  the  metallic  state  at  a boiling  temperature  by  protomuriate  of 
tin.  If,  as  is  probable,  most  of  the  poison  is  already  converted  into 
calomel,  and  thereby  rendered  insoluble,  as  many  veg'etable  fibres  should 
be  picked  out  as  possible,  and  the  whole  digested  with  protomuriate  of 
tin.  The  organic  substances  are  then  dissolved  in  a hot  solution  of 
caustic  potassa,  and  the  insoluble  parts  washed  and  sublimed  to  separate 
the  mercury.  (Christison  on  Poisons,  p.  281.) 

A very  elegant  method  of  detecting  the  presence  of  mercury  is  to 
place  a drop  of  the  suspected  liquid  on  polished  gold,  and  to  touch  the 
moistened  surface  with  a piece  of  iron  wire  or  the  point  of  a penknife, 
when  the  part  touched  instantly  becomes  white,  owing  to  the  formation 
of  an  amalgam  of  gold.  This  process  was  originally  suggested  by  Mr. 
Sylvester,  and  has  since  been  simplified  by  Dr.  Paris.  (MedicalJuris- 
prudence,  by  Paris  and  Fonblanque.) 

Man}"  animal  and  vegetable  solutions  convert  bichloride  of  mercury 
into  calomel,  a portion  of  muriatic  acid  being  set  free  at  the  same  time. 
Some  substances  effect  this  change  slowly;  while  others,  and  especially 
albumen,  produce  it  in  an  instant.  Thus  when  a solution  of  corrosive 
sublimate  is  mixed  with  albumen,  a white  fl Occident  precipitate  sub- 
sides, which  Orfila  has  shown  to  be  a compound  of  calomel  and  albu- 
men, and  which  he  has  proved  experimentally  to  be  inert.  (Toxico- 
logic, vol.  i.)  Consequently,  a solution  of  the  white  of  eggs  is  an 
antidote  to  poisoning  by  corrosive  sublimate.  The  muscular  and 
membranous  parts,  even  of  a living  animal,  produce  a similar  effect; 
and  the  causticity  of  corrosive  sublimate  seems  owing  to  the  destruc- 
tion of  the  animal  fibre,  by  which  the  decomposition  of  the  bichloride 
is  accompanied,  and  which  constitutes  an  essential  part  of  the  chemical 
change. 

Protochloride. —Vroiochlovide  of  mercury,  ov  calomel,  is  always  gen- 
erated when  chlorine  comes  in  contact  with  mercury  at  common  tempe- 
ratures. It  may  be  made  by  precipitation,  by  mixing  muriatic  acid  or 
any  soluble  muriate  with  a solution  of  protonitrate  of  mercury.  It  is 
more  commonly  prepared  by  sublimation.  This  is  conveniently  done 
by  mixing  272  parts  or  one  equivalent  of  the  bichloride  with  200  parts 
or  one  equivalent  of  mercury,  until  the  metallic  globules  entirely  dis- 
appear, and  then  subliming.  When  first  prepared  it  is  always  mixed 
with  Borne  corrosive  sublimate,  and,  therefore,  should  be  reduced  to 


380 


MERCURY. 


powder  and  well  washed  before  being*  employed  for  chemical  or  medical 
purposes. 

Ih’otochloride  of  mercury  is  a rare  mineral  production,  called  horn 
quicksilver,  which  occurs  crystallized  in  quadrangular  prisms,  termina- 
ted by  pyramids.  When  obtained  by  sublimation  it  is  in  semi-transpa- 
rent crystalline,  cakes;  but  as  formed  by  precipitation,  it  is  a white 
powder.  Its  density  is  7.2.  It  is  distinguished  from  the  bichloride  by 
not  being  poisonous,  by  having  no  taste,  and  by  being  exceedingly  in- 
soluble in  water.  Acids  have  little  clTect  upon  it;  but  pure  alkalies  de- 
compose it,  separating  the  black  protoxide  of  mercury  and  uniting  with 
muriatic  acid,— products  wliich  necessarily  imply  decomposition  of  wa- 
ter. When  calomel  is  boiled  in  a solution  of  muriate  of  ammonia,  it  is 
converted  into  corrosive  sublimate  and  metallic  mercury.  Muriate  of 
soda  has  a similar  effect,  though  in  a less  degree. 

Iodides  of  Mercury. — The  protiodide  is  formed  by  mixing  a solution 
of  protonitrate  of  mercury  with  hydriodate  of  potassa;  and  the  deut- 
iodide  by  the  action  of  the  same  hydriodate  on  any  persalt  of  mercury. 
The  former  is  yellow,  and  is  composed  of  one  equivalent  of  iodine  and 
one  equivalent  of  mercury.  The  other  is  of  an  exceedingly  rich  red 
colour,  and  may  be  used  with  advantage  in  painting.  It  contains 
twice  as  much  iodine  as  the  yellow  iodide.  Both  these  compounds  are 
insoluble  in  pure  water,  but  are  dissolved  by  a solution  of  hydriodate  of 
potassa. 

The  deutiodide,  when  exposed  to  a moderate  heat,  gradually  becomes 
yellow;  and  the  particles,  though  previously  in  powder,  acquire  a crys- 
talline appearance.  At  about  400°  F.  it  forms  a yellow  fluid,  which 
slowly  sublimes  in  small  transparent  scales,  or  in  large  rhombic  tables 
when  in  quantity.  The  crystals  remain  unchanged  in  the  air;  but  they 
quickly  become  red  when  rubbed  or  touched. 

Bicyanuret  of  Mercury. — This  compound  is  best  prepared  by  boiling, 
in  any  convenient  quantity  of  water,  eight  parts  of  finely  levigated  fer- 
rocyanate  of  peroxide  of  iron,  quite  pure  and  well  dried  on  a sand-bath, 
with  eleven  parts  of  peroxide  of  mercury  in  powder,  until  the  blue 
colour  of  the  ferrocyanate  entirely  disappears.  A colourless  solution  is 
formed,  which,  when  filtered  and  concentrated  by  evaporation,  yields 
crystals  of  bicyanuret  of  mercury  in  tlie  form  of  quadrangular  prisms. 
In  this  process,  the  oxygen  of  the  oxide  of  mercury  unites  with  the 
iron  and  hydrogen  of  the  ferrocyanic  acid;  while  the  metallic  mercury 
enters  into  combination  with  the  cyanogen.  The  brown  insoluble  mat- 
ter is  peroxide  of  iron.  Pure  ferrocyanate  of  iron  is  easily  procured  by 
digesting  common  Prussian  blue  of  commerce  with  muriatic  acid  diluted 
with  ten  parts  of  water,  so  as  to  remove  the  subsulphate  of  iron  and 
alumina  and  other  impurities  which  it  commonly  contains,  and  then 
edulcorating  the  insoluble  ferrocyanate  till  the  free  acid  is  removed. 
(Edinburgh  Journal  of  Science,  v.) 

Bicyanuret  of  mercury,  wlien  pure,  is  colourless  and  inodorous,  has 
a very  disagreeable  metallic  taste,  and  is  highly  poisonous,  It  does  not 
aficct  tlie  colour  of  litmus  or  turmeric  paper;  and  when  strongly  heated 
it  is  converted  into  cyanogen  and  metallic  mercury.  (Page  259.)  It  is 
more  soluble  in  hot  than  in  cold  water,  and  appears  to  dissolve  in  that 
liquid  witliout  cliange;  for  its  solution  has  not  the  characteristic  odour 
of  the  salts  of  hydrocyanic  acid,  nor  do  alkalies  throw  down  oxide  of 
mercury.  It  is  com])Osed  of  200  ])arts  or  one  equivalent  of  mercury, 
and  52  parts  or  two  equivalents  of  cyanogen. 

Sulpkurcts  of  Mercury. — 'I'be  protosulpluiret  may  be  prepared  by 
transmitting  a current  of  sul|)hiireUcd  hydrogen  gas  through  a dilute 
solution  of  protonitratc  of  mercury,  or  through  water  in  which  calomel 


SILVER. 


381 


is  suspended.  It  is  a black-coloured  substance,  convertible  into  sul- 
phate of  mercury  by  dig*estion  in  strong*  nitric  acid.  When  exposed  to 
heat  it  is  resolved  into  the  bisulphuret  and  metallic  mercury.  It  is  com- 
posed of  200  parts  or  one  equivalent  of  mercury,  and  16  parts  or  one 
equivalent  of  sulphur. 

The  bisulphuret  is  formed  by  fusing  sulphur  with  about  six  times 
its  weight  of  mercury,  and  subliming  in  close  vessels.  When  procured 
by  this  process  it  has  a red  colour,  and  is  known  by  the  name  of  facti- 
tious cinnabar.  Its  tint  is  greatly  improved  by  being  reduced  to  pow- 
der, in  which  state  in  forms  the  beautiful  pigment  vermilion.  It  may 
be  obtained  in  the  moist  way  by  pouring  a solution  of  corrosive  subli- 
mate into  an  excess  of  liydrosulphuret  of  ammonia.  A black  precipi- 
tate subsides,  which  acquires  the  usual  red  colour  of  cinnabar  when  sub- 
limed. I apprehend  the  black  precipitate,  formed  by  the  action  of 
sulphuretted  hydrogen  on  bicyanuret  of  mercury,  is  likewise  a bisul- 
phuret. Cinnabar,  as  already  mentioned,  occurs  native. 

When  equal  parts  of  sulphur  and  mercury  are  triturated  together 
until  metallic  globules  cease  to  be  visible,  the  dark-coloured  mass  called 
ethiops  mineral  results,  which  Mr.  Braude  has  proved  to  be  a mixture 
of  sulphur  and  bisulphuret  of  mercury.  (Journal  of  Science,  vol.  xviii. 
p.  294.) 

Cinnabar  is  not  attacked  by  alkalies,  or  any  simple  acid;  but  it  is  dis- 
solved by  the  nitro-muriatic,  with  formation  of  sulphuric  acid  and  oxide 
of  mercury.  M.  Guibourt  has  shown  that  it  is  composed  of  one  equiv- 
alent of  mercury  and  two  equivalents  of  sulphur. 


SECTION  XXIV. 

SILVER. 

This  metal  frequently  occurs  native  in  silver  mines,  both  massive 
and  in  octohedral  or  cubic  crystals.  It  is  also  found  in  combination  with 
several  other  metals,  such  as  gold,  antimony,  copper,  and  arsenic, 
and  with  sulphur.  In  the  state  of  sulphuret  it  s5  frequently  accompa- 
nies galena,  that  the  lead  of  commerce  is  rarely  quite  free  from  traces 
of  silver. 

Silver  is  extracted  from  its  ores, by  two  processes  which  are  essentially 
distinct;  one  of  them  being  contrived  to  separate  it  from  lead,  the  other, 
the  process  by  amalgamation,  being  especially  adapted  to  those  ores 
w'hich  are  free  from  lead.  The  principle  of  its  separation  from  lead  is 
founded  on  the  different  oxidability  of  lead  and  silver,  and  on  the  ready 
fusibility  of  litharge.  The  lead  obtained  from  those  kinds  of  galena 
which  are  rich  in  sulphuret  of  silver  is  kept  at  a red  heat  in  a flat  fur^ 
nace,  with  a draught  of  air  constantly  playing  on  its  surface:  the  lead 
is  thus  rapidly  oxidized;  and  as  the  oxide,  at  the  moment  of  its  forma-; 
tion,  is  fused,  and  runs  off  through  an  aperture  in  the  side  of  the  fur- 


* An.  de  Ch.  et  de  Ph.  vol.  i.  See  also  some  very  judicious  observa- 
tions on  the  paper  of  M.  Guibourt  by  Mr.  Brande,  in  the  Journal  of 
Science,  xviii.  291. 


382 


SILVER. 


nace,  the  production  of  litharg*e  goes  on  uninterruptedly  until  all  the 
lead  is  removed.  The  button  of  silver  is  again  fused  in  a smaller  fur- 
nace, resting  on  a porous  earthen  dish,  made  with  lixiviated  wood-ashes, 
called  a test,  the  porosity  of  which  is, so  great,  that  it  absorbs  any  re- 
maining portions  of  litharge,  which  may  be  formed  on  the  silver. 

The  ores  commonly  employed  in  the  process  of  amalgamation,  which 
has  been  long  used  at  Freyberg  in  Saxony,  and  is  extensively  practised 
in  the  silver  and  goldmines  of  South  America,  are  native  silver  and  its 
sulphuret.  The  ore  in  fine  powder  is  mixed  with  sea  salt,  and  carefully 
roasted  in  a reverberatory  furnace.  The  production  of  sulphuric  acid 
leads  to  the  formation  of  sulphate  of  soda,  while  the  chlorine  of  the 
sea  salt  combines  with  silver.  The  roasted  mass  is  ground  to  a fine 
powder,  and,  together  with  mercury,  water,  and  fragments  of  iron, 
is  put  into  barrels,  which  are  made  to  revolve  by  machinery.  In  this 
operation,  intended  to  insure  perfect  contact  between  tlie  materials, 
chloride  of  silver  is  decomposed  by  the  iron,  the  silver  unites  with  the 
merciuy,  and  the  chloride  of  iron  is  dissolved  by  the  water.  The  mer- 
cury is  then  squeezed  through  leathern  bags,  through  the  pores  of 
which  the  pure  mercury  passes,  while  the  amalgam  of  silver  is  retained. 
The  combined  mercury  is  then  distilled  off  in  close  vessels,  and  the 
metals  obtained  in  a separate  state. 

Goldsmiths’  silver  commonly  contains  copper  and  traces  of  gold,  the 
latter  appearing  in  dark  flocks  when  the  metal  is  dissolved  in  nitric  acid. 
It  may  be  obtained  pure  for  chemical  uses  by  placing  a clean  piece  of 
copper  in  a solution  of  nitrate  of  silver,  washing  the  precipitate  with 
pure  water,  and  then  digesting  it  in  ammonia,  in  order  to  remove  any 
adhering  copper.  A better  process  is  to  decompose  chloride  of  silver 
by  means  of  carbonate  of  potassa.  For  this  purpose  precipitate 'a  solu- 
tion of  nitrate  of  silver  with  muriate  of  soda,  wash  the  precipitate 
with  water,  and  dry  it.  Then  put  twice  its  weight  of  carbonate  of 
potassa  into  a clean  Hessian  or  black  lead  crucible,  heat  it  to  redness,^ 
and  throw  the  chloride  by  successive  portions  into  the  fused  alkali. 
Effervescence  takes  place  from  the  evolution  of  carbonic  acid  and  oxy- 
gen gases,  chloride  of  potassium  is  generated,  and  metallic  silver 
subsides  to  the  bottom.  The  pure  metal  may  be  granulated  by  pour- 
ing it  while  fused  from  a height  of  seven  or  eight  feet  into  a vessel  of 
water. 

Silver  has  the  clearest  white  colour  of  all  the  metals,  and  is  suscepti- 
ble of  receiving  a lustre  surpassed  only  by  polished  steel.  In  mallea- 
bility and  ductility  it  is  inferior  only  to  gold,  and  its  tenacity  is  consider- 
able. It  is  very  soft  when  pure,  so  that  it  may  be  cut  with  a knife.  Its 
density  after  being  hammered  is  10.51.  At  20®  or  22®  of  Wedgwood’s 
pyrometer  it  fuses. 

Pure  silver  does  not  rust  by  exposure  to  air  and  moisture,  nor  is  it 
oxidized  by  fusion  in  open  vessels.  It  appears,  indeed,  that  a film  of 
oxide  is  formed  when  melted  silver  is  exposed  to  a current  of  air  or 
oxygen  gas;  but  it  spontaneously  parts  with  the  oxygen  as  it  becomes 
solid.  When  silver  in  the  form  of  leaves  or  fine  wire  is  intensely  heated 
by  means  of  electricity,  galvanism,  or  the  oxy-hydrogen  blowpipe,  it 
burns  with  vivid  scintillations  of  a grccnish-wliite  colour. 

The  only  ])ure  acids  that  act  on  silver  are  the  sulphuric  and  nitric 
acids,  by  both  of  which  it  is  oxidized,  forming  with  the  first  a sulphate, 
and  with  the  second  a nitrate  of  silver.  It  is  not  attacked  by  sulphuric 
acid  unless  by  the  aid  of  heat.  Nitric  acid  is  its  proper  solvent,  and 
forms  with  it  a salt,  which,  in  its  (used  state,  is  known  by  the  name  of 
lunar  caustic. 

Oxide  of  Silver, — This  oxide  is  best  procured  by  mixing  a solution  of 


SILVER. 


383 


pure  baryta  with  nitrate  of  silver  dissolved  in  water.  It  is  of  a brown 
colour,  insoluble  in  water,  and  is  completely  reduced  by  a red  heat. 
According  to  Sir  II.  Davy,  it  is  composed  of  110  parts  of  silver  and  8 
parts  of  oxygen;  and,  therefore,  regarding  it  as  the  real  protoxide,  110 
is  the  atomic  weight  of  silver. 

Oxide  of  silver  is  separated  from  its  solution  in  nitric  acid  by  pure 
alkalies  and  alkaline  earths  as  the  brown  oxide,  which  is  redissolved 
by  ammonia  in  excess;  by  alkaline  carbonates  as  a white  carbonate, 
which  is  soluble  in  an  excess  of  carbonate  of  ammonia;  as  a dark 
brown  sulphuretby  sulphuretted  hydrogen;  and  as  a white  curdy  chlo- 
ride of  silver,  which  is  turned  violet  by  light  and  is  very  soluble  in  am- 
monia, by  muriatic  acid  or  any  soluble  muriate.  By  the  last  character, 
silver  may  be  both  distinguished  and  separated  from  other  metallic 
bodies. 

Silver  is  precipitated  in  the  metallic  state  by  most  other  metals. 
AVhen  mercury  is  employed  for  this  purpose,  the  silver  assumes  a beau- 
tiful arborescent  appearance,  called  arbor  Dianas.  A very  good  pro- 
portion for  the  experiment  is  twenty  grains  of  lunar  caustic  to  six 
drachms  or  an  ounce  of  water.  The  silver  thus  deposited  always  con- 
tains mercury. 

AVhen  oxide  of  silver,  recently  precipitated  by  baryta  or  lime-water, 
and  separated  from  adhering  moisture  by  bibulous  paper,  is  left  in  con- 
tact for  ten  or  twelve  hours  with  a strong  solution  of  ammonia,  the 
gi'eater  part  of  it  is  dissolved;  but  a black  powder  remains  which  deto- 
nates violently  from  heat  or  percussion.  This  substance,  which  was 
discovered  by  Berthollet,  (An.  de  Ch.  vol.  i.)  appears  to  be  a compound 
of  ammonia  and  oxide  of  silver;  for  the  products  of  its  detonation  are 
metallic  silver,  water,  and  nitrogen  gas.  It  should  be  made  in  very 
small  quantity  at  a time,  and  dried  spontaneously  in  the  air. 

On  exposing  a solution  of  oxide  of  silver  in  ammonia  to  the  air,  its 
surface  becomes  covered  with  a pellicle,  which  Mr.  Faraday  considers 
to  be  an  oxide  containing  a smaller  proportion  of  oxygen  than  that  just 
described.  This  opinion  he  has  made  highly  probable;  but  further  ex- 
periments are  requisite  before  the  existence  of  this  oxide  can  be  re- 
garded as  certain. 

Chloride  of  Silver. — This  compound,  which  sometimes  occurs  native 
in  silver  mines,  is  always  generated  when  silver  is  heated  in  chlorine 
gas,  and  may  be  prepared  conveniently  by  mixing  muriatic  acid,  or  any 
soluble  muriate,  with  a solution  of  nitrate . of  silver.  As  formed  by 
precipitation  it  is  quite  white;  but  by  exposure  to  the  direct  solar  rays 
it  becomes  violet,  and  almost  black,  in  the  course  of  a few  minutes; 
and  a similar  effect  is  slowly  produced  by  diffused  day-light.  Muriatic 
acid  is  set  free  during  this  change,  and,  according  to  Berthollet,  the 
dark  colour  is  owing  to  a separation  of  oxide  of  silver.  (Statique  Chi- 
j^ique,  vol.  i.  p.  19^) 

Chloride  of  silver,  sometimes  called  luna  cornea  or  horn  silver ^ is  in- 
soluble in  water,  and  is  dissolved  very  sparingly  by  the  strongest  acids; 
but  it  is  soluble  in  ammonia.  Hyposulphurous  acid  likewise  dissolves  it. 
At  a temperature  of  about  500°  F.  it  fuses,  and  forms  a semitransparent 
horny  mass  on  cooling.  It  bears  any  degree  of  heat,  or  even  the  com- 
bined action  of  pure  charcoal  and  heat,  without  decomposition;  but 
hydrogen  gas  decomposes  it  readily  with  formation  of  muriatic  acid. 
According  to  the  experiments  of  Berzelius  and  Dr.  Thomson,  it  is  com- 
posed of  110  parts  or  one  equivalent  of  silver,  and  36  parts  or  one 
equivalent  of  chlorine. 

Iodide  of  Silver. — This  compound  is  formed  when  hydriodate  of  po- 
tassa  is  mixed  with  a solution  of  nitrate  of  silver.  It  is  of  a greenish- 


384 


GOLD. 


yellow  colour,  is  insoluble  in  water  and  ammonia,  and  contains  one 
equivalent  of  each  of  its  elements. 

Cyanuret  of  silver  is  formed  by  mixing  hydrocyanic  acid  with  nitrate 
of  silver.  It  is  a white  curdy  substance,  similar  in  appearance  to  chlo- 
ride of  silver,  insoluble  in  water  and  nitric  acid,  and  soluble  in  a solu- 
tion of  ammonia.  It  is  decomposed  by  muriatic  acid  with  formation  of 
hydrocyanic  acid  and  chloride  of  silver.  It  consists  of  one  equivalent 
of  each  of  its  elements. 

Sulphuret  of  Silver, — Silver  has  a strong  affinity  for  sulphur.  This 
metal  tarnishes  rapidly  when  exposed  to  an  atmosphere  containing  sul- 
phuretted liydrogen  gas,  owing  to  the  formation  of  a sulphuret.  On 
transmitting  a current  of  sulphuretted  hydrogen  gas  through  a solution 
of  lunar  caustic,  a dark  brown  precipitate  subsides,  which  is  a sulphu- 
ret of  silver.  The  silver  glance  of  mineralogists  is  a similar  compound, 
and  tlie  same  sulphuret  may  be  prepared  by  heating  thin  plates  of  silver 
with  alternate  layers  of  sulphur.  I'his  sulphuret  is  remarkable  for  be- 
ing soft  and  even  malleable. 

Sulphuret  of  silver,  according  to  the  experiments  of  Berzelius,  is  a 
compound  of  110  parts  or  one  equivalent  of  silver,  and  16  parts  or  one 
equivalent  of  sulphur. 

Silver  unites  also  by  the  aid  of  heat  with  phosphorus,  fonning  a soft, 
brittle,  crystalline  compound. 


SECTION  XXV. 

GOLD. 

Gold  has  hitherto  been  found  only  in  the  metallic  state,  either  pure 
or  in  combination  with  other  metals.  It  occurs  massive,  capillary,  in 
grains,  and  crystallized  in  octohedrons  and  cubes,  or  their  allied  forms. 
It  is  sometimes  found  in  primary  mountains;  but  more  frequently  in  al- 
luvial depositions,  especially  among  sand  in  the  beds  of  rivers,  having 
been  washed  by  water  out  of  disintegrated  rocks  in  which  it  originally 
existed.  The  richest  gold  mines  of  Europe  are  in  Hungary.  It  is  sep- 
arated from  accompanying  impurities  by  the  process  of  amalgamation, 
similar  to  that  described  in  the  last  section;  by  which  means  it  is  freed 
from  iron  and  all  associated  metals,  excepting  silver.  This  metal  is 
left  in  the  form  of  chloride  when  the  gold  is  dissolved  in  nitro-muriatic 
acid. 

Gold  is  the  only  metal  which  has  a yellow  colour,  a character  by 
which  it  is  distinguished  from  all  other  simple  metallic  bodies.  It  is 
capable  of  receiving  a high  lustre  by  polishing,  but  is  inferior  in  bril- 
liancy to  steel,  silver,  and  mercury.  In  ductility  and  malleability  it  ex- 
ceeds all  other  metals;  but  it  is  surpassed  by  several  in  tenacity.  Its 
density  is  19.3;  when  pure  it  is  exceedingly  soft  and  flexible;  and  it 
fuses  at  32^^  of  Wedgwood’s  pyrometer. 

Gold  may  be  exposed  for  ages  to  air  and  moisture  without  change, 
nor  is  it  oxidized  by  being  kept  in  a state  of  fusion  in  open  vessels. 
When  intensely  ignited  by  means  of  electricity  or  the  oxy-hydrogen 
blowpipe,  it  burns  with  a greenish-blue  flame,  and  is  dissipated  in  the 
form  of  a purple  powder,  which  is  supposed  to  bo  an  oxide. 

Gold  is  not  oxidized  or  dissolved  by  any  of  the  pure  acids;  for  it  may 


GOLD. 


385 


be  boiled  even  in  nitric  acid  without  undergoing  any  change.  Its  only 
solvents  are  chlorine  and  nitro-muriatic  acid;  and  it  appears  from  the 
observations  of  Sir  H.  Davy  that  chlorine  is  the  agent  in  both  cases, 
since  nitro-muriatic  acid  does  not  dissolve  gold,  except  when  it  gives 
rise  to  the  formation  of  chlorine.  (Page  210.)  It  is  to  be  inferred, 
therefore,  that  the  chlorine  unites  directly  with  the  gold.  Wnether  the 
resulting  solution  is  really  a chloride  of  the  metal,  or  a muriate  of  its 
oxide,  generated  by  decomposition  of  water,  is  uncertain;  but  from  the 
observations  of  M.  Pelletier,  which  will  be  mentioned  immediately,  I 
conceive  the  former  opinion  to  be  the  more  probable.  There  is  no  in- 
convenience, however,  in  regarding  it  as  a muriate,  because  reagents 
act  upon  it  as  if  it  were  such. 

The  most  convenient  method  of  forming  a solution  of  gold  is  to  digest 
fragments  of  the  metal  in  a mixture  composed  of  two  measures  of 
muriatic  and  one  of  nhric  acid,  until  the  acid  is  saturated.  The  orange- 
coloured  solution  is  then  evaporated  to  dryness  by  a regulated  heat,  in 
order  to  expel  the  free  acid  without  decomposing  the  residual  chloride 
of  gold.  On  adding  water,  the  chloride  is  dissolved,  forming  a neutral 
solution  of  a reddish-brown  colour. 

Oxides  of  Gold. — The  chemical  history  of  the  oxides  of  gold  is  as  yet 
very  imperfect.  Berzelius  is  of  opinion  that  there  are  three  oxides. 
His  protoxide  is  obtained  by  decomposing  the  protochloride  of  gold  by 
a solution  of  pure  potassa,  and  is  of  a dark  green  colour.  The  deu- 
toxide  or  purple  oxide  is  the  product  of  the  combustion  of  gold.  The 
composition  of  these  oxides  has  not  yet  been  satisfactorily  determined, 
and  the  very  existence  of  the  first,  though  probable,  may  be  questioned. 
The  only  well-known  oxide  is  that  which  is  supposed  to  exist  in  the 
solution  of  gold  combined  with  muriatic  acid.  It  may  be  prepared  by 
mixing  with  a concentrated  neutral  solution  of  gold  a quantity  of  pure 
potassa  exactly  sufficient  for  combining  with  the  muriatic  acid.  A red- 
dish-yellow coloured  precipitate,  the  hydrous  peroxide,  subsides, 
which  is  rendered  anhydrous  by  boiling,  and  assumes  a brownish -black 
colour.*  The  best  method  of  forming  it,  according  to  M.  Pelletier,  is 
by  digesting  the  muriate  with  pure  magnesia,  washing  the  precipitate 
with  water,  and  removing  the  excess  of  magnesia  by  dilute  nitric  acid. 

Peroxide  of  gold  is  yellow  in  the  state  of  hydrate,  and  nearly  black 
when  pure,  is  insoluble  in  water,  and  completely  decomposed  by  solar 
light  or  a red  heat.  Muriatic  acid  dissolves  it  readily,  yielding  the  com- 
mon solution  of  gold;  but  it  forms  no  definite  compound  with  any  acid 
which  contains  oxygen.  It  may  indeed  be  dissolved  by  nitric  and  sul- 
phuric acids;  but  the  affinity  is  so  slight  that  the  oxide  is  precipitated 
by  the  addition  of  water.  It  combines,  on  the  contrary,  with  alkaline 
bases,  such  as  potassa  and  baryta,  apparently  forming  regular  salts,  in 
which  it  acts  the  part  of  a weak  acid.  These  circumstances  have 
induced  M.  Pelletier  to  deny  that  the  peroxide  is  a salifiable  base,  and 
to  contend  that  the  muriatic  solution  of  gold  is  in  reality  a chloride  of 
the  metal.  On  this  supposition  he  proposes  the  term  auric  acid  for 
peroxide  of  gold,  and  to  its  compounds  with  alkalies  he  gives  the  de- 
nomination of  aurates. 

Peroxide  of  gold  is  thrown  down  of  a yellow  colour  by  ammonia,  and 
the  precipitate  is  an  aurate  of  that  alkali.  It  is  a highly  detonating 
compound,  analogous  to  the  fulminating  silver  described  in  the  last 
section. 


• M.  Pelletier  in  the  An.  de  Ch.  et  de  Ph.  vol.  xv. 
33 


386 


GOLD. 


According-  to  the  experiments  of  Berzelius,*  which  are  confirmed  by 
those  of  Javalf  and  Thomson,  100  parts  of  gold  unite  with  12.077  to 
constitute  the  peroxide;  and  if  this  oxide  be  regarded  as  consisting  of 
three  equivalents  of  oxygen  and  one  of  metal,  200  will  be  the  equiva- 
lent of  gold,  and  224  that  of  its  peroxide.  It  is,  therefore,  a tritoxide, 
and  this  opinion  is  corroborated  by  the  constitution  of  the  clilorides  of 
gold. 

Chlorides  of  Go/c?.— On  concentrating  the  solution  of  gold  to  a suffi- 
cient extent  by  evaporation,  the  perchloride  may  be  obtained  in  red 
prismatic  crystals,  which  become  brown  when  brought  to  perfect  dry- 
ness. It  deliquesces  on  exposure  to  the  air,  and  is  dissolved  readily  by 
water  without  residue.  At  a temperature  far  below  that  of  redness,  it 
is  converted,  with  evolution  of  two-tliirds  of  its  chlorine,  into  the  yel- 
low insoluble  protochloride,  from  which  the  chlorine  is  entirely  expelled 
by  a red  heat.  This  protochloride  is  converted,  by  being  boiled  in 
water,  into  the  soluble  perchloride  and  metallic  gold. 

The  composition  of  the  chlorides  of  gold  has  been  ascertained  by 
Berzelius,  and  Mr.  W.  Johnston  has  lately  confirmed  the  accuracy  of 
his  observations.  (Brewster’s  Journal,  N.  S.  iii.  131.)  The  insoluble 
chloride  consists  of  one  equivalent  of  gold  and  one  of  chlorine;  while 
the  soluble  compound  is  a terchloride,  consisting  of  one  equivalent  of 
gold  and  three  of  chlorine.  When  mixed  with  sea-salt,  and'  the  solution 
is  evaporated,  a double  chloride  of  a reddish-yellow  colour  is  obtained, 
which  crystallizes  either  in  prisms  or  four  sided  tables.  They  consist, 
according  to  Berzelius  and  Johnston,  of  one  equivalent  of  terchloride 
of  gold,  one  of  chloride  of  sodium,  and  four  of  water.  A double  chlo- 
ride of  gold  and  potassium  may  be  formed  in  the  same  manner  as  the 
foregoing,  and  its  constitution  is  analogous.  It  crystallizes  sometimes 
in  four-sided  prisms  and  needles,  and  sometimes  in  large  brilliant  thin 
plates.  A similar  compound  may  be  obtained  with  muriate  of  ammo- 
nia, and  with  several  metallic  chlorides,  such  as  those  of  barium,  stron- 
tium, calcium,  magnesium,  manganese,  zinc,  cobalt,  and  nickel. 

The  solution  of  g'old  is  decomposed  by  substances  which  have  a strong 
affinity  for  oxygen.  On  adding  protosulphate  of  iron,  dissolved  in  water, 
the  iron  is  oxidized  to  a maximum,  and  a copious  brown  precipitate  sub- 
sides which  is  metallic  gold  in  a state  of  very  minute  division.  This  preci- 
pitate, when  duly  washed  with  dilute  muriatic  acid,  in  order  to  separate 
adhering  iron,  is  gold  in  a state  of  perfect  purity.  A similar  reduction 
is  effected  by  most  of  the  metals,  and  by  sulphurous  and  phosphorous 
acids.  When  a piece  of  charcoal  is  immersed  in  solution  of  gold,  and 
exposed  to  the  direct  solar  rays,  its  surface  acquires  a coating  of  metal- 
lic gold;  and  ribands  may  be  gilded  by  moistening  them  with  a dilute 
solution  of  gold,  and  exposing  them  to  a current  of  hydrogen  or  phos- 
pJmretted  liydrogen  gas.  When  a strong  aqueous  solution  of  gold  is 
shaken  in  a phial  with  an  equal  volume  of  pure  ether,  two  fluids  result, 
the  lighter  of  which  is  an  etliereal  solution  of  gold.  From  this  liquid 
flakes  of  metal  are  deposited  on  standing,  especially  by  exposure  to 
liglit,  and  substances  moistened  with  it  receive  a coating  of  metallic 
gold.t 

When  protomuriate  of  tin  is  added  to  a dilute  aqueous  solution  of 
gold,  a j)urplc-coloure(l  precipitate,  called  the  purple  of  Cassius,  is 


* An.  de  Ch.  Ixxxiii.  f 

t With  respect  to  tlie  revival  of  gold  from  its  solutions,  the  reader 
may  consult  an  Essay  on  Coinl)Ustion,  by  Mrs.  lulliame,  and  a paper  by 
Count  Buinford  in  tlic  Fhilosophical  Transactions  for  1798. 


PLATINUM. 


3br 

thrown  down,  which  is  the  substance  employed  in  painting  on  porce- 
lain for  g*iving  a pink  colour.  It  appears  to  be  a compound  of  peroxide 
of  tin  and  purple  oxide  of  gold,  in  which  the  former  is  supposed  to  act 
as  an  acid. 

Sulphuret  of  Gold. — On  transmitting  a current  of  sulphuretted  hy- 
drogen gas  through  a solution  of  gold,  a black  precipitate  is  formed, 
which  is  a sulphuret.  It  is  resolved  by  a red  heat  into  gold  and  sulphur, 
and  appears  from  the  analysis  of  Oberkampf  to  be  composed  of  200 
parts  or  one  equivalent  of  gold,  and  48  parts  or  three  equivalents  of 
sulphur. 

The  compounds  of  gold  with  the  other  non-metallic  bodies  have  been 
little  examined. 


SECTION  XXVI. 

PLATINUM. 

This  valuable  metal  occurs  only  in  the  metallic  states  associated  or 
combined  with  various  other  metals,  such  as  copper,  iron,  lead,  titanium, 
chromium,  gold,  silver,  palladium,  rhodium,  osmium,  and  iridium.  It 
has  hitherto  been  found  chiefly  in  Brazil,  Peru,  and  other  parts  of 
South  America,  in  the  form  of  rounded  or  flattened  grains  of  a metal- 
lic lustre  and  white  colour,  mixed  with  sand  and  other  alluvial  deposi- 
tions. The  particles  rarely  occur  so  large  as  a pea;  but  they  are  some- 
times larger,  and  a specimen  brought  from  South  America  by  Humboldt 
was  rather  larger  than  a pigeon’s  egg,  and  weighed  1088.6  grains.  Two 
years  ago,  however,  M.  Boussingault  discovered  it  in  a syenetic  rock  in 
the  province  of  Antioquia  in  South  America,  where  it  occurs  in  veins 
associated  with  gold.  Rich  mines  of  gold  and  platinum  have  also  been 
recently  discovered  in  the  Uralian  mountains.  (Edinburgh  Journal  of 
Science,  v.) 

Pure  platinum  has  a white  colour  very  much  like  silver,  but  of  infe- 
rior lustre.  It  is  the  heaviest  of  known  metals,  its  density  after  forging 
being  about  21.25,  and  21.5  in  the  state  of  wire.  Its  malleability  is 
considerable,  though  far  less  than  that  of  gold  and  silver.  It  may  be 
drawn  into  wires,  the  diameter  of  which  does  not  exceed  the  2000th 
part  of  an  inch.  It  is  a soft  metal,  and  like  iron,  admits  of  being 
welded  at  a high  temperature.  Dr.  Wollaston*  has  observed  that  it  is 
a less  perfect  conductor  of  caloric  than  most  other  metals. 

Platinum  undergoes  no  change  from  the  combined  agency  of  air  and 
moisture;  and  it  may  be  exposed  to  the  strongest  heat  of  a smith’s  forge 
without  suffering  either  oxidation  or  fusion.  On  heating  a small  wire  of 
it  by  means  of  galvanism  or  the  oxy-hydrogen  blowpipe,  it  is  fused,  and 
afterwards  burns  with  the  emission  of  sparks.  The  late  Mr.  Smithson 


* The  reader  will  find,  in  the  Philosophical  Transactions  for  1829,  some 
important  directions  by  Dr.  Wollaston  both  as  to  the  mode  of  extracting 
platinum  from  its  ores,  and  of  communicating  to  the  pure  metal  its 
highest  degree  of  malleability.  The  essay  receives  additional  interest 
from  being  one  of  those  which  were  composed  during  the  last  illness 
of  this  truly  illustrious  philosopher. 


PLATINUM. 


Tennant  showed  that  it  is  oxidized  when  ignited  with  nitre,  (Philos. 
Trans,  for  1797?)  and  a similar  effect  is  occasioned  by  pure  potassaand 
lithia. 

Platinum  is  not  attacked  by  any  of  the  pure  acids.  Its  only  solvents 
are  chlorine  and  nitro-muriatic  acid,  which  act  upon  it  with  gi’eater  diffi- 
culty than  on  gold.  The  resulting  orange-red  coloured  liquid,  from 
which  the  excess  of  acid  should  be  expelled  by  cautious  evaporation, 
may  be  regarded  as  containing  either  chloride  of  platinum,  or  the  mu- 
riate of  its  oxide. 

Oxides  of  Platinum. — According*  to  Berzelius  there  are  two  oxides  of 
platinum,  the  oxygen  of  which  is  in  the  ratio  of  1 to  2.  The  protoxide 
prepared  by  the  action  of  potassa  on  protochloride  of  platinum,  is  of  a 
black  colour,  and  is  reduced  by  a red  heat.  According  to  the  earlier 
experiments  of  Berzelius,  this  oxide  consists  of  8 parts  of  oxygen  and 

96.5  of  platinum;  but  he  now  estimates  the  equivalent  of  platinum  at 

98.6  or  99,  while  the  number  of  Dr.  Thomson  is  96.  The  peroxide  is 
obtained  with  difficulty;  for  on  attempting  to  precipitate  it  from  the 
muriate  by  means  of  an  alkali,  it  either  falls  as  a sub-salt,  or  is  held  alto- 
gether in  solution.  Berzelius  recommends  that  it  should  be  prepared 
by  exactly  decomposing  sulphate  of  platinum  with  nitrate  of  baryta, 
and  adding  pure  soda  to  the  filtered  solution,  so  as  to  precipitate  about 
half  of  the  oxide;  since  otherwise,  a sub-salt  would  subside.  The  ox- 
ide falls  in  the  form  of  a bulky  hydrate,  of  a yellowish-brown  colour: 
it  resembles  rust  of  iron  when  dry,  and  is  nearly  black  when  rendered 
anhydrous.  Like  peroxide  of  gold  it  is  a very  feeble  base,  and  is  much 
disposed  to  unite  with  alkalies. 

Another  oxide  was  described  by  Mr.  E.  Davy  in  the  Philosophical 
Transactions  for  1820.  It  is  of  a gray  colour,  and  is  prepared  by  heat- 
ing fulminating  platinum  with  nitrous  acid.  It  appears  from  his  analysis 
to  be  composed  of  one  equivalent  of  platinum,  and  an  equivalent  and 
a half  of  oxygen.  Mr.  Cooper  has  likewise  described  an  oxide  of 
platinum;  but  its  existence  as  a definite  compound  distinct  from 
those  above  described  has  not,  I conceive,  been  satisfactorily  demon- 
strated. 

Chlorides  of  Platinum. — The  perchloride  is  procured  by  evaporating 
muriate  of  platinum  to  dryness  at  a gentle  heat.  It  is  deliquescent, 
and  is  soluble  in  water,  alcohol,  and  ether.  The  ethereal  solution  is 
decomposed  by  the  agency  of  light,  metallic  platinum  being  deposit- 
ed. It  is  probable,  from  the  analysis  of  the  double  chloride  of  potas- 
sium and  platinum  by  Dr.  Thomson  and  Berzelius,  that  perchloride  of 
platinum  is  composed  of  one  equivalent  of  metal  and  two  equivalents 
of  chlorine.  It  is,  therefore,  a bichloride,  and  corresponds  with  the 
peroxide. 

AVhen  the  bichloride  is  heated  to  the  temperature  of  melting  lead  or 
a little  higher,  it  parts  with  half  of  its  chlorine,  and  is  converted  into 
a protochloride,  whicli  is  resolved  by  a red  heat  into  platinum  and  chlo- 
rine. It  is  insoluble  in  pure  water,  but  is  dissolved  by  a solution  of  the 
perchloride. 

Platinum  is  distinguished  from  all  other  substances  by  the  following 
circumstances.  Wlien  ])ure  potassa  or  a salt  of  potassa  is  added  to  a 
concentrated  solution  of  jdatinuin,  a yellow  crystalline,  precipitate 
subsides,  which  is  very  sjiaringly  soluble  in  water.  When  heated  to 
full  redness  chlorine  gas  is  disengaged,  and  the  residue  consists  of  me- 
tallic })latinum  and  chloride  of  potassium.  It  is  coinjiosed  of  one  equiv- 
alent of  bichloride  of  ])lalinuni  and  one  of  chloride  of  potassium. 

Ammonia,  or  its  salts,  produce  a similar  ])recipitate,  which  consists 
of  one  ccpiivalent  of  the  bichloride,  and  one  of  muriate  of  ammonia. 


PALLADIUM. 


389 


When  this  compound,  which  is  generally  called  the  muriate  of  plati- 
num and  ammonia^  is  heated  to  redness,  chlorine  and  muriate  of  am- 
monia are  evolved,  and  pure  platinum  remains  in  the  form  of  a delicate 
spongy  mass,  the  power  of  which  in  kindling  an  explosive  mixture  of 
oxygen  and  hydrogen  gases  has  already  been  mentioned.  (Page  147.) 
This  salt  affords  an  easy  method  of  procuring  platinum  in  a metallic  state 
and  of  separating  it  from  other  metals. 

Soda  forms  with  muriate  of  platinum  a double  salt,  which  is  soluble 
in  water  and  alcohol,  and  crystallizes  in  flattened,  oblique,  four-sided 
prisms  of  an  orange-red  colour.  According  to  Dr.  Thomson  it  is  a com- 
pound of  one  equivalent  of  bichloride  of  platinum,  one  equivalent  of 
chloride  of  sodium,  and  eight  equivalents  of  water. 

Sulphuret  of  Platinum. — When  sulphuretted  hydrogen  gas  is  trans- 
mitted through  a solution  of  muriate  of  platinum,  a black  precipitate  is 
thrown  down,  which  was  regarded  by  Vauquelin  as  a hydrosulphuret  of 
oxide  of  platinum.  It  absorbs  oxygen  from  the  air  while  in  a moist 
state,  giving  rise  to  the  formation  of  sulphuric  acid.  Its  composition 
has  not  been  determined  with  accuracy. 

A black  sulphuret  of  platinum  was  procured  by  Mr.  E.  Davy  by 
heating  the  metal  with  sulphur,  and  Vauquelin  obtained  a similar  com- 
pound by  igniting  the  yellow  muriate  of  platinum  and  ammonia  with 
twice  its  weight  of  sulphur.  According  to  the  analysis  of  these  chem- 
ists, it  contains  about  16  per  cent,  of  sulphur. 

Hydrosulphuret  of  platinum  is  converted  by  the  action  of  nitric  acid 
into  a sulphate  which  possesses  remarkable  properties.  On  boiling  it 
in  strong  alcohol,  a black  powder  is  precipitated,  which  consists,  ac- 
cording to  Mr.  E.  Davy,  of  96  per  cent,  of  platinum,  together  with  a 
little  oxygen,  nitrous  acid,  and  carbon,  the  last  of  which  is  supposed 
to  be  accidental.  When  this  powder  is  placed  on  bibulous  paper 
moistened  with  alcohol,  a strong  action  accompanied  with  a hissing 
noise  ensues,  and  the  powder  becomes  red-hot,  and  continues  so  until 
the  alcohol  is  consumed.  The  substance  which  remains  is  pure  pla- 
tinum. 

Fulminating  platinum  may  be  prepared  by  the  action  of  ammonia  in 
.slight  excess  on  a solution  of  sulphate  of  platinum.  (E.  Davy.)  It  is 
analogous  to  the  detonating  compounds  which  ammonia  forms  with  the 
oxides  of  gold  and  silver. 


SECTION  XXVII. 


PALLADIUM.— RHODIUM.— OSMIUM.— IRIDIUM. 

The  four  metals  to  be  described  in  this  section  are  all  contained  in 
the  ore  of  platinum,  and  have  hitherto  been  procured  in  very  small 
quantity.  When  the  ore  is  digested  in  nitro-muriatic  acid,  the  plati- 
num, together  with  palladium,  rhodium,  iron,  copper,  and  lead,  is 
cissolvedi  while  a black  powder  is  left,  consisting  of  osmium  and 
indium. 


33* 


390 


PALLADIUM. 


Palladium. 

This  metal  was  discovered  in  1803  by  Dr.  Wollaston.*  On  adding- 
bicyanuret  of  mercury  dissolved  in  water  to  a neutral  solution  of  the  ore 
of  platinum,  either  before  or  after  the  separation  of  that  metal  by  mu- 
riate of  ammonia,  a yellowish-white  flocculent  precipitate  is  gradually 
deposited,  which  is  cyanuret  of  palladium.  When  this  compound  is 
heated  to  redness,  the  cyanogen  is  expelled,  and  pure  palladium  re- 
mains. In  order  to  obtain  it  in  a malleable  state,  the  metal  should  be 
heated  with  sulphur,  and  the  resulting  sulphuret  purified  by  cupellation 
in  an  open  crucible  with  borax  and  a little  nitre.  It  is  then  roasted  at  a 
low  red  heat  on  a flat  brick,  and  when  reduced  to  a pasty  consistence, 
it  is  pressed  into  a square  or  oblong,  perfectly  flat,  cake.  It  is  again 
to  be  roasted  very  patiently,  at  a low  red  heat,  until  it  becomes  spongy 
on  the  surface;  and  when  quite  cold,  it  is  condensed  by  frequent  tap- 
pings with  a light  hammer.  By  alternate  roastings  and  tappings,  the 
sulphur  is  burned  off,  and  the  metal  rendered  sufficiently  dense  to  be 
laminated.  Thus  prepared  it  is  rather  brittle  while  hot,  which  Dr. 
Wollaston  supposed  to  arise  from  a small  remnant  of  sulphur.  (Phil. 
Trans.  1829.  p.  7.) 

Palladium  resembles  platinum  in  colour  and  lustre.  It  is  ductile  as 
well  as  malleable,  and  is  considerably  harder  than  platinum.  Its  spe- 
cific. gravity  varies  from  11.3  to  11.8.  (Wollaston.)  In  fusibility  it  is 
intermediate  between  gold  and  platinum,  and  is  dissipated  in  sparks, 
when  intensely  heated  by  the  oxy-hydrogen  blowpipe.  At  a red  heat 
in  oxygen  gas  its  surface  acquires  a fine  blue  colour,  owing  to  super- 
ficial oxidation;  but  the  increase  of  weight  is  so  slight  as  not  to  be  ap- 
preciated. 

Palladium  is  oxidized  and  dissolved  by  nitric  acid,  and  even  the  sul- 
phuric and  muriatic  acids  act  upon  it  by  the  aid  of  heat;  but  its  proper 
solvent  is  nitro-muriatic  acid.  Its  oxide  forms  beautiful  red-coloured 
salts,  from  which  metallic  palladium  is  precipitated  by  protosulphate  of 
iron  and  all  the  metals  described  in  the  foregoing  sections,  excepting 
silver,  gold,  and  platinum. 

Oxide  of  palladium  is  precipitated  by  pure  potassa,  as  an  orange- 
coloured  hydrate,  which  becomes  black  when  dried,  and  is  decompos- 
ed by  a red  heat.  It  may  be  regarded  as  the  protoxide,  and  according 
to  the  late  researches  of  Berzelius  consists  of  one  equivalent  of  oxygen, 
and  53  parts,  or  what  he  considers  one  equivalent  of  palladium.  An 
oxide  with  twice  as  much  oxygen  may  be  thrown  down  by  alkalies  from 
a solution  of  the  bichloride.  It  falls  as  a hydrate  of  a deep  yellowish- 
brown  colour,  which  retains  a little  alkali  in  combination;  but  on  heat- 
ing the  solution  to  212°  F.,  the  alkali  is  dissolved,  and  a black  oxide 
separates.  (An.  de  Ch.  etde  Ph.  xl.  72.) 

Berzelius  describes  two  chlorides.  The  protochloride  is  formed  by 
evaporating  the  nitro-muriatic  solution  to  dryness.  When  crystallized 
in  solution  with  cliloride  of  ])Otassium  it  forms  a double  cldoride,  which 
crystallizes  citlicr  in  small  needles  of  a golden  yellow  tint,  or  in  larger 
prisms  of  a brownish-yellow  colour.  It  is  soluble  in  water  and  alcohol; 
but  in  distilling  the  spirituotis  solution,  most  of  the  palladium  is  reduced. 
It  contains  an  etpiivalcnt  of  each  chloride. 

On  evaporating  this  double  compound  with  nitro-muriatic  acid,  deut- 
oiide  of  nitrogen  is  disengaged,  and  microscopic  crystals  of  a cinna- 


Philosophical  Transactions  for  1804  and  1805. 


RHODIUM. 


391 


bar-red  colour  are  deposited;  but  when  large  enough  to  be  appreciated, 
their  colour  appears  reddish-brown,  and  their  form  that  of  the  regular 
octohedron.  They  consist  of  one  equivalent  of  bichloride  of  palladium 
and  one  of  chloride  of  potassium.  It  is  converted  by  heat  into  the  dou- 
ble protochloride,  with  evolution  of  chlorine;  and  water  occasions  a 
similar  change. 

Rhodium, 

This  metal  was  discovered  by  Dr.  Wollaston  at  the  time  he  was  oc- 
cupied with  the  discovery  of  palladium.  On  immersing  a thin  plate  of 
clean  iron  into  the  solution  from  which  palladium  and  the  greater  part  of 
the  platinum  have  been  precipitated,  the  rhodium,  together  with  small 
quantities  of  platinum,  copper,  and  lead,  is  thrown  down  in  the  me- 
tallic state;  and  on  digesting  the  precipitate  in  dilute  nitric  acid,  the 
two  last  metals  are  removed.  The  rhodium  and  platinum  are  then  dis- 
solved by  means  of  nitro-muriatic  acid,  and  the  solution,  after  being 
mixed  with  some  muriate  of  soda,  is  evaporated  to  dryness.  Two  dou- 
ble chlorides  result,  that  of  platinum  and  sodium,  and  of  rhodium  and 
sodium,  the  former  of  which  is  soluble,  and  the  latter  insoluble  in  al- 
cohol; and  they  may,  therefore,  be  separated  from  each  other  by  this 
menstruum.  The  double  chloride  of  rhodium  is  then  dissolved  in  water, 
and  metallic  rhodium  precipitated  by  insertion  of  a rod  of  zinc. 

Rhodium,  thus  procured,  is  in  the  form  of  a black  powder,  which 
requires  the  strongest  heat  that  can  be  produced  in  a wind  furnace  for 
fusion,  and  when  fused  has  a white  colour  and  metallic  lustre.  It  is 
brittle,  is  extremely  hard,  and  has  a specific  gravity  of  about  11.  It 
attracts  oxygen  at  a red  heat,  a mixture  of  peroxide  and  protoxide  be- 
ing formed.  It  is  not  attacked  by  any  of  the  acids  when  in  its  pure 
state;  but  if  alloyed  with  other  metals,  such  as  copper  or  lead,  it  is 
dissolved  by  nitro-muriatic  acid,  a circumstance  which  accounts  for  its 
presence  in  the  solution  of  crude  platinum.  It  is  oxidized  by  being*  ig- 
nited either  with  nitre,  or  bisulphate  of  potassa.  When  heated  with 
the  latter,  sulphurous  acid  gas  is  evolved,  and  a double  sulphate  of 
rhodium  and  potassa  is  generated,  which  dissolves  readily  in  hot  water, 
and  yields  a yellow  solution.  The  presence  of  rhodium  in  platinum, 
iridium,  and  osmium,  may  thus  be  detected,  and  by  repeated  fusion  a 
perfect  separation  be  accomplished.  (Berzelius.) 

Chemists  are  acquainted  with  two  oxides  of  rhodium.  The  protoxide 
is  black,  and  the  peroxide,  which  is  the  base  of  the  salts  of  rhodium, 
is  of  a yellow  colour.  Most  of  its  salts  are  either  red  or  yellow;  and  the 
rose-red  tint  of  the  muriate  suggested  the  name  of  rhodium.  (From 
po^ov,  a rose.)  According  to  Dr.  Thomson,  the  equivalent  of  rhodium 
is  44,  and  the  oxygen  in  its  two  oxides  is  in  the  ratio  of  1 to  2;  but  the 
number  selected  by  Berzelius,  as  the  result  of  his  recent  researches,  is 
about  52;  and  the  oxygen  in  the  two  oxides  is  as  1 to  1.5.  (An.  de  Ch. 
et  de  Ph.  xl.  51.) 

Berzelius  succeeded  in  preparing  two  chlorides,  the  composition  of 
which  is  similar  to  that  of  the  oxides  of  rhodium,  that  is,  an  equivalent 
of  the  metal  is  united  in  one  of  them  with  one  equivalent,  and  in  the 
other  with  one  equivalent  and  a half  of  chlorine.  The  latter,  or  sesqui- 
chloride,  forms  a double  chloride  both  with  chloride  of  potassium  and 
sodium.  The  former  consists  of  one  equivalent  of  each  chloride;  but 
in  the  latter  one  equivalent  of  sesquichloride  of  rhodium  is  combined 
with  an  equivalent  and  a half  of  chloride  of  sodium. 


392 


OSMIUM  AND  IRIDIUM. 


Osmium  and  Iridium, 

These  metals  were  discovered  by  the  late  Mr.  Tennant  in  the  year 
1803,*  and  the  discovery  of  iridium  was  made  about  the  same  time  by 
M.  Descotils  in  France.  The  black  powder  mentioned  at  the  begMuning* 
of  this  section  is  a compound  of  iridium  and  osmium,  an  alloy  whicli  Dr. 
Wollaston  has  detected  in  the  form  of  flat  white  grains  among  frag- 
ments of  crude  platinum.  This  alloy,  which  is  quite  insoluble  in  nitro- 
muriatic  acid,  is  the  source  from  which  iridium  and  osmium  are  ex- 
tracted. 

Osmium. — This  melal  is  separated  from  the  alloy  just  mentioned  by 
fusion  with  soda  or  nitre;  and  the  following  process,  given  by  Dr. 
Wollaston,  may  be  resorted  to  with  advantage.  (Phil.  Trans.  182*9.  p. 
8.)  The  pulverulent  alloy  is  ground  into  a fine  powder  with  a third  of 
its  weight  of  nitre,  and  the  mixture  heated  to  redness  in  a silver  cruci- 
ble, until  it  is  reduced  to  a pasty  state,  when  the  characteristic  odour 
of  oxide  of  osmium  will  be  perceptible.  Dissolve  the  soluble  parts, 
which  contain  oxide  of  osmium  in  combination  with  potassa,  in  the 
smallest  possible  quantity  of  water,  and  acidulate  the  solution,  intro- 
duced into  a retort,  with  sulphuric  acid  diluted  with  its  own  weight  of 
water.  By  distilling  rapidly  into  a clean  receiver  as  long  as  osmic  fumes 
pass  over,  the  oxide  will  be  collected  on  its  sides  in  the  form  of  a white 
crust,  and,  there  melting,  it  will  run  down  in  drops  beneath  the  wa- 
tery solution,  forming  a fluid  flattened  globule  at  the  bottom.  As  the 
receiver  cools,  the  oxide  becomes  solid  and  crystallizes. 

Osmium  is  precipitated  from  the  solution  of  its  oxide  by  all  the 
metals,  excepting  gold  and  silver.  A convenient  mode  of  reduction  is 
to  agitate  it  with  mercury,  adding  muriatic  acid  to  decompose  the  pro- 
toxide of  mercury  which  is  formed,  and  then  expelling  the  mercury 
and  calomel  by  heat.  The  osmium  is  left  as  a black  porous  powder, 
which  acquires  metallic  lustre  by  friction.  If  it  has  been  exposed  to  a 
very  gentle  heat,  its  specific  gravity  is  7,  It  takes  fire  when  heated  in 
the  open  air,  and  is  readily  oxidized  and  dissolved  by  fuming  nitric 
acid;  but  a red  heat  gives  it  greater  compactness,  and  in  that  state  it 
ceases  to  be  attacked  by  acids,  and  may  be  freely  heated  without  oxi- 
dation. In  its  densest  state  Berzelius  found  its  specific  gravity  to  be  10. 
(An.  de  Ch.  et  de  Ph.  xl.  257,  and  xlii.  185  ) 

Oxides. — Recent  researches  have  induced  Berzelius  to  consider  the 
equivalent  of  osmium  as  identical  with  that  of  platinum,  being  about 
99.  He  has  enumerated  five  degrees  of  oxidation.  The  protoxide  is 
precipitated  by  pure  alkalies  from  the  protochloride,  and  falls  of  a deep 
green,  nearly  black,  colour,  as  a hydrate,  which  is  soluble  in  acids, 
and  detonates  when  heated  with  combustible  matter.  The  deutoxide 
is  thrown  down  as  a hydrate  of  a deep  brown  colour,  when  a saturated 
solution  of  the  bichloride,  is  heated  with  carbonate  of  soda.  It  retains 
a little  alkali  in  combination;  but  the  soda  is  easily  removed  by  dilute 
muriatic  acid,  without  the  oxide  being  dissolved.  The  tritoxide  is 
prepared  in  like  manner  from  the  terchloride.  The  sequi-oxide  has 
not  been  obtained  in  a separate  state;  but  it  is  procured  in  combination 
with  ammonia  wlicn  tlie  deutoxide  is  treated  with  a large  excess  of  pure 
ammonia,  nitrogen  gas  being  disengaged  at  the  same  time. 

The  highest  stage  of  oxidation  is  the  volatile  oxide,  which  consists  of 
four  equivalents  of  oxygen  and  one  of  osmium.  (Berzelius.)  It  is  the 


Philosophical  Transactions  for  1804. 


IRIDIUM. 


393 


product  of  the  oxidation  of  osmium  by  acids,  by  combustion,  or  by 
fusion  with  nitre  or  alkalies;  and  it  may  be  procured  by  the  process 
above  mentioned  in  colourless  transparent  elongated  crystals,  or  as  a 
colourless  solution  in  water.  Its  vapour  is  very  acrid,  exciting  cough, 
irritating  the  eyes,  and  producing  a copious  flow  of  saliva;  and  its  odour 
is  disagreeable  and  pungent,  somewhat  like  that  of  chlorine;  a proper- 
ty which  suggested  the  name  of  osmium.*  It  does  not  combine  with 
acids;  on  the  contrary,  though  it  has  no  acid  reaction,  it  unites  with 
alkalies,  and  the  compound  sustains  a strong  heat  without  decomposi- 
tion. It  is  hence  sometimes  called  osmic  acid.  When  touched  it  com- 
municates a stain  which  cannot  be  removed  by  washing.  With  the  in- 
fusion of  gall-nuts  it  yields  a purple  solution,  which  afterwards  acquires 
a deep-blue  tint;  a character  which  forms  a sure  and  extremely  delicate 
test  for  peroxide  of  osmium.  By  sulphurous  acid  it  is  deoxidized,  and 
the  colour  of  the  solution  passes  through  the  shades  of  yellow,  orange, 
brown,  green,  and  lastly  blue,  when  it  resembles  sulphate  of  indigo. 
These  changes  correspond  to  sulphates  of  different  oxides  of  osmium, 
the  last  or  blue  oxide  being  a compound  of  protoxide  and  sesqui-oxide 
of  osmium. 

Berzelius  has  described  four  chlorides  of  osmium,  corresponding  to 
the  four  first  degrees  of  oxidation  above  mentioned.  When  osmium  is 
heated  in  a tube  in  a current  of  dry  chlorine  gas,  a deep-green  subli- 
mate is  formed,  which  is  the  protochloride.  On  continuing  the  process 
it  yields  a red  sublimate,  which  is  the  bichloride.  For  the  remaining 
details,  which  are  rather  minute,  I may  refer  to  the  essay  already  cited. 
Several  of  these  chlorides  yield  double  compounds  with  sodium,  potas- 
sium, and  ammonia. 

Osmium  unites  with  sulphur  in  the  dry  way,  or  when  precipitated 
from  the  chlorides  by  sulphuretted  hydrogen.  The  sulphurets  corres- 
pond to  the  number  of  the  oxides.  (Berzelius.) 

Iridium. — In  the  process  already  described  for  separating  osmium 
from  its  ore,  oxide  of  iridium  is  left  in  combination  with  potassa,  after 
the  soluble  compound  of  osmium  has  been  removed  by  the  action  of 
water.  On  digesting  the  mass  in  muriatic  acid,  a blue  solution  is  ob- 
tained; but  it  afterwards  becomes  of  an  olive-green  hue,  and  subse- 
quently acquires  a deep-red  tint.  This  variety  of  colour,  which  sug- 
gested the  name  of  iridium,  is  owing  to  the  metal  passing  through  dif-. 
ferent  stages  of  oxidation.  In  general,  after  treatment  with  muriatic 
acid,  some  undecomposed  ore  remains,  which,  from  its  refractory  na- 
ture, often  requires  repeated  fusion  with  nitre. 

Muriate  of  iridium,  when  deprived  of  its  excess  of  acid  by  heat,  may 
be  procured  by  evaporation  in  crystals  of  a deep  brown  colour.  This 
compound,  which  is  probably  rather  a chloride  than  a muriate,  is  dis- 
tinguished by  forming  with  water  a red  solution,  which  is  rendered  col- 
ourless by  the  pure  alkalies  or  alkaline  earths,  by  sulphuretted  hydro- 
gen, infusion  of  gall-nuts,  or  ferrocyanate  of  potassa.  It  is  decompo- 
sed by  nearly  all  the  metals  except  gold  and  platinum,  iridium  being 
thrown  down  in  the  metallic  state.  The  metal  may  also  be  procured  by 
exposing  the  chloride  to  a red  heat. 

Iridium  is  a brittle  metal,  and  apt  to  fall  into  powder  when  burnish- 
ed; but  with  care  it  may  be  polished,  and  then  acquires  the  appearance 
of  platinum.  Of  all  known  metals  it  is  the  most  infusible.  Mr.  Chil- 
dren, by  means  of  his  large  galvanic  battery,  fused  it  into  a globule  of 
a brilliant  metallic  lustre  and  white  colour,  having  a density  of  18.68; 


* From  odour. 


394 


PLUEANIUxM  AND  KHUTENIUM. 


but  the  attempts  at  fusion  by  Berzelius  were  unsuccessful.  Its  greatest 
specific  gravity  in  the  unfusecl  state  is  15.8629.  It  is  oxidized  at  a red 
heat  in  tlie  open  air,  if  in  a state  of  fine  division,  but  not  otherwise; 
and  it  is  attacked  with  difficulty  even  by  nitro- muriatic  acid. 

According  to  the  late  researches  of  Berzelius,  the  equivalent  of  iri- 
dium is  identical  with  that  of  platinum,  and  it  is  capable  of  forming  four 
oxides  corresponding  to  analogous  chlorides.  The  protoxide,  sesqui- 
oxide,  and  tritoxide  are  precipitated  by  alkalies  from  the  chloride  to 
which  they  are  respectively  proportional.  The  protoxide  is  green- 
ish-gray as  a hydrate,  and  black  when  anhydrous.  The  sesqui- 
oxide  is  bluish-black  in  the  dry  state,  and  deep-brown'^  as  a hydrate. 
The  hydrated  tritoxide  is  of  a yellowish-brown  or  greenish  colour.  The 
deutoxide  has  not  hitherto  been  insulated.  Berzelius  has  not  fully  de- 
cided the  nature  of  the  compound  which  is  considered  as  the  blue 
oxide,  that  which  forms  a blue  solution  with  acids;  but  he  believes  it  to 
be  a compound  of  the  protoxide  and  sesqui-oxide.  This  variety  of 
oxides,  together  with  the  facility  with  which  they  appear  to  pass  from 
one  to  the  other,  amply  accounts  fqr  the  diversity  of  tints  sometimes 
observed  in  solutions  of  iridium. 

Besides  forming  four  simple  chlorides,  proportional  to  the  oxides 
above  mentioned,  iridium  forms  double  chlorides  with  sodium  and  potas- 
sium, for  an  account  of  which  I refer  to  the  essays  of  Berzelius  already 
cited  in  the  history  of  osmium. 

Iridium  has  a considerable  affinity  for  carbon,  combining  with  it  when 
a piece  of  metal  is  held  in  the  flame  of  a spirit  lamp.  The  resulting 
cai’buret  contains  19.8  per  cent,  of  carbon. 

Pluranium  and  Rhutenium. 

From  some  observations  by  M.  Osann,  it  appears  that  the  insoluble 
residue  left  after  the  action  of  nitro-muriatic  acid  on  the  Uralian  ore  of 
platinum,  contains  two  new  metals,  to  which  he  has  given  the  names  of 
pluranium  and  rhutenium.  Of  their  properties  little  is  known,  and 
the  certainty  that  they  are  new  metals  has  not  yet  been  established. 
(Phil.  Mag.  and  Annals,  v.  233.)* 


* As  an  appendix  to  Dr.  Turner’s  account  of  the  metals,  it  may  be 
proper  to  give  a short  notice  of  vanadium,  a metal  discovered  since  the 
last  London  edition  of  this  work  was  published. 

Vanadium  was  discovered  by  M.  Sefstrbm,  director  of  the  school  of 
Mines  of  Fahlun  in  Sweden,  while  examining  a specimen  of  malleable 
iron,  extracted  from  the  ore  of  Taberg,  in  Smoland.  The  cast  iron 
from  the  same  ore,  contained  more  of  the  new  substance,  a circum- 
stance which  led  M.  Sefstrom  to  presume  that  the  scoriae  separated  in 
the  operation  of  refining,  would  be  found  to  contain  a still  lai*ger  quan- 
tity. This  proved  to  be  the  fact,  and  by  treating  the  scoriae,  the  Swe- 
dish chemist  was  enabled  to  obtain  a sufficient  quantity  of  the  new  metal 
to  study  its  properties. 

Vanadium  was  obtained  in  the  form  of  a coherent  mass,  possessing  a 
feeble  metallic  lustre,  and  forming  a good  conductor  of  electricity. 
Before  the  blow))i|)e,  it  colours  the  flux,  like  chromium,  of  a hand- 
some green  colour.  It  combines  wit!i  oxygen  in  two  proportions, 
forming  an  acid  and  an  oxide.  I'lie  acid,  called  vanadic  acid,  is  red, 
pulverulent,  and  fusible.  After  fusion,  it  takes  the  form  of  a crystal- 
line mass  on  cooling.  It  is  somewhat  soluble  in  water,  reddens  litmus, 
and  forms  yellow  neutral  salts,  and  orange-coloured  bi-salts.  The  oxide 


METALLIC  COMBINATIONS. 


395 


SECTION  XXVIII. 

ON  METALLIC  COMBINATIONS. 

Havi:n^g  completed  the  history  of  the  individual  metals,  and  of  the 
compounds  resulting*  from  their  union  with  the  simple  non-metallic 
bodies,  I shall  treat  briefly  in  the  present  section  of  the  combinations  of 
the  metals  with  each  other.  These  compounds  are  called  alloys'^  and 
to  those  alloys  of  which  mercury  is  a constituent,  the  term  amalgam  is 
applied.  It  is  probable  that  each  metal  is  capable  of  uniting  in  one  or 
more  proportions  with  every  other  metal,  and  on  this  supposition  the 
number  of  alloys  would  be  exceedingly  numerous.  This  department  of 
chemistry,  however,  owing  to  its  having  been  cultivated  with  less  zeal 
than  most  other  branches  of  the  science,  is  as  yet  limited,  and  our 
knowledge  concerning  it  imperfect.  On  this  account  I shall  mention 
those  alloys  only  to  which  some  particular  interest  is  attached. 

Metals  do  not  combine  with  each  other  in  their  solid  state,  owing  to 
the  influence  of  chemical  affinity  being  counteracted  by  the  force  of 
cohesion.  It  is  necessary  to  liquefy  at  least  one  of  them,  in  which 
ase  they  always  unite,  provided  their  mutual  attraction  is  ener- 
getic. Thus,  brass  is  formed  when  pieces  of  copper  are  put  into  melted 
zinc;  and  gold  unites  with  mercury  at  common  temperatures  by  mere 
contact. 

Metals  appear  to  unite  with  one  another  in  every  proportion  precisely 
in  the  same  manner  as  sulphuric  acid  and  water.  Thus  there  is  no  limit 
to  the  number  of  alloys  of  gold  and  copper.  It  is  certain,  however, 
that  metals  have  a tendency  to  combine  in  definite  proportion;  for  sev- 
eral atomic  compounds  of  this  kind  occur  native.  The  crystallized 
amalgam  of  silver,  for  example,  is  composed,  according  to  the  analysis 
of  Klaproth,  of  64  parts  of  mercury  and  36  of  silver,  numbers  which 
are  so  nearly  in  the  ratio  of  200  to  110,  that  the  amalgam  may  be  infer- 
red to  'bontsin  one  equivalent  of  each  of  its  elements.  It  is  indeed  pos- 
sible that  the  variety  of  proportion  is  rather  apparent  than  real,  arising 
from  the  mixture  of  a few  definite  compounds  with  each  other,  or  with 
uncombined  metal;  an  opinion  not  only  suggested  by  the  mode  in 


is  of  a brown  colour,  approaching  to  black.  It  dissolves  readily  in 
acids,  forming  deep  brown  coloured  salts,  which  assume  a beautiful 
blue  tint  on  the  addition  of  nitric  acid,  with  the  occurrence  of  effer- 
vescence. The  change  of  colour  thus  induced,  is  due  to  the  formation 
of  a compound  between  vanadic  acid  and  oxide  of  vanadium. 

Oxide  of  vanadium,  when  formed  in  the  moist  way,  is  soluble  in  wa- 
ter and  in  alkalies.  The  new  metal  does  not  combine  with  sulphur,  but 
is  capable  of  uniting  with  chlorine  and  fluorine. 

Vanadium  has  many  analogies  with  chromium,  and  is  liable  to  be  con- 
founded with  it.  Since  the  observations  of  Sefstrom,  it  has  been  de- 
tected by  Wohler  in  the  brown  lead  ore  of  Zimapan  in  Mexico,  in  which, 
twenty  years  before.  Professor  Del  Rio  supposed  he  had  discovered  a 
new  metal,  though  overruled  in  his  opinion  by  Collet-Descotils,  who 
pronounced  the  specimens  sent  to  him  to  be  merely  impure  chromium. 
More  recently,  Mr.  J.  F.  W.  Johnston  has  discovered  it  in  a mineral 
from  Wanlockhead  in  Scotland,  which  proves  to  be  a vanadiate  of 
lead.  B. 


/ 


396  AMALGAMS. 

which  alloys  are  prepared,  but  in  some  measure  supported  by  observa- 
tion. Thus,  on  adding*  successive  small  quantities  of*  silver  to  mer- 
cury, a ^reat  variety  of  fluid  amalgams  are  apparently  produced;  but, 
in  reality,  the  chief,  if  not  the  sole  compound,  is  a solid  amalgam, 
which  is  merely  diffused  throughout  the  fluid  mass,  and  may  be  sepa- 
rated by  pressing  the  liquid  mercury  through  a piece  of  thick  leather. 

Alloys  are  analogous  to  metals  in  their  chief  physical  properties. 
They  are  opake,  possess  the  metallic  lustre,  and  are  good  conductors 
of  electricity  and  caloric.  They  often  differ  materially  in  some  res- 
pects from  the  elements  of  which  they  consist.  The  colour  of  an  alloy 
is  sometimes  different  from  that  of  its  constituents,  of  which  brass  is  a 
remarkable  example.  The  hardness  of  a metal  is  in  general  increased  by 
being  alloyed,  and  for  this  reason  its  elasticity  and  sonorousness  are  fre- 
quently improved.  The  malleability  and  ductility  of  metals,  on  the 
contrary,  are  usually  impaired  by  combination.  Alloys  formed  of  two 
brittle  metals  are  always  brittle;  and  an  alloy  composed  of  a ductile  and 
a brittle  metal  is  generally  brittle,  especially  if  the  latter  predominate. 
An  alloy  of  two  ductile  metals  is  sometimes  brittle. 

The  density  of  an  alloy  is  sometimes  less,  sometimes  greater,  than 
the  mean  density  of  the  metals  of  which  it  is  composed. 

The  fusibility  of  metals  is  greatly  increased  by  being  alloyed.  Thus 
pure  platinum,  which  cannot  be  completely  fused  in  the  ‘most  intense 
heat  of  a wind  furnace,  forms  a very  fusible  alloy  with  arsenic. 

The  tendency  of  metals  to  unite  with  oxygen  is  considerably  aug- 
mented by  being  alloyed.  This  effect  is  particularly  conspicuous  when 
dense  metals  are  liquefied  by  combination  with  quicksilver,  and  is  mani- 
festly owing  to  the  loss  of  their  cohesive  power.  Lead  and  tin,  for  in- 
stance, when  united  with  mercury,  are  soon  oxidized  by  exposure  to  the 
atmosphere;  and  even  gold  and  silver  combine  with  oxygen,  when  the 
amalgams  of  those  metals  are  agitated  with  air.  The  oxidability  of  one 
metal  in  an  alloy  appears  in  some  instances  to  be  increased  in  conse- 
quence of  a galvanic  action.  Thus,  Mr.  Faraday  observed,  that  an 
alloy  of  steel  with  100th  of  its  weight  of  platinum  was  dissolved  with 
effervescence  in  dilute  sulphuric  acid,  which  was  so  weak  that  it  scarcely 
acted  on  common  steel; — an  effect  which  he  ascribes  to  the  steel  in  the 
alloy  being  rendered  positive  by  the  presence  of  the  platinum. 

Amalgams. 

Quicksilver  unites  w’ith  potassium  when  agitated  in  a glass  tube  with 
that  metal,  forming  a solid  amalgam.  When  the  amalgam  is  put  into 
water,  the  potassium  is  gradually  oxidized,  hydrogen  gas  is  disengaged, 
and  the  mercury  resumes  its  liquid  form.  A similar  compound  may  be 
obtained  with  sodium.  These  amalgams  may  also  be  procured  by 
placing  the  negative  wire  in  contact  with  a globule  of  mercury  during 
the  process  of  decomposing  potassa  and  soda  by  galvanism. 

A solid  amalgam  of  tin  is  employed  in  making  looking-glasses;  and  an 
amalgam  made  of  one  part  of  lead,  one  of  tin,  two  of  bismuth,  and  four 
parts  of  mercury,  is  used  for  silvering  the  inside  of  hollow  glass  globes. 
This  amalgam  is  solid  at  common  temperatures;  but  is  fused  by  a slight 
degree  of  heat. 

'I'hc  amalgam  of  zinc  and  tin,  used  for  promoting  the  action  of  the 
electrical  machine,  is  made  !)y  fusing  one  part  of  zinc  with  one  of  tin, 
and  then  agitating  the  fKjuid  mass  with  two  parts  of  mercury  placed  in 
a wooden  box.  Mercury  evinces  little  disposition  to  unite  with  iron, 
and,  on  this  account,  it  is  usually  preserved  in  iron  bottles. 

The  amalgam  of  silver,  as  already  mentioned,  is  a mineral  production. 
I’he  process  of  separating  silver  from  its  ores  by  amalgamation,  prac- 


ALLOYS. 


397 


tised  on  a larg’e  scale  at  Freyberg  in  Germany,  is  founded  on  the  affinity 
of  mercury  for  silver.  On  exposing  the  amalgam  to  heat,  the  quick- 
silver is  volatilized,  and  pure  silver  remains. 

Gold  unites  with  remarkable  facility  with  mercury,  forming  a white- 
coloured  compound.  An  amalgam  composed  of  one  part  of  gold  and 
eight  of  mercury  is  employed  in  gilding  brass.  The  brass,  after  being 
rubbed  with  nitrate  of  mercury  in  order  to  give  it  a thin  film  of  quick- 
silver, is  covered  with  the  amalgam  of  gold,  and  then  exposed  to  heat 
for  the  purpose  of  expelling  the  mercury. 

Alloys  of  Arsenic, 

Arsenic  has  a tendency  to  render  the  metals,  with  which  it  is  alloyed, 
both  brittle  and  fusible.  It  has  the  property  of  destroying  the  colour  of 
gold  and  copper.  An  alloy  of  copper,  with  a tenth  part  of  arsenic,  is 
so  very  similar  in  appearance  to  silver,  that  it  has  been  substituted  for  it. 
The  whiteness  of  this  alloy  affords  a rough  mode  of  testing  for  arsenic, 
for  if  arsenious  acid  and  charcoal  be  heated  between  two  plates  of  cop- 
per, a white  stain  afterwards  appears  upon  its  surface,  owing  to  the  form- 
ation of  an  arseniuret  of  copper. 

The  presence  of  arsenic  in  iron  has  a very  pernicious  effect^  for 
even  though  in  small  proportion,  it  renders  the  iron  brittle,  especially 
when  heated. 

The  alloy  of  tin  and  arsenic  is  employed  for  forming  arseniuretted 
hydrogen  gas  by  the  action  of  muriatic  acid.  The  tin  of  commerce 
sometimes  contains  a minute  quantity  of  this  alloy. 

An  alloy  of  platinum  with  ten  parts  of  arsenic  is  fusible  at  a heat  a 
little  above  redness,  and  may,  therefore,  be  cast  in  moulds.  On  ex- 
posing the  alloy  to  a gradually  increasing  temperature  in  open  vessels, 
the  arsenic  is  oxidized  and  expelled,  and  the  platinum  recovers  its  purity 
and  infusibility. 

Alloys  of  TiUy  Lead^  Antimony^  and  Bismuth, 

Tin  and  lead  unite  readily  when  fused  together.  Equal  parts  of  these 
metals  constitute  an  alloy  which  is  more  fusible  than  either  separately, 
and  is  the  common  solder  of  the  glaziers.  Its  point  of  fusion  is  about 
360^  F.  M.  Kupfer  has  observed  that  most  of  the  alloys  of  tin  and  lead 
made  in  atomic  proportion,  have  a specific  gravity  less  than  their  calcu- 
lated density;  from  which  it  is  manifest  that  they  expand  in  uniting. 
The  amalgams  of  lead  and  tin,  on  the  contrary,  occupy  less  space,  when 
combined,  than  their  elements  did  previously. 

Tin,  alloyed  with  small  quantities  of  antimony,  copper,  and  bismuth, 
forms  the  best  kind  of  pewter.  Inferior  sorts  contain  a large  proportion 
of  lead. 

Tin,  lead,  and  bismuth,  form  an  alloy  which  is  fused  by  a temperature 
below  212^  Fahr.  The  best  proportion,  according  to  M.  D’Arcet,  is 
eight  parts  of  bismuth,  five  of  lead,  and  three  of  tin. 

An  alloy  of  three  parts  of  lead  to  one  of  antimony  constitutes  the 
substance  of  which  types  for  printing  are  made. 

Alloys  of  Copper, 

Copper  forms  with  tin  several  valuable  alloys,  which  are  characterized 
by  their  sonorousness.  Bronze  is  an  alloy  of  copper  with  about  eight  or 
ten  per  cent  of  tin,  together  with  small  quantities  of  other  metals  which 
are  not  essential  to  the  compound.  Cannons  are  cast  with  an  alloy  of  a 
similar  kind. 

The  best  bell-metal  is  composed  of  80  parts  of  zinc  and  20  of  tin; — 
the  Indian  gong,  celebrated  for  the  richness  of  its  tones,  contains  cop- 

34 


398 


ALLOYS. 


per  and  tin  in  this  proportion.  A specimen  of  English  bell-mctal  was 
found  by  Dr.  Thomson  to  consist  of  80  parts  of  copper,  10.1  of  tin, 

5.6  of  zinc,  and  4.3  of  lead.  Lead  and  antimony,  though  in  small 
quantity,  have  a remarkable  effect  in  diminishing  the  elasticity  and  sono- 
rousness of  the  compound.  Speculum-metal^  with  which  mirrors  for 
telescopes  are  made,  consists  of  about  two  parts  of  copper  and  one  of 
tin.  The  whiteness  of  the  alloy  is  improved  by  the  addition  of  a little 
arsenic. 

Copper  and  zinc  unite  in  several  proportions,  forming  alloys  of  great 
importance  in  the  arts.  The  best  brass  consists  of  four  parts  of  copper 
to  one  of  zinc;  and  when  the  latter  is  in  a greater  proportion,  com- 
pounds are  generated  which  are  called  iomhac.  Dutch-gold,  and  pinchbeck. 
The  white  copper  of  the  Chinese  is  composed,  according  to  the  analysis 
of  Dr.  Fyfe,  of  40.4  parts  of  copper,  25.4  of  zinc,  31.6  of  nickel,  and 

2.6  of  iron. 

The  art  of  tinning  copper  consists  in  covering  that  metal  with  a thin 
layer  of  tin,  in  order  to  protect  its  surface  from  rusting.  For  this  pur- 
pose, pieces  of  tin  are  placed  upon  a well  polished  sheet  of  copper, 
which  is  heated  sufficiently  for  fusing  the  tin.  As  soon  as  the  tin  lique- 
fies, it  is  rubbed  over  the  whole  sheet  of  copper,  and  if  the  process  is 
skilfully  conducted,  adheres  uniformly  to  its  surface.  The  oxidation  of 
the  tin,  a circumstance  which  would  entirely  prevent  the  success  of  the 
operation,  is  avoided  by  employing  fragments  of  resin  or  muriate  of  am- 
monia, and  regulating  the  temperature  with  great  care.  The  two  metals 
do  not  actually  combine;  but  the  adhesion  is  certainly  owing  to  their 
mutual  affinity.  Iron,  which  has  a weaker  attraction  than  copper  for 
tin,  is  tinned  with  more  difficulty  than  that  metal. 

Alloys  of  Steel, 

Messrs.  Stodart  and  Faraday  have  succeeded  in  making  some  very  im- 
portant alloys  of  steel  with  other  metals.  (Fhilos.  Trans,  for  1822.) 
Their  experiments  induced  them  to  believe  that  the  celebrated  Indian 
steel,  called  wootz,  is  an  alloy  of  steel  with  small  quantities  of  silicium 
and  aluminium;  and  they  succeeded  in  preparing  a similar  compound, 
possessed  of  all  the  properties  of  wootz.  They  ascertained  that  silver 
combines  with  steel,  forming  an  alloy  which,  although  it  contains  only 
l-500th  of  its  weight  of  silver,  is  superior  to  wootz  or  the  best  cast 
steel  in  hardness.  The  alloy  of  steel  with  100th  part  of  platinum, 
though  less  hard  than  that  with  silver,  possesses  a greater  degree  of 
toughness,  and  is,  therefore,  highly  valuable  when  tenacity  as  well  as 
hardness  is  required.  The  alloy  of  steel  with  rhodium  even  exceeds 
the  two  former  in  hardness.  The  compound  of  steel  with  palladium, 
and  of  steel  with  iridium  and  osmium,  is  likewise  exceedingly  hard; 
but  these  alloys  cannot  be  employed  extensively,  owing  to  the  rarity  of 
the  metals  of  which  they  are  composed. 

Alloys  of  Silver. 

Silver  is  capable  of  uniting  with  most  other  metals,  and  suffers 
gi’eatly  in  malleability  and  ductility  by  their  presence.  It  may  contain 
a large  quantity  of  copper  without  losing  its  white  colour.  The  stand- 
ard silver  for  coinage  contains  about  1-I3th  part  of  copper,  which  in- 
creases its  hardness,  and  thus  renders  it  more  fit  for  coins  and  many 
other  purposes. 

Alloys  of  Gold, 

I'he  presence  of  other  metals  in  gold  has  a remarkable  effect  in  im- 
pairing its  malleability  and  ductility.  The  metals  which  possess  this 


ALLOYS. 


399 


property  in  the  greatest  degree  are  bismuth,  lead,  antimony,  and  arse- 
nic. Thus,  when  gold  is  alloyed  with  l-1920th  part  of  its  weight  of 
lead,  its  malleability  is  surprisingly  diminished.  A very  small  propor- 
tion of  copper  has  an  influence  over  the  colour  of  gold,  communicating 
to  it  a red  tint,  which  becomes  deeper  as  the  quantity  of  copper  in- 
creases. Pure  gold,  being  too  soft  for  coinage  and  many  purposes 
in  the  arts,  is  always  alloyed  either  with  copper  or  an  alloy  of  copper 
and  silver,  which  increases  the  hardness  of  the  gold  without  mate- 
rially affecting  its  colour  or  tenacity.  Gold  coins  contain  about  l-12th 
of  copper. 


400 


SALTS. 


SALTS. 

GENERAL  REMARKS  ON  SALTS. 

In  the  preceding*  pag*es  I have  been  chiefly  occupied  with  the  de- 
scription either  of  elementary  principles,  or  of  compounds  immediately 
resulting*  from  their  union.  The  class  of  bodies  now  to  be  described  is 
of  a different  nature,  being*  exclusively  compounds  derived  from  the 
combination  of  other  compound  bodies. 

The  term  salt  is  often  somewhat  vaguely  employed  in  chemistry,  but 
according  to  the  usage  of  most  chemists,  it  denotes  a definite  compound 
of  an  acid,  and  an  alkaline  or  salifiable  base,  both  of  which  are  in  every 
case  composed  of  at  least  two  simple  substances.  Sulphate  of  potassa, 
for  instance,  is  a salt,  the  acid  of  which  consists  of  oxygen  and  sulphur, 
and  the  base  of  oxygen  and  potassium.  A different  view  may  indeed 
be  formed  of  the  nature  of  a salt.  Thus,  to  employ  the  example  al- 
ready adduced,  sulphate  of  potassa  contains  sulphur,  oxygen,  and  po- 
tassium; and  it  maybe  thought  that  these  three  elements  do  notexist  in 
the  salt  as  sulphuric  acid  and  potassa,  but  are  combined  directly  and  in- 
discriminately with  each  other.  But  such  an  opinion  is  gratuitous  and 
untenable.  Sulphate  of  potassa  is  said  to  contain  sulphuric  acid  and 
potassa,  because,  in  the  first  place,  it  is  formed  by  the  direct  mixture 
of  these  two  substances;  secondly,  because  the  acid  and  the  alkali, 
after  combination,  may  be  separated  and  again  procured  in  their  original 
state  by  the  agency  of  galvanism;  and,  thirdly,  because  no  known 
affinity  is  in  operation  by  which  the  tendency  of  potassium  to  constitute 
potassa  with  oxygen,  or  of  sulphur  to  form  sulphuric  acid  with  the 
same  element,  may  be  counteracted.  It  is  probable,  indeed,  that  all 
compounds  consisting  of  three  or  more  elementary  principles,  are  com- 
posed of  binary  compounds  united  with  each  other. 

In  studying  the  salts,  it  is  important  to  set  out  with  correct  ideas  con- 
cerning the  nature  of  an  acid  and  an  alkaline  base,  and,  therefore,  a 
few  preliminary  remarks  will  be  made  concerning  the  nature  and  char- 
acteristic properties  of  these  two  classes  of  compounds. 

An  acid  is  commonly  regarded  as  a substance  which  has  a sour  taste, 
reddens  litmus  paper,  and  neutralizes  alkalies.  But  these  properties, 
though  very  conspicuous  in  all  the  powerful  acids,  are  not  altogether 
general,  and,  therefore,  cannot  serve  the  purpose  of  a definition. 
Thus  insoluble  acids,  owing  to  their  insolubility,  do  not  taste  sour,  nor 
redden  litmus  paper,  and  some  bodies,  such  as  carbonic  acid  and  sul- 
phuretted hydrogen,  the  title  of  which  to  be  placed  among  the  acids 
cannot  be  called  in  question,  are  unable  to  destroy  the  alkaline  reaction 
of  potassa.  '^Fhe  most  correct  definition  of  an  acid  with  which  I am  ac- 
quainted is  tlie  following: — an  acid  is  a compound  which  is  capable  of 
uniting  in  definite  ])ropoi*tion  with. alkaline  bases,  and  which,  when 
liquid  or  in  a state  of  solution,  has  either  a sour  taste,  or  reddens  litmus 
paper. 

Most  of  the  acids  contain  oxygen  as  one  of  their  elements,  a circum- 
stance which  induced  Lavoisier  to  suppose  that  oxygen  possesses  some 
specific  power  of  causing  acidity,  and  for  this  reason  he  regarded  it  as 
the  acidifying  principle,  I'he  acquisition  of  new  facts,  however,  has 


GENERAL  REMARKS  ON  SALTS. 


401 


shown  the  fallacy  of  his  opinion.  Acids  may  and  do  exist  which  con- 
tain no  trace  of  oxygen,  nor  does  its  presence  necessarily  give  rise  to 
acidity.  The  compounds  of  oxygen  are  frequently  alkaline  instead  of 
acid;  and  in  many  instances  they  are  neither  acid  nor  alkaline.  No  sub- 
stance, excepting  deutoxide  of  hydrogen,  contains  a larger  proportional 
quantity  of  oxygen  than  water,  and  yet  this  fluid  does  not  possess  the 
slightest  degree  of  acidity.  The  progress  of  science,  indeed,  seems  to 
justify  the  opinion  that  there  is  no  body  to  which  the  term  acidifying 
principle  is  strictly  applicable.  The  acidity  of  any  substance  cannot  be 
referred  to  one  of  its  elements  rather  than  the  other;  but  it  is  a new 
property  peculiar  to  the  compound,  and  to  which  each  of  its  constitu- 
ents contributes. 

An  alkali  is  characterized  by  a peculiar  pungent  taste,  by  its  alkaline 
reaction  on  vegetable  colours,  and  by  neutralizing  acids.  There  are 
many  salifiable  bases,  however,  which  do  not  possess  these  characters. 
Thus  pure  magnesia,  though  it  is  a strong  alkaline  base  and  forms  neu- 
tral salts  with  acids,  is  insipid,  and  barely  produces  an  appreciable  eifect 
on  yellow  turmeric  paper, — an  inaction  obviously  owing  to  its  insolubi- 
lity. Some  compounds  neutralize  the  properties  of  acids  in  an  imper- 
fect manner,  although  they  form  perfect  salts.  For  these  reasons  it  is 
desirable  to  define  precisely  what  is  meant  by  a salifiable  base,  and  the 
following  definition  appears  to  me  to  answer  the  purpose.  Every  com- 
pound may  be  regarded  as  an  alkaline  or  salifiable  base,  which  forms 
definite  compounds  with  acids,  and  which,  when  liquid  or  in  a state  of 
solution,  has  an  alkaline  reaction.  All  alkaline  bases,  with  the  excep- 
tion of  ammonia  and  the  vegetable  alkalies,  are  metallic  oxides. 

The  nomenclature  of  the  salts  was  explained  on  a former  occasion. 
(Page  108.)  The  insufficiency  of  the  division  into  neutral,  super,  and 
s«^6-salts  will  be  made  apparent  by  the  following  remarks.  In  the  first 
place,  some  alkaline  bases  form  more  than  one  super-salt,  in  which  case 
two  or  more  different  salts  would  be  included  under  the  same  name. 
Secondly,  some  salts  have  an  acid  reaction,  and  might  therefore  be  de- 
nominated super-salts,  although  they  do  not  contain  an  excess  of  acid. 
Nitrate  of  lead,  for  instance,  has  the  property  of  reddening  litmus  paper; 
whereas  it  consists  of  one  equivalent  of  oxide  of  lead,  and  one  equiva- 
lent of  nitric  acid,  and,  therefore,  in  composition  is  precisely  analogous 
to  nitrate  of  potassa,  which  is  a neutral  salt.  This  fact  was  noticed  some 
years  ago  by  Berzelius,  who  accounted  for  the  circumstance  in  the  fol- 
lowing manner.  The  colour  of  litmus  is  naturally  red,  and  it  is  only 
rendered  blue  by  the  colouring  matter  combining  with  an  alkali.  If  an 
acid  be  added  to  the  blue  compound,  the  colouring  matter  is  deprived 
of  its  alkali,  and  thus,  being  set  free,  it  resumes  its  red  tint.  Now  on 
bringing  litmus  paper  in  contact  with  a salt,  the  acid  and  base  of  which 
have  a weak  attraction  for  each  other,  it  is  possible  that  the  alkali  con- 
tained in  the  litmus  paper  may  have  a stronger  affinity  for  the  acid  of  the 
salt  than  the  base  has  with  which  it  was  combined;  and  in  that  case,  the 
alkali  of  the  litmus  being  neutralized,  its  red  colour  will  necessarily  be 
restored.  It  is  hence  apparent  that  a salt  may  have  an  acid  reaction 
without  having  an  excess  of  acid. 

As  every  acid,  with  few  exceptions,  is  capable  of  uniting  with  every 
alkaline  base,  and  frequently  in  two  or  more  proportions,  it  is  manifest 
that  the  salts  must  constitute  a very  numerous  class  of  bodies.  It  is  ne- 
cessary, on  this  account,  to  facilitate  the  study  of  them  as  much  as  pos- 
sible by  classification.  They  may  be  conveniently  arranged  by  placing 
together  those  salts  which  contain  either  the  same  salifiable  base  or  the 
same  acid.  It  is  not  very  material  which  principle  of  arrangement  is 
adopted;  but  I give  the  preference  to  the  latter,  because,  in  describing 


402 


GENERAL  REMARKS  ON  SALTS. 


t'le  individual  oxides,  1 have  already  mentioned  the  characteristic  fea- 
tures of  their  salts,  and  liave  thus  anticipated  the  chief  advantage  that 
arises  from  the  former  mode  of  classification.  I shall,  therefore,  divide 
the  salts  into  groups,  placing  together  those  saline  combinations  which 
consist  of  the  same  acid,  united  with  different  salifiable  bases.  The 
salts  of  each  group,  in  consequence  of  containing  the  same  acid,  pos- 
sess certain  characters  in  common,  by  which  they  may  all  be  distinguish, 
ed;  and,  indeed,  the  description  of  many  salts,  to  which  no  particular 
interest  is  attached,  is  sufficiently  comprehended  in  that  of  its  group, 
and  may,  therefore,  be  omitted. 

Nearly  all  salts  are  solid,  and  most  of  them  assume  crystalline  forms 
when  their  solutions  are  spontaneously  evaporated. 

The  colour  of  salts  is  very  variable.  Those  that  are  composed  of  a 
colourless  base  and  acid  are  always  colourless.  There  is  no  necessary 
connexion  between  the  colour  of  an  oxide  or  an  acid  and  that  of  its  salts. 
A salt,  though  formed  of  a coloured  oxide  or  acid,  may  be  colourless; 
and  if  it  is  coloured,  the  tint  may  differ  from  that  of  both  its  constituents. 

All  soluble  salts  are  more  or  less  sapid,  while  those  that  are  insoluble 
in  water  are  insipid.  Few  salts  are  possessed  of  odour:  the  only  one 
which  is  remarkable  for  this  property  is  carbonate  of  ammonia. 

Salts  differ  remarkably  in  their  affinity  for  water.  Thus  some  salts, 
such  as  the  nitrates  of  lime  and  magnesia,  are  deliquescent,' W\2X  is,  at- 
tract moisture  from  the  air,  and  become  liquid.  Others,  which  have 
a less  powerful  attraction  for  water,  undergo  no  change  when  the  air  is 
dry,  but  become  moist  in  a humid  atmosphere;  and  others  may  be  ex- 
posed without  change  to  an  atmosphere  loaded  with  watery  vapour. 

Salts  differ  likewise  in  the  degree  of  solubility  in  water.  Some  dis- 
solve in  less  than  their  weight  of  water;  while  others  require  several 
hundred  times  their  weight  of  this  liquid  for  solution,  and  others  are 
quite  insoluble.  This  difference  depends  on  two  circumstances,  namely, 
on  the  degree  of  their  afi^ty  for  water,  and  on  their  cohesion;  their 
solubility  being  in  direct  ratio  with  the  first,  and  in  inverse  ratio  with 
the  second.  One  salt  may  have  a greater  affinity  for  W'ater  than  another, 
and  yet  be  less  soluble;  an  effect  which  may  be  produced  by  the  cohe- 
sive power  of  the  salt  which  has  the  stronger  attraction  for  w^ater,  being 
greater  than  that  of  the  salt,  which  has  a less  powerful  affinity  for  that 
liquid.  The  method  proposed  by  Gay-Lussac  for  estimating  the  rela- 
tive degrees  of  affinity  of  salts  for  water  (An.  de  Ch.  Ixxxii.)  is  by  dis- 
solving equal  quantities  of  salts  in  equal  quantities  of  water,  and  apply- 
ing heat  to  the  solutions.  That  salt  which  has  the  greatest  affinity  for 
the  menstruum  will  retain  it  with  most  force,  and  will,  therefore,  require 
the  highest  temperature  for  boiling. 

Salts  which  are  soluble  in  water  crystallize  more  or  less  regularly 
when  their  solutions  aro  evaporated.  If  the  evaporation  is  rendered  ra- 
pid by  heat,  the  salt  is  usually  deposited  in  a confused  crystalline  mass; 
but  if  it  take  place  slowly,  regular  crystals  are  formed.  The  best  mode 
of  conducting  the  process  is  to  dissolve  a salt  in  hot  water,  and  when  it 
has  become  quite  cold,  to  i)Our  the  saturated  solulion  into  an  evapo- 
rating* basin,  which  is  to  be  set  aside  for  several  days  or  weeks  without 
being  moved.  As  the  water  evaporates,  the  salt  assumes  the  solid  form; 
and  the  slower  the  cva])oration,  the  more  regular  arc  the  crystals.  Some 
salts  which  are  much  more  soluble  in  hot  than  in  cold  water,  crystallize  with 
considerable  regularity  when  a boiling  saturated  solution  is  slowly  cool- 
ed. The  form  which  salts  assume  in  crystallizing  is  constant  under  the 
same  circumstances,  and  constitutes  an  excellent  character  by  which 
they  may  be  distinguished  from  one  another. 

Many  salts,  during  the  act  of  crystallizing,  unite  chemically  with  ade- 


GENERAL  REMARKS  ON  SALTS. 


403 


finite  portion  of  water,  which  forms  an  essential  part  of  the  crystal,  and 
is  termed  the  water  of  crystallization.  The  quantity  of  combined  water 
is  very  variable  in  different  saline  bodies,  but  is  uniform  in  the  same 
salt.  A salt  may  contain  more  than  half  its  weight  of  water,  and  yet  be 
quite  dry.  On  exposing  a salt  of  this  kind  to  heat,  it  is  dissolved,  if  so- 
luble, in  its  own  water  of  crystallization,  undergoing  what  is  termed  the 
watery  fusion.  By  a strong  heat,  the  whole  of  the  water  is  expelled; 
for  no  salt  can  retain  its  water  of  crystallization  when  heated  to  redness. 
Some  salts,  such  as  sulphate  and  phosphate  of  soda,  lose  a portion  of 
their  water,  and  crumble  down  into  a white  powder,  by  mere  exposure 
to  the  air,  a change  which  is  called  efflorescence.  The  tendency  of  salts 
to  undergo  this  change  depends  on  the  dryness  and  coldness  of  the  air; 
for  a salt  which  effloresces  rapidly  in  a moderately  dry  and  warm  atmos- 
phere, may  often  be  kept  without  change  in  one  which  is  damp  and 
cold. 

Salts,  in  crystallizing,  frequently  enclose  mechanically  within  their 
texture  particles  of  water,  by  the  expansion  of  which,  when  heated,  the 
salt  is  burst  with  a crackling  noise  into  smaller  fragments.  This  pheno- 
menon is  known  by  the  name  of  decrepitation.  Berzelius  has  correctly 
remarked  that  those  crystals  decrepitate  most  powerfully,  such  as  the  ni- 
trates of  baryta  and  of  lead,  which  contain  no  water  of  crystallization. 

The  atmospheric  pressure  is  said^to  have  considerable  influence  on  the 
crystallization  of  salts.  If,  for  example,  a concentrated  solution,  com- 
posed of  about  three  parts  of  sulphate  of  soda  in  crystals  and  two  of 
water,  is  made  to  boil  briskly,  and  the  flask  which  contains  it  is  then 
tightly  corked,  while  its  upper  part  is  full  of  vapour,  the  solution  will 
cool  down  to  the  temperature  of  the  air  without  crystallizing,  and  may 
in  that  state  be  preserved  for  months  without  change.  Before  removal 
of  the  cork,  the  liquid  may  often  be  briskly  agitated  without  losing  its 
fluidity;  but  on  re-admitting  the  air,  crystallization  commonly  com- 
mences, and  the  whole  becomes  solid  in  the  course  of  a few  seconds. 
The  admission  of  the  air  sometimes,  indeed,  fails  in  causing  the  effect; 
but  it  may  be  produced  with  certainty  by  agitation  or  the  introduction 
of  a solid  body.  The  theory  of  this  phenomenon  is  not  very  apparent. 
Gay-Lussac  has  shown  that  it  does  not  depend  on  atmospheric  pressure; 
(An.  de  Ch.  vol.  Ixxxvii.)  for  he  finds  that  the  solution  maybe  cooled  in 
open  vessels  without  becoming  solid,  provided  its  surface  be  covered 
with  a film  of  oil;  and  I have  frequently  succeeded  in  the  same  experi- 
ment without  the  use  of  oil,  by  causing  the  air  of  the  flask  to  communi- 
cate with  the  atmosphere  by  means  of  a moderately  narrow  tube.  It 
appears  from  some  experiments  of  Mr.  Graham,  published  in  the  Philo- 
sophical Transactions  of  Edinburgh  for  1828,  that  the  influence  of  the 
air  may  be  ascribed  to  its  uniting  chemically  with  water;  for  he  has 
proved  that  gases  which  are  more  freely  absorbed  than  atmospheric  air, 
act  more  rapidly  in  producing  crystallization.  Indeed,  the  rapidity  of 
crystallization,  occasioned  by  the  contact  of  gaseous  matter,  seems  pro- 
portional to  the  degree  of  its  affinity  for  water. 

The  same  quantity  of  water  may  hold  several  different  salts  in  solu- 
tion, provided  they  do  not  mutually  decompose  each  other.  The  sol- 
vent power  of  water  with  respect  to  one  salt  is,  indeed,  sometimes  in- 
creased by  the  presence  of  another,  owing  to  combination  taking  place 
between  the  two  salts. 

Most  salts  produce  cold  during  the  act  of  dissolving  in  water,  espe- 
cially when  they  are  dissolved  rapidly  and  in  large  quantity.  The  great- 
est reduction  of  temperature  is  occasioned  by  those  which  contain  water 
of  crystallization. 

All  salts  are  decomposed  by  Voltaic  electricity,  provided  tliey  are 


404 


ON  CRYSTALLIZATION. 


either  moistened  or  in  solution.  The  acid  appears  at  the  positive  pole 
of  the  battery,  and  the  oxide  at  its  opposite  extremity;  or  if  the  oxide 
is  of  easy  reduction,  the  metal  itself  goes  over  to  the  negative  side,  and 
its  oxygen  accompanies  the  acid  to  the  positive  wire. 

The  composition  of  salts  is  subject  to  the  laws  of  chemical  union; 
and,  indeed,  the  study  of  these  compounds  by  Wenzel,  Richter,  and 
Berzelius,  together  with  the  facts  ascertained  by  Dr.  Wollaston  and  Dr. 
Thomson,  tended  materially  to  establish  the  doctrine  of  definite  pro- 
portion. All  salifiable  bases,  consisting  of  one  equivalent  of  a metal 
and  one  equivalent  of  oxygen,  are  converted  into  neutral  salts,  that  is, 
into  salts  without  excess  either  of  acid  or  base,  by  uniting  with  one 
equivalent  of  an  acid.  When  a metal  forms  two  salifiable  bases  with 
oxygen,  the  peroxide  manifests  a tendency  to  unite  with  more  acid  than 
the  protoxide,  and  Gay-Lussac  has  demonstrated  the  existence  of  the 
following  law: — ihat  the  quantity  of  acid  which  the  oxides  of  the  same 
metal  require  for  saturation,  is  in  the  same  ratio  as  the  quantity  of  oxygen 
contained  in  their  oxides.  (^Memoires  D’Arcueil,  vol.  ii.)  Thus,  wfiile 
protosulphate  of  iron  contains  one  equivalent  of  each  of  its  elements, 
the  soluble  persulphate  is  composed  of  one  equivalent  of  peroxide  of 
iron,  and  one  equivalent  and  a half  of  sulphuric  acid.  In  like  manner, 
the  peroxides  of  mercury  and  copper  are  disposed  to  unite  with  two 
equivalents  of  acid,  or  twice  as  much  as  would  form  a neutral  salt  with 
the  protoxides  of  those  metals.  Hence,  when  a peroxide  unites  with 
one  equivalent  of  an  acid,  the  product  is  commonly  a subsalt. 

The  combination  of  salts  with  one  another  gives  rise  to  compounds 
which  were  formerly  called  triple  salts;  but  as  the  term  double  salt,  pro- 
posed by  Berzelius,  gives  a more  correct  idea  of  their  nature  and  con- 
stitution, it  will  always  be  employed  by  preference.  These  salts  may 
be  composed  of  one  acid  and  two  bases,  of  two  acids  and  one  base,  and 
most  probably  of  two  different  acids  and  two  different  bases.  Nearly 
all  the  double  salts  hitherto  examined  consist  of  the  same  acid  and  two 
different  bases. 

On  Crystallization, 

The  particles  of  liquid  and  gaseous  bodies,  during  the  formation  of 
solids,  sometimes  cohere  together  in  an  indiscriminate  manner,  and  give 
rise  to  irregular  shapeless  masses;  but  more  frequently  they  attach  them- 
selves to  each  other  in  a certain  order,  so  as  to  constitute  solids  possess- 
ed of  a regularly  limited  form.  The  process  by  which  such  a body  is 
produced  is  called  crystallization;  the  solid  itself  is  termed  a crystal; 
and  the  science,  the  object  of  which  is  to  study  the  form  of  crystals,  is 
crystallography. 

Most  bodies  crystallize  under  favourable  circumstances.  The  condi- 
tion by  which  the  process  is  peculiarly  favoured  is  the  slow  and  gradual 
change  of  a fluid  into  a solid,  the  arrangement  of  the  particles  being 
at  the  same  time  undisturbed  by  motion.  This  is  exemplified  during 
the  slow  cooling  of  a fused  mass  of  sulphur  or  bismuth,  or  the  sponta- 
neous evaporation  of  a saline  solution;  and  the  origin  of  the  numerous 
crystals,  which  are  found  in  the  mineral  kingdom,  may  be  ascribed  to 
the  influence  of  the  same  cause. 

Crystallograplicrs  have  observed  tliat  certain  crystalline  forms  are 
peculiar  to  certain  substances.  Thus,  calcareous  spar  crystallizes  in 
rhomboliedrons,  fluor  spar  in  cubes,  and  quartz,  in  six-sided  pyramids; 
and  these  forms  are  so  far  peculiar  to  those  substances,  that  fluor  spar  is 
never  found  in  rhomcoliedrons  or  six-sided  pyramids,  nor  does  calcareous 
spar  or  quartz  ever  occur  in  cubes.  C.iystalline  form  may  therefore 
serve  as  a ground  of  distinction  between  diflerent  substances.  It  is  ac- 


ON  CRYSTALLIZATION. 


405 


cordingly  employed  by  mineralogists  for  distinguishing  one  mineral 
species  from  another;  and  it  is  very  serviceable  to  the  chemist  as  afford- 
ing a physical  character  to  salts.  On  this  account  I have  thought  it 
would  be  useful,  before  describing  the  individual  salts,  to  introduce  a 
few  pages  on  crystallization;  but  from  the  great  extent  of  the  subject, 
which  now  constitutes  a separate  science,  my  remarks  must  necessarily 
be  limited,  and  comprehend  little  else  than  an  enumeration  of  the  pri- 
mary forms.  To  those  who  are  desirous  of  more  ample  information,  I 
may  recommend  Mr.  Brooke’s  “Familiar  Introduction  to  Cry  stall  ogi-a- 
phy,”  or  the  translation  of  Mohs’s  Treatise  on  Mineralogy  by  Mr.  Hai- 


Ab  ^ 

A 

y ; 

I CL 

1 

a 

\cL 

/ 

i. 

dinger. 

The  surfaces  which  limit  the  figure  of  crystals  are  called  planes  or 
faces,  and  are  generally  flat.  The  lines  formed  by  Fig.  1. 
the  junction  of  two  planes  are  cdWed  edges;  and  the  b 

angle  formed  by  two  such  edges  is  a plane  angle, 

A solid  angle  is  the  point  formed  by  the  meeting  of  ^ 
at  least  three  planes.  Thus  in  the  cube  or  hexahe- 
dron, figure  1,  aaa  are  planes,  hb  are  edges,  and  cc 
solid  angles.  The  cube  it  is  apparent  has  six  planes 
or  faces,  twelve  edges,  and  eight  solid  angles.  Each 
of  the  faces  has  four  angles,  which  are  rectangular. 

The  forms  of  crystals  are  exceedingly  diversified.  They  are  divided 
by  crystallographers  into  what  are  cdW^di  primitive,  primary,  derivative^ 
ov  fundamental  forms,  and  into  secondary  or  derived  forms.  This  distinc- 
tion is  founded  on  the  fact,  that  the  same  substance  frequently  assumes 
different  crystalline  forms;  which,  however,  though  actually  different, 
are  in  general  geometrically  allied  to  each  other.  A Fig:,  2. 

body,  for  instance,  whose  ordinary  figure  is  a cube, 
may  assume  a shape  represented  by  figure  2,  where 
the  general  outline  is  cubic,  but  the  solid  angles  are 
replaced  by  triangular  faces;  just  as  if  the  crystal 
had  been  originally  a perfect  cube,  and  its  eight 
solid  angles  subsequently  removed  by  mechanical 
means.  Instead  of  the  solid  angles  the  edges  of 
the  cube  may  be  wanting,  and  a new  form,  such  as 
figure  3,  be  produced;  If  the  new  planes  are  small 
the  crystal  will  preserve  its  cubic  appearance;  but 
if  they  are  larger,  the  outline  of  the  cube  will  be 
less  distinct;  and  should  the  faces  of  the  original 
cube  wholly  disappear,  a form  altogether  different 
will  result  Secondary  crystals  are  those  which 
may  be  thus  deduced  by  the  substitution  of  planes 
for  the  edges  or  angles  of  some  primary  form;  and 
the  primary  or  fundamental  form  is  that  from  which 
the  former  are  derived.  The  replacement  is  commonly  produced  by 
a tangent  plane,  by  which,  in  reference  to  the  edge  of  a crystal,  is  meant 
a plane  inclined  equally  to  the  two  adjacent  primary  planes,  and  paral- 
lel to  the  edge  which  it  replaces.  In  allusion  to  a solid  angle,  a tangent 
plane  is  equally  inclined  on  all  the  primary  planes  of  which  the  solid 
angle  is  constituted. 

The  number  and  kind  of  primary  forms  are  stated  differently  by  dif- 
ferent crystallographers,  according  to  the  system  which  they  adopt; 
but  I apprehend  it  will  be  most  advantageous  to  the  chemical  student  to 
be  acquainted  with  those  enumerated  by  Mr.  Brooke  in  the  work  above 
mentioned.  They  are  fifteen  in  number. 

1.  The  first  is  the  hexahedron  or  cube  of  geometricians,  a figure 
bounded  by  six  square  faces.  All  the  angles  of  its  edges  are  also  equal 
to  90  degrees.  (Fig.  1.) 


406 


ON  CRYSTALLIZATION. 


2.  The  tetrahedron,  a regular  solid  of  geome- 
try, is  contained  under  four  equilateral  triangles 
and  therefore  all  its  plane  angles  are  equal  to  60 
degrees.  The  faces  incline  to  each  other  at  the 
edges  at  an  angle  of  70°  31'  44".  (Fig.  4.) 


3.  The  regular  octohedron  is  contained  under 
eight  equilateral  triangles,  figure  5,  and  conse- 
quently all  its  plane  angles  are  equal  to  60  de- 
grees. The  base  of  the  octohedron  hhhh  is  a 
square,  and  the  planes  incline  on  each  other  at 
the  edges  at  an  angle  of  109°  28'  16".  The  oc- 
tohedron is  a regular  solid  of  geometry. 


Fig.  4. 


Fig.  5. 


Fig.  6. 


4.  The  rhombic  dodecahedron,  figure  6,  is 
limited  by  twelve  similar  rhombic  faces,  the 
plane  angles  of  which  are  equal  to  109°  28'  16" 
and  70°  31'  44".  The  faces  incline  to  each  other 
at  the  edges  at  an  angle  of  120°. 


5.  The  octohedron  with  a square  base,  figure 
7,  is  bounded  by  eight  faces  which  are  similar 
isosceles  triangles.  The  base  hhhb  is  always  a 
square,  and  this  is  the  only  part  of  the  figure 
which  is  constant. 


Fig.  7. 

CL 


6.  The  rectangular  octohedron,  figure  8,  is 
limited  by  eight  isosceles  triangles,  four  of  which 
are  different  from  the  other  four.  The  base  hhhb 
is  always  a rectangle;  but  the  ratio  of  its  two 
sides,  as  well  as  all  the  other  dimensions  of  the 
figure,  is  variable. 


Fig.  8. 


ON  CRYSTALLIZATION. 


407 


7.  The  rhombic  octohedron,  figure  9,  is  con- 
tained under  eight  faces  which  are  similar  scalene 
triangles,  and  the  base  bbbb  is  a rhomb.  All  its 
dimensions  are  variable. 


8.  The  right  square  prism,  figure  10,  is  a six- 
sided  figure,  which  differs  from  the  cube  only  in 
its  four  lateral  planes  cccc  being  rectangles.  The 
extreme  or  terminal  planes  aa  are  square.  The 
term  right  denotes  that  the  lateral  and  terminal 
planes  are  inclined  to  each  other  at  a right  angle. 
It  is  used  in  opposition  to  oblique^  which  signifies 
that  the  sides  are  not  perpendicular,  but  form  an 
oblique  angle  with  the  terminal  planes. 


Fig.  9. 


ct 


ct 


Fig.  10. 


Fig.  11. 


9.  The  right  rectangular  prism,  figure  11, 
differs  from  the  former  in  the  terminal  planes  aa 
being  rectangular  instead  of  square. 


CL 


71 


CL 


K 


Fig.  12. 


10.  The  right  rhombic  prism,  figure  12,  differs 
om  the  two  preceding  forms  only  in  its  termi- 
nal planes  aa  being  rhombs. 


11.  The  right  rhomb  oidal  prism,  figure  13, 
differs  from  the  preceding  form  in  the  terminal 
planes  aa  being  rhomboids. 


12.  In  the  oblique  rhombic  prism  the  terminal 
planes  aa  are  rhombic,  and  the  lateral  planes 
form  an  oblique  angle  with  them.  (Fig.  14.) 


408 


ON  CRYSTALLIZATION. 


Fig*.  15. 

13.  The  oblique  rhomboidal  prism,  sometimes 
called  the  doubly  oblique  prism,  figure  15,  dif- 
fers from  the  preceding  form  in  the  terminal 
planes  aa  being  rhomboids. 


Fig.  16. 


14.  The  rhombohedron,  figure  16,  is  bounded 
by  six  rhombic  faces,  which  are  exactly  of  the 
same  size  and  form. 


15.  The  regular  hexagonal  prism,  figure  17,  Fig.  17. 

is  bounded  by  six  perpendicular  or  lateral,  and 
two  horizontal  or  terminal  planes,  which  are  at 
right  angles  to  the  former.  Like  the  regular 
hexagon  of  geometry,  the  lateral  planes  incline 
to  each  other  at  an  angle  of  120  degrees.  If 
these  angles  are  not  of  120  degrees,  the  prism  is 
irregular. 

16.  The  four  first  forms  are  geometrically  allied 
to  each  other.  Thus  if  the  six  solid  angles  of 
the  regular  octohedron  are  replaced  by  tangent 
planes,  as  in  figure  18,  and  these  are  enlarged 
until  they  intersect  each  other,  and  the  faces  of 
the  octohedron  disappear,  a perfect  cube  is  pro- 
duced. If  the  twelve  edges  of  the  octohedron 
are  replaced  by  tangent  planes,  as  in  figure  19, 
and  these  are  extended  till  they  mutually  inter- 
sect, the  rhombic  dodecahedron  will  be  formed. 

The  cube  may  by  analogous  changes  be  con- 
verted into  the  octohedron,  tetrahedron,  and 
rhombic  dodecahedron.  For  if  the  eight  solid 
angles  of  the  cube  be  replaced  by  equilateral 
triangles,  (fig.  2.)  and  these  are  enlarged  till 
the  planes  of  the  original  cube  are  destroyed,  the 
octohedron  results.  The  tetrahedron  may  be 
formed  by  replacing  the  four  solid  angles  cc  and 
dd  of  the  cube  (fig.  1.)  by  tangent  planes,  so 
that  all  its  original  faces  disappear.  By  re- 
placing the  twelve  edges  of  the  cube  with  tangent  planes  as  in  figure 
3,  until  tlie  new  faces  intersect  each  other,  the  rhombic  dodecahedron 
will  be  produced.  By  tlie  combination  of  the  planes  of  different  pri- 
mary forms,  various  secondary  ones  are  created,  as  is  made  obvious  by 
the  figures,  and  will  be  rendered  still  clearer  by  making  the  transitions 
above  described  with  an  a])])le  or  potato.  The  study  of  such  allied 
forms  is  very  important,  because  the  same  substance  often  occurs  in 
several  of  these  iigurcs,  and  may  assume  all  of  them. 

The  octohedron  with  a square  base  is  allied  to  the  right  square 
prism.  Tlius  If  in  figure  7 two  tangent  planes  are  substituted  for  the 
solid  angles  au,  and  the  edges  of  the  base  are  replaced  by  faces  per- 


ON  CRYSTALLIZATION. 


409 


pendicular  to  the  former,  new  forms  will  result.  If  the  faces  of  the 
octohedron  disappear,  the  rig’ht  square  prism  is  formed;  but  if  traces 
of  them  remain,  secondary  forms  intermediate  between  the  two  primary 
ones  will  be  produced. 

The  rectang'ular  and  rhombic  octohedrons  and  the  right  rectangular 
and  rhombic  prisms  are  associated  with  each  other.  Thus  on  replacing 
the  solid  angles  aa^  and  the  four  edges  of  the  base  of  the  rectangular 
octohedron,  by  tangent  planes,  and  extending  them  till  the  planes  of  the 
octohedron  disappear,  the  right  rectangular  prism  is  formed;  and  the 
rhombic  octohedron  by  a similar  change  is  converted  into  the  right 
rhombic  prism.  By  applying  tangent  planes  to  all  the  edges  of  the 
rhombic  octohedron  except  those  of  the  base,  the  rectangular  octohe- 
dron may  be  produced;  and  by  a reversed  operation  the  latter  is  con- 
verted into  the  former.  In  this  case  the  solid  angles  of  the  rhombic 
octohedron  must  be  so  placed  as  to  bisect  the  edges  of  the  base  of  the 
rectangular  octohedron. 

The  rhombohedron  and  six-sided  or  hexagonal  prism  are  allied  to 
each  other.  If  tangent  planes  are  laid  on  the  two  solid  angles  aa  of 
the  rhombohedron,  (fig.  16.)  and  either  the  six  solid  lateral  angles 
marked  or  the  edges  between  them,  are  replaced  by  equal  planes 
perpendicular  to  the  former,  a six-sided  prism  results;  and  the  six-sided 
prism  may  be  re-converted  into  the  rhombohedron  by  replacing  all  its 
alternate  solid  angles  by  equal  and  similar  rhombic  planes. 

The  six-sided  prism  is  often  associated  in  nature  with  a double  six- 
sided  pyramid,  formed  by  all  its  terminal  edges  being  replaced  by  isos- 
celes triangles.  If  the  faces  of  the  prism  disappear,  the  double  six- 
sided  pyramid  results. 

The  crystalline  forms  which  have  an  intimate  geometrical  connexion 
with  ea;ch  other,  are  considered  by  crystallographers  as  constituting  cer- 
tain groups,  which  are  termed  Systems  of  Crystallization.  Thus,  of  the 
fifteen  primary  forms  above  described,  the  Tessular  System  of  Mohs 
comprehends  the  cube,  the  tetrahedron,  the  regular  octohedron,  and 
the  rhombic  dodecahedron,  together  with  several  others  not  enumerat- 
ed; his  Pyramidal  System  contains  the  octohedron  with  a square  base, 
and  the  right  square  prism;  the  Prismatic  System  contains  the  rectan- 
gular and  rhombic  octohedron,  and  the  right  rectangular  and  right 
rhombic  prisms;  the  Hemiprismatic  System  includes  the  right  rhomboi- 
dal  and  the  oblique  rhombic  prisms;  the  oblique  rhomboidal  prism  be- 
longs to  the  Tetarto-prismatic  System;  and  the  Rhombohedral  System 
comprehends  the  rhombohedron  and  the  regular  hexagonal  prism.  This 
distinction  is  so  far  important,  that  all  the  forms  which  a salt,  or  any 
substance,  almost  always  assumes,  belong  to  the  same  system  of  crys- 
tallization. 

Besides  the  distinction  arising  from  external  form,  minerals  are  fur- 
ther distinguished  by  differences  in  the  mechanical  connexion  of  their  par- 
ticles, peculiarities  which  mineralogists  designate  by  the  name  of  struc- 
ture, The  structure  of  a mineral  arises  from  its  particles  adhering  at  some 
parts  less  tenaciously  than  at  others,  and  consequently  yielding  to  force 
in  one  direction  more  readily  than  at  another.  Structure  is  sometimes 
visible  by  holding  a mineral  between  the  eye  and  the  light;  but  in  gene- 
ral it  is  brought  into  view  by  effecting  the  actual  separation  of  parts 
by  mechanical  means. 

The  structure  of  minerals  may  be  regular  or  irregular.  It  is  regular 
when  the  separation  takes  place  in  such  a manner,  that  the  detached 
surfaces  are  smooth  and  even  like  the  planes  of  a crystal;  and  it  is  irre- 
gular, when  the  new  surface  does  not  possess  this  character. 

A mineral  which  possesses  a regular  structure  is  said  to  be  cleavabkf 

35 


410 


ON  CRYSTALLIZATION. 


or  to  admit  of  cleavage^  the  surfaces  exposed  by  spliting  or  cleaving  a min- 
eral are  termed  the  faces  of  cleavage^  and  the  direction  in  wliicli  it  may 
be  cleaved  is  called  the  direction  of  cleavage.  Sometimes  a mineral  is 
cleavable  only  in  one  direction,  and  is  then  said  to  have  a single  cleav- 
age. Others  may  be  cleaved  in  two,  three,  four,  or  more  directions, 
and  are  said  to  have  a double,  treble,  fourfold  cleavage,  and  so  on,  ac- 
cording to  their  number. 

Minerals  that  are  cleavable  in  more  than  two  directions  may,  by  tlie 
removal  of  layers  parallel  to  the  planes  of  their  cleavage,  be  often 
made  to  assume  regular  primary  forms,  tliough  they  may  originally 
have  possessed  a different  figure.  Calcareous  spar,  for  example,  occurs 
in  rhombohedrons  of  different  kinds,  in  hexagonal  prisms,  in  six-sided 
pyramids,  and  in  various  combinations  of  these  forms;  but  it  has  three 
sets  of  cleavage,  which  are  so  inclined  to  each  other  as  to  constitute  a 
rhombohedron  of  invariable  dimensions,  and  into  that  form  every  crys- 
tal of  calcareous  spar  may  be  reduced.  Lead  glance  possesses  a treble 
cleavage,  the  planes  of  which  are  at  right  angles  to  each  other;  and 
hence  it  is  always  convertible  by  cleavage  into  the  cube.  The  cleavages 
of  fluor  spar  are  fourfold,  and  in  a direction  parallel  to  the  planes  of 
the  regular  octohedron,  into  which  form  every  cube  of  fluor  may  be 
converted. 

Cleavage  not  only  affords  a useful  character  for  distlngulsliing  mine- 
rals, but  is  frequently  employed  by  mineralogists  for  detecting  the  pri- 
mary forms  of  crystals.  If  a mineral  occur  in  two  or  more  of  those  forms 
which  have  been  enumerated  as  primary,  tliat  one  is  usually  selected 
as  fundamental,  which  may  be  produced  by  cleavage.  Thus  fluor  spar 
is  met  with  in  cubes,  in  the  form  of  the  regular  octohedron,  and  as  the 
rhombic  dodecahedron.  Of  these  the  cube  is  by  far  the  most  frequent; 
and  yet  the  octohedron  is  usually  adopted  as  the  fundamental  form,  be- 
cause fluor  has  four  equally  distinct  cleavages  parallel  to  the  planes  of 
that  figure.  It  is,  indeed,  a practice  very  common  among  mineralogists, 
not  only  to  consider  cleavage  as  the  most  influential  circumstance  in 
fixing  the  primary  form  of  a crystal,  but  to  adopt  as  such  no  figure 
which  is  inconsistent  with  its  cleavages. 

Since  the  forms  above  enumerated  as  belonging  to  the  tessular  sys- 
tem of  crystallization  are  possessed  of  fixed  invariable  dimensions,  it  is 
obvious  that  minerals,  or  other  crystallized  bodies  included  in  that  sys- 
tem, must  often  in  their  primary  forms  be  identical  with  each  other.  In 
the  other  systems  of  crystallization  this  identity  is  not  necessary,  be- 
cause the  dimensions  of  their  forms  are  variable.  Thus  octoheclrons 
with  a square  base  may  be  distinguished  by  the  relative  length  of  their 
axis,  some  being  flat  and  others  acute.  Rhombic  octohedrons  may  be 
distinguished  from  each  other  by  the  relative  length  of  their  axis,  and 
the  angles  of  their  base.  By  Haliy  it  was  regarded  as  an  axiom  in  crys- 
tallography, that  minerals  not  belonging  to  the  tessular  system  are  cha- 
racterized by  tlieir  form;  that  though  two  minerals  may  in  form  be  ana- 
logous, each  for  instance  being  a rhombic  prism,  the  dimensions  of 
tliosc  prisms  arc  different.  Identity  of  form  in  crystals  not  included  in 
the  tessular  system  was  thought  to  indicate  identity  of  composition. 
But  in  the  year  1819  a discovery  extremely  important  both  to  mineralo- 
gy and  chemistry  was  made  by  Professor  Mitschcrlich  of  Berlin,  relative 
to  the  connexion  between  the  crystalline  form  and  composition  of  bo- 
dies. It  appears  from  his  researclics*,  that  certain  substances  are  capa- 


* Annalcs  de  Ch.  ct  dc  Physique,  vol.  xiv.  172,  xix.  350,  and  xxiv. 
264  and  355. 


ON  CRYSTALLIZATION. 


411 


ble  of  being  substituted  for  each  other  in  combination,  without  influ- 
encing the  form  of  the  compound.  This  singular  circumstance  has 
been  ably  traced  by  Professor  Mitscherlich  in  the  salts  of  phosphoric 
and  arsenic  acids.  Thus,  neutral  phosphate  and  biphosphate  of  soda  have 
exactly  the  same  form  as  arseniate  and  binarseniate  of  soda.  Phosphate 
and  biphosphate  of  ammonia  correspond  in  like  manner  to  arseniate  and 
binarseniate  of  ammonia.  The  neutral  phosphate  and  arseniate  of  potas- 
sa  could  not  be  obtained  In  crystals  lit  for  examination;  but  the  biphos- 
phate and  binarseniate  of  that  alkali  have  the  same  form.  Each  arseni- 
ate  has  a corresponding  phosphate,  possessed  of  the  same  form,  and 
containing  the  same  number  of  equivalents  of  acid,  alkali,  and  water. 
These  series  of  salts,  in  fact,  dilfer  in  nothing  but  in  one  containing 
arsenic  and  the  other  phosphoric  acid. 

Prom  these  and  analogous  facts  it  appears  that  certain  substances, 
when  similarly  combined  with  the  same  body,  are  disposed  to  affect  the 
same  crystalline  form.  This  discovery  has  led  to  the  formation  of 
groups,  each  comprehending  substances  which  crystallize  in  the  same 
manner,  and  which  are  hence  said  to  be  isomorphous.  The  salts  of  ar- 
senic acid  are  isomorphous  with  those  of  phosphoric  acid.  The  oxide  of 
lead,  baryta,  and  strontia,  when  combined  with  the  same  acid,  yield 
salts  which  are  said  by  Professor  Mitscherlich  to  be  isomorphous.  The 
salts  of  lime  are  isomorphous  with  thosa  of  magnesia,  protoxide  of  man- 
ganese, iron,  cobalt,  and  nickel,  oxide  of  zinc,  and  peroxide  of  cop- 
per. The  salts  of  selenic  and  sulphuric  acids,  when  similarly  united 
with  water  and  the  same  base,  assume  the  same  form;  and  the  salts  of 
peroxide  of  iron  are  isomorphous  with  those  of  alumina. 

The  similarity  of  the  chemical  constitution  of  isomorphous  bodies  is 
peculiarly  striking.  The  first  singularity  of  the  kind,  which  merits  no- 
tice, is  the  tendency  of  some  isomorphous  salts  to  combine  with  the 
same  quantity  of  water  of  crystallization.  This  is  especially  remark- 
able in  the  salts  of  arsenic  and  phosphoric  acids.  The  biphosphate  and 
binarseniate  of  potassa  crystallize  with  two  equivalents  of  water.  The 
neuti*al  phosphate  and  arseniate  of  soda  contain  twelve  and  a half  equiv- 
alents of  water;  and  in  the  biphosphate  and  binarseniate  of  soda  four 
equivalents  of  water  are  present.  The  quantity  of  water  contained  in 
the  arseniates  of  ammonia  corresponds  to  that  of  the  phosphates  of  am- 
monia. Indeed  scarcely  any  crystallized  artificial  arseniate  is  known,  to 
which  a corresponding  phosphate  has  not  been  discovered.  If,  on  the 
contrary,  two  isomorphous  salts  crystallize  with  different  equivalent 
quantities  of  water,  their  forms  are  found  to  differ  also.  The  common 
sulphates  of  manganese  and  copper  differ  in  form  from  the  sulphates  of 
iron  and  zinc;  whereas  when  their  crystals  contain  the  same  number  of 
equivalents  of  water,  their  form  is  ideittical.  Mitscherlich  has  remark- 
ed that  isomorphous  salts,  which  when  pure  combine  with  diflferent  pro- 
portional  quantities  of  water,  are  disposed  in  crystallizing  together  to 
unite  with  the  same  number  of  equivalents  of  water,  and  assume  the 
same  form.  The  mixed  sulphates  of  iron  and  copper  crystallize  toge- 
ther with  great  facility;  and  the  crystals,  though  containing  a consider- 
able ([uantity  of  copper,  have  the  same  proportional  quantity  of  water 
and  the  same  form  as  pure  protosulphate  of  iron.  According  to  Mits- 
cheiTich,  the  sulphates  of  zinc  and  copper,  of  copper  and  magnesia, 
of  copper  and  nickel,  of  zinc  and  manganese,  and  of  magnesia  and 
manganese,  crystallize  together  with  six  equivalents  of  water  of  crys- 
tallization, (the  same  number  he  states  as  in  protosulphate  of  iron,) 
and  have  the  same  form  as  green  vitriol,  without  containing  a trace  of 
iron.  In  these  instances  the  isomorphous  salts  do  not  occur  in  definite 
proportions;  so  that  though  they  crystallize  together,  they  do  not  ap«i 
pear  to  be  chemically  united. 


412 


ON  CRYSTALLIZATION. 


The  similarity  in  the  chemical  constitution  of  isomorphous  substances 
may  be  illustrated  in  a different  way.  Thus,  in  isomorphous  salts  the 
proportional  quantities  of  acid  and  base  are  the  same.  A neutral  phos- 
phate does  not  correspond  to  a binarseniate,  nor  a bi phosphate  to  a 
neutral  arseniate.  There  is  in  g*eneral  also  an  exact  similarity  in  the 
composition  of  the  constituents  of  isomorphous  substances.  Thus  all 
chemists  agree  that  the  atomic  constitution  of  arsenic  and  phosphoric 
acids  is  the  same^  and  the  fact  is  still  further  evinced  by  the  composi- 
tion of  selenic  and  sulphuric  acids.  This  singular  coincidence  led  Pro- 
fessor MitscheiTich  to  believe,  that  the  form  of  crystals  depends  on  their 
atomic  constitution.  He  at  first  suspected  that  identity  of  crystalline 
form  is  determined  solely  by  the  number  of  atoms,  and  the  mode  in 
which  they  are  united,  quite  independently  of  their  nature.  Subsequent 
observation,  however,  induced  him  to  abandon  this  view;  and  his  opin- 
ion now  appears  to  be,  that  certain  elements,  which  are  themselves 
isomorphous,  when  combined  in  the  same  manner  with  the  same  sub- 
stance, communicate  the  same  form.  Similarly  constituted  salts  of 
arsenic  and  phosphoric  acids  yield  crystals  of  the  same  figure,  because 
the  acids,  it  is  thought,  are  themselves  isomorphous;  and  as  the  atomic 
constitution  of  these  acids  is  similar,  each  containing  the  same  number 
of  atoms  of  oxygen  united  with  the  same  number  of  atoms  of  the  other 
ingredient,  it  is  inferred  that  phosphorus  is  isomorphous  with  arsenic. 
In  like  manner  it  is  believed  that  selenic  acid  must  be  isomorphous  with 
sulphuric  acid,  and  selenium  with  sulphur;  and  the  same  identity  of 
form  is  ascribed  to  all  those  oxides  above  enumerated,  the  salts  of  which 
are  isomorphous.  The  accuracy  of  this  ingenious  view  has  not  yet 
been  put  to  the  test  of  extensive  observation,  because  the  crystalline 
forms  of  the  substances  in  question  are  for  the  most  part  unknown. 
But  our  knowledge,  so  far  as  it  goes,  is  favourable;  for  peroxide  of  iron 
and  alumina,  the  salts  of  which  possess  the  same  form,  are  themselves 
isomorphous.  It  may  hence  be  inferred  as  probable,  that  isomorphous 
compounds  in  general  arise  from  isomorphous  elements  uniting  in  the 
same  manner  with  the  same  substance. 

The  discovery  of  Professor  Mitscherlich,  while  it  serves  as  a caution 
to  mineralogists  against  too  exclusive  reliance  on  crystallographic  char- 
acter, is  in  several  respects  of  deep  interest  to  the  chemist.  It  tends 
to  lay  open  fields  of  inquiry  which  may  not  otherwise  have  been  thought 
of,  and  thus  lead  to  the  discovery  of  new  substances.  The  tendency 
of  isomorplious  bodies  to  crystallize  together  accounts  for  the  difficulty 
of  purifying  mixtures  of  isomorphous  salts  by  crystallization.  The  same 
property  sets  the  chemist  on  his  guard  against  the  occurrence  of  isomor- 
phous substances  in  crystallized  minerals.  The  native  phosphates,  for 
example,  frequently  contain  arsenic  acid,  and  conversely  the  native 
arseniates,  phosphoric  acid,  without  the  form  of  the  crystals  being 
thereby  affected  in  the  slightest  degree.  -It  may  afford  a useful  guide 
in  discovering  the  atomic  constitution  of  compounds.  Thus,  two  isomor- 
phous oxides  are  most  likely  composed  of  the  same  number  of  atoms  of 
metal  and  oxygen;  so  that  if,  as  Berzelius  supposes,  peroxide  of  iron 
consists  of  two  atoms  of  iron  and  three  atoms  of  oxygen,  alumina, 
v/hich  is  isomorphous  with  it,  will  ])robably  have  a similar  atomic  con- 
stitution. 'fbe  similarity  in  the  composition  of  several  other  iso'morphous 
compounds  gives  considerable  weight  to  the  argument;  but  our  know- 
ledge of  this  subject  is  as  yet  too  limited  to  excite  much  confidence. 
It  is  possible  that  aluminium  and  iron  may  not  be  isomoriffious,  and  yet 
yield  isomori)hous  oxides  by  uniting'  with  oxygen  in  different  propor- 
tions. The  phenomena  presented  by  isomorphous  bodies  afford  a pow- 
erful argument  in  favour  of  the  atomic  theory.  I'he  only  rpode  of  satis- 


SULPHATES. 


413 


factorily  accounting*  for  the  striking  identity  of  crystalline  form  observ- 
able, first,  between  two  substances,  and,  secondly,  between  all  their 
compounds  which  have  an  exactly  similar  composition,  is  by  supposing 
them  to  consist  of  ultimate  particles  possessed  of  the  same  figure,  and 
arranged  in  precisely  the  same  order.  Hence  it  appears,  that,  in  ac- 
counting for  the  connexion  between  form  and  composition,  it  is  neces- 
sary to  employ  the  very  same  theory,  by  which  alone  the  laws  of  chem- 
ical union  can  be  adequately  explained. 

In  one  of  the  essays  above  referred  to,  Professor  Mitscherlich  ob- 
served that  biphosphate  of  soda  is  capable  of  yielding  two  distinct  kinds 
of  crystals,  which,  though  difierent  in  form,  in  composition  appeared 
to  be  identical.  The  more  uncommon  of  the  two  forms  resembled  bin- 
arseniate  of  soda;  but  the  more  usual  form  is  quite  dissimilar.  He  has 
since  discovered,  that  su]»phur  is  capable  of  yielding  two  distinct  kinds 
of  crystals;  and  infers  from  his  observations  that  a body,  whether  simple 
or  compound,  may  assume  two  different  crystalline  forms.  The  cause 
of  this  unexpected  fact  is  not  yet  ascertained. 

The  same  close  observer  has  noticed,  that  the  form  of  salts  is  some- 
times changed  by  heat,  without  their  losir^  the  solid  state.  This  change 
was  first  noticed  in  sulphate  of  magnesia,  and  also  in  sulphate  of  zinc 
and  iron.  In  appears,  in  these  instances  at  least,  to  be  owing  to  decom- 
position of  the  hydrous  salt  effected  by  increased  temperature;  a change 
of  composition  which  is  accompanied  with  a new  arrangement  in  the 
molecules  of  the  compound. 


SECTION  L 

SULPHATES.— SULPHITES.— HYPOSULPHATES.— HYPO- 
SULPHITES. 

Sulphates, 

The  salts  of  sulphuric  acid  in  solution  may  be  detected  by  muriate  of 
baryta.  A white  precipitate,  sulphate  of  baryta,  invariably  subsides, 
which  is  Insoluble  in  acids  and  alkalies,  a character  by  which  the  pre- 
sence of  sulphuric  acid,  whether  free  or  combined,  may  always  be  re- 
cognised. An  insoluble  sulphate,  such  as  sulphate  of  baryta  or  strontia, 
may  be  detected  by  mixing  it,  in  fine  powder,  with  three  times  its 
weight  of  carbonate  of  potassa  or  soda,  and  exposing  the  mixture  in  a 
platinum  crucible  for  half  an  hour  to  a red  heat.  Double  decomposi- 
tion ensues;  and  on  digesting  the  residue  in  water,  filtering  the  solu- 
tion, neutralizing  the  free  alkali  by  pure  muriatic,  nitric,  or  acetic  acid, 
and  adding  muriate  of  baryta,  the  insoluble  sulphate  of  that  base  is 
precipitated. 

Several  sulphates  exist  in  nature,  but  the  only  ones  which  are  abun- 
dant are  the  sulphates  of  lime  and  baryta.  All  of  them  may  be  formed 
by  the  action  of  sulphuric  acid  on  the  metals  themselves,  on  the  metal- 
lic oxides  or  their  carbonates,  or  by  way  of  double  decomposition. 

The  solubility  of  the  sulphates  is  very  variable.  There  are  six  only 
which  may  be  regarded  as  really  insoluble;  namely,  the  sulphate  of 
baryta,  tin,  antimony,  bismuth,  lead,  and  mercury.  The  sparingly 

35* 


414 


SULPHATES. 


soluble  sulphates  are  those  of  stronlia,  lime,  zirconia,  yttrla,  cerium, 
and  silver.  All  the  others  are  soluble  in  water. 

All  the  sulphates,  those  of  potassa,  soda,  lithia,  baryta,  strontia,  and 
lime  excepted,  are  decomposed  by  a white  heat.  One  part  of  the  sul- 
phuric acid  of  the  decomposed  sulphate  escapes  unchan.^ed,  and  another 
portion  is  resolved  into  sulj)hurous  acid  and  oxyg’en.  Those  which  are 
easily  decomposed  by  heat,  such  as  sulpliate  of  iron,  yield  the  larg’est 
quantity  of  undecomposcd  sulphuric  acid. 

When  a sulphate,  mixed  witli  carbonaceous  matter,  is  ignited,  the 
oxygen  both  of  the  acid  and  of  the  oxide  unites  with  carbon,  carbonic 
acid  is  disengaged,  and  a metallic  sulphuret  remains.  A similar  change 
is  produced  by  hydrogen  gas  at  a red  heat,  with  formation  of  water, 
and  frequently  of  some  sulphuretted  hydrogen.  In  some  instances  the 
hydrogen  entirely  deprives  the  metal  of  its  sulphur. 

The  composition  of  the  sulphates,  so  far  as  they  are  subject  to  gen- 
eral laws,  has  already  been  described.  (Page  138.) 

Sulphate  of  Potassa. — This  salt  is  easily  prepared  artificially  by  neu- 
tralizing carbonate  of  potassa  with  sulphuric  acid;  and  it  is  procured 
abundantly  by  neutralizing  with  carbonate  of  potassa  the  residue  of  the 
operation  for  preparing  nitric  acid.  (Page  171.)  Its  taste  is  saline  and 
bitter.  It  generally  crystallizes  in  six-sided  prisms,  bounded  by  pyra- 
mids with  six  sides;  the  size  of  which  is  said  to  be  much  increased  by 
the  presence  of  a little  carbonate  of  potassa.  Its  primary  form,  accord- 
ing to  Mitscherlich,  is  a rhombic  octohedron,  and  it  is  isomorphous 
with  chromate  and  seleniate  of  potassa.  (Poggendorlf’s  Annalen,  xviii. 
168.)  The  crystals  contain  no  water  of  crystallization,  and  suffer  no 
change  by  exposure  to  the  air.  They  decrepitate  when  heated,  and 
enter  into  fusion  at  a red  heat.  They  require  sixteen  times  their  weight 
of  water  at  60®  F.  and  five  of  boiling  water  for  solution. 

Sulphate  of  potassa  is  composed  of  40  parts  or  one  equivalent  of  sul- 
phuric acid,  and  48  parts  or  one  equivalent  of  potassa. 

Bisulphate  of  potassa,  which  contains  twice  as  much  acid  as  the  fore- 
going salt,  is  easily  formed  by  digesting  88  parts  or  one  equivalent  of 
tiie  neutral  sulphate,  with  water  containing  about  50  parts  of  concen- 
trated sulphuric  acid,  and  evaporating  the  solution.^  The  primary  form 
of  its  crystals  is  a right  rhombic  prism,  but  which  is  in  general  so  flat- 
tened as  to  be  tabular.  It  has  a strong  sour  taste,  and  reddens  litmus 
paper.  It  is  much  more  soluble  than  the  neutral  sulphate,  requiring 
for  solution  only  twice  its  weight  of  water  at  60®,  and  less  than  an  equal 
weight  at  212®  F.  It  is  resolved  by  heat  into  sulphuric  acid  and  the 
neutral  sulphate. 

Mr.  Phillips  has  described  a sesquisulphate,  obtained  in  the  form  of 
acicular  crystals  from  the  residue  of  the  process  for  making  nitric  acid. 
The  conditions  for  ensuring  its  production  have  not  been  determined. 
(Phil.  Mag.  and  Annals,  ii.  421.) 

Sulphate  of  Soda. — This  compound,  commonly  called  Glauber^ s salt, 
is  occasionally  met  witli  on  the  surface  of  the  earth,  and  is  frequently 
contained  in  mineral  springs.  It  may  be  made  by  the  direct  action  of 
sulphuric  acid  on  carbonate  of  soda;  and  it  is  procured  in  large  quantity 
as  a residue  in  the  processes  for  forming  muriatic  acid  and  chlorine. 
(Pages  204  and  207.) 

Sulphate  of  soda  has  a cooling,  saline,  and  bitter  taste.  It  commonly 
yields  four  and  six-sided  prismatic  crystals,  but  its  primary  form  is  a 
rliornbic  octohedron.  Its  crystals  effloresce  rapidly  when  exposed  to 
the  air,  losing  the  whole  of  their  water,  and,  according  to  Berzelius, 
are  composed  of  72  parts  or  one  equivalent  of  the  neutral  sulphate,  and 
90  parts  or  ten  equivalents  of  water.  The  crystals  I’cadily  undergo  the 


SULPHATES. 


415 


watery  fusion  when  heated.  At  32°  F.  100  parts  of  water  dissolve  12 
parts  of  the  crystals,  48  parts  at  64.5°,  100  parts  at  77°,  270  at  89.5°, 
and  322  at  91.5°.  On  increasing’  the  heat  beyond  this  point,  a portion 
of  the  salt  is  deposited,  being  less  soluble  than  at  91.5°.  (Gay-Lussac.) 
If  a solution  saturated  at  91.5°  is  evaporated  at  a higher  temperature, 
the  salt  is  deposited  in  opake  anhydrous  prisms,  the  primary  form  of 
which  is  a rhombic  octohedron.  Its  specific  gravity  in  this  state  is  2.462. 
(Haidinger. ) 

Bisulphate  of  soda  may  be  formed  in  the  same  manner  as  the  analo- 
gous salt  of  potassa. 

Sulphate  of  Lit]ua.’—T\\is  salt  is  very  soluble  in  water,  fuses  by 
heat  more  readily  than  the  sulphates  of  the  other  alkalies,  but  crystal- 
lizes in  prisms,  which  resemble  sulphate  of  soda  in  appearance,  but  do 
not  effloresce  on  exposure  to  the  air.  Its  taste  is  saline,  without  being 
bitter. 

Sulphate  of  Ammonia. — This  salt  is  easily  prepared  by  neutralizing 
carbonate  of  ammonia  with  dilute  sulphuric  acid;  and  is  contained  in 
considerable  quantity  in  the  soot  from  coal.  It  crystallizes  in  long  flat- 
tened six-sided  prisms.  It  dissolves  in  two  parts  of  water  at  60°,  and 
in  an  equal  weight  of  boiling  water.  It  is  sublimed  by  heat,  but  is  par- 
tially decomposed  at  the  same  time.  The  crystals  are  composed  of  40 
parts  or  one  equivalent  of  acid,  and  17  parts  or  one  equivalent  of  am- 
monia, combined  according  to  Dr.  Thomson  with  one  and  according  to 
Berzelius  with  two  equivalents  of  water. 

Sulphate  of  Baryta. — Native  sulphate  of  baryta,  commonly  called 
heavy  spar,  occurs  abundantl}^  chiefly  massive,  but  sometimes  in  anhy- 
drous crystals,  the  form  of  which  is  variable,  being  sometimes  prismatic 
and  sometimes  tabular.  Its  primary  form  is  a right  rhombic  prism.  Its 
density  is  about  4.4.  It  is  easily  formed  artificially  by  double  decompo- 
sition. This  salt  bears  an  intense  heat  without  fusing  or  undergoing  any 
other  change,  and  is  one  of  the  most  insoluble  substances  with  which 
chemists  are  acquainted.  It  is  sparingly  dissolved  by  hot  and  concen- 
trated sulphuric  acid,  but  is  precipitated  by  the  addition  of  water.  It 
consists  of  an  equivalent  of  each  ingredient. 

Sulphate  of  Strontia. — This  salt,  the  celestine  of  mineralogists,  is  less 
abundant  than  heavy  spar.  It  occurs  in  prismatic  crystals  of  peculiar 
beauty  in  Sicily,  and  its  primary  form  is  a right  rhombic  prism.  Its 
density  is  3.858.  As  obtained  by  the  way  of  double  decomposition,  it 
is  a white  heavy  powder,  very  similar  to  sulphate  of  baryta.  It  requires 
about  3840  times  its  weight  of  boiling  water  for  solution.  According  to 
Dr.  Thomson  it  consists  of  52  parts  or  one  equivalent  of  strontia,  and 
one  equivalent  of  sulphuric  acid. 

Sulphate  of  Lime. — This  salt  is  easily  formed  by  mixing  a solution  of 
muriate  of  lime  \vith  any  soluble  sulphate.  It  occurs  abundantly  as  a 
natural  production.  The  mineral  anhydrites  anhydrous  sulphate 

of  lime;  and  all  the  varieties  of  gypsum  are  composed  of  the  same  salt, 
united  with  water.  The  pure  crystallized  specimens  of  gypsum  are 
sometimes  called  selenite;  and  the  white  compact  variety  is  employed  in 
statuary  under  the  name  of  alabaster.  The  crystals  are  generally  flat- 
tened prisms,  the  primary  form  of  which  is  a rhombic  prism.  The  an- 
hydrous compound  consists  of  one  equivalent  of  acid,  and  28  parts  or 
one  equivalent  of  lime;  and  pure  gypsum,  according  to  Dr.  Thomson, 
is  composed  of  68  parts  or  one  equivalent  of  sulphate  of  lime,  and  18 
parts  or  two  equivalents  of  water.  The  hydrous  salt  is  deprived  of 
its  water  by  a low  red  heat,  and  in  this  state  forms  plaster  of  Paris. 
Its  property  of  becoming  hard,  when  made  into  a thin  paste  with  water, 
is  owing  to  the  anliydrous  sulphate  combining  chemically  with  that  li- 
quid, and  thus  depriving  it  of  its  fluidity. 


416 


SULPHATES. 


Sulphate  of  lime  has  hardly  any  taste.  It  is  considerably  more  solu- 
ble than  the  sulphates  of  baryta  or  strontia,  requiring*  for  solution  about 
500  parts  of  cold,  and  450  of  boiling-  water.  Owing  to  this  circum- 
stance, and  to  its  existing  so  abundantly  in  the  earth,  it  is  frequently 
contained  in  spring  water,  to  which  it  communicates  the  property  called 
hardness.  When  freshly  precipitated,  it  may  be  dissolved  completely 
by  dilute  nitric  acid.  It  is  commonly  believed  to  sustain  a white  heat 
without  decomposition;  but  Dr.  Thomson  states,  that  it  parts  with 
some  of  its  acid  when  heated  to  redness. 

Sulphate  of  Magnesia. — 'fhis  sulphate,  generally  known  by  the  name 
of  Epsom  salt,  is  frequently  contained  in  mineral  springs.  It  may  be 
made  directly,  by  neutralizing  dilute  sulphuric  acid  witli  carbonate  of 
magnesia;  but  it  is  procured  for  the  purposes  of  commerce  by  the  ac- 
tion of  dilute  sulphuric  acid  on  magnesian  limestone,  native  carbonate 
of  lime  and  magnesia. 

Sulphate  of  magnesia  has  a saline,  bitter,  and  nauseous  taste.  It 
crystallizes  readily  in  small  quadrangular  prisms,  which  effloresce  slight- 
ly in  a dry  air.  It  is  obtained  also  in  larger  crystals,  which  are  irregu- 
lar six-sided  prisms,  terminated  by  six-sided  summits.  Its  primary  form 
is  a right  rhombic  prism,  the  angles  of  which  are  90®  30'  and  89®  30'. — 
(Brooke.)  Its  crystals  are  soluble  in  an  equal  weight  of  water  at  60®, 
and  in  three-fourths  of  their  weight  of  boiling  water.  They  undergo 
the  watery  fusion  when  heated;  and  the  anhydrous  salt  is  deprived  of  a 
portion  of  its  acid  at  a white  heat.  The  crystals  are  composed,  accord- 
ing to  Gay-Lussac,  of  60  parts  or  one  equivalent  of  the  dry  sulphate, 
and  63  parts  or  seven  equivalents  of  water. 

On  mixing  solutions  of  sulphate  of  magnesia  and  sulphate  of  potassa 
in  atomic  proportion,  and  evaporating,  a double  salt  is  formed,  which 
consists  of  one  equivalent  of  each  of  the  salts  and  six  equivalents  of 
water.  The  crystals  are  prismatic,  but  of  a complicated  nature,  and 
are  connected  with  an  oblique  rhombic  prism.  A similar  double  salt, 
isomorphous  with  the  preceding,  is  formed  by  spontaneous  evapora- 
tion from  the  mixed  solutions  of  sul})hate  of  ammonia  and  sulphate  of 
magnesia.  The  crystals  contain  one  equivalent  of  each  of  the  two  salts, 
and  eight  equivalents  of  water. 

Sulphate  of  Alumina. — The  pure  sulphate  is  a compound  of  little  in- 
terest; but  with  sulphate  of  potassa  it  forms  an  interesting  double  salt, 
the  well-known  alum  of  commerce. 

Alum  has  a sweetish  astringent  taste.  It  is  soluble  in  five  parts  of 
water  at  60®  F.,  and  in  little  more  than  its  own  weight  of  boiling  water. 
The  solution  reddens  litmus  paper;  but  it  is  doubtful  whether  this  is 
owing  to  an  excess  of  acid,  or  to  the  weak  afflnity  existing  between 
alumina  and  sulphuric  acid.  (Page  401.)  It  crystallizes  readily  in  oc- 
tohedrons,  or  in  segments  of  the  octohedron,  and  the  crystals  contain 
almost  50  per  cent  of  water  of  crystallization.  On  being  exposed  to 
heat,  they  froth  up  remarkably,  and  part  with  all  the  water,  forming 
anhydrous  alum,  the  alumen  ustum  of  the  Pharmacopoeia.  At  a full  red 
heat  the  alumina  is  deprived  of  its  acid. 

There  is  some  doubt  as  to  the  real  composition  of  alum.  According 
to  Dr.  Thomson,  it  is  composed  of 


Sulphate  of  alumina. 

174 

three  equivalents. 

Sulphate  of  potassa. 

88 

one  equivalent, 
twenty-five  equivalents. 

Water, 

225 

Mr.  Phillips,  on  the  contrary,  regards  it  as  a compound  of  two  equiv- 
alents of  sulphate  of  alumina,  one  equivalent  of  bisulphate  of  potassa, 
and  twenty-five  equivalents  of  water. 


SULPHATES. 


417 


Sulphate  of  alumina  forms  with  sulphate  of  ammonia,  and  with  sul- 
phate of  soda,  double  salts,  which  are  v^ry  analog'ous  to  common  alum. 

Alum  is  employed  in  the  formation  of  a spontaneously  inflammable 
mixture  long*  known  under  the  name  of  Jlomberg^s  pyrnphorus.  It  is 
made  by  mixing  equal  weights  of  alum  ai\d  brown  sugar,  and  stirring 
the  mass  over  the  fire  in  an  iron  or  other  i^onvenient  vessel  till  quite 
dry;  when  it  is  put  into  a glass  tube  or  bottle,  and  heated  to  moderate 
redness  without  exposure  to  the  air  until  inflammable  gas  ceases  to  be 
evolved.  A more  convenient  mixture  is  made  with  three  parts  of  lamp- 
black, four  of  burned  alum,  and  eight  of  carbonate  of  potassa.  "When 
the  pyrophorus  is  well  made,  it  speedily  becomes  hot  on  exposure  to 
the  air,  takes  fire,  and  burns  like  tinder;  but  the  experiment  frequently 
fails  from  the  difficulty  of  regulating  the  temperature. 

From  some  recent  experiments  by  Gay-Lussac,  it  appears  that  the 
essential  ingredient  of  Homberg’s  pyrophorus  is  sulphuret  of  potassium 
in  a state  of  minute  division.  The  charcoal  and  alumina  act  only  by 
being  mechanically  interposed  between  its  particles;  but  when  the  mass 
once  kindles,  the  charcoal  takes  fire  and  continues  the  combustion. 
He  finds  that  an  excellent  pyrophorus  is  made  by  mixing  27  parts  of 
sulphate  of  potassa  with  15  parts  of  calcined  lamp-black,  and  heating  the 
mixture  to  redness  in  a common  Hessian  crucible,  of  course  excluding 
the  air  at  the  same  time.  (An.  de  Ch.  et  de  Ph.  xxxvii.  415.) 

Sulphate  of  Manganese. — This  salt  is  best  obtained  by  dissolving  pure 
carbonate  of  manganese  in  moderately  dilute  sulphuric  acid,  and  set- 
ting the  solution  aside  to  crystallize  by  spontaneous  evaporation.  The 
crystals  are  transparent,  and  of  a slight  rose  tint,  in  taste  resemble  Glau- 
ber’s salt,  and  occur  in  flat  rhombic  prisms.  It  is  insoluble  in  alcohol, 
but  dissolves  in  twice  and  a half  times  its  weight  of  cold  water.  If  grad- 
ually heated  it  may  be  long  exposed  to  a moderate  red  heat,  without 
losing  any  of  its  acid.  The  crystals  are  composed  of  40  parts  or  one 
equivalent  of  sulphuric  acid,  36  parts  or  one  equivalent  of  protoxide  of 
manganese,  and,  according  to  Mitscherlich,  of  45  parts  or  five  equiva- 
lents of  water. 

With  sulphate  of  ammonia  this  salt  yields  a double  sulphate  of  am- 
monia and  manganese,  consisting  of  one  equivalent  combined  with  eight 
of  water.  It  is  isomorphous  with  the  analogous  salts  of  magnesia  and 
protoxide  of  iron. 

Sulphate  of  Iron. — Sulphate  of  the  protoxide  of  iron,  commonly  call- 
ed green  vitrioh  is  formed  by  the  action  of  dilute  sulphuric  acid  on  me- 
tallic iron  (page  149),  or  by  exposing  protosulphuret  of  iron  in  frag- 
ments to  the  combined  agency  of  air  and  moisture.  This  salt  has  a 
strong  styptic,  inky  taste.  Though  neutral  in  composition,  being  com- 
posed of  one  equivalent  of  each  element,  it  reddens  the  vegetable  blue 
colours.  It  is  insoluble  in  alcohol,  but  soluble  in  two  parts  of  cold, 
and  in  three-fourths  of  its  weight  of  boiling  water.  It  occurs  in  right 
rhombic  prisms,  which  are  transparent,  and  of  a pale-green  colour.  It 
consists  of  76  parts  or  one  equivalent  of  the  dry  salt,  combined  accord- 
ing to  Thomson  with  seven,  and  according  to  Mitscherlich  with  six, 
equivalents  of  water.  In  the  anliydrous  state  it  is  of  a dirty-white  co- 
lour. It  is  this  salt  which  is  employed  in  the  manufacture  of  fuming 
sulphuric  acid.  (Page  186.) 

Protosulphate  of  iron  forms  double  salts  with  sulphate  of  potassa  and 
sulphate  of  ammonia,  the  former  of  which  contains  six  and  the  latter 
eight  equivalents  of  water.  They  are  isomorphous  with  the  analogous 
double  sulphates  of  magnesia. 

Protosulphate  of  iron  absorbs  oxygen  from  the  air,  especially  when 
in  solution,  by  which  an  insoluble  subsulphate  of  the  peroxide  of  iron 


418 


SULPHATES. 


is  generated,  consisting,  according  to  Rerzelius,  of  one  equivalent  of 
sulphuric  acid,  and  four  equivalents  of  peroxide  of  iron. 

When  a solution  of  protosulphate  of  iron  is  boiled  with  a little  nitric 
acid,  until  the  liquid  acquires  a red  colour,  and  is  then  evaporated  to 
dryness  by  a moderate  heat,  a salt  remains,  the  greater  part  of  which 
is  soluble  both  in  alcoliol  and  water,  and  which  attracts  moisture  from 
the  atmospliere.  The  analysis  of  Berzelius  has  proved  it  to  be  a com- 
pound of  40  parts  or  one  equivalent  of  peroxide  of  iron,  and  60  parts 
or  an  equivalent  and  a half  of  sulphuric  acid.  It  is,  therefore,  a sesqui- 
sulphate  of  the  peroxide  of  iron. 

By  mixing  sulphate  of  potassa  with  persulphate  of  iron,  and  allowing 
the  solution  to  crystallize  by  spontaneous  evaporation,  crystals  are  ob- 
tained similar  to  common  alum  in  form,  colour,  taste,  and  composition. 
In  this  double  salt  sulphate  of  alumina  is  replaced  by  persulphate  of 
iron,  with  which  it  is  isomorphous. 

A similar  double  salt  may  be  made  with  a mixture  of  sulphate  of  am- 
monia and  persulphate  of  iron. 

Sulphate  of  Zinc, — This  salt,  frequently  called  white  vitriol^  is  the  re- 
sidue of  the  process  for  forming  hydrogen  gas  by  the  action  of  dilute 
sulphuric  acid  on  metallic  zinc;  but  it  is  made,  for  the  purposes  of  com- 
merce, by  roasting  native  sulphuret  of  zinc.  It  crystallizes  by  sponta- 
neous evaporation  in  transparent  flattened  four-sided  prisms,  and  the 
primary  form  of  the  crystals  is  a right  rhombic  prism.  The  crystals 
dissolve  in  two  parts  and  a half  of  cold,  and  are  still  more  soluble  in 
boiling  w^ater.  The  taste  of  this  salt  is  strongly  styptic.  It  reddens 
vegetable  blue  colours,  though  in  composition  it  is  a strictly  neutral 
salt,  consisting  of  one  equivalent  of  each  of  its  elements.  The  crys- 
tals are  composed  of  82  parts  or  one  equivalent  of  the  anhydrous  sul- 
phate, and  63  parts  or  seven  equivalents  of  water.  Sulphate  of  potassa 
crystallizes  with  sulphate  of  zinc  as  a double  salt  in  flat  rhombic  prisms, 
the  acute  edges  of  which  are  replaced  by  planes. 

Sulphate  of  Nickel. — This  salt,  like  the  salts  of  nickel  in  general,  is 
of  a green  colour,  and  crystallizes  from  its  solution  in  pure  water  in 
right  rhombic  prisms  exactly  similar  to  the  primary  form  of  sulphate 
of  zinc.  If  an  excess  of  sulphuric  acid  is  present,  the  crystals  are 
square  prisms,  which  according  to  Messrs.  R.  Phillips  and  Cooper  con- 
tain rather  less  water  and  more  acid  than  the  preceding;  though  the 
difference  is  not  so  great  as  to  indicate  a different  atomic  constitution. 
(Annals  of  Philosophy,  xxii.  439.)  Dr.  Thomson  says  he  analyzed  both 
kinds,  and  found  their  composition  identical.  They  consist  of  one  equiv- 
alent of  the  anhydrous  salt  and  seven  equivalents  of  water.  It  is  solu- 
ble in  about  three  times  its  weight  of  water  at  60^  F. 

This  salt  crystallizes  with  great  facility  when  mixed  with  sulphate  of 
potassa,  as  a double  sulphate  of  potassa  and  nickel.  The  crystals  are 
of  an  emerald-green  colour,  soluble  in  nine  parts  of  cold  water,  and  are 
composed  of  one  equivalent  of  sulphate  of  nickel,  one  equivalent  of 
sulphate  of  potassa,  and  six  equivalents  of  water.  Its  primary  form  is 
an  olilicpie  rhombic  ])rism;  but  the  general  outline  of  the  crystals  is 
sometimes  that  of  a six-sided  ])rism.  It  is  isomorphous  with  similar  dou- 
ble .salts  of  iron  and  manganese. 

Sulphate  of  Chromium. — 'I’liis  salt  may  be  formed  by  saturating  dilute 
sulphuric  acid  witli  hydrated  oxide  of  chromium.  It  crystallizes  readily 
as  a doul)le  salt,  in  octohedral  crystals,  with  sulphate  of  potassa  and  sul- 
phate of  ammonia.  'The  double  sulphate  with  ammonia,  which  has 
lately  been  prepared  by  my  assistant,  Mr.  Warrington,  appears  almost 
black  by  reflected,  but  ruby-red  by  transmitted  light.  Sulphate  of  chro- 
mium and  ])otassa  is  similar  in  its  appearance,  and  is  described  in  his 


SULPHATES. 


419 


Lehrhuch  by  Berzelius,  who  states  its  composition  to  be  exactly  analo- 
gous to  that  of  common  alum. 

Sulphates  of  Cojoper.— Sulphate  of  the  protoxide  of  copper  has  not 
been  obtained  in  a separate  state.  The  sulphate  of  the  peroxide,  blue 
vitriol,  employed  by  surgeons  as  an  escharotic  and  astringent,  may  be 
prepared  for  chemical  purposes  by  dissolving  peroxide  of  copper  in  di- 
lute sulphuric  acid;  but  it  is  procured  for  sale  by  roasting  the  native 
sulphuret,  so  as  to  bring  both  its  elements  to  a maximum  of  oxidation. 
This  salt  forms  regular  crystals  of  a blue  colour,  reddens  litmus  paper, 
and  is  soluble  in  about  four  of  cold,  and  in  two  parts  of  boiling  water. 
According  to  the  researches  of  Proust,  Thomson,  and  Berzelius,  it  is 
composed  of  80  parts  or  one  equivalent  of  peroxide  of  copper,  80  parts 
or  two  equivalents  of  acid,  and  90  parts  or  ten  equivalents  of  water.  It 
is,  therefore,  strictly,  a bisulphate. 

When  pure  potassa  is  added  to  a solution  of  bisulphate  of  copper  in  a 
quantity  insufficient  for  separating  the  whole  of  the  acid,  a pale  bluish- 
green  precipitate,  the  subsulphate,  is  thrown  down,  which  is  composed 
of  one  equivalent  of  acid  and  one  equivalent  of  the  peroxide. 

Sulphate  of  copper  and  ammonia  is  generated  by  dropping  pure  am- 
monia into  a solution  of  the  bisulphate,  until  the  subsalt  at  first  thrown 
down  is  nearly  all  dissolved.  It  forms  a dark  blue  solution,  from  which, 
when  concentrated,  crystals  arc  deposited  by  the  addition  of  alcohol.  It 
may  be  formed  also  by  rubbing  briskly  in  a mortar  two  parts  of  crys- 
tallized bisulphate  of  copper  with  three  parts  of  carbonate  of  ammonia, 
until  the  mixture  acquires  a uniform  deep-blue  colour.  Carbonic  acid 
gas  is  disengaged  with  effervescence  during  the  operation,  and  the  mass 
becomes  moist,  owing  to  the  water  of  the  blue  vitriol  being  set  free./ 

This  compound,  which  is  the  ammoniaret  of  copper  of  the  Pharmaco- 
poeia, contains  sulphuric  acid,  peroxide  of  copper,  and  ammonia;  but  its 
precise  nature  has  not  been  determined  in  a satisfactory  manner.  It 
parts  gradually  with  ammonia  by  exposure  to  the  air. 

Sulphates  of  Mercury. — When  two  parts  of  mercury  are  gently  heated 
in  three  parts  of  strong  sulphuric  acid,  so  as  to  cause  slow  effervescence, 
a sulphate  of  'the  protoxide  of  mercury  is  generated.  But  if  a strong 
heat  is  employed  in  such  a manner  as  to  excite  brisk  effervescence,  and 
the  mixture  is  brought  to  dryness,  a pure  sulphate  of  the  peroxide  re- 
sults.* The  former  is  composed  of  one  equivalent  of  sulphuric  acid  and 
one  equivalent  of  the  protoxide;  and  the  latter  of  two  equivalents  of 
acid  and  one  equivalent  of  the  peroxide.  (Thomson.)  When  this  bisul- 
phate, which  is  the  salt  employed  in  making  corrosive  sublimate,  is 
thrown  into  hot  water,  decomposition  ensues,  and  a yellow  subsalt,  for- 
merly called  turpeth  mineral,  subsides.  This  salt  is  composed  of  one 
equivalent  of  the  acid  and  one  equivalent  of  the  peroxide.  The  hot 
water  retains  some  of  the  sulphate  in  solution,  together  with  free  sul- 
phuric acid. 

Sulphate  of  Silver. — As  this  salt  is  rather  sparingly  soluble  in  water,  it 
may  be  formed  by  double  decomposition  from  concentrated  solutions  of 
nitrate  of  silver  and  sulphate  of  soda.  It  may  also  be  procured  by  dis- 
solving silver  in  sulphuric  acid  which  contains  about  a tenth  part  of  ni- 
tric acid,  or  by  boiling  silver  in  an  equal  weight  of  concentrated  sulphu- 
ric acid.  It  requires  about  80  times  its  weight  of  hot  water  for  solution, 
and  the  greater  part  is  deposited  in  small  needles  on  cooling.  By  slow 
evaporation  from  a solution  containing  a little  nitric  acid,  Mitscherlich 
obtained  it  in  the  form  of  a rhombic  octohedron,  the  angles  of  which 


Donovan  in  the  Annals  of  Philosophy,  vol.  xiv. 


420 


SULPHITES. 


are  almost  identical  with  tliose  of  anhydrous  sulphate  of  soda.  Seleniate 
of  silver  is  isomorphous  with  the  sulphate. 

Sulphate  of  silver  forms  with  ammonia  a double  salt,  which  crystal- 
lizes in  rectangular  prisms,  the  solid  angles  and  lateral  edges  of  which 
are  commonly  replaced  by  tangent  planes.  It  consists  of  one  equivalent 
of  oxide  of  silver,  two  of  acid,  and  one  of  ammonia;  and  it  is  formed  by 
dissolving  sulphate  of  silver  in  a hot  concentrated  solution  of  ammonia, 
from  which  on  cooling  tlie  crystals  are  deposited.  This  salt  is  isomor- 
phous with  the  double  chromate  and  arseniate  of  silver,  which  have  a 
similar  constitution,  and  are  formed  in  the  same  manner.  (Mitscherlich 
in  An.  de  Ch.  et  de  Ph.  xxxviii.  62.) 

Double  Sulphates  by  Fusion. — Berthier  has  remarked  that  some  sul- 
phates fuse  together  readily  at  a red  heat,  yielding  uniform  crystalline 
masses,  which  appear  to  be  definite  compounds.  Thus  sulphate  of  soda 
and  sulphate  of  lime,  when  mixed  in  the  ratio  of  their  equivalents,  fuse 
readily,  and  yield  a mass  similar  to  the  mineral  glauberite.  Sulphate  of 
soda,  fused  in  similar  proportions  with  the  sulphate  of  magnesia,  baryta, 
and  lead,  gives  analogous  compounds.  In  all  these  instances,  however, 
the  affinity  is  so  feeble,  that  it  is  overcome  by  the  action  of  water.  An. 
de  Ch.  et  de  Ph.  xxxviii.  255.) 

Sulphites* 

The  salts  of  sulphurous  acid  have  not  hitherto  been  minutely  examin- 
ed. The  sulphites  of  potassa,  soda,  and  ammonia,  which  are  made  by 
neutralizing  those  alkalies  w^ith  sulphurous  acid,  are  soluble  in  water; 
but  most  of  the  other  sulphites,  so  far  as  is  known,  are  of  sparing  solubility. 
The  sulphites  of  baryta,  strontia,  and  lime,  are  very  insoluble;  and  con- 
sequently the  soluble  salts  of  these  earths  decompose  the  alkaline  sul- 
phites. 

The  stronger  acids,  such  as  the  sulphuric,  muriatic,  phosphoric,  and 
arsenic  acids,  decompose  all  the  sulphites  with  effervescence,  owing  to 
the  escape  of  sulphurous  acid,  which  may  easily  be  recognized  by  its 
odour.  Nitric  acid,  by  yielding  oxj/gen,  converts  the  sulphites  into  sul- 
phates. 

When  the  sulphites  of  the  fixed  alkalies  and  alkaline  earths  are 
strongly  heated  in  close  vessels,  a sulphate  is  generated,  and  a portion 
of  sulphur  sublimed.  In  open  vessels  at  a high  temperature  they  ab- 
sorb oxygen,  and  are  converted  into  sulphates;  and  a similar  change 
takes  place  even  in  the  cold,  especially  when  they  are  in  solution.  Gay- 
Lussac  has  remarked,  that  a neutral  sulphite  always  forms  a neutral  sul- 
phate when  its  acid  is  oxidized;  a fact  from  which  it  may  be  inferred, 
that  neutral  sulpliites  consist  of  one  equivalent  of  the  acid  and  one 
equivalent  of  the  base. 

The  hyposulphates  and  hyposulphites  are  of  little  importance,  and 
their  general  character  has  already  been  sufficiently  described.  (Pages 
189  and  190.)  For  a particular  description  of  the  hyposulphates,  the 
reader  is  referred  to  an  essay  by  Dr.  Heeren  (An.  de  Ch.  et  de  Ph.  xl.  30). 


NITRATES. 


421 


SECTION  II. 

NITRATES.— NITRITES.--CHL0RATE&.—10DATES. 

Nitrates, 

The  nitrates  may  be  prepared  by  the  action  of  nitric  acid  on  metals, 
on  the  salifiable  bases  themselves,  or  on  carbonates.  As  nitric  acid  forms 
soluble  salts  with  all  alkaline  bases,  the  acid  of  the  nitrates  cannot  be 
precipitated  by  any  reag-ent.  They  are  readily  distinguished  from  other 
salts,  however,  by  the  three  following  characters: — 1st,  by  deflagrating 
with  red-hot  charcoal;  2d,  by  their  power  of  dissolving  gold  leaf  on  the 
addition  of  muriatic  acid;  3d,  by  the  evolution,  when  mixed  with  sul- 
phuric acid,  of  dense,  white,  acid  vapours,  which  are  easily  recognised  to 
be  nitric  acid  by  their  odour. 

All  the  nitrates  are  decomposed  without  exception  by  a high  tempera- 
ture; but  the  changes  which  ensue  are  modified  by  the  nature  of  the 
oxide.  Nitrate  of  palladium  is  decomposed  at  such  a moderate  tempera- 
ture, that  a grea’t  part  of  the  acid  passes  off  unchanged.  Nitrate  of  lead 
requires  a red  heat,  by  which  it  is  resolved,  as  already  mentioned,  (page 
169)  into  oxygen  and  nitrous  acid.  In  some  instances  the  changes  are 
more  complicated.  With  nitre,  for  example,  a nitrite  of  potassa  is  at 
first  generated,  with  escape  of  oxygen  gas:  as  the  heat  increases,  the 
nitrous  acid  is  converted  into  deutoxide  of  nitrogen  and  oxygen,  the 
former  of  which  remains  in  combination  with  potassa;  the  deutoxide  is 
tlien  resolved  into  protoxide  of  nitrogen  and  oxygen,  the  former  being 
retained  by  the  alkali;  and,  lastly,  nitrogen  gas  is  disengaged,  and  per- 
oxide of  potassium  remains.  If  the  operation  is  performed  in  an  earthen 
vessel,  the  peroxide  will  be  more  or  less  decomposed,  in  consequence 
of  the  affinity  of  the  earthy  substances  for  potassa.  The  preceding  facts 
have  been  chiefly  collected  from  the  observations  of  Phillips  and  Berze- 
lius. The  tendency  of  potassa  and  soda  to  unite  with  protoxide  of  ni- 
trogen was  first  observed  by  Sir  H.  Davy;  and  M.  Hess  has  lately  re- 
marked that  similar  compounds  are  obtained  with  soda,  baryta,  and  lime, 
as  well  as  potassa,  when  their  nitrates  are  heated  until  the  disengaged 
gas  is  found  to  extinguish  a light. 

As  the  nitrates  are  easily  decomposed  by  heat  alone,  they  must  neces- 
sarily suffer  decomposition  by  the  united  agency  of  heat  and  combustible 
matter.  The  nitrates  on  this  account  are  much  employed  as  oxidizing 
agents,  and  frequently  act  with  greater  efficacy  even  than  nitro-muriatic 
acid.  Thus  metallic  titanium,  which  resists  the  action  of  these  acids, 
combines  with  oxygen  when  heated  with  nitre.  The  efficiency  of  this 
salt,  which  is  the  nitrate  usually  employed  for  the  purpose,  depends  not 
only  on  the  affinity  of  the  combustible  for  oxygen,  but  likewise  on  that  of 
the  oxidized  body  for  potassa.  The  process  for  oxidizing  substances  by 
means  of  nitre  is  called  deflagration,  and  is  generally  performed  by  mix- 
ing the  inflammable  body  with  an  equal  weight  of  the  nitrate,  and  pro- 
jecting the  mixture  in  small  portions  at  a time  into  a red-hot  crucible. 

All  the  neutral  nitrates  of  the  fixed  alkalies  and  alkaline  earths,  to- 
gether with  most  of  the  neutral  nitrates  of  the  common  metals,  are  com- 
posed of  one  equivalent  of  nitric  acid,  and  one  equivalent  of  a protoxide. 
Consequently,  the  oxygen  of  the  oxide  and  acid  in  all  such  salts  must  be 
in  the  ratio  of  1 to  5. 


36 


422 


NITRATES. 


The  only  nitrates  found  native  are  those  of  potassa,  soda,  lime,  and 
mag’nesia. 

Nitrale  of  Potassa. — This  salt  is  g'enerated  spontaneously  in  the  soil, 
and  crystallizes  upon  its  surface,  in  several  parts  of  the  world,  and  espe- 
cially in  the  East  Indies,  whence  the  greater  part  of  the  nitre  used  in 
Britain  is  derived.  In  some  parts  of  the  continent,  it  is  prepared  artifi- 
cially from  a mixture  of  common  mould  or  porous  calcareous  earth  with 
animal  and  vegetable  remains  containing  nitrogen.  When  a heap  of 
these  materials,  preserved  moist  and  in  a shaded  situation,  is  moderately 
exposed  to  the  air,  nitric  acid  is  gradually  generated,  and  unites  with  the 
potassa,  lime,  and  magnesia,  which  are  commonly  present  in  the  mixture. 
On  dissolving  these  salts  in  water,  and  precipitating  the  two  earths  by 
carbonate  of  potassa,  a solution  is  formed,  which  yields  crystals  of  nitre 
by  evaporation.  The  nitric  acid  is  probably  generated  under  these  cir- 
cumstances by  the  nitrogen  of  the  organic  matters  combining  during  the 
putrefaction  with  the  oxygen  of  the  atmosphere,  a change  which  must 
be  attributed  to  the  affinity  of  oxygen  for  nitrogen,  aided  by  that  of  ni- 
tric acid  for  alkaline  bases.  The  nitre  made  in  France  is  often  said  to 
be  formed  by  this  process;  but  the  greater  part  is  certainly  obtained  by 
lixiviation  from  certain  kinds  of  plaster  of  old  houses,  where  it  is  gra- 
dually generated. 

Nitrate  of  potassa  is  a colourless  salt,  which  crystallizes  readily  in  six- 
sided  prisms.  Its  taste  is  saline,  accompanied  with  an  impression  of 
coolness.  It  requires  for  solution  seven  parts  of  water  at  60®  F.,  and  its 
own  weight  of  boiling  water.  It  contains  no  water  of  crystallization,  but 
its  crystals  are  never  quite  free  from  water  lodged  mechanically  within 
them.  At  616®  F.  it  undergoes  the  igneous  fusion,  and  like  all  the  ni- 
trates is  decomposed  by  a red  heat. 

Nitre  is  chiefly  employed  in  chemistry  as  an  oxidizing  agent,  and  in 
the  formation  of  nitric  acid.  Its  chief  use  in  the  arts  is  for  making 
gunpowder,  which  is  a mixture  of  nitre,  charcoal,  and  sulphur.  In  the 
East  Indies  it  is  employed  for  the  preparation  of  coaling  mixtures; — an 
ounce  of  powdered  nitre  dissolved  in  five  ounces  of  water  reduces  its 
temperature  by  fifteen  degrees.  It  possesses  powerful  antiseptic  pro- 
perties, and  is,  therefore,  much  employed  in  the  preservation  of  meat 
and  animal  matters  in  general. 

Nitrate  of  Soda. — This  salt  is  analogous  in  its  chemical  properties  to 
the  preceding  compound.  It  sometimes  crystallizes  in  oblique  rhombic 
prisms;  but  it  more  commonly  occurs  as  an  obtuse  rhombohedron,  which 
is  its  primary  form.  (Mr.  Brooke.)  It  is  plentifully  found  in  the  soil 
in  some  parts  of  India. 

Nitrate  of  Ammonia. — Nitrate  of  ammonia  may  be  formed  by  neu- 
tralizing dilute  nitric  acid  by  carbonate  of  ammonia,  and  evaporating  the 
solution.  This  salt  may  be  procured  in  three  different  states,  which 
have  been  described  by  Sir  H.  Davy.  (Researches  concerning  the  Nitrous 
Oxide.)  If  the  evaporation  is  conducted  at  a temperature  not  exceed- 
ing lOU^  F.,  the  salt  is  obtained  in  prismatic  crystals  which  are  com- 
posed, according  to  the  experiments  of  Davy,  Berzelius,  and  Thomson, 
of  71  parts  or  one  equivalent  of  neutral  nitrate  of  ammonia,  and  9 
parts  or  one  equivalent  of  water.  If  the  solution  is  eva])orated  at  212® 
F.,  fibrous  crystals  arc  procured;  and  if  the  heat  be  gradually  increased 
to  300°  F.,  it  forms  a brittle  compact  mass  on  cooling.  The  fibrous  and 
compact  varieties  still  contain  water,  the  former  8.2  per  cent,  and  the 
latter  5.7.  All  these  varieties  are  deliquescent,  and  very  soluble  in  wa- 
ter. 

The  change  which  nitrate  of  ammonia  undergoes  at  a temperature 
varying  between  400®  and  500®  of  F.  has  already  been  explained. 


NITRATES. 


423 


(Page  163.)  When  heated  to  600°,  it  explodes  with  violence,  being 
resolve^  into  water,  nitrous  acid,  deiitoxide  of  niti*ogen,  and  nitrogen. 
The  fibrous  variety  was  found  by  Sir  H.  Davy  to  yield  the  largest  quan* 
tity  of  protoxide  of  nitrogen.  From  one  pound  of  this  salt  he  procured 
nearly  three  cubic  feet  of  the  gas. 

Nitrate  of  Baryta, — This  salt  is  sometimes  used  as  a reagent,  and  for 
preparing  pure  baryta.  It  is  easily  prepared  by  digesting  the  native 
carbonate,  reduced  to  powder,  in  nitric  acid  diluted  with  eight  or  ten 
times  its  weight  of  water.  The  salt  crystallizes  readily  by  evaporation 
in  transparent  octohedrons.  Its  crystals  contain  no  water  of  crystalli- 
zation, and  are  very  apt  to  decrepitate  by  heat  unless  previously  reduced 
to  powder.  They  require  twelve  parts  of  water  at  60°  F.,  and  three  or 
four  of  boiling  water  for  solution.  They  undergo  the  igneous  fusion 
in  the  fire  before  being  decomposed.  They  are  insoluble  in  alcohol. 

Nitrate  of  Strontia. — This  salt  may  be  made  from  strontianite  in  the 
same  manner  as  the  foregoing  compound,,  to  which  it  is  exceedingly 
analogous.  It  is  anhydrous,  crystallizes  in  the  form  of  the  regular  octo- 
hedron,  and  undergoes  no  change  in  a moderately  dry  atmosphere.  On 
spme  occasions  this  salt  contains  water  of  crystallization;  and  then  as- 
sumes the  form  of  a prism  with  ten  sides  and  two  summits.  The  hy- 
drous salt,  according  to  Mr.  Cooper,  contains  27.8  per  cent  of  water. 

Nitrates  of  Lime  and  Magnesia, — These  salts  are  very  deliquescent, 
and  soluble  in  alcohol.  By  this  character  nitrate  of  lime  is  easily  dis- 
tinguished and  separated  from  the  nitrates  of  baryta  and  strontia. 
(Page  306.) 

Nitrate  of  Copper, — This  salt  is  prepared  by  the  action  of  nitric  acid 
on  copper.  (Page  165.)  It  crystallizes,  though  with  some  difficulty, 
in  prisms,  which  are  of  a deep-blue  colour,  and  deliquesce  on  exposure 
to  the  air.  The  crystals  are  composed  of  108  parts  or  two  equivalents 
of  acid,  80  or  one  equivalent  of  the  peroxide,  and  126  or  fourteen 
equivalents  of  water.  (Thomson.)  It  is  therefore  strictly  a binitrate. 
The  green  insoluble  subsalt,  procured  by  exposing  the  binitrate  to  heat, 
contains,  exclusive  of  water,  one  equivalent  of  acid  and  one  equivalent 
of  the  peroxide.  When  heated  to  redness  it  yields  pure  peroxide  of 
copper. 

Nitrate  of  Lead. — This  salt  is  formed  by  digesting  litharge  in  dilute 
nitric  acid.  It  crystallizes  readily  in  octohedrons,  which  are  almost  al- 
ways opake.  These  crystals  are  anhydrous.  This  salt  has  an  acid  re- 
action, but  is  neutral  in  composition,  consisting  of  54  parts  or  one  equiv- 
alent of  acid,  and  112  or  one  equivalent  of  protoxide  of  lead. 

A dinitrate  of  lead,  composed  of  one  equivalent  of  acid  to  two 
equivalents  of  the  protoxide,  was  formed  by  Berzelius  by  adding  to  a 
solution  of  the  neutral  nitrate,  a quantity  of  pure  ammonia  insufficient 
for  separating  the  whole  of  the  acid. 

Nitrates  q/  Mercury. — The  protonitrate  is  conveniently  formed  by  di- 
gesting mercury  in  nitric  acid,  diluted  with  three  or  four  parts  of  water, 
until  the  acid  is  saturated,  and  then  allowing  the  solution  to  evaporate 
spontaneously  in  an  open  vessel.  The  solution  always  contains  at  first 
some  nitrate  of  the  peroxide,  but  if  metallic  mercury  is  left  in  the  liquid 
a pure  protonitrate  is  gradually  deposited.  The  salt  thus  formed  has 
hitherto  been  regarded  as  the  neutral  protonitrate;  but  according  to  the 
analysis  of  M.  C.  Mitscherlich,  (Poggendorfl’^s  Annalen,  ix.  387)  it  is  a 
subsalt,  in  which  the  protoxide  and  acid  are  in  the  ratio  of  208  to 
36.  This  result,  however,  requires  confirmation.  I'he  neutral  proto- 
nitrate is  said  by  M.  C.  Mitscherlich  to  be  obtained  in  crystals,  by  dis- 
solving the  former  salt  in  pure  water  acidulated  with  nitric  acid,  and 
evaporating  spontaneously  without  the  contact  of  metallic  mercury  or 


424 


NITRITES. 


uncombined  oxide.  The  crystals  are  composed  of  208  parts  or  one 
equivalent  of  the  protoxide^  54  parts  or  one  equivalent  of  acid,  and  two 
equivalents  of  water.  These  salts  dissolve  completely  in  water  slightly 
acidulated  with  nitric  acid,  but  in  pure  water  a small  quantity  of  a yel- 
low subsalt  is  generated. 

When  mercury  is  heated  in  an  excess  of  strong  nitric  acid,  it  is  dis- 
solved with  brisk  effervescence  owing  to  the  escape  of  deutoxide  of 
nitrogen,  and  transparent  prismatic  crystals  of  the  pernitrate  are  de- 
posited as  the  solution  cools.  It  is  composed,  according  to  Thomson, 
of  one  equivalent  of  the  peroxide  and  one  of  the  acid;  and  when  ])ut 
into  hot  water  it  is  resolved  into  a soluble  salt,  the  composition  of  which 
is  unknown,  and  into  a yellow  subsalt.  The  latter  was  found  by  M. 
Grouvelle  to  consist  of  one  equivalent  of  acid  to  two  of  the  peroxide. 
(An.  de  Ch.  et  de  Phys.  xix.) 

Nitrate  of  Silver. — Silver  is  readily  oxidized  and  dissolved  by  nitric 
acid  diluted  with  two  or  three  times  its  weight  of  water,  forming  a solu- 
tion which  yields  transparent  tabular  crystals  by  evaporation.  These 
crystals,  which  are  anhydrous,  undergo  the  igneous  fusion  at  426^  F., 
and  yield  a crystalline  mass  in  cooling;  but  when  the  temperature  reaches 
600^  or  700®,  complete  decomposition  ensues,  the  acid  being  resolved 
into  oxygen  and  nitrous  acid,  while  metallic  silver  is  left.  When  lique- 
fied by  heat,  and  received  in  small  cylindrical  moulds,  it  forins  the  lapis 
infernalisy  or  lunar  caustic^  employ td  by  surgeons  as  a cautery.  The 
nitric  acid  appears  to  be  the  agent  which  destroys  the  animal  texture, 
and  the  black  stain  is  owing  to  the  separation  of  oxide  of  silver.  It  is 
sometimes  employed  for  giving  a black  colour  to  the  hair,  and  is  the 
basis  of  the  indelible  ink  for  marking  linen. 

Pure  nitrate  of  silver,  whether  fused  or  in  crystals,  is  colourless  and 
transparent,  and  does  not  deliquesce  by  exposure  to  the  air;  but  com- 
mon lunar  caustic  is  dark  and  opake,  and  dissolves  imperfectly  in  water, 
owing  to  some  of  the  nitrate  being  decomposed  during  its  preparation. 
It  is  impure  also,  always  containing  nitrate  of  copper,  and  frequently 
traces  of  gold.  The  pure  salt  is  soluble  in  its  own  weight  of  cold,  and 
in  half  its  weight  of  hot  water.  It  dissolves  also  in  four  times  its  weight 
of  alcohol.  Its  aqueous  solution,  if  preserved  in  clean  glass  vessels, 
undergoes  little  or  no  change  even  in  the  direct  solar  rays;  but  when 
exposed  to  light,  especially  to  sunshine,  in  coiitact  with  paper,  the  skin, 
or  any  organic  substance,  a black  stain  is  quickly  produced,  owing  to 
decomposition  of  the  salt  and  reduction  of  its  oxide  to  the  metallic  state. 
This  change  is  so  constant,  that  nitrate  of  silver  constitutes  an  extremely 
delicate  test  of  the  presence  of  organic  matter,  and  has  been  properly 
recommended  as  such  by  Dr.  John  Davy.  Its  solution  is  always  kept  in 
the  laboratory  as  a test  for  chlorine  and  muriatic  acid. 

Nitrate  of  silver,  even  after  fusion,  reddens  vegetable  colouring  mat- 
ters; but  it  is  neutral  in  composition,  consisting  of  one  equivalent  of  acid 
and  one  of  the  oxide. 

Nitrites, 

Little  is  known  with  certainty  concerning  the  compounds  of  nitrous 
acid  with  alkaline  bases.  Nitrite  of  [)otassa  is  formed  by  heating  nitre 
to  redne.ss,  and  removing  it  from  the  lire  before  the  decomposition  is 
complete.  On  adding  a strong'  acid  to  the  ])roduct,  red  fumes  of  ni- 
trous acid  arc  disengaged,  a chai’acter  which  is  common  to  all  tho  nitrites. 
'Fwo  niti-itcs  of  lead  liavc  been  described  in  the  Annales  de  Chimie,  vol. 
Ixxxiii.  by  Ohcvreul  and  Berzelius.  It  is  possible,  however,  that  these 
com])ounds  are  hy])onitrites. 


CHLORATKS. 


425 


Chlorates. 


The  salts  of  chloric  acid  are  very  analogous  to  the  nitrates.  As  the 
chlorates  of  the  alkalies,  alkaline  earths,  and  most  of  the  common 
metals,  are  composed  of  one  equivalent  of  chloric  acid  and  one  equiv- 
alent of  a protoxide,  it  follows  that  the  oxygen  of  the  latter  to  that  of 
the  former  is  in  the  ratio  of  1 to  5.  The  chlorates  are  decomposed  by 
a red  heat,  nearly  all  of  them  being  converted  into  metallic  chlorides^ 
with  evolution  of  pure  oxygen  gas.  They  deflagrate  with  inflammable 
substances  with  greater  violence  than  nitrates,  yielding  oxygen  with 
such  facility  that  an  explosion  is  produced  by  slight  causes.  Thus  a 
mixture  of  sulphur  with  three  times  its  weight  of  chlorate  of  potassa 
explodes  when  struck  between  two  hard  surfaces.  With  charcoal  and 
the  sulphurets  of  arsenic  and  antimony,  this  salt  forms  similar  "explo- 
sive mixtures^  and  with  phosphorus  it  detonates  violently  by  percus- 
sion. The  mixture  employed  in  the  percussion  locks  for  guns  consists' 
of  sulphur  and  chlorate  of  potassa;  and  is  improved  by  the  addition  of 
charcoal. 

All  the  chlorates  hitherto  examined  ai-e  soluble  in  water,  except 
ing  the  protochlorate  of  mercury,  which  is  of  sparing  solubility' 
"J'hese  salts  are  distinguished  by  the  action  of  strong  muriatic  ami 
sulphuric  acids,  the  former  of  which  occasions  the  diseno^agement 
of  chlorine  and  protoxide  of  chlorine,  and  the  latter  of  peroxide  of 
chlorine.  ^ ^ 


None  of  the  chlorates  are  found  native,  and  the  only  ones  that  require 
particular  description  are  those  of  potassa  and  baryta.  ^ 

Chlorate  of  Potassa.— -TMis  salt,  formerly  called  oxymuriate  or  hyner 
oxymunate  of  potassa,  is  colourless,  and  crystallizes  in  four  and  six 
sided  scales  of  a pearly  lustre.  Its  primary  form  is  stated  by  Mr  Brooke 
to  be  an  oblique  rhombic  prism.  It  is  soluble  in  sixteen  times  its  weie'ht 
of  water  at  60®  F.,  and  in  two  and  a half  of  boiling  water.  It  is  quite 
anhydrous,  and  when  exposed  to  a temperature  of  400®  or  500®  F un 
dergoes  the  igneous  fusion.  On  increasing  the  heat  almost  to  redness' 
eff^ervescence  ensues,  and  pure  oxygen  gas  is  disengaged,  phenomena 
which  have  been  explained  in  the  section  on  oxygen. 

Chlorate  of  potassa  is  made  by  transmitting  chlorine  gas  through  a 
concentrated  solution  of  pure  potassa,  until  the  alkali  is  completelv 
neutralized.  The  solution,  which,  after  being  boiled  for  a few  minutes^ 
contains  nothing  but  muriate  and  chlorate  of  potassa  (page  205  ^ is 
gently  evaporated  till  a pellicle  forms  upon  its  siirflice,  and  is  then  al 
lowed  to  cool.  The  greater  part  of  the  chlorate  crystallizes,  while  the 
muriate  remains  in  solution.  The  crystals,  after  being  washed  with 
cold  water,  may  be  purified  by  a second  crystallization. 

Chlorate  of  baryta  is  of  interest,  as  being  the  compound  employed  in 
the  formation  of  chloric  acid,  and  the  readiest  mode  of  preparing  it  is 
by  the  process  of  Mr.  Wheeler.  Un  digesting  for  a few  minutes  a con 
centrated  solution  of  chlorate  of  potassa  with  a slight  excess  of  sili 
cated  hydrofluoric  acid,  the  alkali  is  precipitated  in  the  form  of  an  in' 
soluble  double  hydrofluate  of  silica  and  potassa,  while  chloric  acid  re- 
niains  in  solution.  The  liquid  after  filtration  is  neutralized  by  carbonate 
of  baryta,  which  likewise  throws  down  the  excess  of  hydrofluoric  acid 
and  sihca.  The  silicated  hydrofluoric  acid  employed  in  the  process  is 
made  by  conducting  fluosilicic  acid  gas  into  water.  ^ 

36* 


426 


lODATES. 


lodaies. 

From  the  close  analogy  in  the  composition  of  chloric  and  iodic  acids, 
it  follows  that  the  general  character  of  the  iodates  must  be  similar  to 
that  of  the  chlorates.  Thus  in  all  neutral  protiodates,  the  oxygen  con- 
tained in  the  oxide  and  acid  is  in  the  ratio  of  1 to  5.  They  form  defla- 
grating mixtures  with  combustible  matters;  and  on  being  heated  to  low 
redness,  oxygen  gas  is  disengaged  and  a metallic  iodide  remains.  As 
the  affinity  of  iodine  for  metals  is  less  energetic  than  tliat  of  chlorine, 
many  of  the  iodates  part  with  iodine  as  well  as  oxygen  when  heated,  es- 
pecially if  a high  temperature  is  cm])loyed. 

The  iodates  are  easily  recognised  by  the  facility  with  which  their  acid 
is  decomposed  by  deoxidizing  agents.  Thus,  sulphurous,  phosphorous, 
muriatic,  and  hydriodic  acids,  deprive  iodic  acid  of  its  oxygen,  and  set 
iodine  at  liberty.  Sulphuretted  hydrogen  not  only  decomposes  the  acid 
of  these  salts,  but  occasions  the  formation  of  hydriodic  acid  by  yielding 
hydrogen  to  the  iodine.  Hence  an  iodate  may  be  converted  into  a hy- 
driodate  by  transmitting  a current  of  sulphuretted  hydrogen  gas  through 
its  solution. 

None  of  the  iodates  have  been  found  native.  Theyare  all  of  very 
sparing  solubility,  or  actually  insoluble  in  water,  excepting  the  iodates 
of  the  alkalies. 

Iodate  of  Pofassa. — This  salt  is  easily  procured  by  adding  iodine  to  a 
concentrated  hot  solution  of  pure  potassa,  until  the  alkali  is  complete- 
ly neutralized.  The  liquid,  which  contains  iodate  and  hydriodate  of 
potassa  (page  221,)  is  evaporated  to  dryness  by  a gentle  heat,  and  the 
residue,  when  cold,  is  treated  by  strong  alcohol.  The  iodate,  which  is 
insoluble  in  that  menstruum,  is  left,  while  the  hydriodate  of  potassa  is 
dissolved. 

All  the  insoluble  iodates  may  be  procured  from  this  salt  by  double  de- 
composition. Thus  iodate  of  baryta  may  be  formed  by  mixing  muriate 
of  baryta  with  a solution  of  iodate  of  potassa. 

A biniodate  of  potassa  has  lately  been  described  by  Serullas.  It  is 
formed  by  incompletely  neutralizing  chloride  of  iodine  with  potassa  or 
its  carbonate,  and  setting  it  aside  to  cool.  A peculiar  compound  of 
chloride  of  potassium  and  biniodate  of  potassa  falls;  but  on  dissolving 
this  substance,  filtering,  and  exposing  the  solution  to  a temperature  of 
77^  F.,  the  biniodate  is  gradually  deposited  in  right  rhombic  prisms  ter- 
minated by  dihedral  summits.  *It  is  soluble  in  75  times  its  weight  of 
wate»r  at  59  P. 

A teriodate  of  potassa  maybe  formed  by  mixing  a large  excess  of 
sulphuric  acid  with  a moderately  dilute  solution  of  iodate  of  potassa. 
On  evaporating  at  77®  F.,  the  teriodate  is  deposited  in  regular  rhomboi- 
dal  crystals,  which  require  25  times  their  weight  of  water  at  60®  for 
solution. 

Serullas  states  that  the  compound  of  chloride  of  potassium  and  binio- 
date of  potassa,  above  mentioned,  may  be  formed  by  the  action  of  mu- 
riatic acid  on  iodate  of  potassa.  By  spontaneous  evaporation  it  is  ob- 
tained, sometimes  in  brilliant,  transparent,  elongated  prisms,  and  at 
another  in  hexagonal  lamincc;  but  generally  it  crystallizes  in  right  quad- 
rangular prisms  with  its  lateral  edges  truncated,  and  terminated  by  four- 
sided summits.  (An.  de  Ch.  ct  de  Fh.  xliii.  113.) 

liromates.— These  compounds  have  many  characters  in  common  with 
the  chlorates  and  iodates;  but  hitherto  they  have  been  but  partially  ex- 
amined. 


PHOSPHATES. 


SECTION  III. 

SALTS  OF  THE  ACIDS  OF  PHOSPHORUS  AND  ARSENIC. 

Phosphates. 

The  neutral  salts  of  phosphoric  acid  with  fixed  bases  sustain  a red 
heat  without  losing*  any  of  their  acid,  and  ar£  all  fusible  at  a high  tern- 
perature;  but  from  the  effects  of  heat  on  phosphate  of  soda,  it  is  pro- 
bable that  the  phosphates  generally,  by  a strong  heat,  are  converted 
into  pyrophosphates.  The  phosphates  of  the  third  class  of  metals,  at 
least  the  greater  part  "of  them,  are  resolved  into  phosphurets  by  the 
combined  agency  of  heat  and  charcoal.  The  alkaline  phosphates  are 
only  partially  decomposed  under  these  circumstances,  and  the  phos- 
phates of  lime,  baryta,  and  strontia,  undergo  no  change.  The  neutral 
phosphates,  excepting  those  of  potassa,  soda,'  and  ammonia,  are  of 
sparing  solubility  in  pure  water;  but  they  are  all  dissolved  without  effer- 
vescence in  an  excess  of  phosphoric  or  nitric  acid,  and  are  precipitated, 
for  the  most  part  unchanged,  from  the  acid  solutions,  by  pure  ammonia. 
Of  all  the  phosphates,  those  of  baryta,  lime,  and  lead,  and  especially 
the  latter,  are  the  most  insoluble. 

The  presence  of  a neutral  phosphate  in  solution  may  be  distinguish- 
ed by  the  tests  already  mentioned  in  the  section  on  phosphorus.  (Page 
194.)  The  insoluble  phosphates  are  decomposed  when  boiled  with  a 
strong  solution  of  carbonate  of  potassa  or  soda,  the  acid  uniting  with 
the  alkali  so  as  to  form  a soluble  phosphate.  The  earthy  phosphates 
yield  to  this  treatment  with  some  difficulty,  and  require  continued  ebul- 
lition. 

Several  phosphates  are  met  with  in  the  native  state,  such  as  those  of 
lime,  manganese,  iron,  uranium,  copper,  and  lead. 

Phosphate  of  Potassa. — This  salt  may  be  prepared  by  a process  analo- 
gous to  that  described  for  the  formation  of  phosphate  of  soda.  It  is  de- 
liquescent, and  has  not  been  procured  in  regular  crystals.  It  consists 
of  35.71  parts  or  one  equivalent  of  phosphoric  acid,  and  48  parts  or  one 
equivalent  of  potassa. 

The  biphosphate  may  be  formed  by  adding  phosphoric  acid  to  car- 
bonate of  potassa,  until  the  liquid  ceases  to  yield  a precipitate  with  mu- 
riate of  baryta,  and  setting  aside  the  solution  to  crystallize.  The  primary 
form  of  the  crystals  is  an  octohedron  with  a square  base;  but  they  com- 
monly occur  in  square  prisms  terminated  with  the  planes  of  the  pri- 
mary form.  They  are  composed  of  one  equivalent  of  potassa,  two  of 
phosphoric  acid,  and  two  equivalents  of  water.  (Mitscherlich.) 

Phosphate  of  Soda. — Of  the  alkaline  phosphates,  that  with  base  of  so- 
da is  the  one  generally  employed,  owing  to  the  facility  with  which  it  is 
obtained  in  crystals.  It  is  prepared  on  a large  scale  in  chemical  manu- 
factories, by  neutralizing  the  superphosphate  of  lime,  procured  by  the 
action  of  sulphuric  acid  on  burned  bones  (page  191,)  with  carbonate  of 
soda.  The  preci])itated  phosphate  of  lime  is  separated  by  filtration,  and 
the  clear  liquid,  after  being  duly  concentrated,  dep*osites  crystals  of 
phosphate  of  soda  in  cooling.  It  commonly  contains  traces  of  sulphuric 
acid,  from  which  it  may  be  purified  by  repeated  solution  in  distilled  wa- 
ter, and  crystallization.  It  is  customary  in  this  process  to  employ  a slight 
excess  of  the  alkali,  the  presence  of  which  facilitates  the  formation  of 


428 


PHOSPHATES. 


crystals.  On  this  account  phosphate  of  soda  has  commonly  an  alkaline 
reaction;  but  when  carefully  prepared,  Dr.  'rhomson  says  it  is  quite 
neutral. 

This  salt  crystallizes  in  oblique  rhombic  prisms,  which  effloresce  on 
exposure  to  the  air, 'and  require  four  parts  of  cold  or  two  of  boilinj^  water 
for  solution.  Accordinf^  to  the  analysis  of  Mitscherlich,  it  may  be  in- 
ferred to  consist  of  35.71  parts  or  one  equivalent  of  acid,  32  parts  or  one 
equivalent  of  soda,  and  112.5  parts  or  twelve  and  a half  equivalents  of 
water.  This  salt  is  employed  in  medicine  as  a laxative,  and  in  cliemis- 
try  as  a reagent.  By  the  action  of  heat  it  is  converted  into  pyrophosphate 
of  soda,  which  will  be  described  in  the  course  of  this  section. 

Mr.  Clarke  of  Glasg'ow  has  described  a new  phosphate  of  soda,  differ- 
ent from  the  foreg-oing-,  in  so  far  as  it  contains  seven  and  a half  instead 
of  twelve  and  a half  equivalents  of  water.  It  was  formed  by  exposing*  a 
solu;tion  of  the  common  phosphate  to  a uniform  temperature  of  about 
90®  F.  The  crystals  are  permanent  in  the  air, ’and  quite  different  in 
form  from  the  common  phosphate. 

Biphosphate  of  soda  is  prepared  by  adding  phosphoric  acid  to  car- 
bonate of  soda  until  the  solution  ceases  to  precipitate  muriate  of  baryta. 
Being  very  soluble  in  water,  the  solution  must  be  concentrated  in  order 
that  it  may  crystallize.  This  salt  is  capable  of  yielding  two  different 
kinds  of  crystals  without  varying  its  composition.  (Page  .413.)  The 
more  unusual  form,  isomorphous  with  binarseniate  of  soda,  is  a right 
rhombic  prism,  the  smaller  lateral  edge  of  which  is  78®  30',  terminated 
by  pyramidal  planes.  The  primary  form  of  its  ordinary  crystals  is  a 
right  rhombic  prism,  the  smaller  angle  of  which  is  93®  54'. 

A double  pliosphate  of  potassa  and  soda  may  be  formed  by  neu- 
tralizing biphosphate  of  potassa  with  carbonate  of  soda.  The  primary 
form  of  its  crystals  is  an  oblique  rhombic  prism,  which  frequently  oc- 
curs without  any  modification.  'I'he  crystals  consist  of  one  equivalent  of 
each  base,  and  two  of  acid. 

Phosphate  of  Soda  and  Ammonia. — This  salt  is  easily  prepared  by  dis- 
solving one  equivalent  of  muriate  of  ammonia  and  two  equivalents  of 
phosphate  of  soda,  in  a small  quantity  of  boiling  water.  As  the  liquid 
cools,  prismatic  crystals  of  the  double  phosphate  are  deposited,  while 
muriate  of  soda  remains  in  solution.  Their  primary  form  is  an  oblique 
rhombic  prism.  This  salt  has  been  long  known  by  the  name  of  miero- 
cosmic  salt,  and  is  much  employed  as  a flux  in  experiments  with  the 
blowpipe.  When  heated  it  parts  with  its  water  and  ammonia,  and  a 
very  fusible  biphosphate  of  soda  remains.  It  is  composed  of  one  equiv- 
alent of  phosphate  of  soda,  one  equivalent  of  phosphate  of  ammonia, 
and  ten  equivalents  of  water.  (Mitscherlich.) 

Phosphate  of  Ammonia. — This  salt  is  formed  by  adding  ammonia  to 
concentrated  phosphoric  acid  until  a precipitate  appears.  On  applying 
lieat,  the  precipitate  is  dissolved,  and  on  abandoning  the  solution  to  it- 
self, the  neutral  salt  crystallizes.  The  primary  form  of  the  crystals  is 
an  oblique  rhombic  prism,  the  smaller  lateral  angle  of  which  is  84®  30'. 
They  often  occur  in  rhombic  prisms  with  dihedral  summits.  They  ap- 
pear to  contain  an  equivalent  and  a half  of  water.  (Mitscherlich.) 

The  biphosphate  is  made  in  the  .same  manner  as  the  ])receding  bi- 
phosphates. The  crystals  arc  less  soluble  than  the  neutral,  phosphate, 
and  undergo  no  change  on  exposure  to  the  air.  'I'heir  primary  form 
is  an  octohedron  with  a square  base;  but  the  right  square  prism, 
terminated  by  the  faces  of  the  ])rimary  form,  is  the  most  frequent. 
'I'hey  consist  of  one  equivalent  of  ammonia,  two  of  acid,  and  three  of 
water. 

Phosphaic  of  Lime. — Chemists  differ  exceedingly  as  to  the  number  of 


PHOSPHATES. 


429 


compounds  which  phosphoric  acid  is  capable  of  forming-  with  lime. 
There  seems  no  doubt,  however,  from  the  researches  of  Berzelius  and 
others,  that  phosphate  of  lime,  as  it  exists  in  bones,  or  as  obtained  by 
mixing*  muriate  of  lime  with  neutral  phosphate  of  soda  in  excess,  is 
composed  of  35.71  parts  or  one  equivalent  of  phosphoric  acid,  and  28 
or  one  equivalent  of  lime.  This  is  the  compound  of  which  many  uri- 
nary concretions  consist. 

Biphosphate  of  lime  may  be  prepared  by  dissolving  phosphate  of 
lime  in  a slight  excess  of  phosphoric  acid.  Jt  is  very  soluble  in  water, 
but  does  not  crystallize.  A superphosphate  is  also  formed  by  the  ac- 
tion of  sulphuric  acid  on  phosphate  of  lime;  but  whether  it  is  really  a 
bi phosphate  mixed  with  free  phosphoric  acid,  or  some  supersalt  with  a 
still  larger  propoi’tion  of  acid,  is  as  yet  uncertain.  The  biphosphate 
exists  in  the  urine. 

Phosphate  of  Ammonia  and  Magnesia. — The  simple  phosphate  of 
magnesia,  which  is  prepared  by  mixing  a solution  of  sulphate  of  mag- 
nesia with  phosphate  of  soda,  is  of  little  interest;  but  the  double  phos- 
phate is  of  importance  as  constituting  a distinct  species  of  urinary  con- 
cretion. It  is  easily  procured  by  adding  carbonate  of  ammonia  and 
afterwards  phosphate  of  soda  to  a solution  of  sulphate  of  magnesia, 
when  the  double  phosphate  subsides  in  the  form  of  minute  crystalline 
grains.  This  salt  is  insoluble  in  pure  water;  but  is  dissolved  by  most 
acids,  even  by  the  acetic,  and  is  precipitated  unchanged  when  the  solu- 
tion is  neutralized  by  ammonia. 

The  composition  of  this  salt  has  not  been  satisfactorily  determined. 
On  exposure  to  heat  it  emits  water  with  ammonia,  and  a compound  of 
phosphoric  acid  and  magnesia  is  left,  which  is  insoluble  in  water,  but 
is  dissolved  by  strong  acids.  When  strongly  heated  it  undergoes  the 
igneous  fusion,  and  yields  a white  enamel.  According  to  Stromeyer, 
the  salt,  after  being  exposed  to  a red  heat,  contains  37  per  cent,  of 
magnesia. 

Pyrophosphates^ — The  only  pyrophosphates  which  have  been  care- 
fully studied  are  those  of  soda  and  silver.  The  former  is  readily  pre- 
pared by  the  action  of  heat  on  phosphate  of  soda,  as  was  mentioned  in 
the  section  on  phosphorus.  (Page  195.)  When  the  ignited  mass  is 
dissolved  in  water,  and  the  solution  set  aside  to  evaporate  spontaneous- 
ly* crystals  are  obtained,  having  the  general  outline  of  an  iri’egular 
six-sided  prism,  and  the  primary  form  of  which  is  a rhombic  octohe- 
dron..  (Haidinger.)  These  crystals  are  permanent  in  the  air,  much  less 
soluble  in  water  than  the  common  phosphate,  and  contain  five  equiv- 
alents of  water.  - 

I'he  oxides  of  most  metals  of  the  second  and  third  classes  yield  with 
pyrophosphoric  acid  insoluble  or  sparingly  soluble  salts,  which  may  be 
prepared  by  double  decomposition  with  pyrophosphate  of  soda.  It 
should  be  held  in  view',  how'ever,  as  Stromeyer  has  remarked,  that 
most  of  these  salts  are  more  or  less  soluble  in  an  excess  of  pyrophos- 
phate of  soda;  and  that  some  of  them,  such  as  the  pyrophosphate  of 
lead,  copper,  nickel,  cobalt,  uraniuni,  bismuth,  manganese,  and  pro- 
toxide of  mercury,  are  dissolved  by  it  with  great  facility. 

Stromeyer  has  lately  made  a comparative  examination  of  phosphate 
and  pyrophosphate  of  silver.  The  former  is  prepared  by  double  decom- 
position from  nitrate  of  silver  and  phosphate  of  soda,  the  characteristic 
yellow  phosphate  being  generated.  (Page  194.)  The  residual  liquid 
contains  free  nitric  acid  as  well  as  nitrate  of  soda,  phosphoric  acid  unit- 
ing with  more  than  an  equivalent  of  oxide  of  silver; — a tendency  to  the 
formation  of  a subphosphate  being  manifested  by  phosphoric  acid  in  re- 
gard to  baryta  and  some  other  bases,  as  well  as  to  oxide  of  silyer.  The 


430 


ARSKN[TES. 


yellow  phosphate  is  speedily  blackened  by  exposure  to  lig*!!!;  but  when 
protected  from  tliis  ag'ent,  it  yields  on  drying*  an  anhydrous  powder, 
which  has  a specific  gravity  of  7.321.  Jts  colour  changes  on  the  appli- 
cation of  heat  to  a reddish-brown;  but  as  it  cools,  the  original  tint  re- 
turns. It  sustains  a red  heat  without  fusion;  but  it  fuses  at  a white  heat, 
and  if  kept  for  some  time  in  a fused  state,  a portion  of  pyrophosphate 
is  generated.  Pyrophosphate  of  silver  is  formed  by  double  decomposi- 
tion from  pyrophosphate  of  soda  and  nitrate  of  silver,  the  remaining 
solution  being  neutral  as  at  first.  The  white  precipitate  acquires  a red- 
dish tint  by  the  agency  of  light,  and  on  drying  yields  an  anhydrous 
powder,  which  has  a density  of  5.306.  It  fuses  with  extreme  facility, 
even  at  a temperature  below  that  of  redness,  forming  a dark-brown 
coloured  liquid  which,  witliout  suffering  any  appreciable  decomposition, 
becomes  a crystalline  mass  in  cooling.  It  acquires  a brownish-yellow 
tint  on  the  first  impression  of  heat,  and,  when  cold,  retains  a shade  of 
the  same  colour,  lly  digestion  in  phosphate  of  soda,  it  is  rapidly  con- 
verted into  phosphate  of  silver.  The  composition  of  both  salts  was 
formerly  stated.  (Page  196.) 

Phosphites  and  Hypophosphites. — These  compounds  have  hitherto 
been  little  examined,  and  are  of  no  material  importance.  They  do  not, 
therefore,  require  a particular  description.  (Page  197.) 

^rseniates. 

All  the  arseniates  are  sparingly  soluble  in  water,  excepting  those  of 
potassa,  soda,  ammonia,  and  perhaps  lithia:  but  they  are  all  dissolved 
without  effervescence  by  dilute  nitric  acid  as  well  as  most  other  acids 
which  do  not  precipitate  the  base  of  the  salt,  and  are  thrown  down 
again  unchanged  by  pure  ammonia.  Most  of  them  bear  a red  heat 
without  decomposition;  but  they  are  all  decomposed  by  being  heated 
to  redness  along  with  charcoal,  metallic  arsenic  being  set  at  liberty. 
The  arseniates  of  the  fixed  alkalies  and  alkaline  earths  require  a rather 
high  temperature  for  reduction;  while  the  arseniates  of  the  common 
metals,  such  as  those  of  lead  and  copper,  are  easily  reduced  in  a glass 
tube  by  means  of  a spirit-lamp  without  danger  of  melting  the  glass. 
Of  all  the  arseniates  that  of  lead  is  the  most  insoluble. 

The  soluble  arseniates  are  easily  recognised  by  the  tests  described  in 
the  section  on  arsenic  (page  348;)  and  the  insoluble  arseniates,  when 
boiled  in  a strong  solution  of  tlie  fixed  alkaline  carbonates,  are  deprived 
of  their  acid,  which  may  then  be  detected  in  the  usual  manner.  The 
free  alkali,  however,  should  first  be  exactly  neutralized  by  pure  nitric 
acid. 

The  arseniates  of  lime,  nickel,  cobalt,  iron,  copper,  and  lead,  are 
natural  productions. 

Arsenic  acid  unites  in  two  proportions  with  potassa,  soda,  and  ammo- 
nia, forming  neutral  and  bisalts,  all  of  which,  the  neutral  arseniate  of 
potassa  excepted,  may  be  obtained  in  crystals.  They  are  all  formed  by 
adding  arsenic  acid  to  the  alkaline  carbonates  in  the  manner  described  ^ 
for  forming  the  phosphates.  Binarscniate  of  potassa  may  be  formed 
conveniently  by  heating'  to  redness  equal  parts  of  nitrate  of  potassa  and 
arsenious  acid,  and  continuing  the  heat  until  tlie  efiervescence  arising 
from  the  nitre  lias  ceased.  'I'hese  salts  are  so  similar  to  the  correspond- 
ing phosphate  l)oth  in  form  and  composition,  that  a .particular  descrip- 
tion is  unnecessary. 

Jlrsenites. 

The  only  soluble  compounds  of  arsenious  acid  and  salifiable  bases 
known  to  chemists  are  the  arsenites  of  potassa,  soda,  and  ammonia. 


CHROMATES. 


431 


which  may  be  prepared  by  boiling*  a solution  of  these  alkalies  in  arseni- 
oiis  acid.  The  other  arsenites  are  insoluble,  or,  at  most,  sparingly  solu- 
ble in  pure  water;  but  they  are  dissolved  by  an  excess  of  their  own  acid, 
with  great  facility  by  nitric  acid,  and  by  most  other  acids  with  which 
their  bases  do  not  form  insoluble  compounds.  The  insoluble  arsenites 
are  easily  formed  by  the  way  of  double  decomposition. 

On  exposing  the  arsenites  to  heat  in  close  vessels,  they  either  lose 
arsenious  acid  which  is  dissipated  in  vapour,  or  are  converted,  with  dis- 
engagement of  some  metallic  arsenic,  into  arseniates.  Heated  with 
charcoal  or  black  flux,  the  acid  is  reduced  with  facility.  (Page  348.) 

The  soluble  arsenites,  if  quite  neutral,  are  characterized  by  forming 
a yellow  arsenite  of  silver  when  mixed  with  the  nitrate  of  that  base,  and 
a green  arsenite  of  copper,  Scheele’s  green,  with  sulphate  of  copper. 
When  acidulated  with  acetic  or  muriatic  acid,  sulphuretted  hydrogen 
causes  the  formation  of  orpiment.  The  insoluble  arsenites  are  all  de- 
composed when  boiled  in  a solution  of  carbonate  of  potassa  or  soda. 

The  arsenite  of  potassa  is  the  active  principle  of  Fowler’s  arsenical 
solution. 


SECTION  IV. 


CHROMATES.— BORATES.— FLUOBORATES. 

Chromates- 

The  salts  of  chromic  acid  are  mostly  either  of  a yellow  or  red  colour, 
the  latter  tint  predominating  whenever  the  acid  is  in  excess.  The 
chromates  of  the  common  metals  are  decomposed  by  a strong  red  heat, 
by  which  the  acid  is  resolved  into  the  green  oxide  of  chromium  and 
oxygen  gas;  but  the  chromates  of  tho  fixed  alkalies  sustain  a very  high 
temperature  without  decomposition.  They  are  all  decomposed  without 
exception  by  the  united  agency  of  heat  and  combustible  matter. 

The  chromates  are  in  general  sufficiently  distinguished  by  their 
colour.  They  ihay  be  known  chemically  by  the  following  character:  — 
On  boiling  a chromate  in  muriatic  acid  mixed  with  alcohol,  the  chromic 
acid  is  at  first  set  free,  and  is  then  decomposed,  a green  muriate  of  the 
oxide  of  chromium  being  generated. 

The  only  native  chromate  hitherto  discovered  is  the  red  chromate  of 
lead  from  Siberia,  in  the  examination  of  which  Vauquelin  made  the  dis- 
covery of  chromium. 

Chromates  of  Potassa. — The  neutral  chromate,  from  which  all  the 
compounds  of  chromium  are  directly  or  indirectly  prepared,  is  made  by 
heating  to  redness  the  native  oxide  of  chromium  and  iron,  commonly 
called  chromate  of  iron,  with  nitrate  of  potassa,  when  chromic  acid  is 
generated,  and  unites  with  the  alkali  cf  the  nitre.  The  object  to  be 
held  in  view  is  to  employ  so  small  a proportion  of  nitre,  that  the  whole 
of  its  potassa  may  combine  with  chromic  acid,  and  constitute  a neutral 
chromate,  which  is  easily  obtained  pure  by  solution  in  water  and  crystal- 
lization. For  this  purpose  the  chromate  of  iron  is  mixed  with  about  a 
fifth  of  its  weight  of  nitre,  and  exposed  to  a strong  heat  for  a consider- 


432 


BORATES. 


able  time,  and  the  process  is  repeated  with  those  portions  of  the  ore 
which  are  not  attacked  in  the  first  operation.  It  is  deposited  from  its 
solution  in  small  prismatic  anhydrous  crystals  of  a lemon-yellow  colour, 
the  primary  form  of  which,  according*  to  Mr.  Brooke,  is  a rig-ht  rhombic 
prism. 

Chromate  of  potassa  has  a cool,  bitter,  and  disagreeable  taste.  It  is 
soluble  to  great  extent  in  boiling  water,  and  in  twice  its  weight  of  that 
liquid  at  60®  Fah.;  but  it  is  insoluble  in  alcohol.  It  has  an  alkaline  re- 
action, and  on  this  account  M.  Tassaert*  regards  it  as  a subsalt;  but  Dr. 
Thomson  has  proved  that  it  is  neutral  in  composition,  consisting  of  52 
parts  or  one  equivalent  of  chromic  acid,  and  48  parts  or  one  equivalent 
of  potassaf. 

Bichromate  of  potassa,  which  is  made  in  large  quantity  at  Glasgow 
for  dyeing,  is  prepared  by  acidulating  the  neutral  chromate  with  sulphu- 
ric or  still  better  with  acetic  acid,  and  allowing  the  solution  to  crystallize 
by  spontaneous  evaporation.  When  slowly  formed  it  is  deposited  in 
four-sided  tabular  crystals,  the  primary  form  of  which  is  an  oblique 
rhombic  prism.  They  have  an  exceedingly  rich  red  colour,  are  anhy- 
drous, and  consist  of  one  equivalent  of  the  alkali,  and  two  equivalents 
of  chromic  acid.  (Thomson.)  They  are  soluble  in  about  ten  times  their 
weight  of  water  at  60®  F.,  and  the  solution  reddens  litmus  paper. 

The  insoluble  salts  of  chromic  acid,  such  as  the  chromates  of  baryta, 
lead,  protoxide  of  mercury,  and  silver,  are  prepared  by  mixing  the 
soluble  salts  of  those  bases  with  a solution  of  chromate  of  potassa.  The 
two  former  are  yellow,  the  third  orange-red,  and  the  fourth  deep  red  or 
purple.  The  yellow  chromate  of  lead,  which  consists  of  one  equiva- 
lent of  acid,  and  one  equivalent  of  oxide,  is  now  extensively  used 
as  a pigment. 

A dicliromate  of  lead,  composed  of  one  equivalent  of  chromic  acid, 
and  two  equivalents  of  protoxide  of  lead,  may  be  formed  by  boiling 
carbonate  of  lead  with  excess  of  chromate  of  potaasa.  It  is  of  a beau- 
tiful red  colour,  ^and  has  been  recommended  by  Mr.  Badams  as  a pig- 
ment. (Annals  of  Philosophy,  N.  S.  vol.  ix.  p.  303.)  It  may  be  also 
made  by  boiling  chromate  of  lead  with  ammonia  or  lime-water. 

Borates. 

As  the  boracic  is  a feeble  acid,  it  neutralizes  alkalies  imperfectly, 
and  hence  the  borates  of  soda,  potassa,  and  ammbnia  have  always  an 
alkaline  reaction.  For  the  same  reason,  when  the  borates  are  digested 
in  any  of  the  more  powerful  acids,  such  as  the  sulphuric,  nitric,  or 
muriatic,  the  boracic  acid  is  separated  from  its  base.  This  does  not 
happen,  however,  at  high  temperatures;  for  boracic  acid,  owing  to  its 
fixed  nature,  decomposes  at  a red  heat  all  salts,  not  excepting  sulphates, 
the  acid  of  which  is  volatile. 

'I'he  borates  of  the  alkalies  are"  soluble  in  water,  but  all  the  other 
salts  of  this  acid  are  of  sparing  solubility,  d'hey  are  not  decomposed 
by  heat,  and  the  alkaline  and  eartliy  borates  resist  the  action  of  heat 
and  combustible  matter.  Tliey  are  remarkably  fusible  in  the  fire, 
a property  obviously  owing  to  tlie  great  fusibility  of  boracic  acid 
itself. 

I'he  borates  are  distinguished  by  tlic  following  character: — By  di- 
gesting any  borate  in  asliglit  excess  of  strong  sulphuric  acid,  evaporat- 
ing to  dryness,  and  boiling  the  residue  in  strong  alcohol,  a solution  is 


An.  de  Cli.  et  de  Pli.  vol.  xxii.  f Annals  of*  Philosophy,  vol.  xvi. 


CARBONATES.  433 

formed,  which  has  the  property  of  burning  with  a green  flame.  (Page 
199.) 

Biborate  of  Soda. — This  salt,  the  only  borate  of  importance,  occurs 
native  in  some  of  the  lakes  of  Thibet  and  Persia,  and  is  extracted  from 
this  source  by  evaporation.  It  is  imported  from  India  in  a crude  state, 
under  the  name  of  tincal,  which,  after  being  purified,  constitutes  the 
refined  borax  of  commerce.  It  is  frequently  subborate  of  soda,  a 

name  suggested  by  the  inconsistent  and  unphilosophical  practice,  now 
quite  inadmissible,  of  regulating  the  nomenclature  of  salts  merely  by 
their  action  on  vegetable  colouring  matter.  It  crystallizes  in  hexahedral 
prisms,  which  effloresce  on  exposure  to  the  air,  and  require  twenty 
parts  of  cold,  and  six  of  boiling. water,  for  solution.  When  exposed  to 
heat  the  crystals  are  first  deprived  of  their  water  of  crystallization,  and 
then  fused,  forming  a vitreous  transparent  substance  called  of  bo- 
rax.  The  crystals,  according  to  the  analysis  of  Dr.  Thomson,  are  com- 
posed of  48  parts  or  two  equivalents  of  boracic  acid,  32  or  one  equiv- 
alent of  soda,  and  72  or  eight  equivalents  of  water. 

The  chief  use  of  borax  is  as  a flux,  and  for  the  preparation  of  boracic 
acid.  Biborate  of  magnesia  is  a rare  natural  production,  which  is  known 
to  mineralogists  by  the  name  of  boraeite. 

A new  biborate  of  soda,  which  contains  half  as  much  water  of  crys- 
tallization as  the  preceding,  has  been  lately  described  by  M.  Buran.  It 
is  harder  and  denser  than  borax,  is  not  efflorescent,  and  crystallizes  in 
regular  octohedrons.  It  is  made  by  dissolving  borax  in  boiling  water 
until  the  specific  gravity  of  the  solution  is  at  30®  or  32®  of  Baume’s 
hydrometer;  the  solution  is  then  very  slowly  cooled;  and  when  the  tem- 
perature descends  to  about  133®  F.  the  new  salt  is  deposited.  It  is 
found  to  be  more  convenient  for  the  use  of  jewellers  than  common  bo- 
rax. (An.  de  Ch.  et  de  Ph.  xxxvii.  419.) 

Fluoborates. — The  compounds  of  fluoboric  acid  with  salifiable  bases 
are  as  yet  almost  entirely  unknown.  Dr.  Davy  ascertained  that  it  unites 
with  ammoniacal  gas  in  three  proportions,  forming  salts,  one  of  which 
is  solid,  and  the  two  others  liquid. 


SECTION  V. 

CARBONATES. 

The  carbonates  are  distinguished  from  other  salts  by  being  decom- 
posed with  effervescence,  owing  to  the  escape  of  carbonic  acid  gas, 
by  nearly  all  the  acids. 

All  the  carbonates,  excepting  those  of  potassa,  soda,  and  lithia,  may 
be  deprived  of  their  acid  by  heat.  The  carbonate  of  baryta  and  stron- 
tia,  especially  the  former,  requires  an  intense  white  heat  for  decompo- 
sition; those  of  lime  and  magnesia  are  reduced  to  the  caustic  state  by  a 
full  red  heat;  and  the  other  carbonates  part  with  their  carbonic  acid 
when  heated  to  dull  redness. 

All  the  carbonates  excepting  those  of  potassa,  soda,  and  ammonia, 
are  of  sparing  solubility  in  pure  water;  but  all  of  them  are  more  or  less 

37 


434  CARBONATES. 

soluble  in  an  excess  of  carbonic  acid,  owing*  doubtless  to  the  formation 
of  supersalts. 

The  former  nomenclature  of  the  salts  is  peculiarly  exceptionable  as 
applied  to  the  carbonates.  The  two  well-known  carbonates  of  potassa, 
for  example,  are  distinguished  by  the  prepositions  suh  and  super,  as  if 
the  one  had  an  alkaline,  and  the  other  an  acid  reaction;  whereas,  in 
fact,  according  to  their  action  on  test  paper,  they  are  both  subsalts.  I 
shall  adopt  the  nomenclature  which  has  been  employed  with  other  salts, 
applying  the  generic  name  of  carbonate  to  those  salts  which  contain  one 
equivalent  of  carbonic  acid,  and  one  equivalent  of  the  base, — com- 
pounds which  may  be  regarded  as  neutral  in  compositiofi,  however  they 
may  act  on  the  colouring  matter  of  plants. 

Several  of  the  carbonates  occur  native,  among  which  may  be  enu- 
merated the  carbonates  of  soda,  baryta,  strontia,  lime,  magnesia,  man- 
ganese, protoxide  of  iron,  copper,  lead,  and  the  double  carbonate  of 
lime  and  magnesia. 

Cktrbonate  of  Potassa. — This  salt  is  procured  in  an  impure  form  by 
burning  land  plants,  lixiviating  their  ashes,  and  evaporating  the  solution 
to  dryness,  a process  which  is  performed  on  a large  scale  in  Russia  and 
America.  The  carbonate  of  potassa,  thus  obtained,  is  known  in  com- 
merce by  the  names  of  potash  and  pearlash,  and  is  employed  in  many 
of  the  arts,  especially  in  the  formation  of  soap  and  the  manufacture  of 
glass.  When  derived  from  this  source  it  always  contains  other  salts, 
such  as  sulphate  and  muriate  of  potassa;  and  therefore,  for  chemical 
purposes,  it  should  be  prepared  from  cream  of  tartar,  bitartrate  of  po- 
tassa. On  heating  this  salt  to  redness,  the  tartaric  acid  is  decomposed, 
and  a pure  carbonate  of  potassa  mixed  with  charcoal  remains.  The 
carbonate  is  then  dissolved  in  water,  and,  after  filtration,  is  evaporated 
to  dryness  in  a capsule  of  platinum  or  silver. 

Pure  carbonate  of  potassa  has  a taste  strongly  alkaline,  is  slightly 
caustic,  and  communicates  a green  to  the  blue  colour  of  the  violet.  It 
dissolves  in  less  than  an  equal  weight  of  water  at  60®  F.,  deliquesces 
rapidly  on  exposure  to  the  air,  and  crystallizes  with  much  difficulty 
from  its  solution.  In  pure  alcohol  it  is  insoluble.  It  fuses  at  a full  red 
heat,  but  undergoes  no  other  change.  According  to  the  analysis  of 
Dr.  Wollaston,  it  is  composed  of  22  parts  or  one  equivalent  of  carbonic 
acid,  and  48  parts  or  one  equivalent  of  potassa. 

It  is  often  necessary,  for  commercial  purposes,  to  ascertain  the  value 
of  different  samples  of  pearlash;  that  is,  to  determine  the  quantity  of 
real  carbonate  of  potassa  contained  in  a given  weight  of  impure  car- 
bonate. A convenient  mode  of  effecting  this  object  is  described  by 
Mr.  Faraday  in  his  excellent  work  on  Chemical  Manipulation.  Into  a 
tube  sealed  at  one  end,  long,  ^ of  inch  in  diameter,  and  as  cy-. 
lindrical  as  possible  in  its  whole  length,  pour  1000  grains  of  water,  and 
with  a fde  or  diamond  mark  the  place  where  its  surface  reaches;  and 
divide  the  space  occupied  by  the  water  into  100  equal  parts,  as  is  shown 
in  the  annexed  wood-cut.  Opposite  to  the  numbers  23.44,  48.96,  54.63, 
and  65,  draw  a line,  and  at  the  first  write  soda,  at  the  second  potassa, 
at  the  third  carbonate  of  soda,  and  at  the  fourth  carbonate  of  potassa. 
Then  prepare  a dilute  acid  having  the  specific  gravity  of  1.127  at  60®, 
which  may  lie  made  by  mixing  one  measure  of  concentrated  sulphuric 
acid  with  eight  measures  of  distilled  water.  This  is  the  standard  acid 
to  be  used  in  all  the  experiments;  and, if  this  acid  is  poured  into  the 
tube  till  it  reaches  cither  of  the  four  marks  just  mentioned,  we  shall 
obtain  the  exact  quantity  which  is  necessary  for  neutralizing  IWI  grains 


CARBONATES. 


435 


of  the  alkali  written  opposite  to  it.  If, 
when  the  acid  reaches  the  word  carh, 
potasstty  and  when,  consequently,  we  have 
the  exact  quantity  which  will  neutralize 
100  gi’ains  of  that  carbonate,  pure  water 
be  added  until  it  reaches  1,  or  the  begin- 
ning of  the  scale,  each  division  of  this 
mixture  will  neutralize  one  grain  of  car- 
bonate of  potassa.  All  that  is  now  re- 
quired, in  order  to  ascertain  the  quantity 
of  real  carbonate  in  any  specimen  of  pearl- 
ash,  is  to  dissolve  100  grains  of  the  sam- 
ple in  warm  water,  filter  to  remove  all  the 
insoluble  parts,  and  add  the  dilute  acid  in 
successive  small  quantities,  until,  by  the 
test  of  litmus  paper,  the  solution  is  exact- 
ly neutralized.  Each  division  of  the  mix- 
ture indicates  a grain  of  pure  carbonate. 

It  is  convenient,  in  conducting  this  pro- 
cess, to  set  aside  a portion  of  the  alkaline 
liquid,  in  order  to  neutralize  the  acid,  in 
case  it  should  at  first  be  added  too  freely. 

To  this  instrument  the  term  alkalimeter  is 
given,  a name  obviously  derived  from  the 
use  to  which  it  is  applied. 

Bicarbonate  of  potassa  is  made  by  transmitting  a current  of  carbonic 
acid  gas  through  a solution  of  carbonate  of  potassa ^ and  it  is  also  pre- 
pared by  evaporating  a mixture  of  carbonate  of  ammonia  and  carbonate 
of  potassa,  the  ammonia  being  dissipated  in  a pure  state.  By  slow  eva- 
poration, the  bicarbonate  is  deposited  from  the  liquid  in  prisms  with 
eight  sides,  terminated  with  dihedral  summits.  Its  primary  form  is  a 
right  rhomb oidal  prism. 

Bicarbonate  of  potassa,  though  far  milder  than  the  carbonate,  is  al- 
kaline both  to  the  taste  and  to  test  paper.  It  does  not  deliquesce  on 
exposure  to  the  air.  It  requires  four  times  its  weight  of  water  at  60*^ 
F.  for  solution,  and  is  much  more  soluble  at  212^  F. ; but  it  parts  with 
some  of  its  acid  at  that  temperature.  At  a low  red  heat  it  is  converted 
into  the  carbonate.  From  the  analysis  of  Dr.  Wollaston,  the  crystals 
consist  of  one  equivalent  of  potassa,  two  of  acid,  and  one  of  water.  I 
have  likewise' analyzed  this  salt,  and  obtained  a similar  result. 

Dr.  Thomson,  in  his  First  Principles,’*  has  described  a sesquicar- 
bonate,  which  v/as  discovered  by  Dr.  Nimmo  of  Glasgow.  Its  crystals 
are  composed  of  one  equivalent  of  potassa,  an  equivalent  and  a half  of 
carbonic  acid,  and  six  equivalents  of  water. 

Carbonate  of  Soda. — The  carbonate  of  commerce  is  obtained  by  lix- 
iviating the  ashes  of  sea-weeds.  The  best  variety  is  known  by  the 
name  of  barilla,  and  is  derived  chiefly  from  the  salsola  soda  and  salicor- 
nia  herbacea.  A very  inferior  kind,  known  by  the  name  of  kelp,  is 
prepared  from  sea-weeds  on  the  northern  shores  of  Scotland.  The 
purest  barilla,  however,  though  well  fitted  for  making  soap  and  glass, 
and  for  other  purposes  in  the  arts,  always  contains  the  sulphates  and 
muriates  of  potassa  and  soda,  and  on  this  account  is  of  little  service  to 
the  chemist.  A purer  carbonate  is  prepared  by  heating  a mixture  of 
sulphate  of  soda,  saw-dust,  and  lime,  in  a reverberatory  furnace.  By 
the  action  of  carbonaceous  matter,  the  sulphuric  acid  is  decomposed; 
its  sulphur  partly  uniting  with  lime  and  paidly  being  dissipated  in  th^ 


Soda 


Potassa 
Carb.  Soda 


Carb.  Potassa  — 


1 

5 

10 

15 

20 

25 

30 

35 

40 

45 

50 

55 

60 

65 

70 

75 

80 

85 

90 

95 

100 


436 


CARBONATES. 


form  of  sulphurous  acid,  while  tlie  carbonic  acid,  which  is  g'cnerated 
during*  the  process,  unites  with  soda.  The  carbonate  of  soda  is  then 
obtained  by  lixiviation  and  crystallization.  It  is  difficult  to  obtain  tliis 
salt  quite  free  from  sulphuric  acid. 

Carbonate  of  soda  crystallizes  in  octohedrons  with  a rliombic  base, 
the  acute  angles  of  which  are  generally  truncated.  The  crystals 
effloresce  on  exposure  to  the  air,  and,  when  heated,  dissolve  in  their 
water  of  crystallization.  By  continued  heat  they  are  rendered  anhy- 
drous without  loss  of  carbonic  acid.  They  dissolve  in  about  two  parts 
of  cold,  and  in  rather  less  than  their  weight  of  boiling  water,  and  the 
solution  has  a strong  alkaline  taste  and  reaction.  According  to  Dr. 
Thomson,  the  crystals  are  composed  of  22  parts  or  one  equivalent  of 
carbonic  acid,  32  parts  or  one  equivalent  of  soda,  and  90  parts  or  ten 
equivalents  of  water.  The  water  of  crystallization  is  apt  to  vary  ac- 
cording to  the  temperature  at  which  the  crystals  are  formed. 

The  purity  of  different  specimens  of  barilla,  or  other  carbonates 
of  soda,  may  be  ascertained  by  means  of  the  alkalimeter  above  de- 
scribed. 

Bicarhonate  of  Soda. — This  salt  is  made  by  the  same  processes  as 
bicarbonate  of  potassa,  and  is  deposited  in  crystalline  grains  by  evapo- 
ration. Though  still  alkaline,  it  is  much  milder  than  the  carbonate,  and 
far  less  soluble,  requiring  about  ten  times  its  weight  of  water  at  60°  F. 
for  solution.  It  is  decomposed  partially  at  212°  F.  and  is  converted  into 
the  carbonate  by  a red  heat.  It  is  composed,  according  to  Thomson,  of 
two  equivalents  of  acid,  one  of  the  base,  and  one  of  water.  This  re- 
sult I have  confirmed  by  my  own  observation. 

Sesquicarhonate. — This  compound  occurs  native  on  the  banks  of  the 
lakes  of  soda  in  the  province  of  Sukena  in  Africa,  whence  it  is  export- 
ed under  the  name  of  trona.  It  was  first  distinguished  from  the  two 
other  carbonates  by  Mr.  Phillips,*  whose  analysis  corresponds  with  that 
of  Klaproth.  It  consists  of  one  equivalent  of  soda,  an  equivalent  and  a 
half  of  acid,  and  two  equivalents  of  water. 

Carbonate  of  Ammonia. — The  only  method  of  procuring  this  salt  is 
by  mixing  dry  carbonic  acid  over  mercury,  with  twice  its  volume  of 
ammoniacal  gas.  It  is  a dry  white  volatile  powder  of  an  ammoniacal 
odour,  and  alkaline  reaction.  From  the  proportion  of  its  constituents 
by  volume,  it  is  easy  to  infer  that  it  is  composed,  by  weight,  of  22  parts 
or  one  equivalent  of  carbonic  acid,  and  17  parts  or  one  equivalent  of 
ammonia. 

Bicarbonate  of  Ammonia. — This  salt  was  formed  by  Berthollet,  by 
transmitting  a current  of  carbonic  acid  gas  through  a solution  of  the 
common  carbonate  of  ammonia  of  the  shops.  On  evaporating  the  li- 
quid by  a gentle  heat,  the  bicarbonate  is  deposited  in  small  six-sided 
prisms,  which  have  no  smell,  and  very  little  taste;  their  primary  form, 
according  to  Mr.  Miller  of  Cambridge,  is  a right  rhombic  prism.  Ber- 
thollet ascertained  that  it  contains  twice  as  much  acid  as  the  car- 
bonate. 

Sesquicarhonate  of  Ammonia. — The  common  carbonate  of  ammonia 
of  the  sliops,  Sab-carbonas  Ammonix  of  the  Pharmacopoeia,  is  difierent 
from  both  these  compounds.  It  is  prepared  by  heating  a mixture  of 
one  part  of  m\iriate  of  ammonia  with  one  part  and  a half  of 'carbonate 
of  lime,  carefully  dried.  Double  decomposition  ensues  during  the 
process;  muriate  of  lime  remains  in  the  retort,  and  sesquicarhonate  of 


* Journal  of  Science,  voj.  yii, 


CAKBONATES. 


43r 


ammonia  is  sublimed.*  The  carbonic  acid  and  ammonia  are,  indeed,  in 
proper  proportion  in  the  mixture  for  forming*  the  real  carbonate;  but 
from  the  heat  employed  in  the  sublimation,  part  of  the  ammonia  is  dis- 
engaged in  a free  state. 

The  salt  thus  formed  consists,  according  to  the  analysis  of  Mr.  Phil- 
lips, Dr.  Ure,  and  Dr.  Thomson,  of  33  parts  or  an  equivalent  and  a 
half  of  carbonic  acid,  17  parts  or  one  equivalent  of  ammonia,  and  9 
parts  or  one  equivalent  of  water.  When  recently  prepared  it  is  hard, 
compact,  semi-transparent,  of  a crystalline  texture,  and  pungent  am- 
moniacal  odour;  but  if  exposed  to  the  air,  it  loses  weight  rapidly,  and 
is  converted  into  an  opake  brittle  mass,  which  is  the  bicarbonate. 

Carbonate  of  baryta  occurs  abundantly  in  the  lead  mines  of  the  north 
of  England,  where  it  was  discovered  by  Dr.  Withering,  and  has  hence 
received  the  name  of  Wiiherite,  It  may  be  prepared  by  way  of  double 
decomposition,  by  mixing  a soluble  salt  of  baryta  with  any*  of  the  alka- 
line carbonates  or  bicarbonates.  It  is  exceedingly  insoluble  in  distilled 
water,  requiring  4300  times  its  weight  of  water  at  60^  F.,  and  2300  of 
boiling  water  for  solution;  but  when  recently  precipitated,  it  is  dis- 
solved much  more  freely  by  a solution  of  carbonic  acid.  It  is  highly 
poisonous. 

Carbonate  ofstrontia,  which  occurs  native  at  Strontian  in  Argyleshire, 
and  is  known  by  the  name  of  Strontianite,  may  be  prepared  in  the  same 
manner  as  carbonate  of  baryta.  It  is  very  insoluble  in  pure  water,  but 
is  dissolved  by  an  excess  of  carbonic  acid. 

Carbonate  of  Lime. — This  salt  is  a very  abundant  natural  production, 
and  occurs  under  a great  variety  of  forms,  such  as  common  limestone, 
chalk,  marble,  and  Iceland  spar,  and  in  regular  crystals.  It  may  also 
be  formed  by  precipitation.  Though  sparingly  soluble  in  pure  water, 
it  is  dissolved  by  carbonic  acid  in  excess.  On  this  account  the  spring 
water  of  limestone  districts  always  contains  carbonate  of  lime,  which  is 
deposited  when  the  water  is  boiled. 

Carbonate  of  Magnesia. — This  salt  is  easily  prepared  by  adding  car- 
bonate of  potassa  in  slight  excess  to  a hot  solution  of  sulpliate  of  mag- 
nesia, and  edulcorating  the  precipitated  carbonate  with  warm  water. 
It  requires  2493  parts  of  cold,  and  9000  of  hot  water  for  solution.  It 
is  so  soluble  in  an  excess  of  carbonic  acid  that  sulphate  of  magnesia  is 
not  precipitated  at  all  in  the  cold  by  alkaline  bicarbonates,  or  by  ses- 
quicarbonate  of  ammonia.  On  allowing  a solution  of  carbonate  of  mag- 
nesia in  carbonic  acid  to  stand  in  an  open  vessel,  minute  crystals 
are  deposited,  which  consist  of  42  parts  or  one  equivalent  of  the  car- 
bonate, and  27  parts  or  three  equivalents  of  water.  (^Dr.  Henry  and 
Berzelius.) 

Native  carbonate  of  magnesia,  according  to  the  analysis  of  Dr. 
Henry  and  Stromeyer,  is  similar  in  composition  to  the  precipitated  car- 
bonate. 

Carbonate  of  Iron. — Carbonic  acid  does  not  form  a definite  compound 
with  peroxide  of  iron,  but  with  the  protoxide  it  constitutes  a salt  which 
is  an  abundant  natural  production,  occurring  sometimes  massive,  and  at 
other  times  crystallized  in  rhomboids  or  hexagonal  prisms.  This  proto- 
carbonate of  iron  is  contained  also  in  most  of  the  chalybeate  mineral 
waters,  being  held  in  solution  by  free  carbonic  acid;  and  it  may  be 


* Tlie  products  of  this  decomposition  are,  strictly  speaking,  sesqui- 
carbonate  of  ammonia,  water,  and  chloride  of  calcium.  I'he  sesqui- 
carbonate  and  water  sublime  together,  and  chloride  of  calcium  is  left  in 
the  retort.  B. 


37^ 


438 


SALTS  OF  THE  HYDRACIDS. 


formed  by  mixing*  an  alkaline  carbonate  with  protosulpbate  of  iron. 
When  prepared  by  precipitation  it  attracts  oxyg*en  rapidly  from  tlie 
atrnosphere,  and  the  protoxide  of  iron,  passing*  into  the  state  of  per- 
oxide, parts  with  carbonic  acid.  For  this  reason,  the  carbonate  of 
iron  of  the  Pharmacopoeia  is  of  a red  colour,  and  consists  chiefly  of  tlie 
peroxide. 

Carbonate  of  Copper. — The  beautiful  green  mineral,  c2^\Q(}i  malachite, 
is  a carbonate  of  the  peroxide  of  copper;  and  a similar  com])ound  may 
be  formed  from  the  persulphate  by  double  decomposition,  or  by  ex- 
posing metallic  copper  to  air  and  moisture.  According  to  tlie  analysis 
of  malachite  by  Mr.  Phillips,  this  mineral  is  composed  of  80  parts  or 
one  equivalent  of  peroxide  of  copper,  one  equivMent  of  carbonic  acid, 
undone  equivalent  of  water.  (Journal  of  Science,  vol.  iv.) 

^ The  blue  pigment  called  verditer,  said  to  be  prepared  by  decomposing 
nitrate  of  copper  by  chalk,  is  an  impure  carbonate.* 

Carhonate^of  Lead. — This  salt,  which  is  the  white  lead  or  ceruse  of 
painters,  occurs  native,  but  may  be  obtained  by  double  decomposi- 
tion. It  is  prepared  for  the  purposes  of  commerce  by  exposing  coils  of 
thin  sheet  lead  to  the  vapour  of  vinegar,  when,  by  the  action  of  the 
acid  fumes,  the  lead  is  both  oxidized  and  converted  into  a carbonate. 

Double  Carbonates. — Berthier  has  m.ade  some  interesting  experiments 
on  the  production  of  double  carbonates  by  fusion.  Carbonate  of  soda, 
when  fused  with  carbonate  of  baryta,  strontia,  or  lime,  in  the  ratio  of 
their  equivalents,  yields  uniform  crystalline  compounds,  which  have 
all  the  appearance  of  being  definite.  An  equivalent  of  Dolomite,  dou- 
ble carbonate  of  lime  and  magnesia,  fuses  in  like  manner  with  four 
equivalents  of  carbonate  of  soda.  Five  parts  of  carbonate  of  potassa 
and  four  of  carbonate  of  soda,  corresponding  to  an  equivalent  of 
each,  fuse  with  remarkable  facility;  and  this  mixture,  by  reason  of 
its  fusibility,  may  be  advantageously  employed  in  the  analysis  of  earthy 
minerals. 

Compounds  similar  to  the  foregoing  may  be  generated  by  heating  sul- 
phate of  soda  with  carbonate  of  baryta,  strontia,  or  lime,  in  the  ratio 
of  their  equivalents;  or  by  employing  the  sulphate  of  these  bases  and 
carbonate  of  soda.  In  like  manner,  carbonate  of  soda  fuses  with  chloride 
of  barium  or  calcium;  and  chloride  of  sodium  with  carbonate  of  baryta 
or  lime.  (An.  de  Ch.  et  de  Ph.  xxxviii.  246.) 


SECTION  VI. 

SALTS  OF  THE  HYDRACIDS. 

By  tlie  expression  6‘«//5  o/  the  hydracids  is  meant  those  saline  com- 
jioiinds,  tlie  acid  of  which  contains  liydrogen  as  one  of  its  elements. 
'Fhese  salts,  owing  to  tlie  |)eculiar  constitution  of  their  acid,  liave  cer- 
tain common  properties,  and  may,  therefore,  be  described  advan- 


* On  tlie  composition  and  preparation  of  this  pigment,  the  reader 
may  consult  the  rcmai’ks  of  Mr.  Pliillips,  in  the  essay  quoted  in  the 
text. 


SALTS  OF  THE  HYDRACIDS. 


439 


tageously  in  the  same  section.  Many  of  the  circumstances  relative  to 
them  have  already  been  mentioned  in  sufficient  detail,  partly  in  the  re- 
marks introductory  to  the  study  of  the  metals  (page  286, ) and  partly  in 
the  description  of  the  individual  metals  themselves.  It  will  hence  suffice 
to  describe  the  salts  of  the  hydracids  chiefly  in  a general  manner,  giv- 
ing a particular  description  of  those  compounds  only,  which  are  pos- 
sessed of  some  peculiar  interest. 

Most  of  the  salts  which  are  composed  of  a hydracid  and  a metallic 
oxide  are  so  constituted,  that  the  oxygen  of  the  oxide  is  in  a quan- 
tity precisely  sufficient  for  forming  water  with  the  hydrogen  of  the 
acid.  This  is  true  of  all  the  neutral  compounds  containing  a pro- 
toxide without  exception,  and  it  likewise  holds  good  in  many  other 
cases.  Thus,  in  the  soluble  permuriate  of  iron,  the  oxide,  which  con- 
tains an  equivalent  and  a half  of  oxygen,  is  united  with  an  equivalent 
and  a half  of  acid;  and  in  the  soluble  permuriate  of  copper,  the  oxide 
which  contains  two  equivalents  of  oxygen,  is  united  with  two  equiv- 
alents of  acid. 

The  elements  of  the  salts  of  the  hydracids,  as  mentioned  at  page 
286,  are  very  prone  to  arrange  themselves  in  a new  order.  All  these 
salts  are  exposed  to  the  action  of  two  divellent  and  three  quiescent 
affinities.  In  muriate  of  soda,  for  example,  the  forces  which  tend  to 
prevent  a change  are  the  attraction  of  sodium  for  oxygen,  of  chlorine 
for  hydrogen,  and  of  muriatic  acid  for  soda;  while  the  opposite  affini- 
ties are  the  attraction  of  chlorine  for  sodium  and  of  hydrogen  for  oxy- 
gen. The  latter  always  preponderate  when  heat  is  employed,  because 
the  volatility  of  water  favours  the  production  of  that  fluid;  and  in  many 
instances  the  affinities  appear  so  nicely  balanced,  that  the  cohesion  of 
one  of  the  compounds  is  sufficient  to  influence  the  result,  as  is  exem- 
plified by  muriate  of  soda,  which,  in  tbiC  act  of  crystallizing,  is  con- 
verted into  chloride  of  sodium. 

Muriates  or  Hydrochlorates. 

Most  of  the  salts  of  muriatic  acid  are  soluble  in  water,  and  some  of 
them  exist  only  in  a state  of  solution.  They  are  distinguished  from 
other  salts  by  forming  the  white  insoluble  chloride  of  silver  when  mixed 
with  the  nitrate  of  that  base,  and  by  being  decomposed  with  disengage- 
ment of  muriatic  acid  fumes  by  strong  sulphuric  acid.  The  decompo- 
sition of  the  muriates,  owing  to  the  volatile  nature  of  their  acid,  is  ef- 
fected by  phosphoric  and  arsenic  acids  at  the  temperature  of  ebul- 
lition. 

Muriates  of  Potassa  and  Soda. — These  salts  exist  only  in  a state  of 
solution,  and  are  frequently  contained  in  mineral  springs.  Muriate  of 
soda,  as  already  mentioned  in  the  section  on  sodium,  is  the  chief  con- 
stituent of  sea-water. 

Muriate  of  Ammonia. — This  salt,  sal  ammoniac  of  commerce,  was 
formerly  imported  from  Egypt,  where  it  is  procured  by  sublimation 
from  the  soot  of  camel’s  dung;  but  it  is  now  manufactured  in  Europe 
by  several  processes.  I'he  most  usual  method  is  to  decompose  sulphate 
of  ammonia  by  the  muriate  either  of  soda  or  magnesia.  Double  decom- 
position ensues,  giving  rise  in  both  cases  to  muriate  of  ammonia,  and  to 
sulphate  of  soda,  when  the  muriate  of  that  base  is  used,  or  to  sulphate 
of  magnesia,  when  muriate  of  magnesia  is  employed.  The  sal  ammoniac 
is  afterwards  obtained  in  a pure  state  by  sublimation.  Sulphate  of  am- 
monia may  be  conveniently  procured  for  this  purpose,  either  by  lixivia- 
ting the  soot  of  coal,  which  contains  that  salt  in  considerable  quantity; 
or  by  digesting  impure  carbonate  of  ammonia,  procured  by  exposing 


440 


SALTS  OF  THE  IlYDRACIDS. 


bones  and  other  animal  matters  to  a red  heat,  wltli  g-ypsum,  so  as  to 
form  an  insoluble  carbonate  of  lime,  and  a soluble  sulphate  of  ammonia. 

Muriate  of  ammonia  has  a pungent  saline  taste,  and  is  soluble  in  three 
parts  of  water  at  60^  F.,  causing  a considerable  reduction  of  tempera- 
ture during  its  solution.  Boiling  water  dissolves  about  an  equal  weight 
and  the  solution  deposites  crystals  in  cooling.  At  a temperature  below 
redness,  it  sublimes  without  fusing  or  undergoing  any  change  in  com- 
position, and  condenses  on  cool  surfaces  as  an  anhydrous  salt,  which  at- 
tracts humidity  in  a moist  atmosphere,  but  if  pure  is  not  deliquescent. 

When  muriatic  acid  gas  is  mixed  with  an  equal  volume  of  ammonia, 
both  gases  disappear  entirely,  and  pure  muriate  of  ammonia  results.  It 
hence  follows  that  this  salt  is  composed  by  weight  of  37  parts  or  one 
equivalent  of  muriatic  acid,  and  17  parts  or  one  equivalent  of  ammonia. 

Muriate  of  Baryta. — This  compound  is  best  formed  by  dissolving  car- 
bonate of  baryta,  either  native  or  artificial,  in  muriatic  acid  diluted  with 
three  parts  of  water.  It  may  also  be  formed  by  the  action  of  muriatic 
acid  on  hydrosulphuret  of  baryta  (page  303,)  or  by  heating  sulphate  of 
baryta  with  an  equal  weight  of  muriate  of  lime  until  fusion  takes  place, 
and  then  dissolving  the  muriate  of  baryta  which  is  generated,  and  sepa- 
rating it  by  means  of  a filter  from  the  sulphate  of  lime. 

Muriate  of  baryta,  when  its  solution  is  gently  evaporated,  crystallizes 
readily  in  flat  rectangular  plates,  bevelled  at  the  edges,  much  resembling 
crystals  of  heavy  spar.  The  crystals,  according  to  Thomson,  consist  of 
115  parts  or  one  equivalent  of  muriate  of  baryta,  and  9 parts  or  one 
equivalent  of  water.  On  heating  the  crystals  to  redness,  two  equiva- 
lents of  water  are  expelled,  and  106  parts  or  one  equivalent  of  chloride 
of  barium  are  left.  The  crystals,  therefore,  may  be  regarded  as  chlo- 
ride of  barium  with  two  equivalents  of  water  of  crystallization.  The 
fact,  noticed  by  Mr.  Graham,  that  the  pulverized  crystals  lose  two  equiv- 
alents of  water  in  a very  dry  atmosphere,  and  recover  them  again  in  a 
moist  one,  is  very  favourable  to  this  opinion. 

Crystallized  muriate  of  baryta  is  insoluble  in  pure  alcohol.  It  requires 
about  two  and  a half  times  its  weight  of  water  at  60^  F.  for  solution, 
and  is  much  more  soluble  in  boiling  water.  The  crystals  are  permanent 
in  the  air. 

This  salt  is  much  employed  as  a reagent  in  chemistry. 

Muriate  of  stronUa  is  made  in  the  same  manner  as  muriate  of  baryta, 
from  which  it  is  distinguished  by  forming  prismatic  crystals,  by  its  solu- 
bility in  alcohol,  and  by  imparting  a red  tint  to  flame.  The  crystals  con- 
sist of  one  equivalent  of  muriate  of  strontla,  and  eight  equivalents  of 
water;  and  when  heated  to  redness,  nine  equivalents  of  water  are  ex- 
pelled, and  one  equivalent  of  chloride  of  strontium  remains. 

The  crystallized  muriate  attracts  humidity  from  a moist  atmosphere, 
but,  if  pure,  it  is  permanent  in  a moderately  dry  air.  The  crystals  are 
exceedingly  soluble  in  boiling  water,  and  require  for  solution  about 
twice  their  weight  of  water  at  60^  F. 

Muriate  of  lime  is  formed  by  neutralizing  muriatic  acid  with  pure 
marble.  The  salt  is  very  soluble  both  in  water  and  alcoliol,  and  deli- 
quesces with  rapidity  even  in  a dry  atmosphere.  It  crystallizes,  though 
with  considerable  difliculty,  in  ])risms,  wliich  consist,  according  to 
Thomson,  of  one  equivalent  of  muriate  of  lime,  and  six  equivalents  of 
water.  When  heated,  seven  equivalents  of  water  are  expelled  and  a 
chloride  remains.  It  may  of  course  be  regarded  as  chloride  of  calcium 
with  seven  ecjuivalcnts  of  water  of  crystallization. 

The  crystallized  muriate  is  the  compound  whicli  produces  such  an 
intense  degree  of  cold  when  mixed  with  snow.  It  is  prepared  for  this 


SALTS  OF  THE  HYDRACIDS. 


441 


purpose  by  evaporating*  the  solution  until  a drop  of  it  on  falling  upon  a 
cold  saucer  becomes  solid. 

Muriate  of  magnesia  exists  in  many  mineral  springs,  and  is  con- 
tained abundantly  in  sea-water.  When  muriate  of  soda  is  separated 
from  sea-water  by  crystallization,  an  uncrystallizable  liquid,  called  bit- 
tern, is  left,  which  consists  chiefly  of  muriate  of  magnesia,  and  is  much 
employed  in  the  manufacture  of  sal  ammoniac  for  decomposing  sulphate 
of  ammonia. 

Muriate  of  magnesia  has  a bitter  taste,  is  highly  soluble  in  alcohol 
and  water,  and  deliquesces  with  rapidity  in  the  open  air.  When  heated 
to  redness,  it  loses  a portion  of  its  acid  as  well  as  water. 

Muriate  of  Iron, — When  iron  is  dissolved  in  dilute  muriatic  acid,  a 
muriate  of  the  protoxide  is  generated,  which  yields  pale  green  coloured 
crystals  when  the  solution  is  concentrated  by  evaporation.  This  salt  is 
much  more  soluble  in  hot  than  in  cold  water,  and  is  not  deliquescent. 
It  absorbs  oxygen  with  rapidity  from  the  air,  forming  an  insoluble  mu- 
riate of  the  peroxide.  When  boiled  with  a little  nitric  acid  a soluble 
muriate  of  the  peroxide  is  generated,  which  is  of  a red  colour,  crystal- 
lizes with  difficulty,  deliquesces  on  exposure  to  the  air,  and  is  dissolved 
by  alcohol.  It  is  composed  of  one  equivalent  of  the  peroxide,  and  an 
equivalent  and  a half  of  muriatic  acid,  being  a sesquimuriate. 

The  black  oxide  is  also  dissolv  ed. by  muriatic  acid,  forming  a dark  co- 
loured solution,  which  may  be  regarded  as  a mixture  of  the  muriates  of 
the^peroxide  and  protoxide  of  iron.  (Page  332.) 

Muriates  of  lin. — The  protomuriate  is  conveniently  prepared  by 
digesting  granulated  tin  in  strong  muriatic  acid  as  long  as  hydrogen  gas 
is  disengaged,  atmospheric  air  being  excluded  at  the  same  time.  On 
making  a concentrated  hot  solution,  the  salt  is  deposited  in  the  form  of 
small  white  needles;  but  by  slow  evaporation  it  yields  colourless,  trans- 
parent, prismatic  crystals,  which  consist  of  one  equivalent  of  acid,  one 
of  protoxide  of  tin,  and  two  of  water.  From  the  strong  tendency  of 
protoxide  of  tin  to  pass  into  its  highest  stage  of  oxidation,  the  protomu- 
riate is  much  employed  as  a deoxidizing  substance,  especially  for  preci- 
pitating easily  reducible  metals  from  their  solution;  and  owing  to  this 
tendency,  it  absorbs  oxygen  rapidly  from  the  atmosphere.  Its  solution 
should  be  preserved  in  well  stopped  bottles,  in  contact  with  a few  parti- 
cles of  metallic  tin,  which  restores  any  peroxide  that  may  be  formed  to 
its  orig'inal  condition. 

T\\^ permuriate,  so  extensively  employed  as  a base  in  dyeing,  is  gener- 
ally prepared  by  dissolving  tin  in  nitro-muriatic  acid.  The  process  is 
one  of  delicacy;  for  should  the  temperature  be  much  raised  by  the  heat 
disengaged  by  chemical  action,  as  is  sure  to  happen  if  strong  acid  is 
used,  and  much  tin  is  added  at  once,  the  peroxide  will  be  spontaneously 
deposited  as  a bulky  hydrate,  and  be  subsequently  redissolved  with 
great  difficulty.  But  the  operation  will  rarely  fail,  if  the  acid  is  made 
with  two  measures  of  muriatic  acid,  one  of  nitric  acid,  and  one  of  water, 
and  if  the  tin  is  gradually  dissolved,  one  portion  disappearing  before 
another  is  added.  The  most  certain  mode  of  preparation,  however,  is 
to  oxidize  the  protomuriate  either  by  chlorine  or  by  gentle  heat  and 
nitric  acid.  I'he  latter  is  the  most  convenient. 

liydriodates. 

Ilydriodic  acid  unites  with  the  alkalies  and  alkaline  earths,  and  with 
the  oxides  of  manganese,  zinc,  and  iron.  With  several  of  the  metallic 
oxides,  it  does  not  enter  into  combination.  Thus,  on  mixing  hydrio- 
date  of  potassa  with  a salt  of  mercury  or  silver,  the  iodides  of  these 


442 


SALTS  OF  THE  IIYDRACIDS. 


metals  are  deposited.  Wilh  acetate  of  lead,  a yellow  compound  is 
thrown  down,  whicli  is  an  iodide  of  lead. 

The  most  direct  method  of  forming*  the  hydriodates  of  the  alkalies 
and  alkaline  earths,  all  of  which  are  soluble  in  water,  is  by  neutralizing* 
those  bases  with  hydriodic  acid.  The  hydriodates  of  iron  and  zinc  may 
be  made  by  digesting  small  fragments  of  those  metals  with  water  in 
which  iodine  is  suspended. 

All  the  hydriodates  are  decomposed  by  sulphuric  and  nitric  acids,  or 
by  chlorine,  the  hydriodic  acid  being  deprived  of  hydrogen,  and  the 
iodine  set  at  liberty.  (Page  223.)  They  are  not  decomposed  by  expo- 
sure to  the  air. 

The  only  hydriodates  which  have  hitherto  been  found  native  are  those 
of  potassa  and  soda,  the  sources  of  whicli  have  already  been  mentioned 
in  the  section  on  iodine.  Of  these  salts,  hydriodate  of  potassa  is  the 
most  common. 

Hydriodate  of  Potassa. — This  salt,  which  is  the  only  hydriodate  re- 
quiring particular  description,  exists  only  in  solution;  for  it  is  converted 
in  the  act  of  crystallizing  into  iodide  of  potassium.  It  is  exceedingly 
soluble  in  boiling  watei%  and  requires  only  two-thirds  of  its  weight  of 
water  at  60^  F.  for  solution.  It  is  dissolved  freely  by  alcohol;  and  when 
a saturated,  hot,  alcoholic  solution  is  set  aside  to  cool,  iodide  of  potas- 
sium is  deposited  in  cubic  crystals.  A solution  of  hydriodate  of  potassa 
is  capable  of  dissolving  a large  quantity  of  iodine,  a property  which  is 
common  to  all  the  hydriodates. 

Hydriodate  of  potassa  is  easily  made  by  neutralizing  hydriodic  acid 
with  pure  potassa;  but  in  preparing  a considerable  quantity  of  the  salt, 
as  for  medical  use,  it  is  desirable  to  dispense  with  the  preliminary  step  of 
making  the  acid.  With  this  intention  the  following  method,  which  I 
have  described  in  the  Edinburgh  Medical  and  Surgical  Journal  for  July 
1825,  may  be  employed  with  advantage.  The  process  consists  in  adding 
to  a hot  solution  of  pure  potassa  as  much  iodine  as  it  is  capable  of  dis- 
solving, by  which  means  a deep  brownish-red  coloured  fluid  is  formed, 
consisting*  of  iodate  and  hydriodate  of  potassa,  together  with  a large 
excess  of  free  iodine.  Through  this  solution  a current  of  sulphuretted 
hydrogen  gas  is  transmitted  until  the  free  iodine  and  iodic  acid  are  con- 
verted into  hydriodic  acid,  changes  which  may  be  known  to  be  accom- 
plished by  the  liquid  becoming  quite  limpid  and  colourless.  The  solu- 
tion is  then  gently  heated  in  order  to  expel  any  excess  of  sulphuretted 
hydrogen,  and  after  being  filtered,  any  free  hydriodic  acid  is  exactly 
neutralized  by  pure  potassa. 

A still  easier  process  has  been  proposed,  which  consists  in  adding 
iodine  to  a solution  of  hydrosulphate  of  potassa,  or  the  common  hepar 
sulphuris  of  the  Pharmacopoeia  (page  284),  until  the  potassa  is  exactly 
neutralized.  The  hydriodate  is  then  formed  at  once,  without  the  neces- 
sity of  a current  of  sulphuretted  hydrogen  gas;  but  when  made  with 
liver  of  sulphur,  it  contains  a considerable  quantity  of  sulphate  of 
potassa,  and  is  therefore  impure.  Another  mode  of  preparation  is  by 
decomposing  hydriodate  of  zinc  or  iron  by  a quantity  of  carbonate  of 
potassa  just  suflicient  to  precipitate  the  oxide. 

Ily  drohromates. 

Tlie  salts  of  hydrobromic  acid  have  as  yet  been  but  partially  examined, 
and  the  chief  facts  known  respecting  them  have  already  been  mentioned 
in  the  section  on  bromine. 


SALTS  OF  THE  HYDRACIDS. 


443 


Hydrojluates. 

Hydrofluoric  acid  unites  readily  with  the  pure  alkalies,  yielding  solu- 
ble hydrofluates,  which  are  converted  into  metallic  fluorides  by  the 
action  of  heat.  The  neutral  hydrofluates  of  the  alkalies,  those  namely 
that  contain  one  equivalent  of  acid  and  one  equivalent  of  base,  have 
an  alkaline  reaction.  It  may  be  doubted  if  this  acid  can  unite  at  all 
with  the  alkaline  earths;  for  it  yields  with  them  insoluble  compounds, 
which  have  all  the  characters  of  metallic  fluorides.  The  same  remark 
applies  to  the  action  of  hydrofluoric  acid  on  the  earths,  with  the  ex- 
ception of  alumina  and  zirconia,  which  form  soluble  hydrofluates. 

The  salts  of  hydrofluoric  acid  are  recognised  by  forming  with  muriate 
of  lime  a white  gelatinous  precipitate,  which  yields  hydrofluoric  acid 
when  heated  with  concentrated  sulphuric  acid. 

It  is  doubtful  if  any  hydrofluate  exists  ready  formed  in  the  mineral 
kingdom.  Four  minerals  may  be  enumerated  as  such;  namely,  topaz  or 
the  double  hydrofluate  of  silica  and  alumina,  hydrofluate  of  cerium,  the 
double  hydrofluate  of  cerium  and  yttria,  and  cryolite  or  the  double  hy- 
drofluate of  alumina  and  soda.  It  is  probable,  however,  that  these 
compounds,  like  fluorspar,  are  metallic  fluorides. 

Hydrofluate  of  Fotassa. — Potassa  unites  with  hydrofluoric  acid  in  two 
proportions,  forming  a hydrofluate  and  bihydrofluate;  the  former  of 
which  consists  of  one,  and  the  latter  of  two  equivalents  of  acid,  united 
with  one  equivalent  of  potassa.  The  hydrofluate,  which  has  an  alkaline 
reaction,  is  best  prepared  by  supersaturating  carbonate  of  potassa  with 
hydrofluoric  acid,  evaporating  the  solution  to  dryness,  and  expelling  the 
excess  of  acid  by  heat.  The  residue  has  a sharp  saline  taste,  is  deli- 
quescent, and  crystallizes  with  difficulty;  but  when  evaporated  at  a 
temperature  between  95*^  and  104®,  it  forms  cubic  crystals.  These 
crystals,  like  the  salt  after  being  heated,  are  most  probably  fluoride  of 
potassium. 

The  bihydrofluate  is  easily  procured  by  adding  to  hydrofluoric  acid  a 
quantity  of  potassa  insufficient  for  neutralizing  it  completely,  and  con- 
centrating the  solution.  By  slow  evaporation  it  yields  rectangular 
tables,  the  lateral  edges  of  which  are  bevelled.  This  salt  has  an  acid 
reaction,  is  soluble  in  water,  and  decomposed  by  heat. 

Hydrofluate  of  Soda. — The  neutral  and  acid  hydrofluate  of  soda  may 
be  formed  in  the  same  manner  as  the  preceding  salts.  The  acid  hydro- 
fluate consists  of  one  equivalent  of  base  and  two  of  the  acid,  possesses 
a sharp  and  purely  sour  taste,  is  but  sparingly  soluble  in  cold  water,  and 
crystallizes  in  transparent  rhombohedrons.  The  neutral  hydrofluate  is 
sparingly  soluble  in  water,  and  its  solubility  is  not  increased  by  eleva- 
tion of  temperature.  It  is  almost  completely  insoluble  in  alcohol.  It 
commonly  crystallizes  in  cubes  like  chloride  of  sodium,  but  assumes 
the  form  of  an  octohedron  when  carbonate  of  soda  is  present. 

The  neutral  and  acid  hydrofluate  of  lithia  are  sparingly  soluble  in 
water. 

The  neutral  hydrofluate  of  ammonia  may  be  prepared  by  mixing  in  a 
platinum  crucible  one  part  of  sal  ammoniac  and  two  and  a quarter  parts 
of  fluoride  of  sodium,  both  in  fine  powder  and  quite  dry,  and  applying 
a gentle  heat  with  a spirit  lamp.  The  hydrofluate  of  ammonia  sublimes 
and  condenses  in  small  prisms  on  the  lid  of  the  crucible,  if  kept  cool, 
without  any  admixture  of  muriate  of  ammonia.  Chloride  of  sodium  is 
generated  at  the  same  time. 

This  salt  is  permanent  in  the  air,  slightly  soluble  in  alcohol,  and  copi- 
ously dissolved  by  water.  It  corrodes  glass  vessels,  even  in  its  dry  state. 


444 


SALTS  OF  THE  IIYDUACIDS. 


In  solution  it  gradually  parts  with  ammonia,  and  is  converted  into  a 
deliquescent  biliydrofluate. 

It  is  doubtful  if  the  alkaline  earths  combine  at  all  with  hydrofluoric 
acid.  On  digesting  recently  precipitated  carbonate  of  baryta  in  an 
excess  of  this  acid,  carbonic  acid  is  gradually  evolved,  and  a compound 
is  formed,  which  appears  to  be  a fluoride  of  barium.  It  is  very  slightly 
soluble  in  water  and  hydrofluoric  acid;  but  it  is  dissolved  freely  by 
muriatic  acid,  and  ammonia  added  to  the  solution  causes  a precipitate, 
which  is  a compound  of  fluoride  and  chloride  of  barium.  A similar 
substance  is  formed  on  mixing  a solution  of  muriate  of  baryta  with  an 
alkaline  hydrofluatfe. 

On  digesting  newly  precipitated  carbonate  of  lime  in  an  excess  of 
hydrofluoric  acid,  a granular  fluoride  of  calcium  is  generated.  It  is 
insoluble  in  water  and  hydrofluoric  acid,  and  is  very  slightly  dissolved 
by  muriatic  acid.  It  may  also  be  formed  by  double  decomposition;  but 
it  then  forms  a translucid  jelly,  wliich  fills  up  the  pores  of  a filter,  and 
is  therefore  washed  with  difficulty.  This  compound  appears  to  be 
identical  with  the  beautiful  mineral  commonly  known  by  the  name  of 
Jluor  or  Derhyshire  spar.  Tins  mineral  frequently  accompanies  metallic 
ores,  especially  those  of  lead  and  tin;  and  it  often  occurs  crystallized 
either  in  cubes  or  some  of  its  allied  forms.  The  crystals  found  in  the 
lead  mines  of  Derbyshire  are  remarkable  for  the  largeness  of  their 
size,  the  regularity  of  their  form,  and  the  variety  and  beauty  of  their 
colours.  It  is  employed  in  forming  vases,  as  a flux  in  metallurgic  pro- 
cesses, and  in  the  preparation  of  hydrofluoric  acid.  The  nature  and 
composition  of  this  substance  were  considered  on  a former  occasion, 
(Page  233-4.) 

For  an  account  of  the  action  of  hydrofluoric  acid  on  other  metallic 
oxides,  I may  refer  to  an  essay  of  Berzelius  on  this  subject.  (Annals  of 
Philosophy,  xxiv.  335.) 

Hydrosulphurets  or  Hydrosulphates. 

Sulphuretted  hydrogen  forms  soluble  salts  with  the  alkalies  and  alka- 
line earths,  most  of  which  are  capable  of  crystallizing.  With  the  al- 
kalies, indeed,  if  not  with  other  bases,  this  acid  unites  in  two  propor- 
tions, forming  a hydrosulphate  and  a bihydrbsidphate.  It  may  be 
doubted  if  sulphuretted  hydrogen  is  capable  of  uniting  with  any  of  the 
oxides  of  the  common  metals,  for  when  their  salts  are  mixed  with  hy- 
drosulphate of  potassa,  a precipitate  takes  place,  which,  in  most  if  not 
in  all  cases,  is  the  sulphuret  of  a metal,  and  not  the  hydrosulphate  of 
its  oxide.  Thus,  by  the  action  of  hydrosulphate  of  potassa  on  the  ni- 
trates of  lead,  copper,  bismuth,  silver,  or  mercury,  nitrate  of  potassa 
is  formed,  water  is  generated,  and  a metallic  sulphuret  subsides.  The 
precipitates  occasioned  by  hydrosulphate  of  potassa  in  a salt  of  iron, 
zinc,  and  manganese,  may  also  be  regarded  as  sulphurets;  for  though 
sulpliuric  acid  decomposes  these  compounds  with  evolution  of  sulphu- 
retted hydrogen,  it  does  not  follow  that  that  acid  had  previously  existed 
in  them. 

As  sulphuretted  hydrogen  is  a weak  acid,  and  naturally  gaseous,  its 
salts  arc  decomposed  by  most  other  acids,  such  as  the  sulphuric,  mu- 
riatic, and  acetic,  with  disengagement  of  sulphuretted  hydrogen  gas,  a 
character  by  whicli  all  tlie  hydrosulphates  are  easily  recognised.  They 
arc  decomposed,  likewise,  by  chlorine  and  iodine,  with  separation  of 
sulphur,  and  formation  of  a muriate  or  hydriodate.  When  recently 
prepared,  they  form  solutions  which  are  colourless,  or  nearly  so;  but 
on  exposure  to  the  air,  oxygen  gas  is  absorbed,  a portion  of  its  acid  is 
deprived  of  its  hydrogen,  and  a sulphuretted  hydrosulphate  of  a yellow^ 


SALTS  OF  THE  HYDRACIDS. 


445 


colour  is  generated.  By  continued  exposure,  the  whole  of  the  sul- 
phuretted hydrogen  is  decomposed,  water  and  hyposulphurous  acid 
being  produced. 

The  hydrosulphates  of  baryta  and  strontia,  prepared  by  dissolving 
the  sulphurets  of  barium  and  strontium  in  water,  are  sometimes  used  in 
preparing  the  salts  of  those  bases.  The  hydrosulphates  of  potassa  and 
ammonia  are  employed  as  reagents. 

Hydrosulphate  of  Potassa, — This  salt  is  made  by  transmitting  a cur- 
rent of  sulphuretted  hydrogen  gas  into  a solution  of  pure  potassa,  con- 
tained in  Woulfe’s  apparatus,  and  continuing  the  operation  as  long  as 
the  gas  is  absorbed.  When  all  the  alkali  is  combined  with  sulphuretted 
hydrogen,  it  is  no  longer  able  to  precipitate  a salt  of  magnesia.  If  the 
alkali  is  completely  saturated  with  the  gas,  the  resulting  compound, 
though  it  has  still  an  alkaline  reaction,  is  a bihydrosulphate.  This  salt 
has  an  alkaline  bitter  taste,  arid  crystallizes  in  six-sided  prisms,  which 
are  deliquescent  and  soluble  in  alcohol  as  well  as  water. 

Hydrosulphate  of  Ammonia, — d'his  salt  is  obtained  in  the  form  of  a 
volatile  fluid,  c.^\\ed.  fuming  liquor  of  Boyky  by  heating  a mixture  of 
one  part  of  sulphur,  two  of  sal  ammoniac,  and  two  of  unslaked  lime. 
The  changes  which  ensue  have  lately  been  examined  by  Gay-Lussac. 
The  volatile  products  are  ammonia  and  hydrosulphuret  of  ammonia;  and 
the  fixed  residue  consists  of  sulphate  of  lime  with  chloride  and  sulphu- 
ret  of  calcium.  I'he  sulphuretted  hydrogen  is  formed  from  the  hydro- 
gen of  muriatic  acid  uniting  with  sulphur,  and  the  oxygen  of  the  sul- 
phuric acid  is  derived  from  decomposed  lime,  the  calcium  of  which  is 
divided  between  the  chlorine  of  the  muriatic  acid  and  sulphur.  Hydro- 
sulphuret of  ammonia  may  also  be  formed  by  the  direct  union  of  its 
constituent  gases,  and  if  they  are  mixed  in  a glass  globe  kept  cool  by 
ice,  the  salt  is  deposited  in  crystals.  It  is  much  used  as  a reagent,  and 
for  this  purpose  is  usually  prepared  by  saturating  a solution  of  ammonia 
with  sulphuretted  hydrogen  g’as. 

Hydroseleniates. — These  salts  have  been  little  examined,  owing  to 
the  Scarcity  of  selenium.  The  researches  of  Berzelius  have  demon- 
strated, however,  that  hydroselenic  acid  forms  with  the  alkalies  soluble 
compounds,  which  are  very  analogous  in  their  chemical  relations  to  the 
hydrosulphates,  and  which  precipitate  the  salts  of  the  common  metals, 
giving  rise  in  most  if  not  in  all  cases  to  the  formation  of  a metallic  sele- 
niuret. 

Hydrocyanates. 

H5"drocyanic  acid  unites  with  alkalies  and  alkaline  earths,  and  proba- 
bly with  several  other  bases;  but  these  compounds  have  as  yet  been 
studied  in  a very  imperfect  manner.  Hydrocyanate  of  potassa  is  the 
best  known.  It  is  generated  by  decomposition  of  water  when  cyanuret 
of  potassium  is  put  into  that  fluid,  and  may  be  made  directly  by  mixing 
hydrocyanic  acid  with  a solution  of  potassa.  M.  Robiquet  recommends 
that  it  should  be  prepared  by  exposing  ferrocyanate  of  potassa  to  a long- 
continued  red  heat,  by  which  means  the  ferrocyanic  acid  is  decomposed, 
and  a dark  mass  consisting  of  cyanuret  of  potassium,  mixed  with  char- 
coal and  iron,  remains  in  the  crucible.  This  process  succeeds  well  if 
carefully  performed;  but  it  is  difficult  to  destroy  the  whole  of  the  fer- 
rocyanic acid,  without  decomposing  at  the  same  time  the  cyanuret  of 
potassium.  If  the  decomposition  of  the  ferrocyanate  is  complete,  the 
residue  should  form  a colourless  solution,  which  does  not  produce  Prus- 
sian blue  with  a salt  of  the  peroxide  of  iron. 

Hydrocyanate  of  potassa  appears  to  exist  only  in  solution;  for  when 
evaporated  to  dryness,  it  is  converted  into  cyanuret  of  potassium,  a 

38 


446 


SALTS  OF  THE  HYDRACIDS. 


compound  which  is  far  less  liable  to  spontaneous  decomposition  than 
hydrocyanic  acid,  and  is  capable  of  supporting  a very  high  tempera- 
ture in  close  vessels  without  change.  It  is  deliquescent,  and  highly 
soluble  in  water.  The  solution  gives  a green  colour  to  violets,  and  has 
an  alkaline  taste,  accompanied  with  the  flavour  and  a faint  odour  of 
hydrocyanic  acid.  It  is  decomposed  by  nearly  all  the  acids,  even  by 
the  carbonic,  and  on  this  account  should  be  preserved  in  well-closed 
Vessels.  It  acts  upon  the  animal  system  in  the  same  manner  as  hydro- 
cyanic acid,  and  MM.  Robiquet  and  Villerm^  have  proposed  its  em- 
ployment in  medical  practice,  as  being  more  uniform  in  strength,  and 
less  prone  to  decomposition,  than  hydrocyanic  acid.  (Journ.  de  Physi- 
ologic, vol.  iii.) 

Ferrocyanates, 

The  neutral  ferrocyanates,  so  far  as  is  known,  appear  to  be  formed 
in  the  same  manner  as  the  salts  of  the  hydracids  in  general;  namely,  the 
hydrogen  of  the  acid  is  in  exact  proportion  for  forming  water  with  the 
oxygen  of  the  salifiable  base  with  which  it  is  united.  Thus,  ferro- 
cyanate  of  potassa  is  composed  of  one  equivalent  of  ferrocyanic  acid, 
which  contains  two  equivalents  of  hydrogen  (page  270,)  and  two  of 
potassa.  With  the  alkalies  and  alkaline  earths  this  acid  forms  soluble 
compounds;  but  it  precipitates  nearly  all  the  salts  of  the  common  metals, 
giving  rise  either  to  the  ferrocyanate  of  an  oxide  or  the  ferrocyanuret  of 
a metal. 

Ferrocyanate  of  Potassa. — This  salt,  sometimes  called  triple prussiate 
of  potassa,  is  prepared  by  digesting  pure  ferrocyanate  of  the  peroxide 
of  iron  in  potassa  until  the  alkali  is  neutralized,  by  which  means  the 
peroxide  of  iron  is  set  free,  and  a yellow  liquid  is  formed,  which  yields 
crystals  of  ferrocyanate  of  potassa  by  evaporation.  This  salt  is  made 
on  a large  scale  in  the  arts  by  igniting  dried  blood  or  other  animal  mat- 
ters, such  as  hoofs  and  horns,  with  potassa  and  iron.  By  the  mutual 
reaction  of  these  substances  at  a high  temperature,  ferrocyanuret  of 
potassium,  consisting  of  one  equivalent  of  the  radical  of  ferrocyanic 
acid  (page  271,)  and  two  equivalents  of^potassium,  is  generated.  Such 
at  least  is  inferred  to  be  the  product;  for  on  digesting  the  residue  in 
water,  a solution  of  ferrocyanate  of  potassa  is  obtained. 

Ferrocyanate  of  potassa  is  a perfectly  neutral  salt,  which  is  soluble  in 
less  than  its  own  weight  of  water,  and  forms  large,  transparent,  four- 
sided tabular  crystals,  derived  from  an  acute  rhombic  octohedron,  the 
apices  of  which  are  deeply  truncated.  The  colour  of  the  salt  is  lemon- 
yellow;  it  is  inodorous,  has  a slightly  bitter  taste,  but  quite  different 
from  that  of  hydrocyanic  acid,  and  is  permanent  in  the  air.  When 
heated  to  212®  F.;  or  even  below  that  temperature,  each  equivalent  of 
the  salt  parts  with  three  equivalents  of  water,  leaving  one  equivalent  of 
ferrocyanuret  of  potassium.  The  water,  indeed,  is  disengaged  with 
such  facility,  that  Berzelius  regards  the  crystals  as  consisting  of  ferro- 
cyanuret of  potassium  combined  with  three  equivalents  of  water  of 
crystallization.  (An.  de  Ch.  et  de  Ph.  vol.  xv.)  On  heating  the  dry 
compound  to  full  redness  in  close  vessels,  decomposition  takes  place, 
nitrogen  gas  is  disengaged,  and  cyanuret  of  potassium  mixed  with  car- 
buret of  iron  remains  in  the  retort.  • 

Very  great  diversity  of  opinion  prevails  respecting  the  atomic  consth 
tution  of  this  salt.  I'herc  is  good  reason  to  believe  from  the  experi- 
ments of  Berzelius,  iMiillips,  and  others,  that  one  equivalent  of  the 
crystallized  salt  contains  the  following  substances:— 


SALTS  OF  THE  HYDRACIDS. 


447 


Cyanogen 

78  or 

three  equivalents, 

Potassium 

80 

two  equivalents. 

Iron 

28 

one  equivalent. 

Hydrogen 

3 

three  equivalents. 

Oxygen 

24 

three  equivalents. 

213 

Its  solution  in  water  has  all  the  properties  that  may  be  expected  from 
the  presence  of  ferrocyanic  acid  and  potassa,  and  I shall  accordingly 
regard  it,  when  in  that  state,  as  containing  both  these  substances.  In 
the  form  of  crystals,  it  is  perhaps  more  simple  to  consider  it  with  Ber- 
zelius as  a double  cyanuret  of  iron  and  potassium  with  water  of  crystal- 
lization. The  reader  will  find  a discussion  of  this  subject  in  the  Philo- 
sophical Magazine  and  Annals,  i.  110,  by  Mr.  Phillips. 

Ferrocyanate  of  potassa  is  employed  in  the  preparation  of  several 
compounds  of  cyanogen,  and  as  a reagent  for  detecting  the  presence  of 
iron  and  other  substances. 

Red  Cyanuret  of  Iron  and  Potassium. — This  compound,  discovered 
by  L.  Gmelin,  is  generated  by  transmitting  chlorine  gas,  freed  by  wash- 
ing from  muriatic  acid,  into  a rather  strong  solution  of  ferrocyanate  of 
potassa,  until  it  ceases  to  give  a precipitate  with  persalts  of  iron.  The 
liquid  is  then  concentrated  to  two-thirds  of  its  volume,  and  set  aside  in 
a moderately  warm  stove  to  crystallize.  Tufts  of  slender,  yellow,  bril- 
liant crystals  are  gradually  deposited  in  the  form  of  roses;  and  by  a se- 
cond crystallization  very  brilliant  ruby-coloured  crystals  are  obtained, 
the  form  of  which  appears  to  be  an  elongated  octohedron.  Chloride  of 
potassium  is  generated  at  the  same  time;  and  the  red  crystals  are  quite 
anhydrous,  and  are  composed  of  three  equivalents  of  cyanogen,  one 
and  a half  of  potassium,  and  one  of  iron.  They  differ  in  composition 
from  ferrocyanate  of  potassa  which  has  been  dried  at  212°,  by  contain- 
ing half  an  equivalent  less  of  potassium. 

The  solution  of  the  red  double  cyanuret  is  remarkable  for  detecting 
protosalts  of  iron,  causing  a blue  or  green  precipitate,  according  to  the 
strength  of  the  solution.  According  to  M.  Girardin,  it  indicates  the 
presence  of  protoxide  of  iron  dissolved  in  90,000  parts  of  water.  The 
crystals  require  for  solution  twice  their  weight  of  cold,  and  less  than 
their  weight  of  boiling  water;  but  are  insoluble  in  alcohol.  A dilute 
solution  of  the  crystals  has  a greenish*red  tint;  but  when  concentrated, 
the  colour  is  so  deep  that  it  appears  almost  black.  A very  small  quan- 
tity renders  a considerable  portion  of  water  green.  (Phil.  Mag.  and  Ann. 
V.  148.) 

Ferrocyanate  of  baryta  is  prepared  by  digesting  purified  Prussian 
blue  with  a solution  of  pure  baryta.  It  is  soluble  in  water,  and  forms 
yellow  crystals  by  evaporation.  It  is  used  in  the  formation  of  ferrocy- 
anic acid. 

When  ferrocyanate  of  potassa  is  mixed  in  solution  with  a salt  of  lead, 
a white  precipitate  subsides,  which  Berzelius  has  proved  to  be  similar 
in  composition  to  ferrocyanuret  of  potassium,  consisting  of  one  equiv- 
alent of  the  radical  ferrocyanic  acid,  and  two  equivalents  of  lead.  With 
salts  of  mercury  and  silver,  analogous  compounds,  likewise  of  a white 
colour,  are  generated.  With  a persalt  of  copper,  ferrocyanate  of  po- 
tassa causes  a brownish-red  precipitate,  which  appears  to  be  ferrocy- 
anate of  the  peroxide  of  copper. 

Ferrocyanate  of  peroxide  of  iron,  which  is  formed  by  mixing  ferrocy- 
anate of  potassa  with  a persalt  of  iron  in  slight  excess,  and  washing  the 
precipitate  with  water,  is  characterized  by  an  intensely  deep  blue  colour, 


448 


SALTS  OF  THE  HYDRACIDS. 


and  is  the  basis  of  the  beautiful  pigrnent  called  Prussian  blue.  It  is 
insipid  and  inodorous,  insoluble  in  water,  and  is  not  decomposed  by 
dilute  muriatic  or  sulphuric  acid.  Concentrated  muriatic  acid,  by  the 
aid  of  heat,  separates  the  acid,  and  strong’  sulphuric  acid  renders  it 
white — a change  the  nature  of  which  has  not  been  explained.  'I  he  al- 
kalies and  alkaline  earths  decompose  it  readily,  uniting  with  the  ferro- 
cyanic  acid  and  separating  the  peroxide  of  iron.  Peroxide  of  mercury, 
as  already  mentioned  (page  380,)  effects  the  complete  decomposition 
of  the  salt,  forming  bicyanuret  of  mercury.  Very  complicated  changes 
are  produced  by  an  elevated  temperature.  On  heating  the  ferrocyanate 
to  redness  in  a close  vessel,  a considerable  quantity  of  water  and  car- 
bonate of  ammonia,  together  with  a small  portion  of  hydrocyanate  of 
ammonia,  are  generated,  while  a carburet  of  iron  remains  in  the  retort 
— phenomena  which,  in  conjunction  with  the  facts  above  stated,  leave 
no  doubt  of  this  compound  containing  ferrocyanic  acid  and  peroxide  of 
iron.  The  precise  proportion  of  its  constituents  has  not  been  satisfac- 
torily determined;  but  it  most  probably  consists  of  one  equivalent  of  the 
peroxide  and  an  equivalent  and  a half  of  the  acid.* 

Prussian  blue,  the  discovery  of  which  was  made  in  1710,  has  been 
studied  by  several  chemists,  especially  by  Proust,  (An.  de  Chimie,  lx  ) 
and  by  Berzelius,  Porrett,  and  Robiquet,  whose  essays  were  referred 
to  in  the  description  of  ferrocyanic  acid.  The  colouring  matter  of  this 
pigment  is  ferrocyanate  of  peroxide  of  iron,  which  is  mixed  with  alu- 
mina and  peroxide  of  iron,  together  with  the  subsulphates  of  one  or 
both  of  those  bases.  It  is  prepared  by  heating  to  redness  dried  blood, 
or  other  animal  matters,  with  an  equal  weight  of  pearlash,  until  the 
mixture  has  acquired  a pasty  consistence.  The  residue,  which  consists 
chiefly  of  cyanuret  of  potassium  and  carbonate  of  potassa,  is  dissolved 
in  water,  and  after  being  filtered,  is  mixed  with  a solution  of  two  parts 
of  alum  and  one  part  of  protosulphate  of  iron.  A dirty-greenish  pre- 
cipitate ensues,  which  absorbs  oxygen  from  the  atmosphere,  and  passes 
through  different  shades  of  green  and  blue,  until  at  length  it  acquires 
the  proper  colour  of  the  pigment. 

The  chemical  changes  which  take  place  in  this  process  are  of  a com- 
plicated nature.  The  precipitate,  which  is  at  fjrst  thrown  down,  is 
occasioned  by  the  potassa,  and  consists  chiefly  of  alumina  and  protoxide 
of  iron.  Ferrocyanic  acid  is  generated  by  the  protoxide  reacting  upon 
some  of  the  hydrocyanic  acid,  so  as  to  form  water  and  cyanuret  of  iron, 
which  then  unites  with  undecomposed  hydrocyanic  acid.  The  ferrocy- 
anic acid,  thus  produced,  combmes  with  oxide  of  iron;  and  when  the 
latter  has  attained  its  maximum  of  oxidation,  the  compound  acquires 
its  characteristic  blue  tint.  Dr.  Thomson,  knowing  the  protoxide  to 
be  necessary  to  the  success  of  the  operation,  concludes  that  this  oxide 
enters  into  the  composition  of  Prussian  blue;  but  here  this  acute  chem- 


* In  this  statement.  Dr.  Turner  does  not  appear  to  have  adverted  to 
the  fact  that  ferrocyanic  acid  contains  two  equivalents  of  hydrogen.  It 
is  altogether  probable,  that  in  Prussian  blue,  the  acid  and  base  are 
united  in  such  proportions,  that  the  hydrogen  of  the  former  and  the 
oxygen  of  tlm  latter  are  in  tlie  proper  ratio  to  form  water.  Now  one 
equivalent  of  peroxide  of  iron  contains  an  equivalent  and  a half  of  oxy- 
gen, and  it  would  require  thrcc-fourtlis  of  an  equivalent  of  the  acid, 
supposing  it  to  unite  with  a quantity  of  the  latter  containing  an  equiv- 
alcnt  and  u half  of  hydrogen.  Doubling  tlicse  quantities,  the  probable 
])roportions  would  be,  two  c(]uivalcnts  of  peroxide  of  iron  to  an 
pquivulcnt  and  a half  of  the  aci(i.  B, 


HALOID  SALTS  AND  SULPHO-SALTS. 


449 


ist  is  certainly  in  error.  The  only  use  of  protoxide  of  iron  is  to  convert 
hydrocyanic  into  ferrocyanic  acid;  a purpose  for  which  its  presence  is 
essential,  because  peroxide  of  iron  does  not  produce  this  effect,  or  at 
least  in  a very  slow  and  imperfect  manner.  In  every  good  specimen  of 
Prussian  blue  which  I have  examined,  the  ferrocyanic  acid  was  in  com- 
bination with  peroxide  of  iron  only. 

Sulphocyanates.—T\\Q  salts  of  sulphocyanic  acid  have  been  chiefly 
studied  by  Mr.  Porrett  and  Berzelius.  Sulphocyanate  of  potassa,  which 
is  the  most  interesting  and  the  best  known  pf  these  compounds,  is  pre- 
pared by  heating  ferrocyanate  of  potassa  with  sulphur,  a process  first 
proposed  by  Grotthus,  and  since  modified  by  M.  Vogel  and  myself.  The 
most  convenient  method  of  performing  it  is  to  mix  the  ferrocyanate,  in 
fine  powder,  with  an  equal  weight  of  sulphur,  and  to  place  the  mix- 
ture, contained  in  a porcelain  capsule,  just  above  a pan  of  burning 
charcoal,  so  that  it  may  be  exposed  to  a very  strong  heat,  but  short  of 
redness.  The  mixtui’e  is  speedily  fused,  takes  fire,  and  burns  briskly 
for  one  or  two  minutes,  during  which  it  should  be  well  stirred.  The 
combustion  then  ceases  spontaneously,  and  the  dark-coloured  residue, 
consisting  of  unburned  sulphur,  sulphocyanuret  of  potassium,  and  sul- 
phuret  of  iron,  on  being  dissolved  in  water  and  filtered,  yields  a very 
pure  and  neutral  sulphocyanate  of  potassa.  To  ensure  the  decomposi- 
tion of  all  the  ferrocyanate  of  potassa,  the  mass  may  be  allowed  to  re- 
main in  a fused  condition  for  a few  minutes  after  the  combustion  has 
ceased,  previous  to  withdrawing  it  from  the  fire. 

In  this  process  the  iron  and  cyanogen  of  the  ferrocyanate  combine 
with  separate  portions  of  sulphur,  forming  a sulphuret  of  iron  and  a 
sulphuret  of  cyanogen,  the  latter  of  which  unites  with  potassium.  On 
the  addition  of  water,  a portion  of  that  liquid  is  decomposed,  and  sul- 
phocyanate of  potassa  is  generated. 

Sulphocyanate  of  potassa  (and  most  of  the  salts  of  this  group  have 
probably  a similar  constitution)  contains  one  equivalent  of  the  acid,  and 
one  equivalent  of  the  oxide;  so  that  the  oxygen  anel  hydrogen  are  in 
due  proportion  for  the  production  of  water.  This  salt,  indeed,  exists 
only  in  a liquid  state;  for  the  crystals  which  are  deposited  from  a con- 
centrated solution,  when  separated  from  adhering  moisture  by  bibulous 
paper,  do  not  contain  either  water  or  its  elements,  but  are  a pure  sul- 
phocyanuret of  potassium.  The  crystals  are  very  deliquescent  on  ex- 
posure to  the  air,  and  dissolve  freely  in  water,  yielding  a solution  which 
is  quite  neutral.  In  form,  taste,  and  fusibility,  they  are  very  analogous 
to  nitre. 

Sulphocyanate  of  potassa  is  employed  in  preparing  sulphocyanic 
acid,  and  as  a test  for  detecting  the  presence  of  peroxide  of  iron. 


SECTION  VII. 

ON  HALOID  SALTS  AND  SULPHO-SALTS. 

With  the  salts  properly  so  called  Berzelius  has  of  late  associated  two 
other  series  of  compounds,  which  are  closely  analogous  to  salts  either 
in  appearance  or  composition;  and  as  the  high  rank  which  Berzelius 
has  so  justly  attained  soon  gives  currency  to  his  language  and  opinions, 
at  least  among  continental  chemists,  a brief  statement  of  his  views  can- 

38* 


450 


HALOID  SALTS  AND  SULPIIO-SALTS. 


not  fail  of  being*  both  useful  and  agreeable  to  the  reader.  Some  notice 
of  the  sulpho-salts  is  even  necessary;  because,  under  this  title,  Derze- 
lius  has  described  several  iiiteresting  compounds  wliich  were  new  to 
chemists,  and  which  could  hot  so  conveniently  be  noticed  in  other  parts 
of  this  treatise.  For  a full  history  of  these  compounds,  the  student 
may  refer  to  tlie  essay  by  Berzelius  in  the  Jinnahs  de  Chimie  et  de  Phy- 
siquCy  xxxii.  60,  or  to  his  Lehrhuch  der  Chemie. 

Haloid  7-This  term  comprehends  all  those  compounds  which 

consist  of  a metal  on  the  one  hand,  and  of  chlorine,  iodine,  and  the 
radicals  of  the  hydracids  in  general,  excepting  sulphur,  on  the  other. 
The  word  haloidy  being  derived  from  sea-salt,  and  appear- 

ance, is  very  appropriate,  since  the  substances  to  which  it  is  applied, 
such  as  the  chlorides  and  iodides,  cannot  in  many  instances  be  distin- 
guished by  their  aspect  from  real  salts;  but  in  point  of  composition  they 
resemble  oxides  rather  than  salts,  and  in  connexion  with  these  they  have 
already  been  described. 

Berzelius  has  correctly  remarked,  that  the  number  of  ha-loid  salts, 
which  a metal  is  capable  of  yielding  with  the  same  element,  generally 
corresponds  to  the  salifiable  oxides  which  it  forms  with  oxygen.  I’hus, 
there  are  two  chlorides  and  two  iodides  of  mercury,  proportional  to  the 
two  oxides  of  mercury;  and  potassium,  which  has  bvit  one  salifiable 
oxide,  unites  in  one  proportion  only  with  chlorine  and  iodine.  Besides 
simple  haloid  salts,  Berzelius  distinguishes  three  different  combinations  of 
them.  The  first  of  these  is  an  acid  haloid  salt,  formed  of  a simple  haloid 
salt  and  the  hydracid  of  its  radical.  A compound  of  the  kind  may  be 
obtained  by  evaporating  a muriatic  solution  of  gold  with  excess  of  acid 
at  a very  moderate  temperature,  when  crystals  are  obtained  consisting 
of  chloride  of  gold  and  muriatic  acid.  The  compound  of  fluoride 
of  potassium  and  hydrofluoric  acid  offers  another  example.  These  com- 
pounds may  h&  c2\\e(X  hydro-haloid  salts.  The  second  mode  of  combi- 
nation, which  is  more  frequent,  gives  rise  to  what  may  be  termed  oxy~ 
haloid  salts,  being  composed  of  a metallic  oxide  united  with  a haloid  salt 
of  the  same  metal.  Thus,  chloride  of  lead  combines  with  oxide  of  lead; 
and  submuriate  of  iron,  obtained  by  evaporating  permuriate  of  iron  in 
an  open  vessel  by  a rather  strong  heat,  is  considered  by  Berzelius  as  a 
similar  compound.  The  third  kind  of  combination  is  productive  of 
double  haloid  salts.  I'hey  may  consist,  first,  of  two  simple  haloid  salts 
which  contain  different  metals,  but  the  same  non-metallic  ingredient, 
as  the  double  chloride  of  potassium  and  gold,  or  the  double  fluoride  of 
potassium  and  silicium;  secondly,  of  two  haloid  salts  consisting  of  the 
same  metal,  but  in  which  the  other  element  is  different,  as  the  com- 
pound of  chloride  of  lead  with  fluoride  of  lead;  and,  thirdly,  of  two 
simple  haloid  salts,  of  which  both  elements  are  entirely  different.  In 
some  cases  haloid  salts  unite  with  common  salts;  as,  for  example,  when 
chloride  of  sodium  is  fused  with  carbonate  of  baryta,  or  carbonate  of 
soda  with  chloride  of  barium.  (Page  438.)  A compound  containing  ni- 
trate of  oxide  of  silver  and  cyanuret  of  silver,  observed  by  Wohler,  is 
an  instance  of  the  same  description. 

Sulpho-salts. — The  substances  comprised  under  this  term  are  merely 
double  sulphurcts,  in  the  constitution  of  which  Berzelius  has  traced  a 
close  analogy  to  salts.  The  constituents  of  ordinary  salts,  irt  reference 
to  the  electro  chemical  theory,  are.conceived  to  be  oppositely  electrical, 
the  acid  being  negative,  and  the  alkali  positive;  and  the  two  sulphii- 
rets  in  a sulpho-salt  are  believed  by  Berzelius  to  have  in  general  a simi- 
lar relation  to  each  other.  Metallic  bodies  are  divided  by  this  chemist 
into  electro-positive  and  electro-negative  metals.  (Page  100.)  To  the 
former  belong  those  metals,  tlie  protoxides  of  which  are  strong  salifia- 


HALOID  SALTS  AND  SULPIIO-SALTS, 


451 


ble  bases;  and  among  the  latter  are  those  which  are  capable  of  yielding 
acids  with  oxygsn.  Now,  in  most  of  the  sulpho-salts,  the  negative  in- 
gredient is  the  sulphuret  of  an  electro-negative  metal,  while  the  positive 
body  is  the  sulphuret  of  an  electro-positive  metal.  The  negative  sul- 
phuret is  proportional  in  composition  to  the  acid  of  the  same  metal,  and 
tlie  positive  sulphuret  corresponds  to  the  salifiable  base  of  its  metal; 
so  that  if  each  metal  were  combined  with  the  same  number  of  equiva- 
lents of  oxygen  as  it  possesses  of  sulphur,  the  negative  metal  would 
form  an  acid,  and  the  positive  metal  an  alkaline  base;  and  a regular 
salt  would  be  thus  produced.  Hence,  the  electro-negative  sulphuret  is 
thought  to  act  the  part  of  an  acid,  and  the  positive  sulphuret  of  an  al- 
kali. Some  of  these  compounds  are  insoluble;  but  many  of  them  are 
soluble  in  water,  and  may  be  obtained  in  crystals  by  evaporation. 

The  electro-negative  sulphurets,  known  to  yield  sulpho-salts,  are 
those  of  arsenic,  antimony,  tungsten,  molybdenum,  tellurium,  tin  and 
gold;  and  the  sulphurets  of  several  other  substances  not  metallic  are 
capable  of  acting  as  the  negative  ingredient.  The  compounds  to  which 
Berzelius  attributes  this  property  are  sulphuret  of  selenium,  sulphu- 
retted hydrogen,  sulphuret  of  carbon,  and  sulphocyanic  acid.  He  adds 
also,  that  in  the  same  manner  as  positive  oxides  sometimes  combine,  so 
may  sulpho-salts  be  formed  by  the  union  of  electro-positive  sulphurets. 
The  native  double  sulphuret  of  copper  and  iron,  and  a considerable 
number  of  similar  compounds,  are  instances  of  this  nature. 

Several  methods  for  preparing  sulpho-salts  are  enumerated  by  Berze- 
lius. 1.  A negative  sulphuret  is  digested  in  an  aqueous  solution  of 
sulphuret  of  potassium  until  it  is  saturated.  The  resulting  sulpho-salt 
may  be  employed  to  prepare  insoluble  sulpho-salts,  by  means  of  double 
decomposition.  2.  A solution  of  hydrosylphuretted  sulphuret  of  po- 
tassium, which  is  itself  regarded  as  a sulpho-salt,  is  mixed  with  a 
negative  sulphuret  in  powder;  when  the  latter  unites  with  sulphuret 
of  potassium,  and  displaces  the  less  negative  sulphuretted  hydrogen, 
which  is  disengaged  with  eflTervesence  3.  By  dissolving  a negative 
sulphuret  in  solution  of  potassa.  In  this  operation,  some  of  the  al- 
kali exchanges  elements  with  a portion  of  the  electro-negative  sul- 
phuret, giving  rise  to  sulphuret  of  potassium  and  an  acid  of  the  ne- 
gative metal.  This  acid  constitutes  a salt  with  undecomposed  potassa, 
and  the  undecomposed  negative  sulphuret  generates  a sulpho  salt  by 
uniting  with  sulphuret  of  potassium.  For  example,  when  orpiment  is 
dissolved  in  solution  of  potassa,  the  oxygen  of  a portion  of  potassa 
unites  with  arsenic,  and  potassium  with  sulphur:  arsenious  acid  and  sul- 
phuret of  potassium  result;  and  v,  hile  the  former  attaches  itself  to  the 
alkali,  forming  arsenite  of  potassa,  the  latter  combines  with  sulphuret 
of  arsenic.  Similar  changes  ensue  when  sulphuret  of  antimony,  and 
other  electro-negative  sulphurets,  are  boiled  with  alkalies.  A regular 
salt,  the  acid  of  which  is  formed  of  oxygen  and  the  electro-negative 
metal,  is  always  generated;  and  this  salt,  if  soluble  in  water,  remains 
together  with  the  sulpho-salt  in  solution.  4.  The  last  method  which 
requires  mention,  is  by  exposing  a mixture  of  an  electro-negative  sul- 
phuret and  an  alkaline  carbonate  to  a red  heat  in  a covered  vessel.  Car- 
bonic acid  gas  is  disengaged;  and  an  interchange  of  elements,  similar 
to  that  just  explained,  takes  place  between  a portion  of  the  alkali  and 
sulphuret.  The  fused  mass,  accordingly,  always  contains  a salt,  the  acid 
of  which  consists  of  oxygen  and  the  negative  metal,  as  well  as  a sulpho- 
salt.  This  tendency  to  the  formation  of  a double  sulphuret  is  the  rea- 
son why,  in  decomposing  orpiment  by  black  flux,  the  whole  of  the 
arsenig  is  never  sublimed:  a part  is  uniformly  retained  in  the  form  of  a 
double  sulphuret  of  potassium  and  arsenic. 


452 


HALOID  SALTS  AND  SULPHO-SALTS. 


In  this  description,  which  will  suffice  for  conveying*  a g*eneral  know- 
ledge of  the  subject,  the  opinions  and  explanations  of  Herzelius  have 
been  preserved;  and  to  these  the  advantage  of  greater  simplicity  must, 
as  I apprehend,  be  conceded.  But  the  phenomena  clearly  admit  of  a 
different  explanation.  Instead  of  a double  sulphuret  being  held  in 
solution  in  the  three  first  methods  above  mentioned,  the  liquid  may 
contain  double  salts  of  sulphuretted  hydrogen,  formed  by  decomposition 
of  water.  In  like  manner,  the  oxygen  of  the  arsenious  acid,  which  is 
generated  in  the  example  above  adduced,  may  be  derived  from  decom- 
posed water,  as  well  as  from  potassa.  If  this  view  be  taken-^and  there 
seems  no  decisive  objection  against  it — the  existence  of  a sulpho-salt  in 
solution  will  no  longer  be  admitted;  and  in  that  case  the  chief  interest 
attached  to  the  new  opinions  of  Berzelius  will  be  destroyed. 


PART  III. 


ORGANIC  CHEMISTRY. 


The  department  of  org’anic  chemistry  comprehends  the  history  of 
those  compounds  wliich  are  solely  of  animal  or  vegetable  origin,  and 
which  are  hence  called  organic  substance^.  These  bodies,  viewed  col- 
lectively, form  a remarkable  contrast  with  those  of  the  mineral  king- 
dom. Such  substances  in  general  are  characterized  by  containing  some 
principle  peculiar  to  each.  Thus  the  presence  of  nitrogen  in  nitric, 
and  of  sulphur  in  sulphuric  acid,  establishes  a wide  distinction  between 
these  substances;  and  although  in  many  instances  two  or  more  inorganic 
bodies  consist  of  the  same  elements,  as  is  exemplified  by  the  com- 
pounds of  sulphur  and  oxygen,  or  of  nitrogen  and  ox}  gen,  they  are 
always  few  in  number,  and  distinguished  by  a well-marked  difference 
in  the  proportion  in  which  they  are  united.  The  products  of  animal 
and  vegetable  life,  on  the  contrary,  consist  essentially  of  the  same  ele- 
mentary principles,  the  number  of  which  is  very  limited.  They  are 
nearly  all  composed  of  carbon,  hydrogen,  and  oxygen,  in  addition  to 
which  some  of  them  contain  nitrogen.  Besides  these,  portions  of 
phosphoru.s,  sulphur,  iron,  silica,  potassa,  lime,  and  other  substances 
of  a like  nature,  may  sometimes  be  detected;  but  their  quantity  is  ex- 
ceedingly minute  when  compared  with  the  principles  above  mentioned. 
In  point  of  composition,  therefore,  most  organic  substances  differ  only 
in  the  proportion  of  their  constituents,  and  on  this  account  may  not  un- 
frequently  be  converted  into  one  another. 

I'he  constitution  of  organic  bodies  is  subject  to  the  general  laws  of 
chemical  union;  but  chemists  are  not  agreed  as  to  the  mode  in  which 
they  conceive  the  elements  to  be  combined.  Berzelius,  for  instance,  is 
of  opinion  that  the  elements  of  organic  substances  do  not  form  binary 
compounds  in  the  same  manner  as  the  constituents  of  inorganic  bodies, 
(page  400,1  but  are  united  indiscriminately  with  each  other.  Thus  al- 
cohol, which  consists  of  three  equivalents  of  hydrogen,  one  of  oxygen, 
and  two  of  carbon,  is  supposed  by  that  chemist  to  consist  of  all  these 
six  equivalents,  combined  directly  with  each  other,  the  oxygen  belong- 
ing as  much  to  the  carbon  as  to  the  hydrogen.  (Annals  of  Philosophy, 
vol.  iv. ) Tliis  opinion,  however,  is  not  universally  adopted.  Gay- 
Lussac,  for  instance,  regards  alcohol  as  a compound  of  olefiant  gas  and 
water,  a view  which  is  not  only  justified  by  the  number  of  equivalents 
contained  in  that  compound,  but  which,  as  I conceive,  harmonizes  with 
the  constitution  of  other  bodies  better  than  that  of  Berzelius.  It  may, 
therefore,  be  admitted  as  probable,  that  the  elements  of  organic  sub- 
stances are  arranged  in  a similar  manner. 

When  org'anic  oubotanoco  arc  heated  to  rcdncss  with  pure  potassa  or 

soda,  they  invariably  yield  alkaline  carbonates;  but  at  a temperature  of 


454 


OUGANIC  CHEmSTRY. 


1 


about  400^  or  450®  F.,  many  of  them  are  decomposed  with  formation 
of  oxalic  acid.  This  lact  has  been  noticed  by  Gay-Lussac,  who  observ- 
ed it^  with  cotton,  sawdust,  sugar,  starch,  gum,  sugar  of  milk,  and 
tartaric,  citric,  and  mucic  acids.  The  other  products  of  course  vary 
with  the  nature  of  the  substance;  but  water  and  acetic  acid  are  general- 
ly formed.  (Quarterly  Journal  of  Science,  N.  S.  vi.  4l5.) 

Organic  substances,  owing  to  the  energetic  affinities  with  which  their 
elements  are  endowed,  are  very  prone  to  spontaneous  decomposition. 
The  prevailing  tendency  of  carbon  and  hydrogen  is  to  appropriate  to 
themselves  so  much  oxygen  as  shall  convert  them  into  carbonic  acid  and 
water;  and  hence,  in  whatever  manner  these  three  elements  may  be 
mutually  combined  in  a vegetable  substance,  they  are  always  disposed 
to  resolve  themselves  into  the  compounds  just  mentioned.  If,  at  the 
tinie  this  change  occurs,  there  is  an  insufficient  supply  of  oxygen  to 
oxidize  the  hydrogen  and  carbon  completely,  then,  in  addition  to  car- 
bonic acid  and  water,  carbonic  oxide  and  carburetted  hydrogen  gases 
will  probably  be  generated.  One  or  both  of  these  combustible  products 
must  in  every  case  be  formed,  except  when  oxygen  is  freely  supplied 
from  extraneous  sources;  because  organic  bodies  are  so  constituted  that 
their  oxygen  is  never  in  sufficient  quantity  for  converting  the  carbon 
into  carbonic  acid,  and  the  hydrogen  into  water. 

If  substances  composed  of  oxygen,  hydrogen,  and  carbon,  are  liable 
to  spontaneous  decomposition,  that  tendency  becomes  much  stronger 
when,  in  addition  to  these  elements,  nitrogen  is  annexed.  Other  and 
powerful  affinities  are  then  superadded  to  those  above  enumerated,  and 
especially  that  of  hydrogen  for  nitrogen.  A body  which  contains  these 
principles  is  peculiarly  liable  to  change,  and  the  usual  products  are  wa- 
ter, carbonic  acid,  and  ammonia;  the  two  latter,  having  a "strong  at- 
traction for  each  other,  being  always  in  combination. 

Another  circumstance  which  is  characteristic  of  organic  products  is 
the  impracticability  of  forming  them  artificially  by  direct  union  of  their 
elements.  Thus  no  chemist  has  hitherto  succeeded  in  causing  oxjgen, 
hydrogen,  and  carbon  to  unite  directly  so  as  to  form  gum  or  sugar. 
When  these  principles  are  made  to  combine  by  chemical  means,  they 
always  give  rise  to  the  production  of  water  and  carbonic  acid. 

Animal  and  vegetable  substances  are  all  decomposed  by  a red  heat, 
and  nearly  all  are  partially  affected  by  a temperature  far  below  ignition. 
When  heated  in  the  open  air,  or  with  substances  which  yield  oxygen 
freely,  they  burn,  and  are  converted  into  water  and  carbonic  acid;  but 
if  exposed  to  heat  in  vessels  from  which  atmospheric  air  is  excluded, 
very  complicated  products  ensue.  A compound  consisting  of  carbon, 
hydrogen,  and  oxygen,  yields  water,  carbonic  acid,  carbonic  oxide, 
carburetted  hydrogen  of  various  kinds,  and  probably  pure  hydrogen. 
Besides  these  products,  some  acetic  acid  is  commonly  generated,  to- 
gether with  a volatile  oil  which  has  a dark  colour  and  burnt  odour, 
and  is  hence  called  empyreumatic  oil.  An  azotized  substance,  in 
addition  to  these,  yields  ammonia,  cyanogen,  and  probably  free  ni- 
trogen. 

From  tlic  foregoing  remarks,  it  appears  that  organic  products  are 
characterized  by  the  following  circumstances: — 1st,  by  being  composed 
of  the  same  elements;  2d,  by  the  facility  with  which  they  undergo 
spontaneous  decomposition;  3d,  by  tlie  impracticability  of  forming  them 
by  the  direct  union  of  their  principles;  and,  4th,  by  being  decomposed 
at  a red  heat. 


ORGANIC  CHEMISTRY. 


455 


Vegetable  Chemistry, 

All  bodies  which  are  of  vegetable  origin  are  termed  vegetable  sub- 
stances. They  are  nearly  pU  composed  of  oxygen,  hydrogen,  and  car- 
bon, and  in  a few  of  them  nitrogen  is  likewise  present.  Every  distinct 
compound  which  exists  ready  formed  in  plants,  is  called  a proximate  or 
immediate  principle  of  vegetables.  Thus  sugar,  starch,  and  gum  are 
proximate  principles.  Opium,  though  obtained  from  a plant,  is  not  a 
proximate  principle;  but  consists  of  several  proximate  principles,  mixed 
more  or  less  intimately  with  each  other. 

The  proximate  principles  of  vegetables  are  sometimes  distributed 
over  the  whole  plant,  while  at  others  they  are  confined  to  a particular 
part.  The  methods  by  which  they  are  procured  are  very  variable. 
Thus  gum  exudes  spontaneously,  and  the  saccharine  juice  of  the  maple 
tree  is  obtained  by  incisions  made  in  the  bark.  In  some  cases  a particular 
principle  is  mixed  with  such  a variety  of  others,  that  a distinct  process 
is  required  for  its  separation.  Of  such  processes  consists  the  proximate 
analysis  of  vegetables.  Sometimes  a substance  is  separated  by  mechan- 
ical means,  as  in  the  preparation  of  starch.  On  other  occasions,  advan- 
tage is  taken  of  the  volatility  of  a compound,  or  of  its  solubility  in 
some  particular  menstruum.  Whatever  method  is  employed,  it  should 
be  of  such  a nature  as  to  occasion  no  change  in  the  composition  of  the 
body  to  be  prepared. 

The  reduction  of  the  proximate  principles  into  their  simplest  parts 
constitutes  their  ultimate  analysis.  By  this  means  chemists  ascertain 
the  quantity  of  oxygen,  carbon,  and  hydrogen  present  in  any  compound. 
The  former  method  of  performing  this  operation  was  by  what  is  termed 
destructive  distillation;  that  is,  by  exposing  the  compounds  to  a red  heat 
in  close  vessels,  and  collecting  all  the  products.  So  many  diflTerent 
substances,  however,  are  procured  in  this  way,  such  as  water,  carbonie 
acid,  carbonic  oxide,  carburetted  hydrogen,  and  the  like,  that  it  is  al- 
most impossible  to  arrive  at  a satisfactory  conclusion.  A more  simple 
and  effectual  method  was  proposed  by  Gay-Lussac  and  Thenard  in  the 
second  volume  of  their  celebrated  Recherches  Physico-chimiques.  The 
object  of  their  process,  which  is  applicable  to  the  ultimate  analysis  of 
animal  as  well  as  vegetable  substances,  is  to  convert  the  whole  of  the 
carbon  into  carbonic  acid,  and  the  hydrogen  into  water,  by  means  of 
some  compound  which  contains  oxygen  in  so  loose  a state  of  combina- 
tion, as  to  give  it  up  to  those  elements  at  a red  heat. 

The  agent  first  employed  by  these  chemists  was  chlorate  of  potassa. 
This  substance,  however,  is  liable  to  the  objection,  that  it  not  only  gives 
oxygen  to  the  substance  to  be  analyzed,  but  is  itself  decomposed  by 
heat.  On  this  account  it  is  now  very  rarely  employed  in  ultimate  ana- 
lysis, peroxide  of  copper,  likewise  proposed  by  Gay-Lussac  and  The- 
nard, having  been  substituted  for  it.  This  oxide,  if  alone,  maybe 
heated  to  whiteness  without  parting  with  oxygen;  whereas  it  yields 
oxygen  readily  to  any  combustible  substance  with  which  it  is  ignited. 
It  is  easy,  therefore,  by  weighing  it  before  and  after  the  analysis,  to 
discover  the  precise  quantity  of  oxygen  which  has  entered  into  union 
with  the  carbon  and  hydrogen  of  'the  substance  submitted  to  examina- 
tion. 

The  ultimate  analysis  of  organic  bodies  is  one  of  the  most  delicate 
operations  with  which  the  analytical  chemist  can  be  engaged.  The 
chief  cause  of  uncertainty  in  the  process  arises  from  the  presence  of 
moisture,  which  is  retained  by  some  animal  and  vegetable  substances 
with  such  force,  that  it  can  be  expelled  only  by  a temperature  which 


456 


ORGANIC  CHEMISTRY. 


endanj^ers  the  decomposition  of  the  compbiind  itself.  The  best  mode 
of  drying  organic  matters  for  the  purpose,  is  by  confining  them  with 
sulphuric  acid  \inder  tlie  exhausted  receiver  of  an  air-pump,  and  ex- 
posing them  at  the  same  time  to  a temperature  of  212®  F. — a method 
adopted  by  Berzelius,  and  for  which  a neat  apparatus  has  been  described 
by  Dr.  Prout.  (Annals  of  Philosophy,  vol.  vi.  p.  272.)  Another  source 
of  difficulty  is  occasioned  by  atmospheric  air  within  the  apparatus, 
owing  to  the  presence  of  which  nitrogen  may  be  detected  in  the  pro- 
ducts, without  having  been  contained  in  the  substance  analyzed. 

But  though  the  ultimiite  analysis  of  organic  substances  is  difficult  in 
practice,  in  theory  it  is  exceedingly  simple.  It  consists  in  mixing  three 
or  four  grains  of  the  body  to  be  analyzed  with  about  two  hundred  grains 
of  peroxide  of  copper,  heating  the  mixture  to  redness  in  a glass  tube, 
and  collecting  the  gaseous  products  in  a graduated  glass  jar  over  mer- 
cury. From  the  quantity  of  carbonic  acid  procured  by  measure,  its 
weight  may  readily  be  inferred  (page  182),  and  from  this,  the  quantity 
of  carbonaceous  matter  may  be  calculated,  by  recollecting  that  every 
22  grains  of  the  acid  contain  16  of  oxygen  and  6 of  carbon. 

In  order  to  ascertain  xhe  quantity  of  hydrogen,  the  gaseous  products 
are  transmitted  through  a tube  filled  with  fragments  of  fused  chloride  of 
calcium,  which  absorbs  all  the  watery  vapour;  and  by  its  increase  in 
weight  indicates  the  precise  quantity  of  that  fluid  generated.  Every  9 
grains  of  water  thus  collected  correspond  to  1 grain  of  hydrogen  and  8 
of  oxygen. 

If  the  quantity  of  oxygen  contained  in  the  carbonic  acid  and  water 
corresponds  precisely  to  that  lost  by  the  oxide  of  copper,  it  follows^  that 
the  organic  substance  itself  was  free  from  oxygen.  But  if,  on  the 
other  hand,  more  oxygen  exists  in  the  products  than,  was  lost  by  the 
copper,  it  is  obvious  that  the  difference  indicates  the  amount  of  oxygen 
contained  in  the  subject  of  analysis. 

If  nitrogen  enters  into  the  constitution  of  the  organic  substance,  it 
will  pass  over  in  the  gaseous  state,  mixed  with  carbonic  acid.  Its  quan- 
tity may  be  ascertained  by  removing  the  carbonic  acid  by  means  of  a 
solution  of  pure  potassa. 

It  need  scarcely  be  observed,  that  if  the  analysis  has  been  successfully 
performed,  the  weight  of  the  different  products,  added  together,  should 
make  up  the  exact  weight  of  the  organic  substance  employed. 

In  analyzing  an  animal  or  vegetable  fluid,  the  foregoing  process  will 
require  slight  modification.  If  the  fluid  is  Of  a fixed  nature,  it  may  be 
made  into  a paste  with  oxide  of  copper,  and  heated  in  the  usual  manner. 
But  if  it  is  volatile,  a given  weight  of  its  vapour  is- conducted  over  per- 
oxide of  copper  heated  to  redness  in  a glass  tube. 

The  constitution  of  vegetable  substances  is  not  yet  sufficiently  known 
to  admit  of  their  being  classified  in  a purely  scientific  order.  l*he 
chief  data  hitherto  furnished  towards  forming  a systematic  arrangement 
are  derived  from  a remarkable  agreement  between  the  composition  and 
general  properties  of  several  vegetable  compounds,  first  noticed  by 
Gay-Lussac  and  Thenard.  (llecherches,  vol.  ii.)  From  the  ultimate 
analysis  of  a considerable  variety  of  proximate  principles,  these  chemists 
draw  the  three  following  conclusions: — 1st,  A veg'etable  substance  is  al- 
ways acid,  when  it  contains  more  than  a sufficient  quantity  of  o^xygen  for 
converting  all  its  hydrogen  into  water;  2dly,  It  is  always  resinous,  oily, 
or  alcoholic,  S<,c.  when  it  contains  less  than  a sufficient  quantity  of  oxy- 
gen for  combining  with  the  hydrogen;  and,  3dly,  it  is  neither  acid  nor 
resinous,  but  in  a state  analogous  to  sugar,  gum,  starch,  or  the  woody 
fibre,  when  the  oxygen  and  hydrogen,  which  it  contains,  are  in  the 
exact  proportion  for  lorming  water.  'I'hese  laws,  indeed,  are  not  rigidly 


VEGETABLE  ACIDS. 


457 


exact,  nor  do  they  include  the  vep^etable  products  containing*  nitrogen? 
but  for  want  of  a better  principle  of  classification,  I shall  follow  M. 
Thenard  in  making  them,  to  a certain  extent,  the  basis  of  my  arrange- 
ment. The  proximate  principles  of  plants  will  accordingly  be  arranged 
in  five  divisions.  The  first  includes  the  vegetable  acicjs;  the  second 
vegetable  alkalies;  the  third  comprises  those  substances  which  contain 
an  excess  of  hydrogen;  the  fourth  includes  tliose,  the  oxygen  and  hy- 
drogen of  which  are  in  proportion  for  forming  water;  and  the  fifth  com- 
prehends those  bodies  which,  so  far  as  is  known,  do  not  belong  to^either 
of  the  other  divisions. 


SECTION!., 

VEGETABLE  ACIDS. 

Those  compounds  are  regarded  as  vegetable  acids  which  possess  the 
properties  of  an  acid,  and  are  derived  from  the  vegetable  kingdom. 
These  acids,  like  all  organic  principles,  are  decomposed  by  a red  heat. 
They  ave  in  general  less  liable  to  spontaneous  decomposition  than  othe;* 
vegetable  substances;  a circumstance  which  probably  arises  from  the 
large  proportion  of  oxygen  which  the}’^  contain.  They  are  nearly  all 
decomposed  by  concentrated  hot  nitric  acid,  by  which  they  are  con- 
verted into  carbonic  acid  and  water. 

Jlcetic  Acid, 

Acetic  acid  exists  ready  formed  in  the  sap  of  many  plants,  either  free 
or  combined  with  lime  or  potassa;  it  is  generated  during  the  destructive 
distillation  of  vegetable  matter,  and  is  an  abundant  product  of  the 
acetous  fermentation. 

Common  vinegar,  the  acidifying  principle  of  which  is  acetic  acid,  is 
commonly  prepared  in  this  country  by  fermentation  from  an  infusion  of 
malt,  and  in  Trance  from  the  same  process  taking  place  in  weak  wine. 
Vinegar,  thus  obtained,  is  ^a  very  impure  acetic  acid,  containing  the 
saccharine,  mucilaginous,  glutinous,  and  other  matters  existing  in  the 
fluid  from  which  it  is  prepared.  It  is  separated  from  these  impurities 
by  distillation.  Distilled  vinegar  was  formerly  called  acetous  acidf  on 
the  supposition  of  its  differing  chemically  from  strong  acetic  acid;  but 
it  is  now  admitted  that  distilled  vinegar  is  real  acetic  acid  merely  diluted 
with  water,  and  commonly  containing  a small  portion  of  einpyreu- 
matic  oil,  formed  during  the  distillation.,  and  from  which  it  receives  a 
peculiar  flavour.  It  may  be  rendered  stronger  by  exposure  to  cold, 
when  a considerable  part  of  the  water  is  frozen,  while  the  acid  remains 
liquid. 

The  distilled  vinegar,  which  is  now  generally  employed  for  chemical 
purposes,  is  prepared  by  the  distillation  of  wood,  and  is  sold  under  the 
name  of  pyroligneous  acid.  When  first  made  it  is  very  impure,  and  of 
a dark  colour,  holding  in  solution  tar  and  volatile  oil.  In  this  state  it  is 
mixed  with  chalk,  and  obtained  in  the  state  of  acetate  of  lime,  which 

39 


458 


VEGETABLE  ACIDS. 


is  decomposed  by  dig-estion  with  sulphate  of  soda:  the  resulting-  acetate 
of  soda  is  then  fused  at  a high  temperature,  insufficient  to  decompose 
the  salt,  but  sufficient  to  expel  or  char  the  impurities.  Tlie  acetate  of 
soda  is  thus  obtained  pure  and  in  crystals,  and  is  decomposed  by  sul- 
phuric acid. 

Concentrated  acetic  acid  is  best  obtained  by  decomposing  the  acetates 
either  by  sulphuric  acid,  or  in  some  instances  by  heat.  A convenient 
process  is  to  distil  acetate  of  potassa  with  half  its  weight  of  concentrat- 
ed sulphuric  acid,  the  recipient  being  kept  cool  by  the  application  of 
ice.  Tlie  acid  is  at  first  contaminated  with  sulphurous  acid;  but  by 
mixing  it  with  a little  peroxide  of  manganese,  and  redistilling,  it  is 
rendered  quite  pure.  A strong  acid  may  likewise  be  procured  from 
binacetate  of  copper  by  the  sole  action  of  heat.  The  acid  when  first 
collected  has  a greenish  tint,  owing  to  the  presence  of  copper,  from 
which  it  is  freed  by  a second  distillation.  The  density  of  the  product 
varies  from  1.056  to  1.08,  the  lightest  acid  being  procured  towards 
the  end  of  the  process.  MM.  Derosnes,  indeed,  have  remarked  that 
the  liquid  which  passes  over  towards  the  end  of  the  process  is  lighter 
than  water,  and  contains  very  little  acetic  acid.  On  neutralizing  the 
latter  with  pure  solid  potassa,  and  distilling  by  a gentle  heat,  they 
procured  an  ethereal  fluid,  to  which  they  applied  the  term  of  pyro-acetic 
ether,  • 

Strong  acetic  acid  is  exceedingly  pungent,  and  even  raises  a blister  ' 
when  kept  for  some  time  in  contact  with  the  skin.  It  has  a very  sour 
taste  and  an  agreeable  refreshing  odour.  Its  acidity  is  well  marked,  as 
it  reddens  litmus  paper  powerfully,  and  forms  neutral  salts  with  the 
alkalies.  It  is  exceedingly  volatile,  rising  rapidly  in  vapour  at  a mod- 
erate temperature  without  undergoing  any  change.  Its  vapour  is  in- 
flammable, and  burns  with  a white  light.  In  its  most  concentrated  form 
it  is  a definite  compound  of  one  equivalent  of  water,  and  one  equiva- 
lent of  acid;  and  in  this  state  it  crystallizes  when  exposed  to  a low  tem- 
perature, retaining  its  solidity  until  the  thermometer  rises  to  ^50®  F.  It 
is  decomposed  by  being  passed  through  red-hot  tubes;  but  owing  to  its 
volatility,  a larg-e  quantity  of  it  escapes  decomposition. 

Dr.  Front  has  established  the  singular  fact,  relative  to  the  constitution 
of  this  acid,  that  its  oxygen  and  hydrogen  are  in  exact  proportion  to 
form  water,*  and  that  it  contains  47.05  per  cent,  of  carbon.  (Phil. 
Trans.  1827,  355.)  It  may  hence  be  inferred  to  consist  of  24  parts  or 
four  equivalents  of  carbon,  24  parts  or  three  equivalents  of  oxygen, 
and  three  of  hydrogen.  This  would  make  the  combining  proportion  of 
acetic  acid  51,  instead  of  50  as  stated  by  Dr.  Thomson. 

The  only  correct  mode  of  estimating  the  strength  of  acetic  acid  is 
by  its  neutralizing  power.  Its  specific  gravity  is  no  criterion,  as  will 
appear  from  the  following  table.  (Thomson’s  First  Principles,  vol.  ii. 
p.  135.) 


* Gay-Lussac  and  Thcnard  established  this  fact  as  nearly  as  possible, 
by  their  analysis  of  acetic  acid,  reported  in  their  llecherches  Physico- 
chim'Kjues.  'Jdic  ])ropoitions  of  oxygen  and  hydrogen  which  they  ob- 
tained are  very  nearly  in  the  ratio  to  form  water.  It  is  true  that  Thenard 
in  his  TraiU  gives  the  ox3'gen  as  if  in  excess;  but  this  statement  is 
evidently  made  up  in  accordance  with  a former  ratio  for  the  composi- 
tion of  water,  which  is  not  at  ])rc.scnt  admitted  by  the  French  chemist 
himself.  Thcnardy  Traitd  dc  Chimle,  Seme  ^dilioiiy  tom,  hi.  p,  598.  B. 


VEGETABLE  ACIDS. 


459 


Talk  exhibiting  the  Density  of  Acetic  Acid  of  different  Strengths, 


sp.gr.  at  60®  F, 


Acid.  Water. 


1.06296 

1.07060 

1.07084 

1.07132 

1.06820 

1.06708 

1.06349 

1.05974 

1.05794 

1.05439 


1 atom  + 1 atom 


1 4-6 

1 4-^7' 

1 4-8 

1 +9 

1 4-10 


The  acetic  is  distinguished  from  all  other  acids  by  its  flavour,  odour, 
and  volatility.  Its  salts,  which  are  called  acetates,  are  all  soluble  in  hot 
and  most  of  them  in  cold  water,  are  destroyed  by  a high  temperature, 
and  are  decomposed  by  sulphuric  acid. 

Acetate  of  Potassa. — This  salt  is  made  by  neutralizing  carbonate  of 
potassa  with  acetic  acid,  or  by  decomposing  acetate  of  lime  with  sul- 
phate of  potassa.  When  cautiously  evaporated  it  forms  irregular  crys- 
tals, which  are  obtained  with  difficulty  owing  to  the  deliquescent  pro- 
perty of  the  salt.  According  to  Dr.  Thomson,  the  crystals  are  com- 
posed of  one  equivalent  of  neutral  acetate  of  potassa,  and  two  equiva- 
lents of  water.  It  is  commonly  prepared  for  pharmaceutic  purposes  by 
evaporating  the  solution  to  dryness,  and  heating  the  residue  so  as  to 
cause  the  igneous  fusion.  On  cooling  it  becomes  a white  crystalline 
foliated  mass,  which  is  generally  alkaline. 

This  salt  is  highly  soluble  in  water,  and  requires  twice  its  weight  of 
boiling  alcohol  for  solution. 

Dr.  Thomson  procured  a binacetate  by  mixing  acetic  acid  and  car- 
bonate of  potassa  in  the  proportion  of  two  equivalents  of  the  former  to 
one  of  the  latter.  On  confining  the  solution  along  with  sulphuric  acid 
under  the  exhausted  receiver  of  an  air-pump,  the  binacetate  was  de- 
posited in  large  transparent  flat  plates.  The  crystals  contain  six  equiv- 
alents of  water,  and  deliquesce  rapidly  on  exposure  to  the  air. 

Acetate  of  soda  is  prepared  in  large  quantity  by  manufacturers  of 
pyroligneous  acid  by  neutralizing  the  impure  acid  with  chalk,  and  then 
decomposing  the  acetate  of  lime  by  sulphate  of  soda.  It  crystallizes 
readily  by  gentle  evaporation,  and  its  crystals,  which  are  not  deliquesr 
cent,  are  composed  of  50  parts  or  one  equivalent  of  acetic  acid,  32  parts 
or  one  equivalent  of  soda,  and  54  parts  or  six  equivalents  of  water. 
(Berzelius  and  Thomson.)  The  form  of  its  crystals  is  very  complicated, 
and  derived  from  an  oblique  rhombic  prism.  (Brooke.)  When  heated 
to  550®  F.  it  is  deprived  of  its  water,  and  undergoes  the  igneous  fusion 
without  parting  with  any  of  its  acid.  At  600®  F.  decomposition  takes 
place. 

Acetate  of  soda  is  much  employed  for  the  preparation  of  concentrated 
acetic  acid. 

Acetate  of  ammonia  is  made  by  neutralizing  carbonate  of  ammonia 
with  acetic  acid.  It  crystallizes  with  difficulty  in  consequence  of  being 
deliquescent  and  highly  soluble.  It  has  been  long  used  in  medicine  as 
a febrifuge  under  the  name  of  spirit  of  Mindererus. 

^ The  acetates  of  baryta,  strontia,  and  lime  are  of  little  importance. 
The  former,  which  is  occasionally  employed  as  a reagent,  crystallizes 
in  irregular  six-sided  prisms  terminated  by  dihedral  summits,  the  pri- 
mary form  of  \\^hich  is  a right  rhoinboidal  prism.,  The  latter  crystallizes 


460 


VEGETABLE  ACIDS. 


in  very  slender  acicular  crystals  of  a silky  lustre,  and  is  chiefly  em- 
ployed  in  the  preparation  of  acetate  of  soda. 

Acetate  of  alumina  is  formed  by  adding*  acetate  of  lead  to  sulphate  of 
alumina,  when  the  sulphate  of  lead  subsides  and  acetate  of  alumina  re- 
mains in  solution.  It  is  used  by  dyers  and  calico-printers  as  a basis  or 
mordant. 

Acetate  of  Lead. — This  salt,  long*  known  by  the  names  of  sugar  of 
lead  {saccharvm,  Saturni)  and  cerussa  acetata^  is  made  by  dissolving 
either  carbonate  of  lead  or  litharge  in  distilled  vinegar.  The  solution 
has  a sweet,  succeeded  by  an  astringent  taste,  does  not  redden  litmus 
paper,  and  deposites  shining  acicular  crystals  by  evaporation.  When 
more  regularly  crystallized  it  occurs  in  six-sided  prismatic  crystals, 
cleavable  parallel  to  the  lateral  and  terminal  planes  of  a right  rhombic 
prism,  which  maybe  regarded  as  its  primary  form.  (Mr.  Brooke.)  The 
crystals  effloresce  slowly  by  exposure  to  the  air,  and  require  about  four 
times  their  weight  of  water  at  60®  F.  for  solution.  They  are  composed, 
according  to  Berzelius  and  Thomson,  of  50  parts  or  one  equivalent  of 
the  acid,  112  parts  or  one  equivalent  of  protoxide  of  lead,  and  27  parts 
or  three  equivalents  of  water. 

Acetate  of  lead  is  partially  decomposed,  with  formation  of  car- 
bonate of  lead,  by  water  which  contains  carbonic  acid,  or  by  exposure 
to  the  air;  but  a slight  addition  of  acetic  acid  renders  the  solution  quite 
clear. 

This  salt  is  much  used  in  the  arts,  in  medical  and  surgical  practice  as  a 
sedative  and  astringent,  and  in  chemistry  as  a reagent. 

Subacetate  of  lead,  commonly  called  extmetum  Saturni^  is  prepared 
by  boiling  one  part  of  the  neutral  acetate,  and  two  parts  of  litharge, 
deprived  of  carbonic  acid  by  heat,  with  twenty-five  parts  of  water. 

This  salt  is  less  sweet  and  less  soluble  in  water  than  the  neutral  ace- 
tate, has  an  alkaline  reaction,  and  crystallizes  in  white  plates  by  evapor- 
ation. It  is  decomposed  by  a current  of  carbonic  acid,  with  production 
of  pure  carbonate  of  lead;  and  forms  a turbid  solution,  owing  to  the 
formation  of  a carbonate,  when  it  is  mixed  with  water  in  which  carbonic 
acid  is  present.  It  appears  from  the  analysis  of  Berzelius  to  consist  of 
one  equivalent  of  acid  and  three  equivalents  of  oxide  of  lead,  and  is, 
therefore,  a trisacetate. 

A diacetate  may  likewise  be  formed  by  boiling  with  water  a mixture  of 
litharge  and  acetate  of  lead  in  atomic  proportion.  (Thomson.) 

Acetate  of  Copper. — The  pigment  called  verdigris,  which  is  an  impure 
acetate  of  peroxide  of  copper,  may  be  formed  by  exposing  metallic 
copper  to  the  vapour  of  vinegar,  when  the  metal  gradually  absorbs 
oxygen  from  the  atmosphere,  and  then  unites  with  the  acid.  It  is  pre- 
pared in  large  quantity  in  the  south  of  France  by  covering  copperplates 
with  the  refuse  of  the  grape  after  the  juice  has  beem  extracted  for  mak- 
ing wine  The  saccharine  matter  contained  in  the  husks  furnishes  acetic 
acid  by  fermentation,  and  in  four  or  six  weeks  the  plates  acquire  a coat- 
ing of  the  acetate. 

Verdigris  is  commonly  of  a pale  green,  but  sometimes  of  a blue 
colour.  Its  essential  constituent  is  an  acetate  of  copper,  composed, 
according  to  Mr.  Fliillips,'^  of  80  parts  or  one  equivalent  of  peroxide 
of  cop|)er,  50  parts  or  one  equivalent  of  acetic  acid,  and  six  equiva- 
lents of  water.  'I  hls  compound  is  decomposed  by  water,  and  is  con- 
verted into  an  insoluble  green  diacctatc,  and  into  a soluble  hinacetate  of 
copper,  'fhe  former,  as  its  name  implies,  consists  of  one  equivalent 


Annals  of  Fhilosophy,  N,  S.  yol,  i.  ii.  and  iy, 


VEGETABLE  ACIDS. 


f <61 

of  acid  and  two  equivalents  of  the  oxide.  The  binacetate  crystallizes 
readily  in  rhombic  octohedrons  of  a g'reen  colour,  and  is  soluble  in 
twenty  times  its  weight  of  cold,  and  five  of  boiling  vvater.  It  is  con- 
veniently prepared  by  dissolving  verdigris  in  distilled  vinegar,  and  eva- 
porating the  solution.  The  crystals  consist  of  t\yo  equivalents  of  acid 
and  one  equivalent  of  peroxide  of  copper,  combined,  according  to  Mr. 
Phillips  with  three,  and  according  to  Berzelius  and  Dr.  Ure  with  two 
equivalents  of  water. 

Besides  these  compound^  Berzelius  has  described  three  other  ace- 
tates of  copper;  but  as  they  are  of  little  importance,  I refer  the  reader 
to  the  original  paper  on  the  subject.  (Annals  of  Philosophy,  N.  S.  vol. 
viii.) 

Acetate  of  Zinc. — This  salt  may  be  prepared  by  way  of  double  decom- 
position by  mixing  sulphate  of  zinc  with  acetate  of  lead  in  equivalent 
proportions.  When  made  in  this  way  it  is  very  apt  to  retain  some  sul- 
phate of  lead  in  solution.  The  best  mode  of  obtaining  it  quite  pure,  is 
by  suspending  metallic  zinc  in  a dilute  solution  of  acetate  of  lead,  until 
all  the  lead  is  removed.  (Page  37'4,)  This  is  known  to  be  accomplished 
by  the  addition  of  sulphuretted  hydrogen,  which  then  occasions  a pure 
white  precipitate.  This  salt  is  frequently  employed  as  an  astringent 
collyrium. 

Acetate  of  Mercury  .—The  only  interesting  compound  of  mercury  and 
acetic  acid  is  the  acetate  of  the  protoxide,  which  is  sometimes  employ- 
ed in  the  practice  of  medicine.  It  is  prepared  by  mixing  crystallized 
protonitrate  of  mercury  with  neutral  acetate  of  potassa  in  the  ratio  of 
one  equivalent  of  each.  If  both  salts  are  dissolved  in  a considerable 
quantity  of  hot  water,  the  solutions  retain  their  transparency  after  being 
mixed;  but  on  cooling,  the  protacetate  of  mercury  is  deposited  in  white 
scales'of  a silky  lustre.  It  is  easily  decomposed;  and  it  should  be  dried 
by  a very  gentle  heat,  and  washed  with  cold  water  slightly  acidulated 
with  acetic  acid. 

Oxalic  Acid. 

Oxalic  acid  exists  ready  formed  in  several  plants,  especially  in  the 
rumex  aceiosa  or  common  sorrel,  and  in  the  oxalis  acetosella  or  wood 
sorrel;  but  it  almost  always  occurs  in  combination  either  with  lime  or 
potassa.  These  plants  contain  binoxalate  of  potassa;  and  the  oxalate  of 
lime  has  been  found  in  large  quantity  by  M.  Braconnot  in  several  species 
of  lichen. 

Oxalic  acid  is  easily  made  artificially  by  digesting  sugar  in  five  or  six 
times  its  weight  of  nitric  acid,  and  expelling  the  excess  of  that  acid  by 
distillation,  until  a fluid  of  the  consistence  of  syrup  remains  in  the  re- 
tort. The  residue  in  cooling  yields  crystals  of.  oxalic  acid,  the  weight 
of  which  amounts  to  rather  more  than  half  the  quantity  of  the  sugar 
employed.  They  should  be  purified  by  repeated  solution  in  pure  water, 
and  re-crystallization;  for  they  are  very  apt  to  retain  traces  of  nitric 
acid,  the  odour  of  which  becomes  obvious  when  the  crystals  are  heat- 
ed. In  the  conversion  of  sugar  into  oxalic  acid,  changes  of  a very  com- 
plicated nature  ensue,  during  which  a portion  of  nitric  acid  is  resolved, 
chiefly,  into  oxygen  and  de\*toxide  of  nitrogen,  while  the  sugar  is  con- 
verted, with  formation  of  carbonic  acid  and  water,  into  oxadic  acid.  A 
small  quantity  of  malic  and  acetic  acids  are  generated  at  the  same  time. 
As  oxalic  acid  does  not  contain  any  hydrogen,  and  has  a smaller  propor- 
tional quantity  of  carbon  than  sugar,  there  can  be  no  doubt  that  the 
production  of  this  acid  essentially  depends  upon  the  sugar  being  de- 
prived of  all  its  hydrogen  and  a portion  of  its  carbon  by  oxygen  derived 
from  the  nitric  acid. 


462 


VEGETABLE  ACIDS. 


Many  org'anic  substances  besides  sugar,  such  as  starch,  giim,  most  of 
the  vegetable  acids,  wool,  hair,  and  silk,  are  converted  iilto  oxalic  by 
the  action  of  nitric  acid;— a circumstance  which  is  explicable  on  the 
fact  that  oxalic  acid  contains  more  oxygen  than  any  other  principle, 
whether  of  animal  or  vegetable  origin.  It  is  also  generated  by  heating 
organic  substances  with  potassa.  (Page  454.) 

Oxalic  acid  crystallizes  in  slender,  flattened,  four  and  six  sided  prisms 
teminated  by  two  sided  summits;  but  their  primary  form  is  an  oblique 
rhombic  prism.  It  has  an  exceedingly  sour  reddens  litmus  paper 
strongly,  and  forms  neutral  salts  with  alkalies.  The  crystals  undergo 
no  change  in  ordinary  states  of  the  air,  but  when  the  atmosphere  is 
very  dry,  slight  efflorescence  ensues.  They  are  soluble  without  limit 
in  boiling  water,  and  according  to  Christison  in  eleven  times  their 
weight  of  cold  water;  but  the  solubility  is  increased  by  the  presence  of 
nitric  acid.  They  are  dissolved  also  by  alcohol,  though  less  freely  than 
in  water.  They  contain  rather  more  than  42  percent,  of  water  of  crys- 
tallization, part  of  which  only,  amounting  to  about  28  per  cent.,  can 
be  expelled  by  heat  without  decomposing'the  acid  itself. 

The  atomic  weight  of  oxalic  acid,  as  determined  by  Dr.  Thomson,  is 
precisely  36;  and  the  crystals  consist  of  36  parts  or  one  equivalent  of 
real  acid,  and  27  parts  or  three  equivalents  of  water.  (Berzelius  and 
Prout.)  It  differs  in  composition  from  nearly  all  other  vegetable  acids 
in  containing  noliydrogen,  the  absence  of  which  seems  fully  establish- 
ed by  the  analyses  of  Berzelius,  Thomson,  and  Ure.  From  the  re- 
searches of  these  chemists,  oxalic  acid  is  composed  of  one  part  of  car- 
bon and  two  parts  of  oxygen;  and  since  its  equivalent  is  36,  it  must  be 
regarded  as  a compound  of 

Carbon,  12  two  equiv.  Carbonic  oxide,  14  . one  equiv. 

Oxygen,  24  three  equiv.  y ’ Carbonic  acid,  22  . one  equiv. 


It  is,  therefore,  intermediate  between  carbonic  oxide  and  carbonic 
acid;  and,  as  is  obvious  from  the  numbers  above  stated,  it  may  be  re- 
garded as  a compound  of  these  gases.  Consistently  with  this  view, 
Dobereiner  found  that  oxalic  acid  is  converted  into  carbonic  acid  and 
carbonic  oxide  by  the  action  of  a very  large  excess  of  fuming  sulphuric 
acid.  (An.  de  Ch.  et  de  Ph.  xix.)  The  experiment  succeeds  so  readily 
with  common  oil  of  vitriol,  that  I habitually  prepare  carbonic  oxide  by 
this  process. 

Oxalic  acid  is  one  of  the  most  powerful  and  rapidly  fatal  poisons 
which  we  possess;  and  frequent  accidents  have  occurred  from  its  being 
sold  and  (aken  by  mistake  for  Epsom  salt,  with  the  appearance  of  which 
its  crystals  have  some  resemblance.  These  substances  may  be  easily 
distinguished,  however,  by  the  strong  acidity  of  oxalic  acid,  which 
may  be  tasted  witliout  danger,  while  sulphate  of  mag'nesia  is  quite  neu- 
tral, and  has  a bitter  saline  taste.  In  cases  of  poisoning  with  this  acid, 
chalk  mixed  witli  water  should  be  administered  as  an  antidote,  an  in- 
soluble oxalate  being  formed,  which  is  inert.  Chalk  was  first  suggest- 
ed for  this  purpose  by  my  colleague.  Dr.  A.  T.  Thomson,  and  his  opin- 
ion has  been  since  fully  confirmed  by  the  experiments  of  Drs'.  Christison 
and  Coindet,  who  have  recommended  the  use  of  magnesia  with  the 
same  intention.  (Christison  on  Poisons,  140.) 

Oxalic  acid  is  easily  distinguished  from  all  other  acids  by  the  form  of 
its  crystals,  and  by  its  solution  giving  with  lime-water  a white  precipitate 
which  is  insoluble  in  an  excess  of  the  acid. 

The  salts  of  oxalic  acid  are  termed  oxalates.  Most  of  these  compounds 


VEGETABLE  ACIDS. 


463 


are  either  insoluble  or  sparini^ly  soluble  in  water;  but  they  are  all  dis- 
solved by  tl^e  nitric,  and  also  by  muriatic  acid,  except  when  the  latter 
precipitates  the  base  of  the  salts.  The  only  oxalates  which  are  remark- 
able for  solubility  are  those  of  potassa,  soda,  lithia,  ammonia,  alumina, 
and  iron. 

A soluble  oxalate  is  easily  detected  by  adding*  to  its  solution  a neutral 
salt  of  lime  or  lead,  when  a white  oxalate  of  those  bases  will  be  thrown 
down.  On  digesting  the  precipitate  in  a little  sulphuric  acid,  an  insolu- 
ble sulphate  is  formed,  and  the  solution  yields  crystals  of  oxalic  acid  on 
cooling.  All  insoluble  oxalates,  the  bases  of  which  form  insoluble  com- 
pounds with  sulphuric  acid,  may  be  decomposed  in  a similar  manner. 
All  other  insoluble  oxalates  may  be  decomposed  by  potassa,  by  which 
means  a soluble  oxalate  is  procured. 

The  oxalates,  like  all  salts  which  contain  a vegetable  acid,  are  decom- 
posed by  a red  heat,  a carbonate  being  left,  provided  the  oxide  can  re- 
tain carbonic  acid  at  the  temperature  which  is  employed.  As  oxalic 
acid  is  so  highly  oxidized,  its  salts  leave  no  charcoal  when  heated  in 
close  vessels. 

Several  oxalates  are  reduced  to  the  metallic  state,  with  evolution  of 
pure  carbonic  acid,  when  heated  to  redness  in  close  vessels.  (Pages  340 
and  342.)  The  peculiar  constitution  of  oxalic  acid  accounts  for  this 
change;  for  one  equivalent  of  the  acid,  to  be  converted  into  carbonic 
acid,  requires  precisely  one  equivalent  of  oxygen,  which  is  the  exact 
quantity  contained  in  the  oxide  of  a neutral  protoxalate. 

Oxalates  of  Potassa. — Oxalic  acid  forms  with  potassa  three  compounds, 
of  which  the  description  was  given,  and  the  composition  determined, 
in  the  year  1808  by  Dr.  Wollaston.  (Philos.  Trans,  for  1808.)  The  first 
is  the  neutral  oxalate  which  is  formed  by  neutralizing  carbonate  of  po- 
tassa with  oxalic  acid.  It  crystallizes  in  oblique  quadrangular  prisms, 
which  have  a cooling  bitter  taste,  require  about  twice  their  weight  of 
water,  at  60^  F.  for  solution,  and  contain  36  parts  or  one  equivalent  of 
oxalic  acid,  48  parts  or  one  equivalent  of  potassa,  and  one  equivalent  of 
water.  I'his  salt  is  much  employed  as  a reagent  for  detecting  lime. 
Binoxalate  of  potassa  is  contained  in  sorrel,  and  may  be  procured  from 
that  plant  by  solution  and  crystallization.  It  crystallizes  readily  in 
small  rhomboids,  which  are  less  soluble  in  water  than  the  neutral  oxa- 
late. It  is  often  sold  under  the  name  of  essential  salt  of  lemons  for  re- 
moving iron  moulds  from  linen;  an  effect  which  it  produces  by  one 
equivalent  of  its  acid  uniting  with  the  oxide  of  iron  and  forming  a so  - 
uble  oxalate.  The  third  salt  contains  twice  as  much  acid  as  the  prece- 
ding compound,  and  has  hence  received  the  name  of  quadroxalate  of 
potassa.  It  is  the  least  soluble  of  these  salts,  and  is  formed  by  digest 
ing  the  binoxalate  in  nitric  acid,  by  which  it  is  deprived  of  one-half  of 
its  base.  It  is  composed  of  four  equivalents  of  acid,  one  of  potassa, 
and  seven  of  water. 

Oxalate  of  soda,  which  may  be  made  in  the  same  manner  as  oxalate  of 
potassa,  is  very  rarely  employed,  and  is  of  little  importance.  It  like- 
wise forms  a binoxalate,  but  no  quadroxalate  is  known. 

Oxalate  of  ammonia,  prepared  by  neutralizing  that  alkali  with  oxalic 
acid,  is  much  used  as  a reagent.  Jt  is  very  soluble  in  hot  water,  and  is 
deposited  in  acicular  crystals  when  a saturated  hot  solution  is  allowed  to 
cool.  The  crystals  contain  two  equivalents  of  water.  Dr.  Thomson 
has  likewise  described  a binoxalate  of  ammonia,  which  is  less  soluble 
than  the  preceding  and  contains  three  equivalents  of  water. 

Oxalate  of  Lime* — ^This  salt,  like  all  the  insoluble  oxalates,  is  easily 
prepared  by  way  of  double  decomposition.  It  is  a white  finely  divided 
powder,  which  is  remarkable  for  its  extreme  insolubility  in  pure  water. 
On  this  account  a soluble  oxalate  is  an  exceedingly  delicate  test  fot 


464 


VEGETABLE  ACIDS. 


lime.  It  is  soluble,  however,  In  muriatic  and  nitric  acids.  It  is  com- 
posed of  vS6  parts  or  one  ecjuivalent  of  the  acid,  and  28  parts  or  one 
equivalent  of  lime.  It  may  be  exposed  to  a temperature  of  560°  F. 
without  decomposition,  and  is  then  quite  anliydrous.  No  binoxalate  of 
lime  is  known. 

This  salt  is  interesting  in  a pathological  point  of  view,  because  it  is  a 
frequent  ingredient  of  urinary  concretions.  It  is  the  basis  of  what  is 
called  the  mulberry  calculus. 

Oxalate  of  Magnesia. — This  salt  may  be  prepared  by  mixing  oxalate 
of  ammonia  with  a hot  concentrated  solution  of  sulphate  of  magnesia. 
It  is  a white  ])Owdcr,  which  is  very  sparingly  soluble  in  water;  but, 
nevertheless,  when  sulphate  of  magnesia  is  moderately  diluted  with  cold 
water,  oxalate  of  ammonia  occasions  no  precipitate.  On  tliis  fact  is 
founded  the  best  analytic  process  for  separating  lime  from  magnesia. 

Tartaric  field. 

This  acid  exists  in  the  juice  of  several  acidulous  fruits,  but  it  is  almost 
always  in  combination  with  lime  or  potassa.  It  is  prepared  by  mixing 
intimately  198  parts  or  one  equivalent  of  cream  of  tartar,  in  fine  pow- 
der, with  50  parts  or  one  equivalent  of  chalk,  and  tlirowing  the  mixture 
by  small  portions  at  a time  into  ten  times  its  w^eiglit  of  boiling  water. 
On  each  addition  brisk  effervescence  ensues,  owing  to  the  escape  of  car- 
bonic acid,  and  one  equivalent  of  the  insoluble  tartrate  of  lime  subsides; 
while  one  equivalent  of  the  neutral  tartrate  of  potassa  is  held  in  solu- 
tion. On  washing  the  former  wdtli  water,  and  then  digesting  'it,  dif- 
fused through  a moderate  ]mrtion  of  w'ater,  with  one  equivalent  of 
sulphuric  acid,  the  tartaric  acid  is  set  free;  and  after  being  separated 
from  the  sulphate  of  lime  by  a filter,  may  be  procured  by  evaporation 
in  prismatic  crystals,  the  primary  form  of  which  is  a right  rhombic 
prism. 

Tartaric  acid  has  a sour  taste,  wdiich  is  very  agreeable  when  diluted 
with  water.  It  reddens  litmus  paper  strongly,  and  forms  with  alkalies 
neutral  salts,  to  which  the  name  of  tartrates  is  applied.  It  requires  five 
or  six  times  its  W’'eight  of  w^ater  at  60°  for  solution,  and  is  much  more 
soluble  in  boiling  water.  It  is  dissolved  likewise,  though  less  freely,  in 
alcohol.  The  aqueous  solution  is  gradually  decomposed  by  keeping, 
and  a similar  cliange  is  experienced  under  the  same  circumstances  by 
most  of  the  tartrates.  The  crystals  may  be  exposed  to  the  air  without 
change.  They  are  converted  into  the  oxalic  by  digestion  in  nitric  acid. 
When  heated  in  close  vessels,  it  fuses,  froths  up,  and  is  decomposeeb 
yielding,  in  addition  to  the  usual  products  of  destructive  distillation,  a 
distinct  acid  to  which  the  name  of  pyrotartaric  acid  is  applied.  A con- 
siderable quantity  of  charcoal  remains. 

q'lie  atomic  weight  of  tartaric  acid,  inferred  by  Dr.  Thomson  from 
the  tartrates  of  potassa  and  lead,  is  66;  and  the  crystals,  wdiich  cannot 
be  deprived  of  their  water  by  heat  without  decomposition,  consist  of 
66  parts  or  one  equivalent  of  acid,  and  one  equivalent  of  water.  Ac- 
cording to  tlie  analysis  of  Dr.  Front  and  Dr.  Thomson,  wliich  agrees 
pretty  closely  with  tliat  of  Berzelius,  the  acid  itself  is  comj)osed  of 
Carbon  . . .24  or  four  equivalents, 

Oxygen  . . .40  or  five  equivalents, 

Hydrogen  ...  2 or  two  equivalents. 

66 

Tartaric  acid  is  distinguished  fi’om  other  acids  by  forming  a white 
precipitate,  l)ilartratc  of  [)otassa,  when  mixed  with  any  of  the  salts  of 
that  alkali.  'I’his  acid,  therefore,  separates  potassa  from  every  other 


VEGETABLE  ACIDS. 


465 


acid.  It  occasions  with  lime-water  a white  precipitate,  which  is  very 
soluble  in  an  excess  of  the  acid. 

Tartaric  acid  is  remarkable  forks  tendency  to  form  double  salts,  the 
properties  of  which  are  often  more  interesting  than  the  simple  salts. 
The  most  important  of  these  double  salts,  and  the  only  ones  which 
have  been  much  studied,  are  tartrate  of  potassa  and  soda,  and  tartrate 
of  antimony  and  potassa.  I'he  neutral  tartrates  of  the  alkalies,  of  mag- 
nesia, and  copper,  are  soluble  in  water;  but  most  of  the  tartrates  of  the 
other  bases,  and  especially  those  of  lime,  baryta,  strontia,  and  lead,  are 
insoluble.  All  these  neutral  tartrates,  however,  which  are  insoluble  in 
pure  water,  are  soluble  in  an  excess  of  their  acid.  They  are  decom- 
posed by  digestion  in  carbonate  of  potassa;  and  when  an  acid  is  added 
in  excess,  bitartrate  of  potassa  is  precipitated.  All  the  insoluble  tar- 
trates are  easily  procured  from  neutral  tartrate  of  potassa  by  way  of 
double  decomposition. 

Tartrates  of  Potassa. — The  neutral  tartrate,  frequently  called  soluble 
tartar^  is  formed  by  neutralizing  a solution  of  the  bitartrate  with  car- 
bonate of  potassa;  and  it  is  a product  of  the  operation  above  described 
for  making  tartaric  acid.  Its  primary  form  is  a right  rhomboidal  prism, 
but  it  often  occurs  in  irregular  six-sided  prisms  with  dihedral  summits. 
Its  crystals  are  very  soluble  in  water,  and  attract  moisture  when  expos- 
ed to  the  air.  They  consist  of  114  parts  or  one  equivalent  of  the  nen- 
ti’al  tartrate,  and  two  of  water.  They  are  rendered  quite  anhydrous  by 
a temperature  not  exceeding  248^  Fahr. 

Of  the  bitartrate  an  impure  form,  commonly  known  by  the  name  of 
tartar,  is  found  encrusted  on  the  sides  and  bottom  of  wine-casks,  a 
source  from  which  all  the  tartar  of  commerce  is  derived.  This  salt 
exists  in  the  juice  of  the  grape,  and,  owing’  to  its  insolubility  in  alcohol, 
is  gradually  deposited  during  the  vinous  fermentation.  In  its  crude 
state  it  is  coloured  by  the  wine  from  which  it  was  procured;  but  when 
purified,  it  is  quite  white,  and  in  this  state  constitutes  the  cream  of  tar» 
far  of  the  shops. 

Bitartrate  of  potassa  is  very  sparingly  soluble  in  water,  requiring 
sixty  parts  of  cold  and  fourteen  of  boiling  water  for  solution,  and  is 
deposited  from  tlie  latter  on  cooling  in  small  crystalline  grains.  Its 
crystals  are  commonly  irregular  six-sided  prisms,  terminated  at  each 
extremity  by  six  surfaces;  and  its  primary  form  is  either  a right  rectan- 
gular, or  a right  rliombic  prism.  It  has  a sour  taste,  and  distinct  acid 
reaction.  It  consists  of  one  equivalent  of  potassa  and  two  of  the  acid, 
united  according  to  Berzelius  with  one,  and  according  to  Dr.  Thomson 
with  two  equivalents  of  water.  Assuming  the  latter  to  be  correct,  the 
atomic  weight  of  tlie  bitartrate  is  198.  Its  water  of  crystallization  can- 
not be  expelled  without  decomposing  the  salt  itself. 

Bitartrate  of  potassa  is  employed  in  the  formation  of  tartaric  acid  and 
all  the  tartrates.  It  is  likewise  used  in  preparing  pure  carbonate  of 
potassa.  When  exposed  to  a strong  heat,  it  yields  an  acrid  empyreu- 
matic  oil,  some  pyrotartaric  acid,  together  with  water,  carburetted 
hydrogen,  carbonic  oxide  and  carbonic  acid  gases,  the  last  of  which 
combines  with  the  potassa.  The  fixed  products  are  carbonate  of  po- 
tassa and  charcoal,  which  may  be  separated  from  each  other  by  so- 
lution and  filtration.  Wlien  deflagrated  with  half  its  weight  of  nitre, 
by  which  part  of  the  charcoal  is  consumed,  it  forms  black  flax;  and 
when  an  equal  weight  of  nitre  is  used,  so  as  to  oxidize  all  the  carbon 
of  the  tartaric  acid,  a pure  carbonate  of  potassa,  called  white  flux,  is 
procured. 

Tartrate  of  Potassa  and  Soda. — This  double  salt,  which  has  been 
long  employed  in  medicine  under  the  name  of  Seignette  or  Rochelle  salt, 


466 


VEGETABLE  ACIDS. 


is  prepared  by  neutralizing’  bitartrate  of  potassa  witli  carbonate  of  soda. 
By  evaporation  it  yields  prismatic  crystals,  the  sides  of  which  often 
amount  to  ten  or  twelve  in  number;  but  the  primary  form,  as  obtained 
by  cleavage,  is  a right  rhombic  prism.  (Mr.  Brooke.)  The  crystals  are 
soluble  in  five  parts  of  cold  and  in  a less  quantity  of  boiling  water, 
and  are  composed  of  114  parts  or  one  equivalent  of  tartrate  of  potassa, 
98  parts  or  one  equivalent  of  tartrate  of  soda,  and  eight  equivalents  of 
water. 

Tartrate  of  soda  is  of  little  importance.  It  is  frequently  made  extem- 
poraneously by  dissolving  equal  weights  of  tartaric  acid  and  bicarbonate 
of  soda  in  separate  portions  of  water,  and  then  mixing  the  solutions. 
A very  agreeable  effervescing  draught  is  procured  in  this  way.  Soda 
is  better  adapted  for  this  purpose  than  potassa,  because  the  former  has 
little  or  no  tendency  to  form  an  insoluble  bitartrate. 

Tartrate  of  Antimony  and  Potassa, — This  compound,  long  celebrated 
as  a medicinal  preparation  under  the  name  of  tartar  emetic,  is  made  by 
boiling  protoxide  of  antimony  with  a solution  of  bitartrate  of  potassa. 
The  oxide  of  antimony  is  furnished  for  this  purpose  in  various  ways. 
Sometimes  the  glass  or  crocus  of  that  metal  is  employed.  The  Edin- 
burgh college  prepare  an  oxide  by  deflagrating  sulphuret  of  antimony 
with  an  equal  weight  of  nitre;  and  the  college  of  Dublin  employ  the 
submuriate.  Mr.  Phillips  recommends  that  100  parts  of  metallic  anti- 
mony in  fine  powder  be  boiled  to  dryness  in  an  iron  vessel  with  200  of 
sulphuric  acid,  and  that  the  residual  subsulphate  be  boiled  with  an  equal 
weight  of  cream  of  tartar.  The  solution  of  the  double  salt,  however 
made,  should  be  concentrated  by  evaporation,  and  allowed  to  cool  in 
order  that  crystals  may  form. 

Tartrate  of  antimony  and  potassa  yields  crystals,  which  are  transpa- 
rent when  first  formed,  but  become  white  and  opake  by  exposure  to 
the  air.  Its  primary  form  has  been  correctly  described  by  Mr.  Brooke 
as  an  octohedron  with  a rhombic  base  (An.  of  Phil.  N.  S.  vi.  40.);  but 
the  edges  of  the  base  are  frequently  replaced  by  planes  which  commu- 
nicate a prismatic  form,  and  its  summits  are  generally  formed  with  an 
edge  instead  of  a solid  angle,  which  edge  is  frequently  truncated,  pre- 
senting a narrow  rectangular  surface.  It  frequently  occurs  in  segments, 
having  the  outline  of  a triangular  prism,  a form  which  has  deceived 
many  into  the  belief,  that  the  tetrahedron  or  regular  octohedron  is  the 
primary  form  of  tartar  emetic.  It  has  a styptic  metallic  taste,  reddens 
litmus  paper  slightly,  and  is  soluble  in  fifteen  parts  of  water  at  60°,  and 
in  three  of  boiling  water.  (Dr.  Duncan,  jun.)  Its  aqueous  solution, 
like  that  of  all  the  tartrates,  undergoes  spontaneous  decomposition  by 
keeping;  and  therefore,  if  kept  in  the  liquid  form,  alcohol  should  be 
added  in  order  to  preserve  it.  According  to  the  analysis  of  Dr.  Thom- 
son (First  Principles,  vol.  ii.  p.  441),  it  is  composed  of 


Tartaric  acid  . (66  x 2) 

Protoxide  of  antimony  (52  x 3) 
I’otassa  .... 
Water 


132  or  two  equivalents. 
156  or  three  equivalents. 
48  or  one  equivalent. 

18  or  two  equivalents. 


354 


With  this  result  the  amdysis  of  Mr.  Phillips  accords,  except  that  he 
found  three  instead  of  two  equivalents  of  water.  The  atomic  weight 
of  the  salt  would,  on  this  estimate,  be  363. 

Tartar  emetic  is  decomposed  by  many  reagents.  Thus  alkaline  sub- 
stances, from  their  supei*ior  attraction  for  tartaric  acid,  separate  oxide 
of  antimony.  Tlie  pure  alkalies,  indeed,  and  especially  potassa  and 


VEGETABLE  ACIDS. 


467 


soda,  precipitate  it  imperfectly,  owing*  to  their  tendency  to  unite  with 
and  dissolve  the  oxide;  but  the  alkaline  carbonates  throw  down  the 
oxide  much  more  completely.  Lime-water  occasions  a white  precipi- 
tate, which  is  a mixture  of  oxide  or  tartrate  of  antimony  and  tartrate  of 
lime.  The  stronger  acids,  such  as  the  sulphuric,  nitric,  and  muriatic, 
cause  a white  precipitate,  consisting  of  bitartrate  of  potassa  and  a sub- 
salt of  antimony.  Decomposition  is  likewise  effected  by  several  metal- 
lic salts,  the  bases  of  which  yield  insoluble  compounds  with  tartaric 
acid.  Sulphuretted  hydrogen  throws  down  the  orange  sulphuret  of 
antimony.  It  is  precipitated  by  many  vegetable  substances,  especially 
by  an  infusion  of  gall-nuts,  and  other  similar  astringent  solutions,  with 
which  it  forms  a dirty  white  precipitate,  which  is  regarded  as  a com- 
pound of  tannin  and  oxide  of  antimony.  This  combination  is  inert,  and 
therefore  a decoction  of  cinchona  bark  is  recommended  as  an  antidote 
to  tartar  emetic. 

Citric  Acid, 

This  acid  is  contained  in  many  of  the  acidulous  fruits,  but  exists  in 
large  quantity  in  the  juice  of  the  lime  and  lemon,  from  which  it  is  pro- 
cured by  a process  very  similar  to  that  described  for  preparing  tartaric 
acid.  To  any  quantity  of  lime  or  lemon  juice,  finely  powdered  chalk 
is  added  as  long  as  effervescence  ensues;  and  the  insoluble  citrate  of 
lime,  after  being  well  washed  with  water,  is  decomposed  by  digestion 
in  dilute  sulphuric  acid.  The  insoluble  sulphate- of  lime  is  separated 
by  a filter,  and  the  citric  acid  obtained  in  crystals  by  evaporation. 
They  are  rendered  quite  pure  by  being  dissolved  in  water  and  recrys- 
tallized.  The  proportions  required  in  this  process  are  86  parts  or 
one  equivalent  of  dry  citrate  of  lihie,  and  49  parts  or  one  equivalent 
of  strong  sulphuric  acid,  which  shovdd  be  diluted  with  about  ten  parts 
of  water. 

Citric  acid  crystallizes  in  rhomboidal  prisms  terminated  by  four  plane 
surfaces.  The  crystals  are  large  and  transparent,  undergo  no  change 
in  the  air,  and  if  kept  dry  may  be  preserved  for  any  length  of  time 
without  decomposition.  They  have  an  intensely  sour  taste,  redden  lit- 
mus paper,  and  neutralize  alkalies.  1’heir  flavour  when  diluted  is  very 
agreeable.  They  are  soluble  in  an  equal  weight  of  cold  and  in  half 
their  weight  of  boiling  water,  and  are  also  dissolved  by  alcohol.  The 
aqueous  solution  is  gradually  decomposed  by  keeping.  It  is  converted 
into  oxalic  by  the  action  of  nitric  acid.  Exposed  to  heat,  the  crystals 
undergo  the  watery  fusion,  and  the  acid  itself  is  decomposed  before  all 
its  water  of  crystallization  is  expelled.  Besides  the  usual  products  of 
the  decomposition  of  vegetable  matter,  a peculiar  acid  sublimes,  to 
which  the  name  of  pyrocitric  ctac?  is  applied. 

The  atomic  weight  of  citric  acid,  as  deduced  from  the  composition  of 
citrate  of  lead  by  Thomson  and  Berzelius,  is  58;  and  the  crystals  con- 
sist of  58  parts  or  one  equivalent  of  the  acid,  and  18  parts  or  two  equiv- 
alents of  water.  According  to  the  analyses  of  the  same  chemists,  this 
acid  is  inferred  to  consist  of 


Carbon 

. 24  or  four  equivalents. 

Oxygen 

. 32  or  four  equivalents. 

Hydrogen 

. 2 or  two  equivalents. 

58 

The  analysis  of  Gay-Lussac  and  Thenard,  of  Dr.  Prout,  and  Dr. 


468 


VEGETABLE  ACIDS. 


Ere,*  would  lead  to  a different  statciuent;  but  the  forcg-oing  agrees 
better  with  the  atomic  weight  of  tlie  acid. 

Citric  acid  is  characterized  by  its  flavour,  by  the  form  of  its  crys- 
tals, and  by  forming  an  insoluble  salt  with  lime  and  a deliquescent 
soluble  compound  with  potassa.  It  does  not  render  lime-water  tur- 
bid, unless  the  latter  is  in  excess,  and  fully  saturated  with  lime  in  the 
cold.  ^ 

Citric  acid  is  chiefly  employed  as  a substitute  for  lemon  juice.  On 
some  occasions,  as  in  making  effervescing  draughts  or  acidulous  drinks, 
tartaric  acid  may  be  used  with  equal  advantage. 

The  salts  of  citric  acid  are  of  little  importance.  The  citrates  of  po- 
tassa, soda,  ammonia,  magnesia,  and  iron  arc  soluble  in  water.  The  first 
is  often  made  extemporaneously  as  an  effervescing  draught.  'I'he  citrates 
of  lime,  baryta,  and  strontia,  lead,  mercury,  and  silver,  are  very  spa- 
ringly soluble.  All  of  them  are  dissolved  by  an  excess  of  their  own 
acid,  and  are  decomposed  by  sulphuric  acid. 

Malic  Acid, 

This  acid  is  contained  in  most  of  the.  acidulous  fruits,  being  frequent- 
ly associated  with  tartaric  and  citric  acids.  Grapes,  currants,  goose- 
berries, and  oranges  contain  it.  Yauquelin  found  it  in  the  tamarind 
mixed  with  tartaric  and  citric  acids,  and  in  the  house  X^^V'isempervivnm 
tectorum,)  combined  with  lime.  It  is  contained  in  considerable  quanti- 
ty in  apples,  a circumstance  to  which  it  owes  its  name.  It  is  almost 
the  sole  acidifying  principle  of  the  berries  of  tlie  service-tree  (sorbus 
aticupario,)  in  which  it  was  detected  by  Mr.  Donovan,  and  dcvscribed  by 
him  under  the  name  of  sorbic  acid  in  the  Philosophical  'frans’actions  for 
1815;  but  it  was  afterwai’ds  identified  with  the  malic  acid  by  Braconnot 
and  Houton-Labillardiere,  (An.  de  Ch.  et  de  Ph.  viii.) 

Malic  acid  may  be  formed  by  dig-esting  sugar  w^th  three  times  its 
weight  of  nitric  acid;  but  the  best  mode  of  procuring  it  is, from  the 
berries  of  the  service-tree.  The  juice  of  the  unripe  berries  is  diluted 
with  three  or  four  parts  of  water,  filtered,  and  heated;  and  while  boil- 
ing, a solution  of  acetate  of  lead  is  added  as  long  as  any  turbidity  ap- 
pears. The  colouring  matter  of  the  berry  is  thus  precipitated,  while 
malate  of  lead  remains  in  solution.  The  liquid,  wliile  at  a boiling  tem- 
perature, is  then  filtered.  At  first  a small  quantity  of  dark-coloured 
salt  subsides;  but  on  decanting  the  hot  solution  into  another  vessel,  the 
malate  of  lead  is  gradually  deposited,  in  cooling,  in  groups  of  brilliant 
white  crystals.  This  process — a modification  of  the  common  one — has 
lately  been  recommended  by  Wohler.  The  malate  is  tlmn  decomposed 
by  a quantity  of  dilute  sulphuric  acid,  insufficient  for  combining*  with 
all  the  oxide  of  lead;  by  which  means  a solution  is  procured  containing 
malic  acid  together  with  a little  lead.  The  latter  is  afterwards  precipi- 
tated by  sulphuretted  hydrogen. 

Malic  acid  has  a very  pleasant  acid  taste.  It  crystallizes  with  great 
difficulty  and  in  an  imperfect  manner,  attracts  moisture  from  the  at- 
mos])here,  and  is  very  soluble  in  water  and  alcohol.  Its  aqueous  solu- 
tion is  gradually  decomposed  by  keeping.  Nitric  acid  converts  it  into 
oxalic  acid.  Heated  in  close  vessels  it  is  decomposed  with  formation  of 
a new  and  volatile  acid,  which  lias  hence  received  the  name  of  pyro- 
malic  acid. 

According  to  a recent  analysis  of  tlic  malates  of  lime,  lead,  and  cop- 
per by  Dr.  Prout,  100  ])arts  of  anhydrous  malic  acid  consist  of  40.68 


Philosophical  Transactions  for  1812. 


VEGETABLE  ACIDS. 


469 


parts  of  carbon,  54.24  of  oxygen,  and  5.08  parts  of  hydrogen.  This 
result  differs  considerably  from  that  lately  published  by  Liebig,  accord- 
ing to  whose  analysis  of  malate  of  zinc  and  malate  of  silver,  the  acid 
is  composed  of  four  equivalents  of  carbon,  four  of  oxygen,  and  one  of 
hvdrosren:  and  the  equivalent  of  the  acid  is  57.  (An.  de  Ch.  et  de  Ph. 
xliii.  259.) 

Most  of  the  salts  of  malic  acid  are  more  or  less  soluble  in  water. 
The  malates  of  soda  and  potassa  are  deliquescent  and  very  soluble. 
Those  of  lead  and  lime,  the  most  insoluble  of  the  rnalates,  are  sparingly 
soluble  in  cold  water,  but  are  freely  dissolved  by  that  liquid  at  a boiling 
temperature,  a circumstance  which  distinguishes  the  malic  from  oxalic, 
tartaric,  and  citric  acids. 

Benzoic  Acid, 

Benzoic  acid  exists  in  gum  benzoin,  in  storax,  in  the  balsams  of 
Peru  and  Tolu,  and  in  several  other  vegetable  substances.  M.  Vogel 
has  detected  it  in  the  flowers  of  the  trifolium  melilotus  officinalis.  It  is 
found  in  considerable  quantity  in  the  urine  of  the  cow  and  other  herbi- 
vorous animals,  and  is  perhaps  derived  from  the  grasses  on  which  they 
feed.  It  has  also  been  detected  in  the  urine  of  children. 

This  acid  is  commonly  extracted  from  gum  benzoin.  One  method 
consists  in  heating  the  benzoin  in  an  earthen  pot,  over  which  is  placed 
a cone  of  paper  to  receive  the,  acid  as  it  sublimes?  but  since  the  pro- 
duct is  always  impure,  owing  to  the  presence  of  empyreumatic  oil,  it 
is  better  to  extract  the  acid  by  means  of  an  alkali.  The  usual  process 
consists  in  boiling  finely  powdered  gum  benzoin  in  a large  quantity  of 
water  along  with  lime  or  carbonate  of  potassa,  by  which  means  a ben- 
zoate is  formed.  To  the  solution,  after  being  filtered  and  concentrated 
by  evaporation,  muriatic  acid  is  added,  which  unites  with  the  base,  and 
throws  down  the  benzoic  acid.  It  is  then  dried  by  a gentle  heat,  and 
purified  by  sublimation. 

Benzoic  acid  has  a sweet  and  aromatic  rather  than  a sour  taste;  but  it 
reddens  litmus  paper,  and  neutralizes  alkalies.  It  fuses  readily  by  heat, 
and  at  a temperature  a little  above  its  point  of  fusion,  it  is  converted 
into  va])our,  emitting  a peculiar,  fragrant,  and  highly  characteristic 
odour,  and  condensing  on  cool  surfaces  without  change.  When  strong- 
ly heated,  it  takes  fire,  and  burns  with  a clear  yellow  flame.  It  under- 
goes no  change  by  exposure  to  the  air,  and  is  not  decomposed  by  the 
action  even  of  nitric  acid.  It  requires  about  24  parts  of  boiling  water 
for  solution,  and  nearly  the  whole  of  it  is  deposited  on  cooling  in  the 
form  of  minute  acicular  crystals  of  a silky  lustre.  It  is  very  soluble  in 
alcohol,  especially  by  the  aid  of  heat. 

Benzoic  acid  is  easily  distinguished  by  its  odour  and  volatility.  Its 
salts  are  all  decomposed  by  muriatic  acid,  with  deposition  of  benzoic 
acid  if  the  solution  is  moderately  concentrated. 

I’he  atomic  weight  of  benzoic  acid,  as  inferred  from  the  analysis  of 
benzoate  of  lead  by  Berzelius,  and  that  of  perbenzoate  of  iron  by  Dr. 
Thomson,  is  120. 

The  ultimate  analysis  of  this  acid  by  Berzelius,  together  with  the 
number  representing  the.  weight  of  its  combining  proportion,  appears 
to  justify  the  opinion  that  it  is  composed  of 

Carbon  . .90  or  fifteen  equivalents. 

Oxygen  . . 24  or  three  equivalents, 

Hydrogen  . . 6 or  six  equivalents. 

120  • 


40 


470 


VEGETABLE  ACIDS. 


According*  to  the  analysis  of  Dr.  Ure,  it  contains  tliirtccn  instead  of 
fifteen  equivalents  of  carbon.  (Pliilos.  Trans,  for  1822.) 

Most  of  the  benzoates  are  soluble  in  water.  Tliose  of  lead,  mercury, 
and  peroxide  of  iron  are  the  most  insoluble.  The  benzoates  of  soda 
and  ammonia  are  sometimes  employed  for  separating*  iron  from  manga- 
nese. ^ If  the  solution  is  quite  neutral,  peroxide  of  iron  is  completely 
precipitated,  while  the  manganese  remains  in  solution, 

Gallic  Acid, 

This  acid  was  discovered  by  Scheele  in  1786,  and  exists  ready  form* 
ed  in  the  bark  of  many  trees,  and  in  gall-nuts.  It  is  always  associated 
with  tannin,  a substance  to  which  it  is  allied  in  a manner  hitherto  unex- 
plained. 

Several  processes  have  been  described  for  the  preparation  of  gallic 
acid;  but  the  most  economical  appears  to  be  that  of  Scheele  as  modi- 
fied by  M.  Braconnot.  (An.  de  Ch.  et  de  Ph.  ix.)  Any  quantity  of  gall- 
nuts,  reduced  to  powder,  is  infused  for  a few  days  in  four  times  their 
weight  of  water;  and  the  infusion,  after  being  strained  through  linen, 
is  kept  for  two  months  in  a moderately  warm  atmosphere.  During  this 
period,  the  surface  of  the  liquid  becomes  mouldy,  the  tannin  of  the 
gall-nuts  disappears  more  or  less  completely,  and  a yellowish  crystal- 
line matter  is  deposited.  On  evaporating  the  solution  to  the  consistence 
of  syrup,  and  allowing  it  to  cool,  an  additional  quantity  of  the  same 
substance  subsides.  The  gallic  acid,  tllus  procured,  is  impure,  owing 
to  the  presence  of  colouring  matter,  and  a peculiar  acid,  to  which  M. 
Braconnot  has  applied  the  name  of  ellagic  acid.  • The  gallic  acid  is  se- 
parated from  the  latter  by  boiling  water,  in  which  the  ellagic  acid  is 
insoluble;  and  it  is  rendered  white  by  digestion  with  animal  charcoal 
deprived  of  its  phosphate  of  lime  by  muriatic  acid.  When  the  colour- 
less solution  is  concentrated  by  evaporation,  the  gallic  acid  is  deposited 
in  small  white  acicular  crystals  of  a silky  lustre.  Some  crystals  pre- 
pared by  Mr.  Phillips,  and  examined  by  Mr.  Brooke,  were  in  the  form 
of  an  oblique  rhombic  prism. 

Pure  gallic  acid  may  easily  be  procured  by  sublimation.  For  this 
purpose  the  impure  acid  is  exposed  to  a temperature  of  about  350^  F., 
either  in  a wide-mouthed  glass  flask  covered  with  a cone  of  paper,  or 
in  an  earthen  capsule  covered  with  a capsule  of  the  same  kind,  kept 
cool,  for  collecting  the  sublimate.  If  the  process  is  conducted  slowly 
and  at  a very  gentle  heat,  the  crystals  are  colourless  and  in  delicate  long 
scales,  but  they  are  soiled  with  dark  oily  matter,  when  the  heat  is  too 
high. 

Impure  gallic  acid  has  a weak  sour  taste,  accompanied  with  slight 
astringency,  and  an  acid  reaction  with  test  paper;  but  the  pure  sublimed, 
acid  barely  reddens  litmus,  and  has  a faintly  bitter  and  astringent  taste 
without  acidity.  It  fuses  at  276®,  and  at  a few  degrees  higher  sublimes 
slowly,  the  fused  mass  being  darkened  at  the  same  time.  The  odour  of 
its  vapour  is  fiiint,  and  somewhat  resembles  that  of  boracic  acid.  It  is 
soluble  in  twenty-four  parts  of  cold  and  in  three  of  boiling  water;  and 
it  is  likewise  dissolved  by  alcohol.  The  aqueous  solution  becomes 
mouldy  by  keeping.  Nitric  acid  converts  it  into  oxalic  acid.  When 
strongly  heated  in  the  open  air,  it  takes  fire;  and  at  a high  temperature 
in  close  vessels,  it  is  in  part  decomposed,  and  in  part  sublimes,  appa- 
rently without  clninge. 

Tlie  composition  and  atomic  weight  of  gallic  acid  have  not  been  deter- 
mined in  a satisfactory  manner.  From  an  analysis  of  the  gallate  of  lead 
by  Berzelius,  tlic  ecpiivalent  of  the  acid  is  probably  about  63  or  64;  and 
according^  the  same  chemist  it  is  composed  of  (An.  of  Thil.  v.) 


VEGETABLE  ACIDS. 


471 


Carbon 

Oxygen 

Hydrogen 


56.64 

38.36 

5.00 


With  lime-water  gallic  acid  yields  a brownish-green  precipitate,  which 
‘is  redissolved  by  an  excess  of  the  solution,  and  acquires  a reddish  tint. 
It  is  distinguished  from  tannin  by  causing  no  precipitate  in  a solution  of 
gelatin.  With  a salt  of  iron  it  forms  a dark-blue  (coloured  compound, 
which  is  the  basis  of  ink.  The  finest  colour  is  procured  when  the  per- 
oxide and  protoxide  of  iron  are  mixed  tog’ether.  This  character  dis- 
tinguishes gallic  acid  from  every  other  substance  excepting  tannin. 

. The  salts  of  gallic  acid,  called  gallates,  have  been  imperfectly  ex- 
amined. The  gallates  of  potassa,  soda  and  amrnonia  are  soluble  in  wa- 
ter; but  most  of  the  other  gallates  are  of  sparing  solubility.  ^ On  this 
account  many  of  the  metallic  solutions  are.  precipitated  by  gallic  acid. 

Ellagic  acid,  so  called  by  Braconnot  from  the  word  guile  read  back- 
wards, is  left,  in  the  process  above  described,  after  the  gallic  acid  is 
removed  by  hot  water,  in  the  form  of  a gray  powder,  the  greater  part 
of  which  is  soluble  in  a dilute  solution  of  potassa.  On  exposure  to  the 
air,  so  that  the  alkali  may  absorb  carbonic  acid,  small  shining  scales  pe 
deposited.  Tjiese  consist  of  ellagic  acid  and  potassa,  and  by  washing 
them  with  dilute  muriatic  acid  the  former  is  left  as  a yellowish-gray 
powder,  which  is  insoluble  in  water,  alcohol,  and  ether,  has  no  taste, 
and  reddens  litmus  faintly.  Its  real  nature  is  not  yet  determined. 


Succinic  Acid, 


This  acid  is  procured  by  heating  powdered  amber  in  a retort  by  a 
regulated  temperature,  when  the  succinic  acid,  which  exists  ready 
formed  in  amber,  passes  over  and  condenses  in  the  receiver.  As  first 
obtained,  it  has  a yellow  colour  and  peculiar  odour,  owing  to  the  pre- 
sence of  some  empyreumatic  oil;  but  it  is  rendered  quite  pure  and  white 
by  being  dissolved  in  nitric  acid,  and  then  evaporated  to  dryness.  The 
oil  is  decomposed,  and  the  succinic  acid  left  unchanged. 

Succinic  acid  lias  a sour  taste,  and  reddens  litmus  paper.  It  is  sol- 
uble both  in  water  and  alcohol,  and  crystallizes  by  evaporation  in  an- 
hydrous prisms.  When  briskly  heated,  it  fuses,  undergoes  decompo- 
sition, and  in  part  sublimes,  emitting  a peculiar  and  very  characteristic 
odour. 

The  salts  of  succinic  acid  have  been  little  examined.  The  succinates 
of  the  alkalies  are  soluble  in  water.  That  of  ammonia  is  frequently  em- 
ployed for  separating  iron  from  manganese,  persuccinate  of  iron  being 
quite  insoluble  in  cold  water,  provided  the  solutions  are  neutral.  Suc- 
cinate of  manganese,  on  the  contrary,  is  soluble. 

The  atomic  weight  of  succinic  acid,-  deduced  from  the  composition 
of  succinate  of  iron  and  of  lead  by  I'liomson  and  Berzelius,  is  50;  and 
according  to  the  analysis  of  succinate  of  lead  by  Berzelius,  which  has 
lately  been  confirmed  by  Liebig  and  Wohler,  this  acid  is  inferred  to 
consist  of 

Carbon  . . 24  or  four  equivalents. 

Oxygen  . . 24  or  three  equivalents. 

Hydrogen  . . 2 or  two  equivalents. 

50 

It  hence  differs  in  composition  from  acetic  acid,  only  in  containing  one 
equivalent  less  of  hydrogen. 

Cq^mphoric  Acid.— T\\i^  compound  h^^s  not  hitherto  been  found  in  any 


472 


VEGETxVBLE  ACIDS. 


plant,  and  is  procured  only  by  dig’esting’  camphor  for  a considerable 
time  in  a larg'e  excess  of  nitric  acid.  It  is  sparingly  soluble  in  water. 
Its  taste  is  rather  bitter,  and  its  odour  somewhat  similar  to  safliron.  It 
reddens  litmus  paper,  and  combines  with  alkalies,  forming  salts  which 
are  called  camphorates.  This  acid  has  not  been  applied  to  any  useful 
purpose. 

Mucic  or  saccholactic  acid  was  discovered  by  Scheele  in  1780.  It  is 
obtained  by  the  action  of  nitric  acid  on  certain  substances,  such  as  gum, 
manna,  and  sugar  of  milk.  The  readiest  and  cheapest  mode  of  form- 
ing it  is  by  digesting  gum  with  three  times  its  weight  of  nitric  acid.  On 
^ipplyiog  heat,  effervescence  ensues,  and  three  acids — the  oxalic,  malic, 
and  saccholactic — are  the  products.  The  latter,  from  its  insolubility, 
subsides  as  a white  powder,  and  may  be  separated  from  the  others  by 
washing  with  cold  water.  In  this  state  Dr.  Front  says  it  is  very  impure. 
To  purify  it  he  digests  wdth  a slight  excess  of  ammonia,  and  dissolves 
the  resulting  salts  in  boiling  water.  It  is  filtered  while  hot,  and  the 
solution  evaporated  slowly  almost  to  dryness.  I'he  saccholactate  of  am- 
monia is  thus  obtained  in  crystals,  which  are  to  be  washed  with  cold 
distilled  water,  until  they  become  quite  white.  They  are  then  dissolv- 
ed in  boiling  water,  and  the  saturated  hot  solution  dropped  into  cold 
dilute  nitric  acid. 

The  saccholattic  is  a weak  acid,  which  is  insoluble  in  alcohol,  and 
requires  sixty  times  its  weight  of  boiling  water  for  solution.  When 
heated  in  a retort  it  is  decomposed,  and  in  addition  to  the  usual  pro- 
ducts, yields  a volatile  white  substance,  to  which  the  name  of  pyro- 
mucic  acid  has  been  applied.  According  to  the  analysis  of  Dr.  Prout, 
saccholactic  acid  is  composed  of  33  parts  of  carbon,  61.5  of  oxygen, 
and  4.9  of  hydrogen. 

Moroxylic  Acid. — This  compound,  which  was  discovered  by  Klaproth, 
is  found  in  combination  with  lime  on  the  bark  of  the  morns  alba  or  white 
mulberry,  and  has  hence  received  the  appellation  of  moric  or  moroxylic 
acid.  It  is  obtained  by  decomposing  moroxylate  of  lime  by  acetate  o 
lead,  and  then  separating  the  lead  from  the  moroxylate  of  that  base  by 
means  of  sulphuric  acid. 

Hydrocyanic  OY prussic  add,  which  is  not  an  unfrequent  production  of 
plants,  has  already  been  described. 

The  sorbic,  as  already  mentioned,  has  been  shown  to  be  malic  acid. 

RJieumic  Acid, — This  name  was  applied  to  the  acid  principle  contain- 
ed in  the  stem  of  the  garden  rhubarb;  but  M.  Lassaigne  has  shown  it  to 
be  oxalic  acid. 

Boletic  acid  was  discovered  by  M.  Braconnot,  in  the  juice  of  the 
Boletus  pseudo -igniarius.  As  it  is  a compound  of  no  importance,  I refer 
the  reader  to  the  original  paper  for  an  account  of  it.  (Annals  of  Phil, 
vol.  ii.) 

Igasuric  Acid. — MM.  Pelletier  and  Caventou  have  proposed  this  name 
for  the  acid  which  occurs  in  combination  with  strychnia  in  the  nux  vom- 
ica and  St.  Ignatiuses  bean;  but  its  existence,  as  different  from  all  other 
known  acids,  is  doubtful. 

Melliiic  Acid. — This  acid  is  contained  in  the  rare  substance  called 
lioney-slone,  which  is  occasionally  met  with  at  Thuringia  in  Germany. 
The  honey-stone,  according  to  Klaproth,  is  a mcllitate  of  alumina,  and 
on  boiling  it  in  a large  quantity  of  water,  the  acid  is  dissolved,  and  the 
alumina  subsides.  On  concentrating  the  solution,  mellitic  acid  ia  de- 
posited in  minute  acicular  crystals.  Prom  its  rarity  it  has  been  little 
studied,  and  is  of  little  importance.  According  to  a late  analysis  by 
Liebig  and  Wbliler,  it  consists  solely  of  carbon  and  oxygen  in  the  ratio 
of  four  equivalents  of  the  former  to  three  of  the  latter,  giving  an  equiv- 


VEGEtABLE  ACIDS. 


m 


alent  of  48  for  the  acid,  which  is  the  proportion  in  which  it  unites  with 
alkalies.  This  is  exactly  tlie  constitution  of  succinic  acid  without  its 
hydrog*en.  (An.  de  Ch.  et  de  Ph.  xliii.  200.) 

Suberic  acid  is  procured  by  the  action  of  nitric  acid  on  cork.  Its  acid 
properties  are  feeble.  It  is  very  soluble  in  boiling  water,  and  the  greater 
part  of  it  is  deposited  from  the  solution  in  cooling  in  the  form  of  a white 
powder.  Its  salts,  which  have  been  little  examined,  are  known  by  the 
name  of  suherates, 

Zumic  JLcid. — This' compound,  procured  by  Braconnot  from  several 
vegetable  substances  which  had  undergone  the  acetous  fermentation, 
appears  from  the  observations  of  Yogel  to  be  lactic  (acetic)  acid.  (An- 
nals of  Philosophy,  vol.  xii.) 

Kinic  Acid, — This  acid  exists  in  cinchona  bark  in  combination  with 
lime.  On  evaporating  an  infusion  of  bark  to  the  consistence  of  an  ex- 
tract, and  treating  the  residue  with  alcohol,  a viscid  matter  remains, 
consisting  of  kinate  of  lime  and  mucilaginous  matters.  On  dissolving  it 
in  water,  and  allowing  the  concentrated  solution  to  evaporate  sponta- 
neously in  a warm  place,  the  kinate  crystallizes  in  rhombic  prisms  with 
dihedral  summits,  and  sometimes  in  rhomboidal  plates.  From  a solution 
of  this  salt  Vauquelin  precipitated  the  lime  by  means  of  oxalic  acid,  and 
thus  obtained  kinic  acid  in  a pure  state.  (An.  de  Ch.  lix.) 

Kinic  acid  has  an  acid  taste  like  that  of  tartaric  acid,  reddens  litmus, 
and  neutralizes  alkalies.  Its  specific  gravity  is  1.637.  It  is  soluble  in 
water  and  alcohol,  requiring  two  and  a half  times  its  weight  of  the  for- 
mer at  48*^  F.  It  forms  soluble  compounds  with  alkalies  and  alkaline 
earths,  and  is  not  precipitated  by  a salt  of  mercury,  lead,  or  silV^er. 
Kinate  of  soda  crystallizes  in  very  fine  six-sided  prisms. 

According  to  M.  Henry,  jun.  and  Plissoii,  kinic  acid  is  composed  of 
two  equivalents  of  carbon,  four  of  hydrogen,  and  three  of  oxygen,  a 
constitution  which  would  make  its  equivalent  40;  but  judging  from  the 
ratio  in  which  it  combines  with  alkalies,  they  found  its  equivalent  to  be 
183.  (An.  de  Ch.  et  de  Ph.  xli.  325.) 

Meconic  acid,  which  is  combined  with  morphia  in  opium,  will  be  most 
conveniently  described  in  the  following  section. 

Pectic  Acid. — This  substance,  distinguished  by  its  remarkable  tenden- 
cy to  gelatinize,  a property  from  which  its  name  is  derived  (from 
coagulum,)  was  originally  described  by  Braconnot;  and  it  has  since  been 
examined  by  the  late  celebrated  Vauquelin.  (An.  de  Ch.  et  de  Ph. 
xxviii.  173,  and  xli.  46.)  Braconnot  believed  it  to  be  present  in  all 
plants;^  but  he  extracted  it  chiefly  from  the  carrot.  For  this  purpose, 
carrot  is  made  info  a pulp,  the  juice  is  expressed,  and  the  solid  part 
well  washed  with  distilled  water.  It  is  then  boiled  for  about  ten  min- 
utes with  a very  dilute  solution  of  pure  potassa,  or  as  Vauquelin  ad- 
vised, with  bicarbonate  of  potassa  in  the  ratio  of  5 parts  to  100  of  the 
washed  pulp,  and  muriate  of  lime  is  added  to  the  filtered  liquor.  The 
precipitate,  consisting  of  pectic  acid  and  lime,  is  well  washed,  and  the 
lime  removed  by  water  acidulated  with  muriatic  acid. 

Pectic  acid,  as  thus  procured,  is  in  the  form  of  jelly.  It  is  insoluble 
in  cold  water  and  acids,  and  nearly  so  in  boiling  water.  It  has  a slight 
acid  reaction,  and  a feeble  neutralizing  power  with  alkalies,  with  which 
it  forms  soluble  compounds.  ^ The  earthy  pectates  are  very  insoluble, 
knd  on  this  account,  in  preparing  pectic  acid,  pure  water  must  be  used;, 
for  the  process  always  fails,  when  water  containing  earthy  salts  is  em- 
ployed. 

By  digestion  in  a strong  solution  of  potassa,  pectic  acid  disappears, 
the  liquid  becomes  brown,  and  oxalate  of  potassa  is  obtained  by  evapo- 
ration. This  fact  excites  some  suspicion  that  pectic  acid  may  be  a com- 

40» 


474 


VEGETABLE  ACIDS. 


pound  of  oxalic  acid  with  a veg-etable  principle  analogotis  to  giim;  but 
the  conversion  of  org*anic  substances  in  g*eneral  into  oxalic  acid  by  the 
action  of  potassa,  as  already  noticed  at  page  454,  diminishes  the  force 
of  this  objection. 

Carhazotic  Add. — This  name  has  been  applied  by  M.  Liebig  to  a pe- 
culiar acid  formed  by  the  action  of  nitric  acid  on  indigo.  It  was  first 
noticed  by  Hausmann,  and  subsequently  examined  by  Proust,  Fourcroy 
and  Vauquelin,  Chevreul,  and  Liebig.  It  is  made  by  dissolving  small 
fragments  of  the  best  indigo  in  eight  or  ten  times  their  weight  of  mod- 
erately strong  nitric  acid,  and  boiling  as  long  as  nitrous  acid  fumes  arc 
evolved.  During  the  action,  carbonic,  prussic,  and  nitrous  acids  are 
evolved;  and  in  the  liquid,  besides  carbazotic  acid,  is  found  a resinous 
matter,  artificial  tannin,  and  a peculiar  acid,  mistaken  for  the  benzoic 
by  Fourcroy  and  Vauquelin,  and  recognised  as  a distinct  compound 
under  the  name  of  add  of  indigohy  Chevreul.  On  cooling,  carbazotic 
acid  is  freely  deposited  in  transparent  yellow  crystals;  and  on  evaporat- 
ing the  residual  liquid,  and  adding  cold  water,  an  additional  quantity 
of  the  acid  is  procured.  To  render  it  quite  pure  it  should  be  dissolv- 
ed in  hot  water,  and  neutralized  by  carbonate  of  potassa.  As  the  liquid 
cools,  carbazotate  of  potassa  crystallizes,  and  may  be  purified  by  re- 
peated crystallization.  The  acid  may  be  precipitated  from  this  salt  by 
sulphuric  acid. 

Carbazotic  acid  is  sparingly  soluble  in  cold  water;  bufit  is  dissolved 
much  more  freely  by  the  aid  of  heat,  and  on  cooling  yields  brilliant 
crystalline  plates  of  a yellow  colour.  Ether  and  alcohol  dissolve  it 
readily.  It  is  fused  and  volatilized  by  heat  without  decomposition;  but 
when  suddenly  exposed  to  a strong  heat,  it  inflames  without  explosion, 
and  burns  with  a yellow  flame,  with  a residue  of  charcoal.  Its  solution 
has  a bright  yellow  colour,  reddens  litmus  paper,  is  extremely  bitter, 
acts  like  a strong  acid  on  metallic  oxides,  and  yields  crystallizable  salts. 
Its  composition  will  be  stated  in  the  description  of  indigotic  acid. 
(Journal  of  Science,  ii.  210,  and  hi.  490.) 

The  bitter  principle  of  Welter,  formed  by  the  action  of  nitric  acid 
on  silk,  as  also  the  bitter  principle  of  aloes,  which  Braconnot  prepared 
by  heating  aloes  in  nitric  acid  of  1.25  until  reaction  ceased,  is  carbazo- 
tic acid. 

Indigotic  Add.— -The  indigo,  above  noticed,  has  lately  been 

carefully  studied  by  Dr.  Buff.  (An.  de  Ch.  et  de  Ph.  xxxvii.  160,  xxxix. 
290,  and  xli.  174.)  It  is  generated,  with  disengagement  of  carbonic 
acid  and  deutoxide  of  nitrogen  in  equal  measures,  but  without  the  pro- 
duction of  any  carbazotic  acid,  by  boiling  indigo  in  rather  dilute  nitric 
acid,  formed  by  mixing  nitric  acid  of  1.2  with  an  equal  weight  of  wa- 
ter. To  the  solution,  kept  boiling,  indigo  in  coarse  powder  is  gradual- 
ly added,  as  long  as  eflervescence  continues;  and  hot  water  is  occasion- 
ally added  to  supply  loss  by  evaporation.  The  impure  indigotic  acid, 
deposited  in  cooling,  is  boiled  with  oxide  of  lead  and  filtered,  in  ordei 
to  separate  resin;  and  the  clear  yellow  solution  is  decomposed  by  sul- 
phuric acid,  and  again  filtered  at  a boiling  temperature.  On  cooling, 
tlie  acid  crystallizes  in  yellowish-white  needles.  In  order  to  purify 
them  conq)letely,  they  are  digested  in  water  with  carbonate  of  baryta; 
and  the  indigotatc  of  baryta,  deposited  from  the  hot  filtered  solution  in 
cooling,  was  dissolved  in  hot  water,  and  decomposed  by  ai\  acid.  In- 
digotic acid  was  thus  obtained  in  acicular  ci'ystals  of  snowy  whiteness, 
which  contracted  greatly  in  drying,  and  lost  their  crystalline  aspect; 
but  the  dry  muss  was  dazzlingly  white,  and  had  a silky  lustre. 

Indigotic  acid  decomposes  carbonates,  but  it  is  a feeble  acid,  and 
reddens  litmus  faintly.  It  requires  1000  times  its  weight  of  cold  water 


VEGETABLE  ALKALIES. 


4^5 


for  solution,  but  is  soluble  to  any  extent  in  hot  water  and  alcohol. 
Heated  in  a tube  it  fuses,  and  sublimes  without  decomposition;  and  the 
fused  mass,  in  cooling*,  crystallizes  in  six-sided  plates.  When  heated 
in  open  vessels  it  is  inflamed,  and  burns  with  much  smoke.  By  dig’es- 
tion  in  nitric  acid,  it  is  converted  into  carbazotic  acid,  with  evolution  of 
carbonic  apid  and  nitrous  acid  fumes,  and  production  of  a small  quantity 
of  oxalic  acid.  The.chang’e  manifestly  depends  on  the  abstraction  both 
of  carbon  and  oxyg-en,  as  appears  from  the  following*  view  of  the  con- 
stitution of  the  two  acids  as  given  by  Dr.  Buff. 


Indigotic  acid.  Carhazoiic  acid. 

Carbon  . 15  . . 10  equivalents. 

Oxygen  . 10  . , 10  equivalents. 

Nitrogen  . 2 . . 4 equivalents. 

The  substances  called  resin  and  artificial  tannin,  formed  during  the 
preceding  processes,  consist  of  a brown  friable  matter  united  or  mixed 
with  different  proportions  of  indig(5tic  and  nitric  acid.  It  is  insoluble 
in  water  and  alcohol;  but  it  is  dissolved  by  pure  alkalies  and  their  car- 
bonates, and  is  precipitated  from  the  solution  by  acids.  It  is  best  pro- 
cured by  boiling  one  part  of  indigo  with  2 of  nitric  acid  diluted  with  15 
or  20  of  water,  being  purified  from  indigotic  acid  by  the  action  of  hot 
water.  In  order  to  separate  it  from  unchanged  indigo,  it  is  dissolved  by 
carbonate  of  potassa,  and  precipitated  by  an  acid. 


SECTION  II. 

VEGETABLE  ALKALIES. 

UxDEB,  this  title  are  comprehended  those  proximate  vegetable  prin- 
ciples which  are  possessed  of  alkaline  properties.  The  honour  of  dis- 
covering the  existence  of  this  class  of  bodies  is  due  to  Sertuerner,  a 
German  apothecary,  who  published  an  account  of  morphia  so  long  ago 
as  the  year  1803;  but  the  subject  excited  no  notice  until  the  publication 
of  his  second  essay  in  1816.  The  chemists  who  have  since  cultivated 
this  departrneht  with  most  success  are  M.  Robiquet,  and  MM.  Pelletier 
and  Caventdu. 

All  the  vegetable  alkalies,  according  to  the  researches  of  Pelletier 
and  Dumas,  consist  of  carbon,  hydrogen,  oxygen  and  nitrogen.  (An. 
de  Ch.  et  de  Ph.  xxiv.)  They  are  decomposed  with  facility  by  nitric 
acid  and  by  heat,  and  ammonia  is  always  one  of  the  products  of  the 
destructive  distillation.  They  never  exist  in  an  insulated  state  in  the 
plants  which  contain  them;  but  are  apparently  in  every  case  combined 
with  an  acid,  with  which  they  form  a salt  more  or  less  soluble  in  water. 
These  alkalies  are  for  the  most  part  very  insoluble  in  water,  and  of 
sparing  solubility  in  cold  alcohol;  but  they  are  all  readily  dissolved  by 
that  fluid  at  a boiling  temperature,  being  deposited  from  the  solution, 
commonly  in  the  form  of  crystals,  on  cooling.  Most  of  the  salts  are  far 
more  soluble  in  water  than  the  alkalies  themselves,  and  several  of  them 
are  remarkable  for  their  solubility. 

As  the  vegetable  alkalies  agree  in  several  of  their  leading  chemical 
properties,  the  mode  of  preparing  one  of  them  admits  of  being  applied 


476 


VEGETABLE  ALKALIES. 


with  slight  variation  to  all.  The  general  outline  of  the  method  is  as 
follows. — The  substance  containing  tlie  alkaline  principle  is  digested, 
or  more  commonly  macerated,  in  a large  quantity  of  water,  which  dis- 
solves the  salt,  the  base  of  wliich  is  the  vegetable  alkali.  On  adding 
some  more  powerful  salifiable  base,  such  as  potassa  or  ammonia,  or 
boiling  the  solution  for  a few  minutes  with  lime  or  pure  magnesia,  the 
vegetable  alkali  is  separated  from  its  acid,  and  being  in  that  state  inso- 
luble in  water,  may  be  collected  on  a filter  and  washed.  As  thus  pro- 
cured, however,  it  is  impure,  retaining  some  of  the  other  principles, 
such  as  the  oleaginous,  resinous,  or  colouring  matters  with  which  it  is 
associated  in  the  plant.  To  purify  it  from  these  substances,  it  should 
be  mixed  with  a little  animal  charcoal,  and  dissolved  in  boiling  alcohol. 
The  alcoholic  solution,  which  is  to  be  fdtered  while  hot,  yields  the  pure 
alkali,  either  on  cooling  or  by  evaporation;  and  if  not  quite  colourless, 
it  should  again  be  subjected  to  the  action  of  alcohol  and  animal  char- 
coal. In  order  to  avoid  the  necessity  of  employing  a large  quantity  of 
alcohol,  the  following  modification  of  the  process  may  be  adopted. 
The  vegetable  alkali,  after  being  precipitated  and  collected  on  a filter, 
is  made  to  unite  with  some  acid,  such  as  the  acetic,  sulphuric,  or  mu- 
riatic, and  the  solution  boiled  with  animal  charcoal  until  the  colouring 
matter  is  removed.  The  alkali  is  then  precipitated  by  ammonia  or  some 
other  salifiable  base. 

Morphia. 

Opium  contains  a great  diversity  of  different  principles,  among  which 
the  following  may  in  particular  be  enumerated; — morphia,  meconic 
acid,  narcotine,  gummy,  resinous,  and  extractive  colouring  matters, 
lignin,  fixed  oil,  and  a small  quantity  of  caoutchouc.  On  infusing  opium 
in  water,  several  of  these  principles  are  dissolved,  and  especially  me- 
conate  of  morphia,  together  with  narcotine,  which  is  likewise  rendered 
soluble  by  an  acid. 

One  of  the  best  processes  for  preparing  pure  morphia  is  that  recom- 
mended by  M.  Robiquet.  (An.  de  Ch.  et  de  Ph.  v.)  The  concentrated 
infusion  of  a pound  of  opium  is  boiled  for  a quarter  of  an  hour  with 
about  150  grains  of  pure  magnesia,  and  the  grayish  crystalline  precipi- 
tate, which  consists  of  meconate  of  magnesia,  morpjiia,  narcotine, 
colouring  matter,  and  the  excess  of  magnesia,  is  collected  on  a filter 
and  edulcorated  with  eold  water.  This  powder  is  then  digested  at  a 
temperature  of  120°  or  130°  F.  in  dilute  alcohol,  which  removes  the 
narcotine  and  the  greater  part  of  the  colouring  matter.  The  morphia 
is  then  taken  up  by  concentrated  boiling  alcohol,  and  is  deposited  in 
crystals  on  cooling.  Dr.  Christison  informs  me  that  by  this  process, 
conducted  in  the  laboratory  of  M.  Robiquet,  he  procured  three  drachms 
and  a half  of  morphia  from  half  a pound  of  a very  pure  specimen  of 
the  best  Turkey  opium. 

Dr.  Thomson  pi’oposes  to  precipitate  the  morphia  by  ammonia,  and 
to  purify  it  by  solution  in  acetic  acid  and  digestion  with  animal  char- 
coal. (Annals  of  Phil.  vol.  xv.)  This  process  is  very  convenient;  but 
it  docs  not  give  so  large  a product  as  the  foregoing,  as  some  of  tlie 
morphia  is  retained  in  solution.  The  animal  charcoal  should  be  depriv- 
ed of  phosphate  of  lime  by  muriatic  acid  before  being  used. 

Pure  morphia  cryslalli/es  readily  when  its  alcoholic  solution  is  eva- 
porated, and  yields  colourless  crystals  of  a brilliant  lustre.  They  most- 
ly occur  in  irregular  six-sided  ])risnis  with  dihedral  summits;  but  their 
primary  form  is  a right  rhombic  prism,  of  which  the  lateral  planes  only 
appear  in  the  crystals.  (Brooke.)  It  is  almost  wholly  insoluble  in  cold, 
and  to  a very  small  extent  in  hot  water.  It  is  soluble  in  strong  alcohol. 


VEGETABLE  ALKALIES. 


477 


especially  by  the  aid  of  heat.  In  its  pure  state  it  has  scarcely  any  taste; 
i but  when  rendered  soluble  by  combining*  with  an  acid  or  by  solution 
in  alcohol,  it  is  intensely  bitter.  It  has  an  alkaline  reaction,  and  com- 
bines with  acids,*  forming*  neutral  salts,  which  are  far  more  , soluble 
in  water  than  morphia  itself,  and  for  the  most  part  are  capable  of  crys- 
tallizing. 

Strong  nitric  acid  decomposes  morphia,  forming  a red  solution,  which 
by  the  continued  action  of  the  acid  acquires  a yellow  colour,  and  is  ul- 
timately converted  into  oxalic  acid.  This  circumstance  was  first  noticed 
by  Pelletier  and  Caventou;  but  it  is  not  peculiar  to  morphia,  since  nitric 
acid  has  a similar  effect  on  strychnia. 

Morphia  is  the  narcotic  principle  of  opium.  When  pure,  owing  to 
its  insolubility,  it  is  almost  inert^  for  M.  Orfila  gave  twelve  grains  of  it 
to  a dog  without  its  being  followed  by  any  sensible  effect.*  In  a state 
of  solution,  on  the  contrary,  it  acts  on  the  animal  system  with  great 
energy,  Sertuerner  having  noticed  alarming  symptoms  from  so  small  a 
quantity  as  half  a grain.  From  this  it  appears  to  follow  that  the  effects 
of  an  overdose  of  a salt  of  morphia  may  be  prevented  by  giving  a dilute 
solution  of  ammonia,  or  an  alkaline  carbonate,  so  as  to  precipitate  the 
vegetable  alkali.  When  carefully  administered  morphia  may  be  em- 
ployed very  advantageously  in  the  practice  of  medicine;  since,  accord- 
ing to  Magendie,  it  produces  the  soothing  effects  of  opium,  without 
causing  the  feverish  excitement,  heat,  and  headach  which  so  frequent- 
ly accompany  the  employment  of  that  drug.  The  best  mode  of  exhib- 
iting it  is  in  the  form  of  acetate  of  morphia,  a salt  which  is  very  soluble 
in  water,  and  crystallizes  in  divergent  prisms  by  evaporation.  The  basis 
of  Battley’s  sedative  liquor  is  supposed  to  be  acetate  of  morphia.  This 
compound,  from  being  inodorous,  and  therefore  less  easily  detected 
than  opium,  has  been  employed  for  criminal  purposes,  and  M.  Las- 
saigne  has  described  the  following  method  for  discovering  its  presence. 
(An.  de  Ch.  et  de  Ph.  xxv.  103.)  The  suspected  solution  is  evaporated 
by  a temperature  of  212°,  and  the  residue  treated  with  alcohol,  by 
which  the  acetate  of  morphia,  together  with  osmazome  and  some  salts, 
is  dissolved.  The  alcohol  is  next  evaporated,  and  water  added  to  sep- 
arate some  fatty  matter.  The  aqueous  solution  is  then  set  aside  for 
spontaneous  evaporation,  during  which  the  acetate  of  morphia,  if  pre- 
sent, crystallizes  in  divergent  prisms  of  a yellowish  colour.  The  salt  is 
recognised  by  its  bitter  taste,  by  yielding  a precipitate  with  ammonia, 
by  disengagement  of  acetic  acid  on  the  addition  of  concentrated  sul- 
phuric acid,  and  by  the  orange-red  colour  developed  by  nitric  acid. 

Morphia  may  be  distinguished  from  other  vegetable  alkalies  by  de- 
composing iodic  acid.  A grain  of  morphia  dissolved  in  7000  grains  of 
water  may  be  detected  by  this  means;  the  iodine,  which  is  set  free, 
forming  the  characteristic  blue  tint  with  starch.  (Serullas.) 

The  composition  of  morphia,  as  will  appear  from  the  following  num- 
bers, has  been  stated  differently  by  different  chemists.  The  specimen 
analyzed  by  Dr.  Thomson  must  surely  have  been  impure. 


* Judging  from  my  own  experience,  I cannot  believe  that  Orfila  is 
accurate  in  asserting  that  pure  morphia  is  nearly  inert:  I have  myself 
employed  it  on  several  occasions  with  very  marked  effects.  Even  ad- 
mitting that,  as  a general  rule,  insoluble  substances  have  no  action  on 
the  animal  economy,  it  may  be  a question  whether  morphia  is  not  dis- 
solved by  the  acid  which  it  meets  with  in  the  stomach.  B. 


478 


VEGETABLE  ALKALIES. 


Pelletier  and  Dumas. 

Bussy. 

Brande. 

Thomson. 

Carbon 

72.02 

69.0 

72.0 

44.72 

Oxygen 

14.84 

20.0 

17.0 

49.69 

Hydrogen 

7.61 

6.5 

5.5 

5.59 

Nitrogen 

5.53 

4.5 

5.5 

0.00 

100 

100 

100 

100 

Meconic  Acid. — This  acid,  so  named  from  MTjy.m  poppy,  was  procured 
by  M.  Robiquet  from  the  mag-nesian  precipitate  above  mentioned,  after 
the  morpliia  had  been  separated  from  it.  The  meconate  of  mag*nesia  is 
dissolved  in  dilute  sulphuric  acid,  and  muriate  of  baryta  is  then  added, 
which  throws  down  the  sulphate  and  meconate  of  that  base.  By  act- 
ing* on  this  precipitate  with  dilute  sulphuric  acid,  the  meconic  acid  is 
set  free,  and  crystallizes  when  its  solution  is  evaporated.  As  it  retains 
colouring*  matter  very  obstinately,  it  should  be  purified  by  sublimation. 
Meconic  acid  may  easily  be  prepared,  as  recommended  by  Dr.  Hare,  by 
precipitating*  the  acid  from  an  aqueous  infusion  of  opium  with  acetate 
of  lead,  and  decomposing*  the  insoluble  meconate  of  lead,  while  diffus- 
ed throug*h  water,  by  a current  of  sulphuretted  hydrogen  gas.  The 
filtered  solution  yields  crystals  of  meconic  acid  by  evaporation. 

Meconic  acid  has  a sour,  followed  by  a bitter  taste,  reddens  litmus 
paper,  and  is  very  soluble  both  in  water  and  alcohol.  It  is  characteriz- 
ed by  giving  a red  colour  to  a salt  of  the  peroxide  of  iron,  and  commu- 
nicates an  emerald-green  tint  to  sulphate  of  copper.  These  tests,  es- 
pecially the  former,  are  very  delicate,  and  afford  a means  of  inferring 
the  presence  of  opium,  when  the  morphia  cannot  be  detected.  (Ure  in 
Journal  of  Science,  N.  S.  vii.  56.)  It  exerts  no  action  on  the  animal 
system.  Its  presence  even  in  a dilute  solution  of  opium  may  be  de- 
tected by  acetate  of  lead.  The  insoluble  meconate  of  lead,  which 
subsides,  is  decomposed  by  sulphuric  acid,  and  on  adding  a persalt 
of  iron,  the  red  colour  caused  by  the  free  meconic  acid  makes  its  ap- 
pearance. 

Narcotine. — This  substance,  though  not  regarded  as  a vegetable  al- 
kali, may  be  conveniently  noticed  in  connexion  with  morphia.  It  was 
particularly  described  in  1803  by  Derosne,  and  was  long  known  by  the 
name  of  the  salt  of  Derosne.  Sertuerner  supposed  it  to  be  meconate  of 
morphia;  but  Robiquet  proved  that  it  is  an  independent  principle,  and 
applied  to  it  the  name  of  narcotine.  It  is  easily  prepared  by  evaporat- 
ing an  aqueous  infusion  of  opium  to  the  consistence  of  an  extract,  and 
digesting  it  in  sulphuric  ether.  This  solvent,  which  does  not  act  on 
meconate  of  morphia,  takes  up  all  the  narcotine,  and  deposites  it  in 
acicular  crystals  by  evaporation;  and  the  extract  of  opium,  thus  depriv- 
ed of  narcotine,  may  be  advantageously  employed  in  medical  practice. 
Morphia  may  be  purified  from  narcotine  in  the  same  manner. 

Pure  narcotine  is  insoluble  in  cold  and  very  slightly  soluble  in  hot 
water.  It  dissolves  in  oil,  ether,  and  alcohol,  the  latter,  though  dilut- 
ed, acting  as  a solvent  for  it  by  the  aid  of  heat.  It  does  not  possess 
alkaline  properties,  though  it  is  rendered  soluble  in  water  by  means 
of  an  acid.  Its  ])rcsence  in  an  aqueous  solution  of  opium  seems  owing 
to  a free  acid,  whicli  M.  Robiquet  imagines  to  be  different  from  the 
meconic.  Like  the  vegetable  alkalies,  nitrogen  enters  into* its  consti- 
tution. 

'I’he  inqdeasant  stimulating  ])r()])erties  of  opium  are  attributed  by 
Magendie  to  the  presence  of  narcotine,  tlic  ill  clfccts  of  which,  accord- 
ing to  the  experiments  of  the  same  physiologist,  are  in  a great  degree 
counteracted  by  acetic  acid.  These  results,  thougli  they  require  com 


VEGETABLE  ALKALIES. 


479 


firmation,  render  it  probable  that  the  superiority  assigned  to  the  black 
drop  over  the  comuion  tincture  of  opium  of  the  Pharmacopoeia  is  owing 
to  the  vegetable  acids  which  enter  into  its  composition. 

Cinchonia  and  Qumia. 

The  existence  of  a distinct  vegetable  principle  in  cinchona  bark  was 
inferred  by  Dr.  Duncan,  junior,  In  the  year  1803,  who  ascribed  to  it 
the  febrifuge  virtues  of  the  plant,  and  proposed  for  it  the  name  of  cm- 
chonin.*  Dr.  Gomez  of  Lisbon,  whose  attention  was  directed  to  the 
subject  by  the  researches  of  Dr.  Duncan,  succeeded  in  procuring  cin- 
chonin  in  a separate  state;  but  its  alkaline  nature  was  first  discovered  in 
1820  by  Pelletier  and  Caventou.  It  has  been  fully  established  by  the 
labours  of  those  chemists  that  the  febrifuge  property  of  bark  is  possess- 
ed by  two  alkalies,  the  cinchonia  or  cinchonin  of  Dr.  Duncan,  and 
quinia,  both  of  which  are  combined  with  kinic  acid.  These  principles, 
though  very  analogous,  are  distinctly  different,  standing  in  the  same 
relation  to  each  other  as  potassa  and  soda.  The  former  exists  in  Cin- 
chona condaminea,  or  pale  bark;  the  latter  is  present  in  C.  cordifoUa,  or 
yellow  bark;  and  they  are  both  contained  in  C,  ohlongifolia,  or  red  bark. 
They  were  procured  by  Pelletier  and  Caventou  by  a process  similar  to 
that  of  Robiquet  for  preparing  morphia;f  and  slight  modifications  of 
the  method  have  been  proposed  by  Badollier  and  Voreton.t  From  one 
pound  of  yellow  bark  Voreton  procured  80  grains  of  quinia,  which  is 
nearly  1.4  per  cent. 

Pure  cinchonia  is  white  and  crystalline,  requires  2500  times  its  weight 
of  boiling  water  for  solution,  and  is  insoluble  in  cold  water.  Its  proper 
menstruum  is  boiling  alcohol;  but  it  is  dissolved  in  small  quantity  by  oils 
and  ether.  Its  taste  is  bitter,  though  slow  in  being  perceived,  on  ac- 
count of  its  insolubility;  but  when  the  alkali  is  dissolved  by  alcohol  or 
an  acid,  the  bitterness  is  very  powerful,  and  accompanied  by  the  flavour 
of  cinchona  bark.  Its  alkaline  properties  are  exceedingly  well  marked, 
since  it  neutralizes  the  strongest  acids.  The  sulphate,  muriate,  nitrate, 
and  acetate  of  cinchonia  are  soluble  in  water,  and  the  sulphate  crys- 
tallizes in  very  short  six-sided  prisms  derived  from  an  oblique  rhom- 
boidal  pfism.  It  commonly  occurs  in  twin  crystals.  The  neutral  tar- 
trate; oxalate,  and  gallate  of  cinchonia  are  insoluble  in  cold,  but  maybe 
dissolved  by  hot  water,  or  by  alcohol. 

Quinia  or  quinine^  which  was  discovered  by  Pelletier  and  Caventou, 
does  not  crystallize  like  cinchonia  when  precipitated  from  its  solutions; 
but  it  has  a white,  porous,  and  rather  flocculent  aspect.  It  is  very  so- 
luble in  alcohol,  forming  a solution  which  is  intensely  bitter,  and  pos- 
sesses a distinct  alkaline  reaction.  Ether  likewise  dissolves  it,  but  it  is 
almost  insoluble  in  water.  Its  febrifuge  virtues  are  more  powerful  than 
those  of  cinchonia,  and  it  is  now  extensively  employed  in  the  practice  of 
medicine.  It  is  most  commonly  exhibited  in  the  form  of  sulphate,  a 
salt  of  such  activity  that  three  grains  have  been  known  to  cure  an  inter- 
mittent fever.  This  salt,  which  consists  of  90  parts  of  the  alkali  and  10 
of  the  acid,  crystallizes  in  delicate  white  needles,  having  the  appearance 
of  amianthus.  It  is  less  soluble  in  water  than  sulphate  of  cinchonia, 
but  is  very  bitter.  It  dissolves  readily  in  strong  alcohol  by  the  aid  of 
heat,  a character  which  affords  a useful  test  of  its  purity. 

The  analyses  of  different  chemists,  relative  to  the  composition  of  cin- 


* Edinburgh  New  Dispensatory,  11th  edit.  p.  299,  or  Nicholson’s 
Journal  for  1803. 

t Ann.  de  Ch.  et  de  Ph.  vol.  xv.  t Ibid.  vol.  xvii. 


480 


VEGETABLE  ALKALIES. 


clionia  and  quinia,  do  not  correspond  better  than  those  of  morpliia,  as 
appears  by  the  following-  results: — 

Pelletier  and  Dumas.  Brande. 


Carbon 

Cinchonia. 

76.97 

Quinia. 

75.02 

r . 

Cinchonia. 

79.30 

7^ 

Quinia. 

73.80 

Oxygen 

7.79 

10.43 

0.00 

5.55 

Hydrogen 

6.22 

6.66 

7.17 

7.65 

Nitrogen 

9.02 

8.45 

13.72 

13.00 

100.00 

100.56 

100.19 

100.00 

The  neutral  g-allate,  tartrate,  and  oxalate  of  quinia,  like  the  analo- 
gous salts  of  cinchonia,  are  insoluble  in  cold  water. 

From  the  new  facts  which  have  been  ascertained  relative  to  the  con- 
stituents of  bark,  the  action  of  chemical  tests  on  a decoction  of  this 
substance  is  now  explicable.  According  to  the  analysis  of  Pelletier  and 
Caventou,  the  different  kinds  of  Peruvian  bark,  besides  the  kinate  of 
cinchonia  or  quinia,  contain  the  following  substances: — a greenish  fatty 
matter;  a red  insoluble  matter;  a red  soluble  principle,  which  is  a variety 
of  tannin;  a yellow  colouring  matter;  kinate  of  lime;  gum,  starch,  and 
lignin.  It  is  hence  apparent  that  a decoction  of  bark,  owing  to  the 
tannin  which  it  contains,  may  precipitate  a solution  of  tartar  emetic,  of 
gelatin,  or  a salt  of  iron,  without  containing  a trace  of  the  vegetable 
alkali,  and  consequently  without  possessing  any  febrifuge  virtues.  An 
infusion  of  gall-nuts,  on  the  contrary,  causes  a precipitate  only  by  its 
gallic  acid  uniting  with  cinchonia  or  quinia,  and,  therefore,  affords  a test 
for  distinguishing  a good  from  an  inert  variety  of  bark. 

Sulphate  of  quinia,  from  its  commercial  value,  is  frequently  adultera- 
ted. The  substances  commonly  employed  for  the  purpose  are  water, 
sugar,  gum,  starch,  ammoniacal  salts,  and  earthy  salts,  such  as  sulphate 
of  lime  and  magnesia,  or  acetate  of  lime.  When  moderately  dried,  so 
as  to  expel  its  water  of  crystallization,  pure  sulphate  of  quinia  should 
lose  only  from  8 to  10  per  cent  of  water.  Sugar  may  be  detected  by 
dissolving  the  suspected  salt  in  water,  and  adding  precisely^so  much 
carbonate  of  potassa  as  will  precipitate  the  quinia.  The  taste  of  the 
sugar,  no  longer  obscured  by  the  intense  bitter  of  the  quinia,  will  gen- 
erally be  perceived;  and  it  may  be  separated  from  the  sulphate  of  po- 
tassa, by  evaporating  gently  to  dryness,  and  dissolving  the  sugar  by 
boiling  alcohol.  Gum  and  starch  are  left  when  the  impure  sulphate  of 
quinia  is  digested  in  strong  alcohol.  Ammoniacal  salts  are  discovered 
by  the  strong  odour  of  ammonia,  which  may  be  observed  when  the  sul- 
phate is  put  into  a warm  solution  of  potassa.  Earthy  salts  may  be  de- 
tected by  burning  a portion  of  the  sulphate.  Several  of  the  preceding 
directions  are  taken  from  a paper  on  the  subject  by  Mr.  Phillips.  (Phil. 
Mag.  and  Ann.  hi;  111.) 

Sertuerner  states,  cinchona  bark  contains  other  alkalies  besides  cin- 
chonia and  quinia,  and  which  are  to  be  considered  as  modifications  of 
these  alkalies.  One  in  particular  he  has  called  chinoidea.  The  obser- 
vations, however,  appear  to  be  erroneous;  the  mistake  was  occasioned 
by  the  ])r()perties  of  the  well  known  alkalies  being  obscured  by  adher- 
ing impurity.  (Journal  of  Science,  vii.  422.) 

Slrychnia, — Brucia. 

Slrychnia. — Strychnia  was  discovered  in  1818  by  Pelletier  and  Caven- 
tou in  the  fruit  of  tl»c  Slryclinos  ignatia  and  Strychnos  nux  vomica,  and 
has  since  1)een  extracted  by  the  same  chemists  from  the  Upas.  (An, 
de  Ch.  et  de  Ph.  x.  and  xxvi.) 


VEGETABLE  ALKALIES. 


481 


The  most  economical  process  for  preparing  this  alkali  is  that  recom- 
mended by  M.  Corriol.  (Journal  de  Pharmacie  for  October  1825,  p. 
492.)  It  consists  in  treating*  mix  vomica  with  successive  portions  of  cold 
water,  evaporating  the  solution  to  the  consistence  of  syrup,  and  precip- 
itating the  gum,  which  is  present,  by  alcohol.  The  alcoholic  solu- 
tion is  then  evaporated  to  the  consistence  of  an  extract  by  the  heat  of 
a water-bath.  The  extract,  which  consists  almost  entirely  of  igasurate 
of  strychnia,  is  dissolved  by  cold  water,  and  by  this  means  deprived  of 
a little  fatty  matter,  which  had  originally  been  dissolved,  probably 
through  the  medium  of  the  gum.  The  solution  is  next  heated,  and 
the  strychnia  precipitated  by  a slight  excess  of  lime  water,  and  then 
dissolved  by  boiling  alcohol.  On  evaporating  the  spirit,  the  alkali  is 
obtained  pure  except  in  containing  a little  brucia  and  colouring  matter, 
both  of  which  are  effectually  removed  by  maceration  in  dilute  alcohol. 

Strychnia  is  very  soluble  in  boiling  alcohol,  and  is  procured  in  minute 
four-sided  prisms  by  allowing  the  solution  to  evaporate  spontaneously. 
It  is  alm(?st  insoluble  in  water,  requiring  more  tlian  6000  parts  of  cold 
and  2500  of  boiling  water  for  solution;  but  notwithstanding  its  sparing 
solubility,  it  excites  an  insupportable  bitterness  in  the  mouth.  Water 
containing  only  l-600,000th  of  its  weight  of  strychnia  has  a bitter 
taste.  It  has  a distinct  alkaline  reactfon,  and  neutralizes  acids,  forming 
salts,  most  of  which  are  soluble  in  water.  It  is  united  in  the  nux 
vomica  and  St.  Ignatius’s  bean  with  igasuric  acid.  (Page  472.)  By  the 
action  of  strong  nitric  acid  it  yields  a red  colour;  but  it  appears  from 
some  recent  observations  of  Pelletier  and  Caventou,  that  the  red 
tint  is  owing  to  the  presence  of  some  impurity,  which  is  probably 
brucia. 

Strychnia  is  one  of  the  most  virulent  poisons  hitherto  discovered,  and 
is  the  poisonous  principle  of  the  substance  in  which  it  is  contained. 
Its  energy  is  so  great,  that  half  a grain  blown  into  the  throat  of  a rab- 
bit occasioned  death  in  the  course  of  five  minutes.  Its  operation  is 
always  accompanied  with  symptoms  of  locked  jaw  and  other  tetanic 
affections. 

Strychnia,  according  to  the  analysis  of  Pelletier  and  Dumas,  is  com- 
posed of  78.22  of  carbon,  6.38  of  oxygen,  6.54  of  hydrogen,  and  8.92 
of  nitrogen. 

Brucia. — This  alkali  was  discovered  in  the  Brucea  antidysenierica  by 
Pelletier  and  Caventou  soon  after  their  discovery  of  strychnia  (An.  de 
Ch.  et  de  Ph.  vol.  xii.);  and  it  likewise  exists  in  small  quantity  in  the 
St.  Ignatius’s  bean  and  nux  vomica.  In  its  bitter  taste  and  poisonous 
qualities,  it  is  very  similar  to  strychnia,  but  is  twelve  or  sixteen  times 
less  energetic  than  that  alkali.  It  is  soluble  both  in  hot  and  cold  alcohol, 
especially  in  tho  former;  and  it  crystallizes  when  its  solution  is  evapo- 
rated. Even  dilute  alcohol  by  aid  of  heat  dissolves  it,  and  on  this  pro- 
perty is  founded  the  method  of*  separating  it  from  strychnia.  It  is  more 
soluble  in  water  than  most  of  the  other  vegetable  alkalies,  requiring 
only  850  times  its  weight  of  cold,  and  500  of  boiling  water  for  solution. 
It  is  composed  of  75.04  of  carbon,  11.21  of  oxygen,  6.52  of  hydrogen, 

I and  7.22  of  nitrogen.  With  nitric  acid  it  acquires  a deep  blood-red 

j colour,  which  afterwards  passes  into  yellow;  and  when  either  of  these 

I changes  has  taken  place,  the  addition  of  protomuriate  of  tin  produces 

a pretty  violet  tint,  and  a precipitate  of  the  same  colour  subsides. 

Verairia,  Einetia^  Picrotoxia,  Solania,  Delphia^  fyc. 

Veratria. — The  medicinal  properties  of  the  seeds  of  the  Veratrum 
sahadillUi  and  the  root  of  the  Veratrum  album  or  white  hellebore,  and 
Colchicum  autumnale  or  meadow  saffron,  are  owing  to  the  peculiar  al- 

41 


482 


VEGETABLE  ALKALIES. 


kaline  principle  veratria,  which  was  discovered  by  Pelletier  and  Caven- 
touinl819,  and  may  be  extracted  by  the  usual  process.  (Journal  de 
Pharmacie,  vol.  yi.)  This  alkali,  which  appears  to  exist  in  those  plants 
in  combination  with  gallic  acid,  is  white  and  pulverident,  inodorous, 
and  of  an  acrid  taste.  It  recpiires  1000  times  its  weight  of  boiling,  and 
still  more  of  cold  water  for  solution.  It  is  very  soluble  in  alcohol,  and 
may  also  be  dissolved,  though  less  readily,  by  means  of  ether.  It  has 
an  alkaline  reaction,  and  neutralizes  acids;  but  it  is  a weaker  base  than 
morphia,  quinia,  or  strychnia.  It  acts  with  singular  energy  on  the 
membrane  of  the  nose,  exciting  violent  sneezings  though  in  very  min- 
ute quantity.  When  taken  internally  in  very  small  doses,  it  produces 
excessive  irritation  of  the  mucous  coat  of  the  stomach  and  intestines; 
and  a few  grains  were  found  to  be  fatal  to  the  lower  animals. 

Veratria,  according  to  the  analysis  of  Pelletier  and  Dumas,  consists 
of  66.75  of  carbon,  19.6  of  oxygen,  8.54  of  hydrogen,  and  5.04  of 
nitrogen. 

Ipecacuanha  consists  of  an  oily  matter,  gum,  starch,  lig- 
nin, and  a peculiar  principle,  which  was  discovered  in  1817  by  M.  Pel- 
letier, and  to  which  he  has  applied  the  name  of  emftine.  (Journal  de 
Pharmacie,  iii.)  » This  substance^  of  which  ipecacuanha  contains  16 
per  cent.,  appears  to  be  the  sole  cause  of  the  emetic  properties  of  that 
root,  and  is  procured  by  a process  similar  to  that  for  preparing  the  other 
vegetable  alkalies. 

Emetia  is  a white  pulverulent  substance,  of  a rather  bitter  and  dis- 
agreeable taste,  sparingly  soluble  in  cold  but  more  freely  in  hot  water, 
and  insoluble  in  ether.  It  is  readily  dissolved  by  alcohol.  At  122^  it 
fuses.  It  has  a distinct  alkaline  reaction,  and  neutralizes  acids;  but  its 
salts  are  little  disposed  to  crystallize.  (An.  de  Ch.  et  de  Ph.  xxiv.  181.) 
According  to  Pelletier  and  Dumas,  it  consists  of  carbon  64.57,  oxygen 
22.95,  hydrogen  7.77,  and  nitrogen  4.3. 

Picrotoxia.—Th^  bitter  poisonous  principle  of  Cocculus  indicus  was 
discovered  in  1819  by  M,  Bpullay,  who  gave  it  the  name  of  picrotoxin&. 

Its  claim  to  the  title  of  a vegetable  alkali,  among  which  class  of  bodies 
it  was  placed  by  its  discoverer,  has  been  called  in  question  by  M. 
Casaseca,  fi-om  whose  remarks  it  seems  that  picrotoxia  has  no  alkaline 
reaction,  and  does  not<  neutralize  acidity.  It  combines,  however, 
with  acids,  and  with  the  acetic  and  nitric  acids  forms  crystallizable 
compounds.  It  appears,  also,  that  the  menispermic  acid,  supposed 
by  M.  Boullay  to  be  united  in  cocculus  indicus  with  picrotoxia,  is  mere- 
ly a mixture  of  sulphuric  and  malic  acids.  (Edinburgh  Journal  of 
Science,  v. ) 

Corydalin. — This  alkali,  discovered  by  Dr.  Wackenroder,  is  contain- 
ed in  the  root  of  the  fumitory,  (not  the  common  fumitory,  Fumaria 
officinalis,  hwt)  Fumaria  cava  2cni\.  C or ydalis  tuber osa  It 

exists  in  the  plant  as  a soluble  malate,  and  is  precipitated  from  its  aque- 
ous solution  in  the  usual  manner,  and  purified  by  alcohol. 

It  is  soluble  in  alcohol,  and  the  hot  saturated  solution  in  cooling  yields 
coloui-lcss  prismatic- crystals  of  a line  in  length.  By  spontaneous  eva-  , 
poration  fine  laininx  are  formed.  It  is  likewise  soluble  in  ether,  but 
very  sparingly  in  water.  It  is  insi[)id  and  inodorous;  but  when  dissolv- 
ed by  acids  or  alcohol  it  is  very  bitter.  Its  .solution  has  an-alkaline  re- 
action, and  it  neutrali/es  acids.  Cold  dilute  nitric  acid  dissolves  it  and  | 
yields  a colourless  solution;  but  when  he.ated  it  acquires  a red  tint,  and  1 
becomes  blood  i-ed  when  concentrated.  Its  salts  are  precipitated  by  po-  j- 
tas.sa,  pure  or  carbonated,  and  by  infusion  of  gall-nuts.  The  precipitate  / l 
is  white  whe  n the  solution  is  dilute,  and  grayish-yellow  if  concentrated.  ; [ 
(Phil.  Mag.  and  An.  iv.  153.) 


VEGETABLE  ALKALIES. 


483 


Solania, — The  active  principle  of  the  Solarium  dulcamara,  or  woody 
nig'htshade,  was  procured  in  a pure  state  by  Desfosses;  and  the  same 
alkali  exists  in  other  species  of  solarium.  Solania  is  combined  in  the 
plant  with  malic  acid,  and  is  thrown  down  of  a gray  colour  by  ammo- 
nia from  the  expressed  and  filtered  juice  of  the  ripe  beri'ies.  After  be- 
ing well  washed  and  dried,  it  is  purified  by  solution  in  hot  alcohol,  from 
which  by  slow  evaporation  it  is  deposited  as  a white  powder  with  a pearly 
lustre.  It  is  insoluble  in  cold  water,  and  requires  8000  times  its 
weight  of  hot  water  for  solution.  Alcohol  is  its  proper  menstruum:  it 
is  sparingly  dissolved  by  ether,  and  is  insoluble  in  oil.  It  has  a distinct 
alkaline  reaction,  and  with  acids  forms  neutral  salts,  which  have  a bitter 
taste.  (Journ.de  Pharm.  vi.  and  vii.) 

Cynopia. — Professor  Ficinus  of  Dresden  has  discovered  a new  alkali 
in  the  Mihusa  cynapium,  or  lesser  hemlock,  to  which  he  has  given  the 
name  of  cynopia.  It  is  crystallizable,  and  soluble  in  water  and  alcohol, 
but  not  in  ether.  The  crystals  are  in  the  form  of  a I’hombic  prism, 
which  is  also  that  of  the  crystals  of  the  sulphate. 

Delphia. — This  substance  was  discovered  about  the  same  time  by 
Feneuille  and  Lassaigne  in  France,  and  Brandes  in  Germany,  in  the 
seeds  of  the  Delphinium  staphysagria  or  stavesacre.  It  is  easily  prepar- 
ed by  digesting  the  seeds  in  water  acidulated  with  sulphuric  acid,  and 
precipitating  by  magnesia  or  other  alkaline  substance.  It  is  then  puri- 
fied in  the  usual  manner  by  solution  in  alcohol  and  digestion  with  ani- 
mal charcoal.  It  is  left  by  evaporation  as  a white  crystalline  powder, 
which  is  almost  insoluble  in  water,  but  is  dissolved  by  alcohol,  ether, 
and  the  oils.  It  has  a feeble  alkaline  reaction,  and  yields  neutral 
salts  of  a bitter  taste,  but  which  rarely  crystallize.  (An.  de  Ch.  et  de 
Ph.xii.) 

Althea  wdiS  announced  by  M.  Bacon  of  Caen  as  a new  vegetable  alkali, 
said  to  be  procured  from  the  root  of  the  marsh-mallow.  (Althaea  offici- 
nalis.) According  to  M.  Plisson  this  alkali  has  no  existence,  and  what 
was  thought  to  be  supermalate  of  althea  is  asparagin. 

Sanguinaria  is  a vegetable  alkali,  obtained  by  M.  Dana  from  the 
Sanguinaria  Canadensis,  called  hlood-root  in  America  from  the  red  colour 
of  its  juice,  The  powdered  root  is  digested  in  pure  alcohol,  and  the 
red  solution  mixed  with  a little  ammonia  is  poured  into  water,  when  a 
brown  matter  subsides.  After  wasliing  carefully,  and  removing  colour- 
ing matter  by  animal  charcoal,  the  alkali  is  removed  by  hot  alcohol,  and 
obtained  by  evaporation  as  a pearly  white  matter  of  an  acrid  taste  and 
alkaline  reaction,  By  exposure  to  air  it  becomes  yellow.  It  is  insolu- 
ble in  water,  but  dissolved  by  alcohol  and  ether.  Its  salts  have  a red 
colour.  (Phil.  Mag.  and  An.  v.  151.) 

Besides  the  vegetable  alkalies,  already  described,  it  has  been  ren- 
dered highly  probable,  chiefly  by  the  reserrches  of  M.  Brandes,  that 
several  other  plants,  such  as  the  Airopa  belladonna,  Conium  maculatum, 
Hyoscyamus  niger.  Datura  stramonium,  and  Digitalis,  owe  their  activ- 
ity to  the  presence  of  an  alkali.  Vauquelin  rendered  it  ])robable  that 
an  alkali  is  contained  in  the  Daphne  mezereum,  to  which,  if  it  exist, 
the  name  of  daphnia  may  be  applied.  A vegetable  alkali  is  said  also  by 
MM.  Posselt  and  lleimann  to  be  obtained  from  tobacco.  It  is  described 
as  being  volatile,  and  a liquid  atSl^^F.,  characters  so  different  from 
those  of  other  vegetable  alkalies,  that  the  remarks  of  these  chemists 
require  confirmation  before  they  can  be  admitted  as  exact. 


484 


OILS. 


SECTION  III. 

SUBSTANCES  WHICH,  IN  RELATION  TO  OXYGEN,  CONTAIN 
AN  EXCESS  OF  HYDROGEN. 

Oils. 

Oils  are  characterized  by  a peculiar  unctuous  feel,  by  inflamma- 
bility, and  by  insolubility  in  water.  They  are  divided  into  the  fixed 
and  volatile  oils,  the  former  of  which  are  comparatively  fixed  in  the 
fire,  and,  therefore,  give  a permanently  greasy  stain  to  paper;  while 
the  latter,  owing  to  their  volatility,  produce  a stain  which  disappears 
by  gentle  heat. 

Fixed  Oils,—T\\Q.  fixed  oils  are  usually  contained  in  the  seeds  of  plants, 
as  for  example  in  the  almond,  linseed,  rape-seed,  and  poppy-seed;  but 
olive  oil  is  extracted  from  the  pulp  which  surrounds  the  stone.  They 
are  procured  by  bruising  the  seed,  and  subjecting  the  pulpy  matter  to 
pressure  in  hempen  bags,  a gentle  heat  being  generally  employed  at 
the  same  time  to  render  tlie  oil  more  limpid. 

Fixed  oils,  the  palm  oil  excepted,  are  fluid  at  common  temperatures, 
are  nearly  inodorous,  and  have  little  taste.  They  are  lighter  than  wa- 
ter, their  density  in  general  varying  from  0.9  to  0.96.  They  are  com- 
monly of  a yellow  colour,  but  may  be  rendered  nearly  or  quite  colour- 
less by  the  action  of  animal  charcoal.  At  or  near  the  temperatiwe  of 
600®  F.,  they  begin  to  boil,  but  suffer  partial  decomposition  at  the  same 
time,  an  inflammable  vapour  being  disengaged  even  below 500®.  When 
heated  to  redness  in  close  vessels,  a large  quantity  of  the  combustible 
compounds  of  carbon  and  hydrogen  are  formed,  together  with  the 
other  products  of  the  destructive  distillation  of  vegetable  substances; 
and  in  the  open  air  they  burn  with  a clear  white  light,  and  formation  of 
water  and  carbonic  acid.  They  may  hence  be  employed  for  the  pur- 
poses of  artificial  illumination,  as  well  in  lamps,  as  for  the  manufac- 
ture of  gas. 

Fixed  oils  undergo  considerable  change  by  exposure  to  the  air.  The 
rancidity  which  then  takes  place  is  occasioned  by  the  mucilaginous 
matters  whicli  they  contain  becoming  acid.  From  the  operation  of  the 
same  cause,  they  gradually  lose  their  limpidity,  and  some  of  them, 
which  are  hence  called  drying  oils,  become  so  dry  that  they  no  longer 
feel  unctuous  to  the  toucli  nor  give  a stain  to  paper.  This  property, 
for  which  linseed  oil  is  remarkable,  may  be  communicated  quickly 
by  heating  the  oil  in  an  open  vessel.  Drying  oils  are  employed  for 
making  oil  paint,  and  mixed  with  lamp-black  constitute  printer’s 
ink.  During  the  process  of  drying,  oxygen  is  absorbed  in  considerable 
quantity. 

The  ab.sorption  of  oxygen  by  fixed,  and  especially  by  drying  oils,  is 
under  some  circumstances  so  abundant  and  rapid,  and  a'ceompanied 
with  such  free  disengagement  of  caloric,  that  light  porous  combustible 
materials,  such  as  lampblack,  hem]),  or  cotton-wool,  maybe  kindled 
by  it.  Substances  of  this  kind,  moistened  with  linseed-oil,  have  been 
known  to  take  fire  during  tlie  space  of  24  hours,  a circumstance  which 
has  repeatedly  been  the  cause  of  extensive  fires  in  warehouses  and  in 
cotton  manufactories. 


OILS. 


485 


Fixed  oils  do  not  unite  with  water,  but  they  may  be  permanently  sus- 
pended in  that  fluid  by  means  of  mucilag'e  or  sut^ar,  so  as  to  constitute 
an  emulsion.  They  are  for  the  most  part  very  sparing-ly  soluble  in  alco- 
hol and  ether.  Strong*  sulphuric  acid  thickens  the  fixed  oils,  and  forms 
with  them  a tenacious  matter  like  soap;  and  they  are  likewise  rendered 
thick  and  viscid  by  the  action  of  chlorine.  Concentrated  nitric  acid  acts 
upon  them  with  great  energy,  giving  rise  in  some  instances  to  the  pro- 
duction of  flame. 

Fixed  oils  unite  with  the  common  metallic  oxides.  Of  these  com- 
pounds, the  most  interesting  is  that  with  oxide  of  lead.  When  linseed 
oil  is  heated  with  a small  quantity  of  litharge,  a liquid  results  which  is 
powerfully  drying,  and  is  employed  as  oil  varnish.  Olive  oil  combined 
with  half  its  weight  of  litharge  forms  diachylon  plaster. 

The  fixed  oils  are  readily  attacked  by  alkalies.  With  ammonia,  oil 
forms  a soapy  liquid,  to  which  the  name  of  volatile  liniment  is  applied. 
The  fixed  alkalies,  boiled  with  oil  or  fat,  give  rise  to  the  soap  employed 
for  washing,  the  soft  inferior  kind  being  made  with  potassa,  and  the 
hard  with  soda.  The  chemical  nature  of  soap  has  of  late  years  been 
elucidated  by  the  labours  of  M.  Chevreul.  This  chemist  has  found  that 
fixed  oils  and  fats  are  not  pure  proximate  principles,  but  consist  of  two 
substances,  one  of  which  is  solid  at  common  temperatures,  while  the 
other  is  fluid.  To  the  former  he  has  applied  the  name  of  stearine  from 
rrrsocp  y suet,  and  to  the  latter  elciine  from  oil.  Stearine  is  the 

chief  ingredient  of  suet,  butter,  and  lard,  and  is  the  cause  of  their 
solidit}^;  whereas  oils  contain  a greater  proportional  quantity  of  elaine, 
and  are  consequently  fluid.  These  prinoiples  may  be  separated  from 
one  another  by  exposing  fixed  oil  to  a low  temperature,  and  pressing  it, 
when  congealed,  between  folds  of  bibulous  paper.  The  stearine  is 
thus  obtained  in  a separate  form;  and  by  pressing  the  bibulous  paper 
under  water,  an  oily  matter  is  procured,  which  is  elaine  in  a state  of 
purity.  This  principle  is  peculiarly  fitted  for  greasing  the  wheels  of 
watches,  or  other  delicate  machinery,  since  it  does  not  thicken  or  be- 
come rancid  by  exposure  to  the  air,  and  requires  a cold  of  about  20°  F. 
for  congelation.  In  the  formation  of  soap,  the  stearine  and  elaine  dis- 
appear entirely,  being  converted  by  a change  in  the  arrangement  of 
their  elements  into  three  compounds,  to  which  Chevreul*  has  applied 
the  names  of  margaric  and  oleic  acids,  and  glycerine.  The  two  acids 
enter  into  combination  with  the  alkali  employed,  and  the  resulting 
compound  is  soap.  A similar  change  appears  to  be  effected  by  the  ac- 
tion not  only  of  the  alkaline  earths,  but  of  several  of  the  other  metallic 
oxides. 

Soap  is  decomposed  by  acids,  and  by  earthy  and  most  metallic  salts. 
On  mixing  muriate  of  lime  with  a solution  of  soap,  a muriate  of  the 
alkali  is  produced,  and  the  lime  forms  an  insoluble  compound  with  the 
margaric  and  oleic  acids.  A similar  change  ensues  when  a salt  of  lead 
is  employed. 

According  to  the  analysis  of  Gay-Lussac  and  Thenarcl,  100  parts  of 
olive  oil  consist  of  carbon  77.213,  oxygen  9.427,  and  hydrogen  13.36. 
From  these  proportions  it  is  inferred  that  olive  oil  contains  ten  equiva- 
lents of  carbon,  one  of  oxygen,  and  eleven  of'hydrogen. 

Volatile  Oils. — Aromatic  plants  owe  their  flavour  to  the  presence  of  a 
volatile  or  essential  oil,  which  may  be  obtained  by  distillation,  water  being 
put  into^  the  still  along  with  the  plant,  in  order  to  prevent  the  lattex' 
from  being  burned.  The  oil  and  water  pass  over  into  the  recipient,  and 


• Recherches  sur  les  Corps  gras. 
41* 


486 


OILS. 


the  oil  collects  at  the  bottom  or  at  the  surface  of  the  water  accordini? 
to  its  density.  ® 

Essential  oils  have  a penetrating-  odour  and  acrid  taste,  which  are 
often  pleasant  when  sufficiently  diluted.  They  are  soluble  in  alcohol, 
though  in  different  proportions.  They  arc  not  appreciably  dissolved 
by  water;  but  that  fluid  acquires  the  odour  of  the  oil  with  which  it 
is  distilled.  With  the  fixed  oils  they  unite  in  every  proportion,  and 
are  sometimes  adulterated  with  them,  an  imposition  easily  detected  by 
the  mixed  oil  causing  on  paper  a greasy  stain  which  is  not  removed  by 
heat. 

Volatile  oils  burn  in  the  open  air  with  a clear  white  light,  and  the 
sole  products  of  the  combustion  are  water  and  carbonic  acid.  On  ex- 
posure to  the  atmosphere,  they  gradually  absorb  a large  quantity  of 
oxygen,  in  consequence  of  which  they  become  thick,  and  are  at  length 
converted  into  a substance  resembling  resin.  This  change  is  rendered 
more  rapid  by  the  agency  of  light. 

Of  the  acids,  the  action  of  strong  nitric  acid  on  volatile  oils  is  the 
most  energetic,  being  often  attended  with  vivid  combustion,— an  effect 
which  is  rendered  more  certain  by  previously  adding  to  the  nitric  a few 
drops  of  sulphuric  acid. 

Volatile  oils  do  not  unite  readily  with  metallic  oxides,  and  are  attack- 
ed with  difficulty  even  by  the  alkalies.  The  substance  called  Starkey’s 
soap  is  made  by  triturating  oil  of  turpentine  with  an  alkali. 

Volatile  oils  dissolve  sul])hur  in  large  quantity,  forming  a deep  brown 
coloured  liquid,  called  balsam  of  sulphur.  The  solution  is  best  made 
by  boiling  flowers  of  sulphur  in  spirit  of  turpentine.  Phosphorus  may 
likewise  be  dissolved  by  the  same  menstruum. 

The  most  interesting  of  tlie  essential  oils  are  those  of  turpentine, 
caraway,  cloves,  peppermint,  nutmeg,  anise,  lavender,  cinnamon,  ci- 
tron, and  chamomile.  Of  these  the  most  important  is  the  first,  which 
is  much  employed  in  the  preparation  of  varnishes,  and  for  some  medi- 
cal and  chemical  purposes.  It  is  procured  by  distilling  common  turpen- 
tine; and  when  purified  by  a second  distillation,  it  is  spi7'it  or  essence  of 
turpentine.  In  this  state  it  is  limpid  and  colourless,  may  be  distilled 
without  residue,  and  yields  a dense  white  light  in  burning.  Its  boiling 
point  is  324^^  F.:  it  boils  indeed  slightly  at  280®,  but  the  thermometer 
is  not  stationary  until  it  reaches  324®. 

Common  oil  of  turpentine  is  inferred  by  Dr.  Ure  to  consist  of  fourteen 
equivalents  of  carbon,  one  of  oxygen,  and  ten  of  hydrogen.*  Accord- 
ing to  M.  Houton  Labillardiere,  the  purified  oil  contains  no  oxygen,  but 
is  composed  of  carbon  and  hydrogen  in  such  proportions,  that  one  vol- 
ume of  its  vapour  contains  four  volumes  of  olefiant  gas,  and  two  vol- 
umes of  the  vapour  of  carbon.-)- 

Camphor. — 'I'his  inflammable  substance,  which  in  several  respects  is 
closely  allied  to  the  essential  oils,  exists  ready  formed  in  the  Laurus 
camphora  of  Japan,  and  is  obtained  from  its  trunk,  root,  and  branches 
by  sul)limation. 

Camphor  has  a bitterish,  aromatic,  pungent  taste,  accompanied  with 
a sense  of  coolness.  It  is  unctuous  to  the  touch,  and  rather  brittle, 
llioiigh  po.ssessing  a dcgl’cc  of  toughness  which  prevents  it  from  being 
pulverized  with  facility;  but  it  is  easily  reduced  to  powder  by  tritura- 
tion with  a few  drops  of  alcohol.  Its  specific  gravity  is  0.988.  It  is 


• Philosophical  Transactions  for  1822. 
■)•  Journal  dc  Fharmacie,  vol.  iv. 


hesins.  ‘ 48r 

exceecVing’ly  volatile,  being  gradually  dissipated  in  vapour  if  kept  in 
open  vessels.  At  288°  F.  it  enters  into  fusion,  and  boils  at  400®  F. 

Camphor  is  insoluble  in  water;  bwt  when  triturated  with  sugar,  and 
then  mixed  with  that  fluid,  a portion  is  dissolved  sufficient  for  commu- 
nicating its  flavour.  It  is  dissolved  freely  by  alcohol,  and  is  thrown  dpwn 
by  the  addition  of  water.  It  is  likewise  soluble  in  the  fixed  and  volatile 
oils,  and  in  strong  acetic  acid.  Sulphuric  acid  decomposes  camphor, 
converting  it  into  a substance  like  artificial  tannin.  (Mr-  Hatchett.) 
With  the  nitric  it  yields  camphoric  acid. 

Camphor,  according  to  the  analysis  of  Dr.  Ure,  appears  to  consist  of 
ten  equivalents  of  carbon,  one  equivalent  of  oxygen,  and  nine  equiv- 
alents of  hydrogen. 

On  transmitting  a current  of  dry  muriatic  acid  gas  through  the  puri- 
fied oil  of  turpentine,  surrounded  by  a mixture  of  snow  and  salt,  a 
quantity  of  gas  is  absorbed  equal  to  one-third  of  the  weight  of  the  oil; 
the  liquid  acquires  a deep  brown  colour;  and  a white  crystalline  sub- 
stance, very  similar  to  camphor,  is  slowly  generated.  This  matter  was 
discovered  by  Kind,  and  has  since  been  studied  by  Trommsdorf,  Gehlen, 
and  Thenard.  The  last  chemist  maintains  that  this  peculiar  substance 
is  a compound  of  turpentine  and  muriatic  acid,  a view  which  is  sup- 
ported by  the  researches  of  M.  Houton  Labillardiere. 

Coumarin, — This  name  was  first  applied  to  the  odoriferous  principle 
of  the  Tonka  bean  by  M.  Guibourt,  and  has  since  been  adopted  by 
MM.  Boullay  and  Boutron-Charlard.  (Journal  de  Pharmacie  for  October, 
1825.)  It  is  derived  from  the  term  Coumaroima  odorata^  given  by 
Stublet  to  the  plant  which  ytel^s  the  bean. 

Coumarin  is  white,  of  a hot  pungent  taste,  and  distinct  aromatic 
odour.  It  crystallizes  sometimes  in  square  needles,  and  at  other  times 
in  short  prisms.  It  is  moderately  hard,  fracture  clean,  lustre  consider- 
able, and  density  greater  than  that  of  water.  It  fuses  at  a moderate 
temperature  into  a transparent  fluid,  which  yields  an  opake  crystalline 
mass  on  cooling.  Heated  in  close  vessels,  it  is  sublimed  without  change. 
It  is  sparingly  soluble  in  water;  but  is  readily  dissolved  by  ether  and 
alcohol,  and  the  solutions  crystallize  by  spontaneous  evaporation.  It  is 
very  soluble  in  fixed  and  volatile  oils. 

, M.  Vogel  mistook  coumarin  for  benzoic  acid;  but  MM.  Boullay  and 
Boutron-Charlard  maintain,  that  it  has  neither  an  acid  nor  alkaline  re- 
action, and  that  it  is  a peculiar  independent  principle,  nearly  allied  to 
the  essential  oils.  These  chemists  did  not  find  any  benzoic  acid  in  the 
Tonka  bean,  and  consider  coumarin  as  the  sole  cause  of  its  odour. 

Besins. 

Kesins  are  the  inspissated  juices  of  plants,  and  commonly  occur 
either  pure  or  in  combination  with^an  essential  oil.  They  are  solid  at 
common  temperatures,  brittle,  inodorous,  and  insipid.  They  are  non- 
conductors of  electricity,  and  when  rubbed  become  negatively  electric. 
They  are  generally  of  a yellow  colour,  and  semi-transparent. 

Resins  are  fused  by  the  appfication  of  heat,  and  by  a still  higher  tem- 
perature are  decomposed.  In  close  vessels  they  yield  empyreumatic 
oil,  and  a large  quantity  of  carburetted  hydrogen,  a small  residue  of 
charcoal  remaining.  In  the  open  air  they  burn  with  a yellow  flame  and 
much  smoke,  being  resolved  into  carbonic  acid  and  water. 

Resins  are  dissolved  by  alcohol,  ether,  and  the  essential  oils,  and 
the  alcoholic  and  ethereal  solutions  are  precipitated  by  water,  a fluid  in 
which  they  are  quite  insoluble.  Their  best  solvent  is  pure  potassa  and 
soda,  and  they  are  also  soluble  in  the  alkaline  carbonates  by  the  aid  of 


488 


AMBER. 


heat.  The  product  is  in  each  case  a soapy  compound,  which  is  de- 
composed by  an  acid. 

Concentrated  sulphuric  acid  dissolves  resins;  but  the  acid  and  the 
resin  mutually  decompose  each  other,  with  disengag’ement  of  sulphu- 
rous acid,  and  deposition  of  charcoal.  Nitric  acid  acts  upon  them 
with  violence,  converting*  them  into  a species  of  tannin,  which  was 
discovered  by  Mr.  Hatchett.  No  oxalic  acid  is  formed  during  the 
action. 

N The  uses  of  resin  are  various.  Melted  with  wax  and  oil,  resins  consti- 
tute ointments  and  plasters.  Combined  with  oil  or  alcohol,  they  form 
different  kinds  of  oil  and  spirit  varnish.  Sealing-  wax  is  composed  of 
lac,  Venice  turpentine,  and  common  resin.  The  composition  is  colour- 
ed black  by  means  of  lam])-black,  or  red  by  cinnabar  or  red  lead. 
Lamp-black  is  the  soot  of  imperfectly  burned  resin. 

Of  the  different  resins  the  most  important  are  common  resin,  copal, 
lac,  sandarach,  mastich,  elemi,  and  dragon’s  blood.  'I'he  first  is  pro- 
cured by  heating  turpentine,  which  consists  of  oil  of  turpentine  and 
resin,  so  as  to  expel  the  volatile  oil.  The  common  turpentine,  obtain- 
ed by  incisions  made  in  the  trunk  of  the  Scotch  fir-tree  {Finns  sylvestris) 
is  employed  for  tliis  purpose;  but  the  other  kinds  of  turpentine,  such  as- 
Venice  turpentine,  that  from  the  larch  {Finns  larix^)  Canadian  turpen- 
tine from  the  Finns  halsamea,  or  the  Strasburgh  turpentine  from  the 
Finns picea^  yield  resin  by  a similar  treatment. 

When  turpentine  is  extracted  from  the  wood  of  the  fir-tree  by  heat, 
partial  decomposition  ensued,  and  a dark  substance,  consisting  of  resin, 
empyreumatic  oil,  and  acetic  acid  is  the  product.  This  constitutes  tar; 
and  when  inspissated  by  boiling,  it  forms  pitch.  Common  resin  fuses 
at  276^  F.,  is  completely  liquid  at  306^,  and  at  about  316°  bubbles  of 
gaseous  matter  escape,  giving  rise  to  the  appearance  of  ebullition.  By 
distillation  it  yields  empyreumatic  oils:  in  the  first  part  of  the  process  a 
limpid  oil  passes  over,  which  rises  in  vapour  at  300°  F.,  and  boils  at 
360°;  but  subsequently  the  product  becomes  less  and  less  limpid,  till 
towards  the  close  it  is  very  thick.-  This  matter  becomes  limpid  when 
heat  is  applied,  and  boils  at  about  500°  F.  At  a red  heat  resin  is  en- 
tirely decomposed,  yielding  a large  quantity  of  combustible  gas,  which 
is  employed  for  the  purpose  of  artificial  illumination.  (Page  252.) 

Considerable  uncertainty  prevails  as  to  the  composition  of  common 
resin,  as  will  appear  by  the  following  statement; — 


Gay-Lussac  and  Thenard. 

Thomson. 

Tire. 

Carbon,  75.944 

63.15 

75.00 

Oxygen,  13.337 

25.26 

12.50 

Hydrogen,  10.719 

11.59 

12.50 

100 

100 

100 

Amber. — This  substance  is  brought  chiefly  from  the  southern  coast  of 
the  Baltic,  occurring  sometimes  in  beds  of  bituminous  wmod,  and  at 
others  on  the  shore,  being  doubtless  w;^shed  out  from  strata  of  brown 
coal  by  the  action  of  water.  Its  vegetable  origin  is  amply  attested  by 
the  substances  with  which  it  is  associated,  byjts  resinous  nature,  and 
by  the  vegetable  matters  whicli  it  frecpicntly  envelops.  It  is  c'ommonly 
met  with  in  translucent  pieces  of  various  shades  of  yellow  and  brown; 
but  it  is  sometimes  transparent.  Its  specific  gravity  varies  from  1.065 
to  1.07.  It  may  be  regarded  as  a mixture  of  several  substances;  name- 
ly, a volatile  oil,  succinic  acid,  separable  like  the  former  by  heat,  two 
different  modifications  of  resin  both  soluble  in  alcohol  and  ether,  and  a 


CAOUTCHOUC. 


489 


peculiar  bituminous  matter,  which  is  insoluble  in  both,  and  is  the  most 
abundant  principle  in  amber.  (Berzelius.) 

Balsams. — I lie  balsams  are  native  compounds  of  resin  and  benzoic 
acid,  and  issue  from  incisions  made  in  the  trees  which  contain  them,  in 
the  same  manner  as  turpentine  from  the  fir.  Some  of  them,  such  as 
storax  and  benzoin,  are  solid;  while  others,  of  which  the  balsams  of 
Tolu  and  Peru  are  examples,  are  viscid  fluids. 

Gum-resins. — The  substances  to  which  this  name  is  applied  are  the 
concrete  juices  of  certain  plants,  and  consist  of  resin,  essential  oil, 
gum,  and  extractive  vegetable  matter.  The  two  former  principles  are 
soluble  in  alcohol,  and  the  two  latter  in  water.  Their  proper  solvent, 
therefore,  is  proof  spirit.  Under  the  class  of  gum-resins  are  com- 
prehended several  valuable  medicines,  such  as  aloes,  ammoniacum, 
assafatida,  eupliorbium,  galbanura,  gamboge,  myrrh,  scammony,  and 
guaiacum. 

Caoutchouc^  commonly  called  elastic  gum  or  Indian  rubber,  is  the 
concrete  juice  of  the  Hocvea  caoutchouc  and  Jatropa  elastica,  natives  of 
South  America,  and  of  the  Ficus  Indica  and  Artocarpus  mtegrifoUuy 
which  grow  in  the  East  Indies.  It  is  a soft  yielding  solid,  of  a whitish 
colour  when  not  blackened  by  smoke,  possesses  considerable  tenacity, 
and  is  particularly  remarkable  for  its  elasticity.  It  is  inflammable,  and 
burns  with  a bright  flame.  When  cautiously  heated,  it  fuses  without 
decomposition.  It  is  insoluble  in  water  and  alcohol;  but  it  dissolves, 
though  with  some  difficulty,  in  pure  ether.  It  is  very  sparingly  dissolv- 
ed by  the  alkalies,  but  its  elasticity  is  destroyed  by  their  action.  By  the 
sulphuric  and  nitric  acids  it  is  decomposed,  the  former  causing  deposi- 
tion of  charcoal,  and  the  latter  formation  of  oxalic  acid. 

Caoutchouc  is  soluble  in  the  essential  oils,  in  petroleum,  and  in  caju- 
put  oil;  and  may  be  procured  by  evaporation  from  the  two  latter  with- 
out loss  of  its  elasticity.  The  purified  naphtha  from  coal  tar  dissolves 
it  readily,  and  as  the  solvent  is  cheap,  and  ihe  properties  of  the  caout- 
chouc are  unaltered  by  the  process,  the  solution  may  be  conveniently 
employed  for  forming  elastic  tubes,  or  other  apparatus  of  a similar  kind. 
It  is  used  by  Mr.  Mackintosh  of  Glasgow  for  covering  cloth  with  a thin 
stratum  of  caoutchouc,  so  as  to  render  it  impermeable  to  moisture. 
This  property  of  coal  naphtha  was  discovered  by  Mr.  James  Syme, 
Lecturer  on  Surgery  in  Edinburgh.  (Annals  of  Philosophy,  xii.)* 

The  composition  of  caoutchouc  has  not  been  satisfactorily  deter- 
mined. According  to  the  analysis  of  Dr.  Ure,  100  parts  of  it  consist 
of  carbon  90,-  oxygen  0.88,  and  hydrogen  9.12.  But  caoutchouc 


* Dr.  J.  K.  Mitchell,  Lecturer  on  Chemistry  in  the  Philadelphia 
Medical  Institute,  has  discovered  a mode  of  making  sheet-caoutchouc, 
which  possesses  remarkable  properties.  It  is  prepared  by  soaking  the 
caoutchouc  in  ether  until  soft,  which  generally  requires  eight  or  ten 
hours,  and  in  that  state,  cutting  it  into  plates  or  sheets  with  a wet  knife, 
or  stretching  it  to  any  desired  degree  of  thinness.  If  bags  of  this  sub- 
stance are  employed,  they  may  be  expanded  by  means  of  the  breath  to 
the  size  of  between  two  and  three  feet  in  diameter,  and  become  so 
light  as  to  ascend  readily  when  filled  with  hydrogen. 

Sheet-caoutchouc,  prepared  by  this  process,  is  very  soft  and  pleas- 
ant to  the  touch,  possesses  great  extensibility,  and  may  be  made  so 
thin  as  to  ap])ear  nearly  colourless  and  transparent,  yet  retaining  consi- 
derable strength  and  tenacity.  When  two  ])ieces  are  laid  together  and 
cut  with  scissors,  the  cut  edges  adhere  with  considerable  force,  and, 
indeed,  after  some  hours’  maceration,  unite  as  strongly  as  the  rest  of 


490 


WAX. 


yields  ammonia  vvlien  heated  in  close  vessels,  and,  therefore,  must  con- 
tain nitrog'en  as  one  of  its  constituents,  a principle  which  was  not  de- 
tected by  I)r.  Ure. 

Wax. — This  substance,  which  partakes  of  the  nature  of  a fixed  oil, 
is  an  abundant  vegetable  production,  entering  into  the  composition  of 
the  pollen  of  flowers,  covering  the  envelop  of  tlie  plum  ilnd  other  fruits, 
especially  the  berries  of  the  Myrica  cerlferaf  and  in  many  instances 
forming  a kind  of  varnish  to  the  surface  of  leaves.  From  this  circum- 
stance, it  was  long  supposed  that  wax  is  solely  of  vegetable  origin,  and 
that  the  wax  of  tlie  honey-comb  is  derived  from  flowers  only;  but  it  ap- 
pears from  the  observations  of  Huber  that  it  must  likewise  be  regarded 
as  an  animal  product,  since  he  found  bees  to  deposite  wax,  though  fed 
upon  nothing  but  sugar. 

Common  wax  is  always  more  or  less  coloured,  and  has  a distinct  pe- 
culiar odour,  of  both  which  it  may  be  deprived  by  exposure  in  thin 
slices  to  air,  light,  and  moisture,  or  more  speedily  by  the  action  of  chlo- 
rine. At  ordinary  temperatures  it  is  solid,  and  somewhat  brittle;  but  it 
may  easily  be  cut  with  a knife,  and  the  fresh  surface  presents  a char- 
acteristic appearance,  to  which  the  name  of  waxy  lustre  is  applied.  Its 
specific  gravity  is  0.96.  At  about  150*^  F.  it  enters  into  fusion,  and 
bolls  at  a high  temperature.  Heated  to  redness  in  close  vessels  it  suffers 
complete  decomposition,  yielding  products  very  similar  to  those  which 


the  sheet.  In  this  way,  tubes,  bags,  socks,  caps,  &c.  both  water  and 
air-tight  may  be  formed. 

The  properties  of  this  preparation  are  very  similar  to  those  of  the 
sheet-caoutchouc,  made  by  Mr.  Hancock  of  London. 

Dr.  Mitchell  has  also  discovered  a good  solvent  for  caoutchouc.  It  is 
the  essential  oil  of  sassafras,  acting  on  the  substance  after  it  has  been 
softened  by  ether.  A solution  of  it  in  this  oil,  applied  to  glass  or  porce- 
lain, will  form  upon  drying  a thin  pellicle  of  pure 'caoutchouc,  which, 
by  wetting  it  with  water,  can  be  separated  in  the  form  of  a sheet.  Ap- 
plied to  the  surfaces  of  torn  or  cut  caoutchouc,  it  causes  their  firm  and 
inseparable  adhesion.  Durandy  Jow'n.  ef  the  Phil.  College  of  Pharmacy y 
Jan.  1830. 

Since  the  above  note  wa^  written  for  the  preceding  American  edition 
of  ihis  work,  Dr.  Mitchell  has  favoured  me  with  the  following  detailed 
description  of  his  peculiar  mode  of  preparing  bags  of  caoutchouc  of 
large  size: — “ Soak  the  common  bags  in  sulphuric  ether,  sp.  gr.  0.753, 
at  a temperature  not  less  than  50*^  Fahr.  for  a period  of  time  not  less 
than  one  week  (the  longer  the  better.)  Empty  the  bag,  wipe  it  dry, 
put  into  it  some  dry  powder,  such  as  starch,  insert  a tube  into  the  neck, 
and  fasten  it  by  a broad  soft  band  slightly  applied,  and  then  commence 
by  mouth  or  bellows  the  inflation.  If  the  bag  be  unequal  in  thickness, 
restrain  by  the  hand  the  bulging  of  the  thinner  parts,  until  the  thicker 
have  been  made  to  give  way  a little.  When  the  bag  has  become  by 
such  means  nearly  uniform,  inflate  a little  more,  shake  up  the  included 
starch,  and  let  the  bag  collapse.  Repeat  the  inflation,  and  carry  it  to  a 
greater  extent,  again  ])ermit  the  collapse,  again  inflate  still  more  ex- 
tensively, and  so  on,  until  the  bag  is  sufficiently  distended.  Mere  gas 
holders  ai’e  thus  easily  made,  but  it  ]’c([uires  some  dexterit}’’  and  experi- 
ence to  make  them  thin  enough  for  balloons.  The  whole  experiment 
should  not  occupy  more  than  IVom  five  to  twenty  minutes  of  time;  and 
the  pre[)ared  bag  should  be  closed  and  hung  up  to  drj-  for  a day  or 
two.’’  11. 


ALCOHOL. 


491 


are  procured  under  the  same  circumstances  from  oil.  As  it  burns  with 
a clear  white  light,  it  is  employed  for  forming  candles. 

Wax  is  insoluble  in.  water,  and  is  only  sparingly  dissolved  by  boiling 
alcohol  or  ether,  from  which  the  greater  part  is  deposited  on  cooling. 
It  is  readily  attacked  by  the  fixed  alkalies,  being  converted  into  a soap 
which  is  soluble  in  hot  water;  and  according  to  Pfaff,  the  action  is  at- 
tended, as  in  oils,  with  the  formation  of  an  acid,  to  which  the  name  of 
ceric  odd  is  applied.  It  unites  by  the  aid  of  heat  in  every  proportion 
with  the  fixed  and  volatile  oils,  and  with  resin.  With  different  quanti- 
ties of  oil  it  constitutes  the  simple  liniment,  ointment,  and  cerate  of  the 
Pharmacopoeia.  , 

Wax,  according  to  the  observation  of  John,  consists  of  two  different 
principles,  one  of  which  is  soluble,  and  t)ie  other  insoluble  in  alcohol. 
To  the  former  he  has  given  the  name  of  cerhi,  and  to  the  latter  of 
myricin.  From  the  ultimate  analysis  of  Dr.  Ure,  whose  result  cor- 
responds closely  with  that  of  Gay-Lussac  and  Thenard,  100  j^arts  of 
wax  are  composed  of  carbon  80.4,  oxygen  8.3,  and  hydrogen  11.3;  from 
which  it  is  probable  that  it  consists  of  thirteen  equivalents  of  the  first 
element,  one  equivalent  of  the  second,  and  eleven  equivalents  of  the 
third. 

Mcohoh 

Alcohol  is  the  intoxicating  ingredient  of  all  spirituous  and  vinous 
liquors.  It  does  not  exist  ready  formed  in  plants,  but  is  a product  of 
the  vinous  fermentation,  the  theory  of  which  will  be  stated  in  a subse- 
quent section. 

Common  alcohol  or  spirit  of  wdne  is  prepared  by  distilling  whisky  or 
some  ardent  spirit,  and  the  rectified  spirit  of  wine  is  procured  by  a se- 
cond distillation.  The  former  has  a specific  gravity  of  about  0.867,  and 
the  latter  of  0.835  or  0.84.  In  this  state  it  contains  a quantity  of  water, 
from  which  it  may  be  freed  by  the  action  of  substances  which  have  a 
strong  affinity  for  that  liquid.  Thus,  when  carbonate  of  potassa,  heat- 
ed to  about  300®  F.  is  mixed  with  spirit  of  wine,  the  alkali  unites  with 
the  water,  forming  a dense  solution,  which,  on  standing,  separates 
from  the  alcohol,  so  that  the  latter  may  be  removed  by  decantation.  To 
the  alcohol,  thus  deprived  of  part  of  its  water,  fresh  portions  of  the 
dry  carbonate  are  successively  added,  until  it  falls  through  the  spirit 
without  being  moistened.  Other  substances,  which  have  a powerful 
attraction  for  water,  may  be  substituted  for  carbonate  of  potassa.  Gay- 
Lussac  recommends  the  use  of  pure  lime  or  baryta;  (An.  de  Ch.  Ixxxvi.) 
and  dry  alumina  may  also  be  employed  with  advantage.  A very  conve- 
nient process  is  to  mix  the  alcohol  with  chloride  of  calcium  in  powder, 
or  with  quicklime,  and  draw  off  the  stronger  portions  by  distillation. 
Another  process  which  has  been  recommended  for  depriving  alcohol  of 
water  is  to  put  it  into  the  bladder  of  an  ox,  and  suspend  it  over  a sand 
bath.  The  water  gradually  passes  through  the  coats  of  the  bladder, 
while  the  pure  alcohol  is  retained;  but  though  this  method  answers  well 
for  strengthening  weak  spirit,  its  power  of  purifying  strong  alcohol  is 
very  questionable.  (Journal  of  Science,  xviii.)  J'he  strongest  alcohol 
which  can  be  procured  by  any  of  these  processes  has  a specific  gravity 
of  0.796  at  60®  F.  This  is  called  absolute  alcohol,  on  the  supposition  of 
its  being  quite  free  from  water. 

An  elegant  and  easy  process  for  procuring  absolute  alcohol  has  lately 
been  proposed  by  Mr.  Graham.  (Edinburgh  Philos.  Trans,  for  1828.) 
A large  shallow  basin  is  covered  to  a small  depth  with  quicklime  in 
coarse  powder,  and  a smaller  one  containing  three  or  four  ounces  of 
commercial  alcohol  is  supported  just  above  it.  The  whole  is  placed 


492 


ALCOHOL. 


upon  the  plate  of  an  air  pump,  covered  by  a low  receiver,  and  the  air 
withdrawn  until  the  alcohol  evinces  sig’ns  of  ebullition.  Of  the  min- 
gled vapours  of  water  and  alcohol  which  fill  the  receiver,  the  former 
alone  is  absorbed  by  the  quicklime,  while  the  latter  is  unaffected.  Now 
it  is  found  that  water  cannot  remain  in  alcohol,  unless  covered  by  an  at- 
mosphere of  its  own  vapour;  and  consequently  the  water  continues  to 
evaporate  without  interruption,  while  the  evaporation  of  the  alcohol  is 
entirely  arrested  by  tl:e  pressure  of  the  vapour  of  alcohol  on  its  sur- 
face. Common  alcohol  is  in  this  way  entirely  deprived  of  water  in  the 
course  of  about  five  days.  The  temperature  should  be  preserved  as 
uniform  as  possible^during  the  process.  Sulphuric  acid  cannot  be  sub- 
stituted for  quicklime,  since  both  vapours  are  absorbed  by  this  liquid. 

‘Alcohol  is  a colourless  fluid,  of  a penetrating  odour,  and  burning 
taste.  It  is  highly  volatile,  boiling,  when  its  density  is  0 820,  at  the 
temperature  of  176®  F.  The  specific  gravity  of  its  vapour,  according 
to  Gay-Lussac,  is  1.613.  Like  volatile  liquids  in  general,  it  produces 
a considerable  degree  of  cold  during  evaporation.  It  has  hithei-to  re- 
tained its  fluidity  under  every  degree  of  cold  to  which  it  has  been  ex- 
posed. Mr.  Hutton,  indeed,  announced  in  the  34th  volume  of  Nichol- 
son’s Journal,  that  he  had  succeeded  in  freezing  alcohol;  but  the  fact 
itself  is  regarded  as  doubtful,  since  no  description  of  the  method  has 
hitherto  been  published,  In  the  experiments  of  Mr.  AValker,  alcohol 
was  found  to  retain  its  fluidity  at  — 91®  F. 

Alcohol  is  highly  inflammable,  and  burns  with  a lambent  yellowish- 
blue  flame.  Its  colour  varies  considerably  with  the  strength  of  the  al- 
cohol, the  blue  tint  predominating  when  it  is  strong,  and  the  yellow 
when  it  is  diluted.  Its  combustion  is  not  attended  with  the  least  de- 
gree of  smoke,  and  the  sole  products  are  water  and  carbonic  acid 
When  transmitted  through  a red-hot  tube  of  porcelain,  it  is  resolved  into 
carburetted  hydrogen,  carbonic  oxide,  and  water,  and  the  tube  is  lined 
with  a small  quantity  of  charcoal. 

Alcohol  unites  with  water  in  every  proportion.  The  act  of  combin- 
ing is  usually  attended  with  diminution  of  volume,  so  that  a mixture  of 
50  measures  of  alcohol  and  50  of  water  occupies  less  than  100  measures. 
Owing  to  this  circumstance,  the  action  is  accompanied  with  increase  of 
temperature.  Since  the  density  of  the  mixture  increases  as  the  water 
predominates,  the  strength  of  the  spirit  may  be  estimated  by  its  specific 
gravity.  Equal  weights  of  absolute  alcohol  and  water  constitute  proof 
spirit,  the  density  of  which  is  0.917;  but  the  proof  spirit  employed 
by  the  colleges  for  tinctures  has  a specific  gravity  of  0.930,  or  0.935. 

Of  the  salifiable  bases,  alcohol  can  alone  dissolve  potassa,  soda,  lithia, 
ammonia,  and  the  vegetable  alkalies.  None  of  the  earths,  or  other 
metallic  oxides,  are  dissolved  by  it.  Most  of  the  acids  attack  it  by  the 
aid  of  heat,  giving  rise  to  a class  of  bodies  to  which  the  name  of  ether 
is  applied.  All  the  salts  which  are  either  insoluble,  or  sparingly  soluble 
in  water,  arc  insoluble  in  alcohol.  I'he  efflorescent  salts  are,  likewise, 
for  the  most  part  insoluble  in  this  menstruum;  but,  on  the  contrary,  it 
is  capable  of  dissolving  all  the  deliquescent  salts,  except  carbonate  of 
potassa.  Many  of  the  vegetable  ])rinciples,  such  as  sugar,  manna,  cam- 
j)hor,  resins,  balsams,  and  the  essential  oils,  arc  soluble  in  alcohol. 

'I'hc  solubility  of  certain  substances  in  alcohol  appears  owjng  to  the 
formation  of  definite  compounds,  which  are  soluble  in  that  liquid.  This 
has  been  ])roved  of  the  chlorides  of  calcium,  manganese,  and  zinc,  and 
of  the  nitrat(*s  of  lime  and  magnesia,  by  Mr.  Graham  in  the  essay  above 
cited.  It  appears  from  his  expeviments  that  all  these  bodies  unite  with 
alcohol  in  definite  proportion,  and  yield  crystalline  compounds,  which 
are  deliquescent  and  soluble  both  in  water  and  alcohol.  From  their 


ALCOHOL. 


493 


ahalog’y  to  hydrates,  Mr.  Graham  has  applied  to  them  the  name  of  «/- 
coates.  These  are  formed  by  dissolving*  the  substances  in  absolute 
alcohol  by  means  of  heat,  when  on  cooling*  a group  of  crystals  more  cr 
less  irregular  is  deposited.  1'he  salt  and  alcohol  employed  for  the  pur- 
pose should  be  quite  anhydrous;  for  the  crystallization  is  prevented  by 
a very  small  quantity  of  water.  Estimating  the  combining  proportion  of 
alcohol  at  23,  the  alcoate  of  chloride  of  calcium  is  composed  of  one 
equivalent  of  chloride  of  calcium,  and  three  equivalents  and  a half  of 
alcohol.  Nitrate  of  magnesia  crystallizes  with  nine  equivalents  of  alco- 
hol; nitrate  of  lime  with  two  and  a half  equivalents;  protochloride  of 
manganese  with  three  equivalents;  and  chloride  of  zinc  with  half  an 
equivalent  of  alcohol. 

The  constitution  of  alcohol  has  been  ably  investigated  by  M.  Saus- 
sure,  jun.  (An.  de  Ch.  Ixxxix.)  According  to  his  analysis,  which  was 
made  by  transmitting  the  vapour  of  absolute  alcohol  through  a red-hot 
porcelain  tube,. and  examining  the  products,  this  fluid  is  composed  of 
carbon  51.98,  oxygen  34.32,  and  hydrog'en  13.70.  From  these  data, 
alcohol  is  inferred  to  consist  of 


Carbon,  . . 12 

Oxygen,  . . 8 

Hydrogen,  . . 3 

23 


two  equivalents  . 52.17 

one  equivalent  . 34.79 

three  equivalents  . 13.04 


100.00 


These  numbers,  it  is  obvious,  are  in  such  proportion  that  alcohol  may 
be  regarded  as  a cornpound  of  14  parts  or  one  equivalent  of  olefiant 
g*as,  and  9 parts  or  one  equivalent  of  water.  Hence  the  equivalent  of 
alcohol  is  23. 

Knowing  the  composition  of  alcohol  by  weight,  it  is  easy  to  calculate 
the  proportion  of  its  constituents  by  measure.  For  this  purpose  it  is 
only  necessary  to  divide  14  by  0.9722,  (the  sp.  gr.  of  olefiant  gas)  and 
9 by  0.625,  (the  sp.  gr.  of  aqueous  vapour);  and  as  the  quotients  are 
very  nearly  equal,  it  follows  that  alcohol  must  consist  of  equal  measures 
of  aqueous  vapour  and  olefiant  gas.  It  is  inferred,  also,  that  these  two 
gaseous  bodies,  in  uniting  to  form  the  vapour  of  alcohol,  occupy  half 
the  space  which  they  possessed  separately;  because  the  density  ot  the 
vapour  of  alcohol,  as  calculated  on  this  supposition,  (0.9722-^-0. 625= 
1.5972)  corresponds  closely  with  1.613,  the  number  which  was  ascer- 
tained experinaentally  by  Gay-Lussac. 

Considerable  uncertainty  prevailed  a few  years  ago  as  to  the  state  in 
which  alcohol  exists  in  wine.  Some  chemists  were  of  opinion  that  it  is 
generated  by  the  heat  employed  in  the  distillation;  while  others  thought 
that  the  alcohol  is  merely  separated  during  the  process.  This  question 
was  finally  determined  by  Mr.  Brande,  who  made  it  the  subject  of  two 
essays  which  were  published  in  the  Philosophical  Transactions  for  1811 
and  1813.  That  wine  contains  alcohol  ready  formed  he  demonstrated, 
by  separating  it  without  the  aid  of  heat.  His  method  consists  in  pre- 
cipitating the  acid  and  extractive  colouring  matters  of  the  wine  by  sub- 
acetate of  lead,  and  then  depriving  the  alcohol  of  water  by  dry  car- 
bonate of  potassa,  in  the  way  already  mentioned.  The  pure  alcohol, 
which  rises  to  the  surface,  is  then  measured  by  means  of  a nariow 
graduated  glass  tube.  The  same  fact  has  since  been  established  by  tlie 
experiments  of  Gay-Lussac,  who  procured  alcohol  from  wine  by  distil- 
ling it  in  vacuo  at  the  temperature  of  60®  F.  He  also  succeeded  in 
separating  the  alcohol  by  the  method  of  Mr.  Brande ^ but  he  suggests 
the  employment  of  litharge  in  fine  powder,  instead  of  subacetate  of  lead, 
for  precipitating  the  colouring  matter.  (Mem.  d’Arcueil,  vol.  hi.) 


494 


ETHER. 


The  precedinjr  researches  of  Mr.  Brande  led  him  to  examine  the 
quantity  of  alcohol  contained  in  spirituous  and  fermented  licpiors.  Ac- 
cording*  to  his  experiments,  brandy,  rum,  gin,  and  whisky,  contain  from 
51  to  54  per  cent  of  alcohol,  of  specific  gravity  0.825.  Tlie  stronger 
wines,  such  as  Lissa,  Raisin  wine,  Marsala,  Port,  Madeira,  Sherry, 
Teneriffe,  Constantia,  Malaga,  Bucellas,  Calcavella,  and  Vidonia,  contain 
from  between  18  or  19  to  25  per  cent  of  alcohol.  In  Claret,  Sauterno, 
Burgundy,  Hock,  Champagne,  Hermitage,  and  Gooseberry  wine,  the 
quantity  is  from  12  to  17  per  cent.  In  cider,  perry,  ale,  and  porter, 
the  quantity  varies  from  4 to  near  10  per  cent.  In  all  spirits,  such  as 
brandy  or  whisky,  the  alcohol  is  simply  combined  with  water;  whereas 
in  wine  it  is  in  combination  with  mucilaginous,  saccharine,  and  other 
vegetable  principles,  a condition  which  tends  to  diminish  the  action  of 
the  alcohol  upon  the  system.  This  may,  perhaps,  account  for  the  fact 
that  brandy,  which  contains  little  nr.ore  than  twice  as  much  real  alcohol 
as  good  port  wine,  has- an  intoxicating  power  which  is  considerably  more 
than  double. 

Ether. 

The  name  eiher  was  formerl}^  employed  to  designate  the  volatile  in- 
flammable liquid  which  is  formed  by  heating  a mixture  of  alcohol  and 
sulphuric  acid;  but  the  same  term  has  since  been  extended  to  several 
other  compounds  produced  by  the  action  of  acids  on  alcohol,  and  which 
from  their  volatility  and  inflammability,  were  supposed  to  be  identical 
or  nearly  so  with  sulphuric  ether.  It  appears,  however,  from  the  re- 
searches of  several  chemists,  but  especially  of  Thenaid,  that  ethers, 
though  analogous  in  their  leading  properties,  frequently  differ  both  in 
composition  and  in  their  mode  of  formation.  (Memoires  d’Arcueil, 
vol.  i.  and  ii.) 

Sulphuric  Ether. — In  forming  this  compound,  strong  sulphuric  acid 
is  gently  poured  upon  an  equal  weight  of  rectified  spirit  of  wine  con- 
tained in  a thin  glass  retort,  and  after  mixing  the  fluids  together  by  agi- 
tation, which  occasions  a free  disengagement  of  caloric,  the  mixture  is 
heated  as  rapidly  as  possible  until  ebullition  commences.  At  the  be- 
ginning of  the  process  nothing  but  alcohol  passes  over;  but  as  soon  as 
the  liquid  boils,  ether  is  generated,  and  condenses  in  the  recipient, 
which  is  purposely  kept  cool  by  the  application  of  ice  or  moist  cloths. 
When  a quantity  of  ether  is  collected,  equal  in  general  to  about  half  of 
the  alcohol  employed,  white  fumes  begin  to  appear  in  the  retort.  At 
this  period,  the  process  should  be  discontinued,  or  the  receiver  changed; 
for  although  ether  does  not  cease  to  be  generated,  its  quantity  is  less 
considerable,  and  several  other  products  make  their  appearance,  d'hus 
on  continuing  the  operation,  sulphurous  acid  is  disengaged,  and  a yel- 
lowish liquid,  commonly  called  ethereal  oil  ov  oil  of  wine,  passes  over  into 
the  receiver.  If  the  heat  be  still  continued,  a large  quantity  of  olefiant  gas 
is  disengaged,  and  all  the  phenomena  ensue  which  were  mentioned  in 
the  description  of  that  compound.  (Page  245.) 

Ether,  thus  formed,  is  always  mixed  with  alcohol,  and  generally  with 
some  sulphurous  acid.  To  separate  these  impurities,  the  ether  should 
be  agitated  with  a strong  solution  of  potassa,  which  neutralizes  the  acid, 
while  the  water  unites  with  the  alcohol.  The  ether  is  then  distilled  by 
a very  gentle  heat,  and  may  be  rendered  still  stronger  by  distillation 
from  chloride  of  calcium. 

'I'o  comprehend  the  theory  of  the  formation  of  ether,  it  is  necessary 
to  compare  the  composition  of  this  substance  with  that  of  alcohol. 
Ether  was  analyzed  by  Saussure  in  the  same  manner  as  alcohol;  and 
from  the  data  furnished  by  his  analysis,  corrected  by  Gay-Lussac,  (,An. 


ETHER. 


495 


de  Ch.  xcv.  314),  ether  is  inferred  to  consist  of  28  parts  or  two  equiva- 
lents of  olefiant  gas,  and  9 parts  or  one  equivalent  of  water.  But  alcohol 
is  composed  of  one  equivalent  of  olefiant  gas  and  one  equivalent  of  water; 
so  that  if  from  two  equivalents  of  alcohol  one  of  water  be  withdrawn,  the 
remaining  elements  are  in  exact  proportion  for  constituting  ether.  This 
is  the  precise  mode  in  which  sulphuric  acid  is  supposed  to  operate  in 
generating  ether,  an  effect  which  it  is  well  calculated  to  produce,  owing 
to  its  strong  affinity  for  moisture.  (Page  188.)  This  view  was  first 
proposed  by  Fourcroy  and  Vauquelin,  and  accounts  for  the  phenomena 
.in  a very  satisfactory  manner.  These  chemists,  it  is  true,  erred  in 
thinking  that  the  sulphuric  acid  occasions  no  other  change;  since  sub- 
sequent observation  has  proved  that  sulphovinic  acid,  to  the  constitution 
of  which  sulphuric  acid  is  essential,  is  formed  even  at  the  very  com- 
mencement of  the  process.  Notwithstanding  this  error,  however,  the 
production  of  ether  may  be  justly  ascribed  to  the  sulphuric  acid  ab- 
stracting water  or  its  elements  from  the  alcohol,  an  opinion  which  is 
supported  by  various  circumstances.  Thus  it  accounts  for  the  disen- 
gagement of  sulphurous  acid  and  olefiant  gas  towards  the  middle  and 
close  of  the  process;  for  since  the  elements  of  the  alcohol  alone  con- 
tribute to  the  formation  of  ether,  while  all  the  sulphuric  acid  remains 
in  the  retort,  and  most  of  it  in  a free  state,  it  is  apparent  that  the  rela- 
tive quantities  of  alcohol  and  acid  must  be  continually  changing  during 
the  operation,  until  at  length  the  latter  predominates  so  greatly  as  to  be 
able  to  deprive  the  former  of  all  its  water,  and  thus  give  rise  to  the  dis- 
engagement of  olefiant  gas.  (Page  243.)  Accordingly  it  is  well  known 
that  if  fresh  alcohol  be  added  as  soon  as  the  production  of  pure  ether 
ceases,  an  additional  quantity  of  that  substance  will  be  produced.  It 
follows,  also,  from  the  same  doctrine,  that  the  power  of  the  same  por- 
tion of  acid  in  forming  ether  must  be  limited,  because  it  gradually  be- 
comes so  diluted  with  water  that  it  is  at  last  unable  to  disunite  the  ele- 
ments of  the  alcohol.  Consistently  with  the  same  view,  it  is  found 
that  ether,  precisely  analogous  to  that  from  sulphuric  acid,  may  be  pre- 
pared by  digesting  alcohol  with  other  acids  which  have  a strong  affinity 
for  water,  as  for  example  with  phosphoric,  arsenic,  and  fluoboric  acids. 

The  production  of  a peculiar  acid  in  the  preceding  process  was  first 
noticed  by  M.  Dabit,  about  the  year  1800.  This  substance,  to  which 
the  name  of  sulphovinic  acid  is  applied,  has  since  been  examined  by  Ser- 
tuerner,  Vogel,  and  Gay-Lussac,  and  the  two  last  mentioned  philoso- 
phers regarded  it  as  a compound  of  hyposulphurrc  acid  and  a peculiar 
vegetable  matter.  Mr.  Hennel,  however,  has  lately  given  a different, 
and  to  all  appearance  a more  correct  view  of  its  nature.  According  to 
this  chemist,  sulphovinic  acid  and  oil  of  wine  are  both  composed  of  sul- 
phuric acid  and  cai-buret  of  hydrogen.  Oil  of  wine,  which  has  no  acid 
reaction  when  pure,  consists  of  two  equivalents  of  sulphuric  acid,  eight 
of  carbon,  and  eight  of  hydrogen.  When  heated,  it  parts  with  half  of 
its  carbon  and  hydrogen,  and  sulphovinic  acid  remains,  consisting  of  two 
equivalents  of  sulphuric  acid,  four  of  carbon,  and  four  of  hydrogen. 
Oil  of  wine  is  a perfectly  neutral  compound,  in  which  carburet  of  hy- 
drogen acts  the  part  of  an  alkali  in  neutralizing  sulphuric  acid.  In  sul- 
phovinic acid,  half  the  sulphuric  acid  appears  to  be  neutralized  by  car- 
buret of  hydrogen.  (Philos.  Trans,  for  1826,  p.  247,  or  Journal  of 
Science,  xxi.  331.) 

^Additional  researches  by  Mr.  Hennel  have  rendered  it  pi*obable,  that 
sulphovinic  acid  is  in  realit}^  a stage  in  the  formation  of  sulphuric  ether. 
That  acid  is  present  in  greatest  quantity  when  the  ingredients  are  first 
mixed,  and  prior  to  the  application  of  artificial  heat,  one-half  of  the 
sulphuric  acid  being  thep  in  combination  with  carburet  of  hydrogen; 


496 


ErilER. 


but  on  distilling^  the  mixture,  sulphovinic  acid  diminishes  as  the  quantity 
of  ether  increases,  until  towards  the  close  of  the  process  sulphovinic 
acid  entirely  disappears,  and  the  sulphuric  acid,  which  was  previously 
in  combination,  is  set  free.  In  support  of  this  view  Mr.  Ilennel  remarks, 
that  however  the  operation  may  be  conducted,  the  formation  of  ether  is 
always  accompanied  or  preceded  with  that  of  sulphovinic  acid;  and  he 
has  added  the  additional  fact,  that  on  distilling’  sulphovinate  of  pota.ssa 
with  concentrated  sulphuric  acid,  no  alcohol  being-  present,  ether  is 
generated.  It  appears,  then,  that  ether  may  be  directly  developed  from 
sulphovinic  acid;  that,  in  the  ordinary  process,  the  formation  of  the  lat- 
ter always  precedes  tliat  of  the  former;  and  that  during  the  period  of 
ether  being  generate^l,  sulphovinic  acid  js  decomposed.  The.se  facts 
.give  great  plausibility  to  the  opinion  of  Mr.  Ilennel;  but  it  does  not  fol- 
low, nor  does  Mr.  Hennel  maintain,  that  ether  cannot  be  generated  but 
through  the  medium  of  sulphovinic  acid.  I'lie  nature  of  the  difference 
in  the  constitution  of  alcohol  and  ether,  and  the  production  of  ether 
from  alcohol  and  phosphoric  acid,  incline  to  an  opposite  inference. 
(Phil.  Trans.  1828.) 

Mr.  Ilennel  has  succeeded  in  obtaining  alcohol  through  the  medium 
of  ether.  For,  when  ether  and  sulphuric  acid  are  heated  together,  oil 
of  wine  and  sulphovinic  acid  are  among  tlie  products;  and  on  distilling 
sulphovinate  of  potassa  with  sulphuric  acid,  not  concentrated  as  above 
but  previously  diluted  with  half  its  weight  of  water,  alcohol  is  generated. 
It  hence  appears  that  carburet  of  hydrogen,  at  the  moment  of  .separa- 
tion from  sulphuric  acid,  is  in  a st.ate  peculiarly  favourable  for  combining 
with  water;  and  that,  in  doing  so,  it  gives  rise  to  alcohol  or  ether,  ac- 
cording to  the  condition  in  which  it  is  placed. 

Sulphuric  ether  is  a colourless  fluid,  of  a hot  pungent  taste,  and  fra- 
grant odour.  Its  specific  gravity  in  its  purest  form  is  about  0.700,  or 
according  to  Lovitz  0.632;  but  that  of  the  shops  is  0.74  or  even  lower, 
owing  to  the  presence  of  alcohol.  Its  volatility  is  exceedingly  great;  ^ 
under  the  atmospheric  pressure,  ether  of  density  0.720  boils  at  96P  or 
98®  F.,  and  at  about — 40®  F.  in  a vacuum.  (Black’s  Lectures,  i.  151.) 
Its  evaporation,  from  the  rapidity  with  which  it  takes  place,  occasions 
intense  cold,  sufficient  under  favourable  circumstances  for  freezing  mer- 
cury. Its  vapour  has  a density  of  2.586.  At  46  degrees  below  zero  of 
Fahr.  it  is  congealed. 

Ether  combines  with  alcohol  in  every  proportion,  but  is  very  sparingly 
soluble  in  water.  When  agitated  with  that  fluid,  the  greater  part 
separates  on  .standing,  a small  quantity  being  retained,  which  imparts  an 
ethereal  odour  to  the  water.  'I'he  ether  so  washed  is  very  pure,  be- 
cause the  water  retains  the  alcohol  with  which  it  is  mixed. 

Ether  is  highly  inflammable,  burning  with  a blue  flame,  and  formation 
of  water  and  carbonic  acid.  With  oxygen  gas  its  vapour  forms  a mix- 
ture, which  explodes  violently  bn  the  approach  of  flame,  or  by  the 
electric  spark.  On  being  transmitted  through  a red-hot  porcelain  tube 
it  undergoes  decomposition,  and  yields  the  same  products  as  alcohol. 

Wlien  a coil  of  platinum  wire  is  heated  to  redness,  and  then  sus- 
])ended  above  the  sui  face  of  ether  contained  in  an  open  vessel,  the 
wire  instantly  begins  to  glow,  and  continues  in  that  state  until  all  the 
ether  is  consumed.  (Davy.)  During  lliis  slow  combustion,  pungent 
acrid  fumes  are  emitted,  which,  if  received  in  a .separate  vessel,  con- 
dense into  a colourless  licpiid  possessed  of  acid  pro])erties.  Mr.  Daniell, 
who  prepared  a large  (piantity  of  it,  was  at  first  inclined  to  regard  it  as 
a new  acid,  and  described  it  under  the  name  of  lainplc  acid;  but  he  has 
since  ascertained  that  its  acidity  is  owing  to  the  acetic  acid,  which  is 
combined  with  some  compound  of  carbon  and  hydrogen  different  both 


ETHER. 


49r 


from  ether  and  alcohol.  (Journal  of  Science,  vi.  and  xii.)  Alcohol, 
when  similarly  burned,  likewise  yields  acetic  acid. 

If  ether  is  exposed  to  light  in  a vessel  partiall}^  filled,  and  which  is 
frequently  opened,  it  gradually  absorbs  oxygen,  and  a portion  of  acetic 
acid  is  generated.  This  change  was  first  noticed  by  M.  Planche,  and 
has  been  confirmed  by  Gay-Lussac.  (An.  de  Oh.  et  de  Ph.  ii.  98  and 
213.)  M.  Henry  of  Paris  attributes  its  development  to  acetic  ether, 
which  he  believes  to  be  always  contained  in  sulphuric  ether. 

The  composition  of  ether  by  volume  may  be  inferred  in  the  same 
manner  as  in  the  case  of  alcohol  (page  493);  namely,  by  dividing  28  by 
0.9722,  and  9 by  0.625.  Ether  is  thus  found  to  consist  of  two  measures 
of  olefiant  gas  and  one  measure  of  watery  vapour;  and  supposing  these 
three  measures,  in  combining,  to  contract  to  one-third  of  their  volume, 
the  specific  gravity  of  the  vapour  of  ether  will  be  0.9722  X 2 + 0.625 
= 2.5694.  Now  this  is  so  near  2.586,  the  specific  gravity  which  Gay- 
Lussac  found  by  actual  trial,  that  the  preceding  supposition  may  fairly 
be  admitted, 

The  solvent  properties  of  ether  are  less  extensive  than  those  of  alco- 
hol, It  dissolves  the  essential  oils  and  resins,  and  some  of  the  vegetable 
alkalies  are  soluble  in  it.  It  unites  also  with  ammonia;  but  the  fixed 
alkalies  are  insoluble  in  this  menstruum. 

Nitrous  Ether. — This  compound  is  prepared  by  distilling  a mixture  of 
concentrated  nitric  acid  with  an  equal  weight  of  alcohol;  but  as  the  re- 
action is  apt  to  be  exceedingly  violent,  the  process  should  be  conducted 
with  extreme  care.  The  safest  method  is  to  add  the  acid  to  the  alcohol 
by  small  quantities  at  a time,  allowing  the  mixture  to  cool  after  each 
addition  before  more  acid  is  added.  The  distillation  is  then  conducted 
at  a very  gentle  temperature,  and  the  ether  collected  in  Woulfe’s  ap- 
paratus. The  theory  of  the  process  is  in  some  respects  obscure;  but 
as  the  formation  of  ether  is  attended  with  the  disengagement  of  pro- 
toxide and  deutoxide  of  nitrogen,  together  with  free  nitrogen  and  car- 
bonic acid,  it  follows  that  the  alcohol  and  acid  mutually  decompose  each 
other.  Thenard  inferred  from  his  experiments,  that  this  ether  is  a com- 
pound of  alcohol  and  nitrous  acid;  and,  consequently,  that  the  ess^en- 
tial  change  during  its  formation  consists  in  the  conversion  of  nitric  into 
nitrous  acid  at  the  expense  of  one  part  of  the  alcohol,  while  the  re- 
mainder of  that  fluid  combines  with  the  nitrous  acid.  Consistently  with 
this  view,  nitrous  ether  may  be  made  directly  by  the  action  of  anhydrous 
nitrous  acid  on  pure  alcohol. 

In  an  essay  lately  published  by  MM.  Dumas  and  Boullay,  a different 
opinion  has  been  suggested.  According  to  a careful  analysis  of  nitrous 
ether,  they  find  it  to  consist  of  four  equivalents  of  carbon,  five  of. 
hydrogen,  one  of  nitrogen,  and  four  of  oxygen.  These  elements 
are  in  proportion  to  constitute  two  equivalents  of  olefiant  gas,  one  of 
water,  and  one  of  hyponitrous  acid.  (An.  de  Ch.  et  de  Physique,  xxxvii. 
26.) 

The  nitrous  agrees  with  sulphuric  ether  in  its  leading  properties;  but 
it  is  still  more  volatile.  When  recently  distilled  from  quicklime  by  a 
gentle  heat,  h is  quite  neutral;  but  it  soon  becomes  acid  by  keeping. 
The  products  of  its  spontaneous  decomposition  are  alcohol,  nitrous 
acid,  and  a little  acetic  acid.  A similar  change  is  instantly  effected 
by  nriixing  the  ether  with  water,  or  distilling  it  at  a high  tempera- 
ture. It  is  also  decomposed  by  potassa,  and,  on  evaporation,  crystals 
of  the  nitrite  or  hyponitrite  of  that  alkali  are  deposited.  (Memoires 
d^Arcueil,  vol.  i.) 

Acetic  Ether. — This  ether  is  analogous  in  composition  to  the  preced- 
ing,  and  is  formed  by  distilling  acetic  acid  with  an  equal  weight  of 

42* 


498 


BITUMEN. 


alcohol.  When  set  on  fire,  it  burns  with  diseng'ai^ement  of  acetic  acid; 
and  when  mixed  with  a strong*  solution  of  potassa,  and  subjected  to 
distillation,  pure  alcohol  passes  over,  and  acetate  of  potassa  remains  in 
the  retort.  It  is  hence  inferred  by  Tlienard  to  consist  of  acetic  acid  and 
alcohol.  When  pure  it  is  quite  neutral. 

According*  to  Thenard,  the  acetic  is  the  only  vegetable  acid  which 
forms  ether  by  being*  heated  alone  with  alcohol.  Ether  may  also  be 
g'enerated  by  treating*  tartaric,  oxalic,  malic,  citric,  or  benzoic  acid 
with  a mixture  of  alcohol  and  sulphuric  acid,  and  Thenard  reg*ards  these 
ethers  as  compounds  of  a vegetable  acid  with  alcohol.  But  Dumas  and 
Boullay,  in  the  essay  above  referred  to,  declare  that  the  elements  of 
all  these  ethers  are  in  such  proportion  as  to  constitute  one  equivalent  of 
acid,  one  of  water,  and  two  of  olefiant  gas.  They  believe  them,  as 
also  nitrous  ether,  to  be  hydrated  salts,  in  which  carburet  of  hydrogen 
acts  the  part  of  an  alkali.  This  view  is  certainly  supported  by  the  ob- 
servations of  Mr.  Ilennel  relative  to  oil  of  wine,  and  by  the  constitu- 
tion of  muriatic  ether.  The  employment  of  sul  phuric  acid  in  their  for- 
mation is  likewise  favourable  to  this  opinion.  The  alcohol  obtained  by 
distillation  with  potassa,  is  supposed  by  Dumas  and  Boullay  to  be  gen- 
erated during  the  process. 

Muriatic  Ether. — This  compound,  which  is  prepared  by  distilling  a 
mixture  of  concentrated  muriatic  acid  and  pure  alcohol,  was  supposed 
by  Thenard  to  be  analogous  in  composition  to  nitrous  ether.  It  appears, 
however,  from  the  experiments  of  Bobiquet  and  Colin,  that  it  consists 
of  muriatic  acid  and  the  elements  of  olefiant  gas,  and  is,  therefore, 
quite  free  from  oxygen.  (An.  de  Ch.  et  de  Ph.  ii.)  [t  does  not  affect 
the  colour  of  litmus  paper,  is  denser  than  water,  volatilizes  still 
more  rapidly  than  sulphuric  ether,  and  is  highly  inflammable.  Its  com- 
bustion is  attended  with  the  disengagement  of  a large  quantity  of  mu- 
riatic acid  gas. 

Hydriodic  ether^  first  prepared  by  Gay-Lussac,  appears  to  be  similar 
in  composition  to  muriatic  ether.  Serullas  recommends  that  it  should 
be  formed  by  introducing  into  a retort  40  parts  of  iodine  and  100  of  al- 
cohol of  0.827,  and  then  gradually  adding  2.5  parts  of  phosphorus  in 
small  fragments.  The  mixture  is  kept  in  ebullition  till  it  is  nearly  ex- 
hausted, and  then  25  or  30  parts  of  alcohol  are  added  and  distilled  off 
fpom  the  remainder.  The  ether  is  purified  by  washing  with  water;  after 
which  it  is  dried  by  distillation  from  chloride  of  calcium.  (An.  de  Ch. 
et  de  Ph.  xlii.  119.) 

Hydrohromic  ether  may  be  prepared  by  a process  similar  to  the  fore- 
going. 

Liebig  has  prepared  sulphocyanic  ether,  which  he  believes  to  be  a 
compound  of  sulphuret  of  cyanogen  and  carburet  of  hydrogen,  by  dis- 
tilling a mixture  of  1 part  of  sulphocyanuret  of  potassium,  2 of  sul- 
phuric acid,  and  3 of  strong  alcohol.  (An.  de  Ch.  et  de  Ph.  xli.  202.) 

Bituminous  Substances. 

Under  this  title  are  included  several  inflammable  substances,  which, 
though  of  vegetable  origin,  are  found  in  the  earth,  or  issue  from  its 
surface.  They  may  be  conveniently  arranged  under  the  two  heads  of 
biUimen  and  pit-coal.  The  first  comprehends  naphtha,  petroleum,  min- 
ej'al  tar,  mineral  pitch,  asphaltum,  and  retinasphaltum,  of  which  the 
three  first  mentioned  are  liquid,  and  the  others  solid.  The  second 
comprises  brmjun  coal,  the  different  varieties  of  common  or  black  coal, 
and  y;lancc  coal. 

Bitumen. — Naphtha  is  a volatile  limpid  liquid,  of  a strong  peculiar 
odour,  and  generally  of  a light  yellow  colour;  but  it  may  be  rendered 


BITUMEN. 


499 


colourless  by  careful  distillation.  Its  specific  gravity,  when  highly  rec- 
tified, is  0.758.  It  is  very  inflammable,  and  burns  with  a white  flame 
with  much  smoke.  At  186®  F.  it  enters  into  ebullition,  and  its  vapour 
has  a density  of  2.833.  (Saussure.)  It  retains  its  liquid  form  at  zero  of 
Fahrenheit.  It  is  insoluble  in  water,  and  very  soluble  in  alcohol;  but 
it  unites  in  every  proportion  with  sulphuric  ether,  petroleum,  and  oils. 
It  appears  from  the  observations  of  Saussure  to  undergo  no  change  by 
keeping,  even  in  contact  with  air. 

Naphtha  contains  no  oxygen,  and  is  hence  employed  for  protecting  the 
more  oxidable  metals,  such  as  potassium  and  sodium,  from  oxidation.* 
According  to  the  analysis  of  Saussure,  it  is  composed  of  carbon  and 
hydrogen  in  the  proportion  of  six  equivalents  of  the  former  to  five  of 
the  latter.  Dr.  Thomson  states  the  composition  of  naphtha  from  coal 
tar,  which  seems  identical  with  mineral  naphtha,  to  consist  of  six  equiv- 
alents of  carbon  and  six  of  hydrogen.  (Page  248.) 

Naphtha  occurs  in  some  parts  of  Italy,  and  on  the  banks  of  the  Cas- 
pian Sea.  It  may  be  procured  also  by  distillation  from  petroleum. 

Petroleum  is  much  less  limpid  than  naphtha,  has  a reddish-brown  col- 
our, and  is  unctuous  to  the  touch.  It  is  found  in  several  parts  of  Bri- 
tain and  the  continent  of  Europe,  in  the  AVest  Indies,  and  in  Persia.  It 
occurs  particularly  in  coal  districts.  Mineral  tar  is  very  similar  to  petro- 
leum, but  is  more  viscid  and  of  a deeper  colour.  Both  these  species 
become  thick  by  exposure  to  the  atmosphere,  and  in  the  opinion  of  Mr. 
Hatchett  pass  into  solid  bitumen. 

Jhphalturn  is  a solid  brittle  bitumen,  of  a black  colour,  vitreous  lus- 
tre, and  conchoidal  fracture.  It  melts  easily,  and  is  very  inflammable. 
It  emits  a bituminous  odour  when  rubbed,  and  by  distillation  yields 
a fluid  like  naphtha.  It  is  soluble  in  about  five  times  its  weight  of 
naphtha,  and  the  solution  forms  a good  varnish.  It  is  rather  denser  than 
water. 

Asphaltum  is  found  on  the  surface  and  on  the  banks  of  the  Dead  Sea, 
and  occurs  in  large  quantity  in  Barbadoes  and  Trinidad.  It  was  employ- 
ed by  the  ancients  in  building,  and  is  said  to  have  been  used  by  the 
Egyptians  in  embalming. 

Mineral  pitch  or  maltha  is  likewise  a solid  bitumen,  but  is  much  softer 
than  asphaltum.  Elastic  bitumen,  or  mineral  caoutchouc^  is  a rare  varie- 
ty of  mineral  pitch,  found  only  in  the  Odin  mine,  near  Castleton  in 
Derbyshire. 

Retinasphaltum  is  a peculiar  bituminous  substance,  found  associated 
with  the  brown  coal  of  Bovey  in  Devonshire,  and  described  by  Mr. 
Hatchett  in  the  Philosophical  Transactions  for  1804.  It  consists  partly 
of  bitumen,  and  partly  of  resin,  a composition  which  led  Mr.  Hatchett 
to  the  opinion  that  bitumens  are  chiefly  formed  from  the  resinous  prin- 
ciple of  plants. 

Pit-coal — Brown  coal  is  characterized  by  burning  with  a peculiar  bi- 
tuminous odour,  like  that  of  peat.  It  is  sometimes  earthy,  but  the 
fibrous  structure  of  the  wood  from  which  it  is  derived  is  generally  more 
or  less  distinct,  and  hence  this  variety  is  called  bituminous  wood.  Pitch 
coa/ or  jet,  which  is  employed  for  forming  ear-rings  and  other  trinkets, 
is  intermediate  between  brown  and  black  coal,  but  is  perhaps  more 
closely  allied  to  the  former  than  the  latter. 

Brown  coal  is  found  at  Bovey  in  Devonshire,  (Bovey  coal),  in  Ice- 
land, where  it  is  called  surturbrand,  and  in  several  parts  of  the  con- 


* See  note,  page  292.  B. 


500 


COAL. 


tlnent,  especially  at  the  Meissner  in  Ilcssia,  in  Saxony,  I’russia,  and 
Styria. 

Of  \\\Q  black  or  common  coal  iheYQ  vive  several  varieties,  wiiicli  differ 
from  each  other,  not  only  in  the  quantity  of  foicig-n  matters,  such  as 
sulphuret  of  iron  and  earthy  substances,  which  tliey  contain,  but  also 
in  the  proportion  of  what  may  be  regarded  as  essential  constituents. 
Thus  some  kinds  of  coal  consist  almost  entirely  of  carbonaceous  mat- 
ters, and,  therefore,  form  little  flame  in  burning;  while  others,  of  which 
cannel  coal  is  an  example,  yield  a lai-ge  quantity  of  inflammable  gases 
by  heat,  and  consequently  burn  with  a large  flame.  Dr.  I'homson  has 
arranged  the  differeiU  kinds  of  coal  wliich  are  met  with  in  Britain  into 
four  subdivisions.  (An.  of  Phil,  xiv.)  Tlie  first  is  cakins;  coal,  because 
its  particles  are  softened  by  heat  and  adhere  together,  forming  a com- 
pact mass.  The  coal  found  at  Newcastle,  around  Manchester,  and  in 
many  other  parts  of  England,  is  of  this  kind.  The  second  is  termed 
splint  coal,  from  the  splintery  appearance  of  its  fracture.  The  cherry 
cofl/ occurs  in  Staffordshire,  and  in  the  neighbourhood  of  Glasgow.  Its 
structure  is  slaty,  and  it  is  more  easily  broken  than  splint  coal,  which  is 
much  harder.  It  easily  takes  fire,  and  is  consumed  rapidly,  burning 
with  a clear  yellow  flame.  The  fourth  kind  is  cannel  coal,  w'hich  is 
found  of  peculiar  purity  at  Wigan  in  Lancashire.  In  Scotland  it  is 
known  by  the  name  of  parrot  coal.  From  the  brilliancy- of  the  light 
which  it  emits  while  burning',  it  is  sometimes  used  as  a substitute  for 
candles,  a practice  which  is  said  to  have  led  to  the  name  of  cannel  coal. 
It  has  a very  compact  structure,  does  not  soil  the  fingers  when  handled, 
and  admits  of  being  polished.  Snuff  boxes  and  other  ornaments  are 
made  with  this  coal;  and  it  is  peculiarly  well  fitted  for  forming  coal  gas. 
According  to  the  experiments  of  Dr.  'I'homson,  these  varieties  of  coal 
are  thus  constituted: 


Carbon, 

Hydrogen, 

Nitrogen, 

Oxygen, 


Cakms;  Coal, 

Splint  Coal. 

75.28 

75.00 

4.18 

6.25 

15.96 

6.25 

4.58 

12.50 

100.00 

100.00 

Cherry  Coal. 

Cannel  Coal. 

74.45 

64.72 

12.40 

21.56 

10.22 

13.72 

2.93 

0.00 

100.00 

100.00 

Judging  from  the  quantity  of  oxidized  products  (water,  carbonic  acid, 
and  carbonic  oxide)  which  are  procured  during  the  distillation  of  coal. 
Dr.  Henry  infers  that  coal  contains  more  oxygen  than  was  found  by 
Thomson.  (Elements,  11th  Edit.  ii.  p.  34-8.)  This,  opinion  is  support- 
ed by  the  analysis  of  Dr.  Ure,  who  found  26.66  per  cent,  of  oxygen  in 
splint,  and  21.9  in  cannel  coal.  When  coal  is  heated  to  redness  in  close 
vessels,  a great  quantity  of  volatile  matter  is  dissipated,  and  a carbo- 
naceous residue,  called  coke,  remains  in  the  retort.  The  volatile  sub- 
stances are  coal  tar,  acetic  acid,  water,  sulplumePed  hydrogen,  and 
Ijydrosulphurct  and  carbonate  of  ammonia,  together  with  the  several 
gases  formerly  enumerated.  (Page  250.)  'Phe  greater  part  of  these 
substances  arc  real  products,  that  is,  are  generated  during  the  distilla- 
tion. 'i'hc  bituminous  matters  ])robably  exist  ready  formed  in  coal;  but 
Dr.  Thomson  is  of  o])inion  that  these  arc  also  products,  and  that  coals 
are  atomic  compounds  of  carbon,  hydrogen,  nitrogen,  and  oxygen. 

Glance  Coal. — Glance  coal,  or  anthracite,  differs  from  common  coal, 
which  it  frequently  acconqninie.s,  in  containing  no  bituminous  sub- 
stances, and  in  not  yielding  inflammable  gases  by  distillation.  Its  sole 
combustible  ingredient  is  carbon,  and  consequently  it  burns  without 


SUGAR. 


501 


flaiTie.  It  commonly  occurs  in  the  immediate  vicinity  of  basalt,  under 
circumstances  wli'ch  lead  to  the  suspicion  that  it  is  coal  from  which  th« 
volatile  ing’redients  have  been  expelled  by  subterranean  heat.  At  the 
Meissner,  in  Hessia,  it  is  found  between  a bed  of  brown  coal  and  basalt. 
Kilkenny  coal  appears  to  be  a variety  of  glance  coal.  (Thomson,  An.  of 
Phil.  vol.  XV.) 


SECTION  IV. 

SUBSTANCES,  THE  OXYGEN  AND  HYDROGEN  OF  WHICH 
ARE  IN  EXACT  PROPORTION  FOR  FORMING  WATER. 

Sugar, 

Sugar  is  an  abundant  vegetable  product,  existing  in  a great  many 
ripe  fruits,  though  few  of  them  contain  it  in  sufficient  quantity  for  be- 
ing collected.  The  juice  which  flows  from  incisions  made  in  the  trunk 
of  the  American  maple  tree,  is  so  powerfully  saccharine  thatit  may  be 
applied  to  useful  purposes.  Sugar  was  prepared  in  France  and  Ger- 
many during  the  late  war  from  the  beet-root;  and  this  manufacture  is  at 
present  carried  on  in  France  on  a scale  of  considerable  magnitude. 
Proust  extracted  it  in  Spain  from  grapes.  But  nearly  all  "the  sugar  at 
present  used  in  Europe  is  obtained  from  the  sugar-cane  {Arundo  saccha- 
rifera),  which  contains  it  in  greater  quantity  than  any  other  plant. 
The  process,  as  practised  in  our  West  India  Islands,  consists  in  evapor- 
ating the  juice  of  the  ripe  cane  by  a moderate  and  cautious  ebullition, 
until  it  has  attained  a proper  degree  of  consistence  for  crystallizing. 
During  this  operation  lime-water  is  added,  partly  for  the  purpose  of 
neutralizing  free  acid,  and  partly  to  facilitate  the  separation  of  extrac- 
tive and  other  vegetable  matters,  which  unite  with  the  lime  and  rise  as 
a scum  to  the  surface.  When  the  syrup  is  sufficiently  concentrated,  ?t 
is  drawn  off  into  shallow  wooden  coolers,  where  it  becomes  a soft 
solid  composed  of  loose  crystalline  grains.  It  is  then  put  into  barrels 
with  holes  in  the  bottom,  through  which  a black  ropy  juice,  called 
molasses  or  treacle,  gradually  drops,  leaving  the  crystallized  sugar  com- 
paratively white  and  dry.  In  this  state  it  constitutes  raw  or  muscovado 
sugar. 

Raw  sugar  is  further  purified  by  boiling  a solution  of  it  with  white  of 
or  the  serum  of  bullock’s  blood,  lime-water  being  generally  em- 
ployed at  the  same  time.  When  properly  concentrated,  the  clarified 
juice  is  received  in  conical' earthen  vessels,  the  apex  of  which  is  under- 
most, in  order  that  the  fluid  parts  may  collect  there,  and  be  afterwards 
drawn  off  by  the  removal  of  a plug.  In  this  state  it  is  loaf  or  refined 
sugar.  In  the  process  of  refining  sugar,  it  is  important  to  concentrate 
the  syrup  at  a low  temperature;  and  on  this  account  a very  great  im- 
provement was  introduced  some  years  ago  by  conducting  the  evapora- 
tion in  vacuo. 

Pure  sugar  is  solid,  white,  inodorous,  and  of  a very  agreeable  taste. 
It  is  hard  and  brittle,  and  when  two  pieces  are  rubbed  against  each 
other  in  the  dark,  phosphorescence  is  observed.  It  crystallizes  in 


502 


SUGAR. 


tlie  form  of  four  or  six-sided  prisms  bevelled  at  the  extremities.  The 
crystals  are  best  made  by  fixing'  threads  in  syrup,  which  is  allowed  to 
evaporate  spontaneously  in  a warm  room;  and  tlie  crystallization  is  pro- 
moted by  adding  spirit  of  wine.  In  this  state  it  is  known  by  the  name 
of  sugarcandi/. 

Sugar  undergoes  no  change  on  exposure  to  the  air;  for  the  deliques- 
cent property  of  raw  sugar  is  owing  to  impurities.  It  is  soluble  in  an  equal 
weight  of  cold,  and  to  almost  any  extent  in  hot  water.  It  is  soluble  in  about 
four  times  its  weight  of  boiling  alcohol,  and  the  saturated  solution,  by 
cooling  and  spontaneous  evaporation,  deposites  large  crystals.  When 
the  aqueous  solution  of  sugar  is  mixed  with  yeast,  it  undergoes  the 
vinous  fermentation,  the  theory  of  which  will  be  explained  in  a subse- 
quent section. 

Sugar  unites  with  the  alkalies  and  alkaline  earths,  forming  com- 
pounds in  which  the  taste  of  the  sugar  is  greatly  in  jured;  but  it  may  be 
obtained  again  unchanged  by  neutralizing  with  sulphuric  acid,  and  dis- 
solving the  sugar  in  alcohol.  When  boiled  with  oxide  of  lead,  it  forms 
an  insoluble  compound,  which  consists  of  58.26  parts  of  oxide  of  lead, 
and  41.74  parts  of  sugar  (Berzelius);  but  it  is  not  precipitated  by  ace- 
tate or  subacetate  of  lead. 

Sulphuric  acid  decomposes  sugar  with  deposition  of  charcoal; 
and  nitric  acid  causes  the  production  of  oxalic  acid,  as  already  describ- 
ed in  a former  section.  The  vegetable  acids  diminish  the  tendency  of 
sugar  to  crystallize. 

Sug'ar  is  very  easily  affected  by  heat,  acquiring  a dark  colour  and 
burned  flavour.  At  a high  temperature  it  yields  the  usual  products  of 
the  destructive  distillation  of  vegetable  matter,  together  with  a consi- 
derable quantity  of  pyromucic  acid. 

The  analyses  of  sugar  by  different  chemists  are  considerably  discord- 
ant. This  is  accounted  for  not  only  by  errors  of  manipulation,  and 
impurity  in  the  materials;  but  in  part  arises,  according  to  Dr.  Prout, 
from  difference  in  composition.  In  his  Essay  on  Alimentary  Substances, 
published  in  the  Philosophical  Transactions  for  1827,  page  355,  he 
states  that  pure  cane  sugar  as  exemplified  in  sugar  candy  and  the  best 
loaf  sugar,  well  dried  at  212°  F.,  consists  of  42.85  parts  of  carbon,  and 
57.15  of  oxygen  and  hydrogen  in  the  proportion  for  forming  water; 
while  sugar  from  honey  contains  only  36.36  per  cent  of  carbon.  He 
considers  the  sugar  from  starch,  diabetic  urine,  and  grapes,  to  be  nearly 
the  same  as  that  from  honey.  The  sugar  from  the  maple  tree  and  beet 
root  corresponds  with  that  from  the  cane;  but  the  quantity  of  carbon  in 
these  kinds  of  sugar  appears  to  vary  from  40  to  42,85  per  cent.  The 
•atomic  constitution  of  sugar  is  unknown;  but  from  a former  analysis 
of  Dr.  Prout,  it  is  thought  that  its  elements  are  in  the  ratio  of  6 parts 
or  one  equivalent  of  carbon  to  9 parts  or  one  equivalent  of  water,  or  by 
volume  of  one  measure  of  the  vapour  of  carbon  to  one  measure  of 
aqueous  vapour.  This  estimate  is  admitted  by  most  chemists. 

Mo/asses. — 'I'he  saccharine  principle  of  treacle  has  been  supposed  to 
be  diflercnt  from  crystallizable  sugar;  but  it  chiefly  consists  of  common 
sugar,  which  is  prevented  from  crystallizing  by  the  presence  of  foreign 
substances,  sucli  as  saline,  acid,  and  other  vegetable  matters. 

Sugar  of  drapes. — 'Die  sugar  procured  from  the  grape  has  the  es- 
sential properties  of  common  sugar.  Its  taste,  however,  is  not  so  sweet 
as  that  of  common  sugar,  and  according  to  Saussure  and  Prout,  it-  dif- 
fers slightly  in  comj)Ositi()n,  containing  a smaller  quantity  of  carbon.' 
The  saccharine  jirinciple  of  the  acidulous  fruits  has  not  betn  particu- 
larly examined.  It  Is  obtained  with  difliculty  in  a pure  state,- owing  to 
the  presence  of  vegetable  acids,  which  prevent  it  from  crystallizing. 

A saccharine  substance  similar  to  that  from  grapes  may  be  procured 


STARCH.  503 

from  several  ve.^etable  principles,  such  as  starch  and  the  lig’neoiis  fibre, 
by  the  action  of  sulphuric  acid. 

Honey. — According*  to  Proust  honey  consists  of  two  kinds  of  saccha- 
rine matter,  one  of  which  crystallizes  readily  and  is  analogous  to  com- 
mon sugar,  while  the  other  is  uncrystallizable.  They  may  be  separated 
by  mixing  honey  with  alcohol,  and  pressing  the  solution  through  a piece 
of  linen.  The  liquid  sugar  is  removed,  and  the  crystallizabje  portion 
is  left  in  a solid  state.  Besides  sugar  it  contains  mucilaginous,  colouring, 
and  odoriferous  matter,  and  probably  a vegetable  acid.  Diluted  with 
water,  honey  is  susceptible  of  the  vinous  fermentation  without  the  addi- 
tion of  yeast. 

The  natural  history  of  honey  is  as  yet  imperfect.  It  is  uncertain 
whether  honey  is  merely  collected  by  the  bee  from  the  nectaries  of 
flowers,  and  then  deposited  in  the  hive  unchanged,  or  whether  the 
saccharine  matter  of  the  flower  does  not  undergo  some,  change  in  the 
body  of  the  animal. 

Manna. — This  saccharine  matter  is  the  concrete  juice  of  several  spe- 
cies of  ash,  and  is  procured  in  particular  from  the  Fraxinus  ornus.  The 
sweetness  of  manna  is  owing,  not  to  sugar,  but  to  a distinct  principle 
called  mannite^  which  is  mixed  with  a peculiar  vegetable  extractive 
matter.  Manna  is  soluble  both  in  water  and  boiling  alcohol,  and  the 
latter,  on  cooling,  deposites  pure  mannite  in  the  form  of  minute  acicu- 
lar  crystals,  which  are  often  arranged  in  concentrical  groups.  Mannite 
differs  from  sugar  in  not  fermenting  when  mixed  with  water  and  yeast. 
According  to  Dr.  Prout  it  contains  38.7  per  cent  of  carbon,  and  61.3  of 
oxygen  and  hydrogen  in  the  proportion  to  form  water. 

Sugar  of  Liquorice.— T\\q  root  of  the  Glycyrrhiza  glahra,  as  also  the 
black  extract  of  the  root  well  known  under  the  name  of  liquorice.^  con- 
tains a saccharine  principle;  but  it  is  quite  distinct  from  sugar.  It  may 
be  prepared  by  infusing  the  root  in  boiling  water,  filtering  when  cold, 
and  gradually  adding  sulphuric  acid  as  long  as  a precipitate,  which  is  a 
compound  of  the  acid  and  saccharine  matter,  is  formed.  It  is  first 
washed  with  water  acidulated  with  sulphuric  acid,  and  then  with  pure 
water;  and  it  is  subsequently  dissolved  in  alcohol,  which  leaves  a little 
vegetable  albumen  and  mucilage.  Solution  of  carbonate  of  potassa  is 
then  added  very  gradually,  so  as  exactly  to  neutralize  the  acid;  and  af- 
ter the  sulphate  of  potassa  has  subsided,  the  alcoholic  solution  is  decanted 
and  evaporated.  It  may  also  be  obtained  in  a similar  manner  from  the 
extract,  except  that  the  solution,  when  first  made,  must  be  purified  by 
white  of  egg. 

Sugar  of  liquorice  is  thus  procured  in  the  form  of  a yellow  transpa- 
rent mass,  which  is  unchangeable  in  the  air,  and  soluble  in  water  and 
alcohol.  It  is  characterized  by  its  tendency  to  form  sparingly  soluble 
compounds  with  acids,  which  accordingly  precipitate  it  from  its  solution 
in  cold  water.  It  unites  also  i-eadily  with  alkaline  bases;  and  when  di- 
gested in  water  containing  carbonate  of  potassa,  baryta,  or  lime,  cai'bon- 
ic  acid  is  slowly  evolved,  and- a soluble  compound  of  the  base  with  the 
saccharine  matter  is  generated.  (Berzelius.) 

Starch  or  Fecula. — Amidine. 

Starcli  exists  abundantly  in  the  vegetable  kingdom,  being  one  of  the 
chief  ingredients  of  most  varieties  of  grain,  of  some  roots,  such  as  the 
potato,  and  of  the  kernels  of  leguminous  plants.  It  is  easily  procured 
by  letting  a small  current  of  water  fall  upon  the  dough  of  wheat  flour 
enclosed  in  a piece  of  linen,  and  subjecting  it  at  the  same  time  to  pres- 
sure between  the  fingers,  until  the  liquid  passes  off  quite  clear.  The 
gluten  of  the  flour  is  left  in  a pure  state,  the  saccharine  and  mucilagi- 


504 


STARCir. 


nous  matters  are  dissolved,  and  the  starch  is  washed  away  mechanically, 
being  deposited  from  the  water  on  standing  in  the  form  of  a white  pow- 
der. An  analogous  process  is  practised  on  a large  scale  in  the  prepara- 
tion of  the  starch  of  commerce;  and  very  pure  starch  may  also  be  ob- 
tained in  a similar  manner  from  the  potato. 

Starch  is  insipid  and  inodorous,  of  a white  colour,  and  insoluble  in 
alcohol,  ether,  and  cold  water.  It  does  not  crystallize;  but  is  common- 
ly found  in  the  shops  in  six-sided  columns  of  considerable  regularity,  a 
form  occasioned  by  the  contraction  which  it  suffers  in  drying.  Boiling 
water  acts  upon  it  readily,  covertiiig  it  into  a tenacious  bulky  jelly, 
which  is  employed  for  stiflening  linen.  In  a large  quantity  of  hot  water, 
it  is  dissolved  completely,  and  is  not  deposited  on  cooling.  The  aque- 
ous solution  is  precipitated  by  subacetate  of  lead;  but  the  best  test  of 
starch,  by  which  it  is  distinguished  from  all  other  substances,  is  iodine. 
This  principle  forms  a blue  compound  with  starch,  whether  in  a solid 
state  or  when  dissolved  in  cold  water. 

Starch  unites  with  the  alkalies,  forming  a compound  which  is  soluble 
in  water,  and  from  which  the  starch  is  thrown  down  by  acids.  Strong 
sulphuric  acid  decomposes  it.  Nitric  acid  in  the  cold  dissolves  starch; 
but  converts  it  by  the  aid  of  heat  into  oxalic  and  malic  acid. 

The  effects  of  heat  on  starch  are  peculiar,  and  have  lately  been  ex- 
amined by  M.  Caventou.  (An.  de  Chim.  et  de  Ph.  xxxi.)  On  ex- 
posing dry  starch  to  a temperature  a little  above  212*^  F.  it  acquires  a 
slightly  red  tint,  emits  an  odour  of  baked  bread,  and  is  rendered  soluble 
in  cold  water;  and  a similar  modification  is  effected  by  the  action  of  hot 
water.  Gelatinous  starch  is  generally  supposed  to  be  a hydrate  of 
starch;  but  M.  Caventou  maintains  that  the  jelly  cannot  by  any  method 
be  restored  to  its  original  state.  He  regards  this  modified  starch  as 
identical  with  the  substance  described  by  Saussure  under  the  name  of 
amidine.  Saussure  thought  it  was  generated  by  exposing  a paste  made 
with  starch  and  water  for  a long  time  to  the  air;  but  according  to  Ca- 
ventou, the  amidine  was  formed  by  the  action  of  the  hot  water  on  starch 
in  making  the  paste.  Its  essential  character  is  to  yield  a blue  colour 
with  iodine,  and  to  be  soluble  in  cold  water.  On  gently  evaporating  the 
solution  to  dryness,  it  becomes  a transparent  mass  like  horn,  which 
retains  its  solubility  in  cold  water.  To  torrefied  starch,  that  is,  to  starch 
thus  modified  b}^  heat,  whether  in  the  dry  way  or  by  boiling  water,  the 
term  amidine  maybe  applied. 

When  starch  is  exposed  to  a still  higher  temperature  than  is  sufficient 
for  its  conversion  into  amidine,  a more  complete  change  is  effected.  It 
then  assumes  a reddish-brown  colour,  swells  up  and  softens,  dissolves 
with  much  greater  facility  in  cold  water,  and  gives  with  iodine  either  a 
purple  colour  or  none  at  all.  In  this  state  it  is  very  analogous  to  gum, 
and  is  employed  by  calico-printers  under  the  name  of  British  gum;  but 
it  differs  from  real  gum  in  not  yielding  mucic  acid  by  digestion  with 
nitric  acid.  A similar  change  may  be  produced  by  long  continued  ebul- 
lition. 

’'I'hc  starch  from  wheat,  according  to  tlie  analysis  of  Gay-Lussac  and 
Thenard,  is  composed,  in  100  parts,  of  carbon  43.55,  oxygen  49.68, 
and  hydrogen  6.  77;  and  this  result  agrees  with  the  analysis  of  potato 
starch  made  l)y  Berzelius.  The  results  of  Ih’out  and  Marcet  correspond 
closely  with  the  foregoing,  'fhe  proportion  of  the  constituents  of 
starch  is,  therefore,  very  analogous  to  that  of  sugar,  a circumstance 
which  will  account  for  the  conversion  of  the  former  into  the  latter. 
This  change  is  clfected  in  seeds  at  the  period  of  germination,  and  is 
particularly  exemplified  in  the  process  of  malting  barley,  during  which 


GUM. 


505 


the  starch  of  that  grain  is  converted  into  sugar.  Proust*  finds  that 
barley  contains  a peculiar  principle  which  he  calls  hordein^  and  which 
he  conceived  to  be  converted  in  malting  partly  into  starch  and  partly 
into  sugar.  Dr.  Thomson  is  of  opinion  that  hordein  should  rather  be 
regarded  as  a modification  of  starch  than  as  a distinct  proximate  princi- 
ple, f A similar  conversion  of  starch  into  sugar  appears  in  some  in- 
stances to  be  the  effect  of  frost,  as  in  the  potato,  apple,  and  parsnip. 

If  starch  is  boiled  for  a considerable  time  in  water  acidulated  with 
l-12th  of  its  weight  of  sulphuric  acid,  it  is  wholly  converted  into  a 
saccharine  matter  similar  to  that  of  the  grape;  and  this  change  takes 
place  much  more  rapidly  if  the  temperature  is  a few  degrees  above 
212®  F.  This  fact  was  first  observed  by  Kirchoff,  and  has  since  been 
particularly  examined  by  Vogel,  De  la  Rive,  and  Saussure.  It  has  been 
established  by  Saussui’e  that  thfe  oxygen  of  the  air  exerts  no  influence 
over  the  process,  that  no  gas  is  disengaged,  that  the  quantity  of  acid 
suffers  no  diminution,  and  that  100  parts  of  starch  yield  110. 14  of  sugar. 
By  careful  analysis,  he  found  that  the  only  difference  in  the  composi- 
tion of  starch  and  sugar  is,  that  the  latter  contains  more  of  the  elements 
of  water  than  the  former.  He  hence  inferred  that,  in  Kirchoff’s  pro- 
cess, the  starch  is  converted  into  sugar  by  its  elements  combining  with 
a certain  quantity  of  oxygen  and  hydrogen  in  the  proportion  to  form 
water;  and  that  the  acid  acts  only  by  increasing  the  fluidity  of  the  mass. 
(An.  of  Philosophy,  vi.)  M.  Saussure  also  found  that  a large  quantity 
of  saccharine  matter  is  produced,  when  gelatinous  starch  or  amidine  is 
kept  for  a longtime  either  with  or  without  the  access  of  air.  (An.  de 
Ch.  et  de  Ph.  vol.  xi.) 

The  recent  researches  of  M.  Caventou,  already  referred  to,  hav« 
thrown  considerable  light  on  the  chemical  nature  of  several  of  the 
amylaceous  principles  of  commerce.  The  Indian  arrow  root^  which  is 
prepared  from  the  root  of  the  Maranta  arundinacea,  has  all  the  characters 
of  pure  starch.  Sago,  obtained  from  the  pith  of  an  East  India  palm  tree, 
{Cycas  circinalis)  and  tapioca  and  cassava,  from  theroot  of  the  latropha 
Manihot,  are  chemically  the  same  substance.  I'hey  both  exist  in  the 
plants  from  which  they  are  extracted  in  the  form  of  starch;  but  as  heat 
is  employed  in  their  preparation,  the  starch  is  more  or  less  completely 
converted  into  amidine.  It  hence  follows  that  pure  potato  starch  may 
be  used  instead  of  arrow  root;  and  that  the  same  material,  modified  by 
heat,  would  afford  a good  substitute  for  sago  and  tapioca.  Salep,  which 
is  obtained  from  the  Ordds  masculay  consists  almost  entirely  of  the  sub- 
stance called  bassorin,  together  with  a small  quantity  of  gum  and  starch. 

When  starch  moistened  with  water  is  digested  with  an  equal  weight 
of  peroxide  of  manganese,  a volatile  acid,  possessed  of  an  odour  simi- 
lar to  prussic  acid,  passes  over.  Its  discoverer,  M.  Tunnermann,  who 
has  given  it  the  name  of  amylic  acid,  considers  it  a compound  of  three 
equivalents  of  oxygen  and  two  and  a half  of  carbon;  but  it  requires 
further  examination  before  being  enumerated  as  a distinct  acid.  (Journal 
of  Science,  N.  S.  iv.  444.) 

Gum, 

Gum  is  a common  proximate  principle  of  vegetables,  and  is  not  con- 
fined to  any  particular  part  of  plants.  The  purest  variety  is  gum  arabic, 
the  concrete  juice  of  several  species  of  the  mimosa  or  acadOy  natives  of 
Africa  and  Arabia. 

Gum  arabic  occurs  in  small,  rounded,  transparent,  friable  grains. 


* An.  de  Ch.  et  de  Ph.  vol.  v.  f Annals  of  Philosophy,  vol.  x. 

43 


506 


LIGNIN. 


commonly  of  a pale  yellow  colour,  inodorous,  and  nearly  tasteless.  It 
softens  when  put  into  water,  and  then  dissolves,  forming*  a viscid  solu- 
tion called  mucilage.  It  is  insoluble  in  alcohol  and  ether,  and  the  for- 
mer precipitates  gum  from  its  solution  in  water  in  the  form  of  opake 
white  flakes.  It  is  soluble  both  in  alkaline  solutions  and  in  lime-water, 
and  is  precipitated  unchanged  by  acids.  The  dilute  acids  dissolve,  and 
the  concentraled  acids  decompose  gum.  Sulphuric  acid  causes  the  for- 
mation of  water  and  acetic  acid,  and  deposition  of  charcoal.  Digested 
with  strong  nitric  acid,  it  yields  saccholactic  acid,  a property  wliich 
forms  a good  character  for  gum.  Malic  and  oxalic  acids  are  generated 
at  the  same  time. 

The  aqueous  solution  of  gum  may  be  preserved  a considerable  time 
without  alteration;  but  at  length  it  becomes  sour,  and  exhales  an  odour 
of  acetic  acid;  a change  which  takes  place  without  exposure  to  the 
air,  and  must,  therefore,  be  owing  to  a new  arrangement  of  its  own 
elements. 

Gum  is  precipitated  from  its  solution  in  water  by  several  metallic 
salts,  and  especially  by  subacetate  of  lead,  which  occasions  a curdy 
precipitate,  consisting  of  38.25  parts  of  oxide  of  lead  and  61.75  parts  of 
gum.  (Berzelius.) 

When  gum  is  heated  to  redness  in  close  vessels,  it  yields,  in  addi- 
tion to  the  usual  products,  a small  quantity  of  ammonia,  which  is  pro- 
bably derived  from  some  impurity.  It  affords  a large  residue  of  ash, 
when  burned,  which  amounts  to  three  percent.,  and  consists  chiefly 
of  the  carbonate,  together  with  some  phosphate  of  lime,  and  a little 
iron. 

From  the  analysis  of  Gay-Lussac  and  Thenard,  if  appears  that  100 
parts  of  gum  arabic  consist  of  carbon  42.23,  oxygen  50.84,  and 
hydrogen  6.93.  This  result  corresponds  very  closely  with  that  of 
Berzelius. 

Besides  gum  arabic,  there  are  several  well-marked  kinds  of  the  princi- 
ple, especially  gum  tragacanth,  cherry-tree  gum,  and  the  mucilage  from 
linseed.  All  these  varieties,  though  distinguishable  from  one  another  by 
some  peculiarity,  have  the  common  character  of  yielding  the  saccholac- 
tic by  the  action  of  nitric  acid.  (Dr.  Bostock  in  Nicholson’s  Journal, 
vol.  xviii.)  The  substance  called  vegetable  jelly,  such  as  is  derived  from 
the  currant,  appears  to  be  mucilage  or  some  modification  of  gum  com- 
bined with  vegetable  acid. 

Lignin. 

' Lignin  or  woody  fibre  constitutes  the  fibrous  structure  of  vegetable 
substances,  and  is  the  most  abundant  principle  in  plants.  The  different 
kinds  of  wood  contain  about  96  per  cent,  of  lignin.  It  is  prepared  by 
digesting  the  sawings  of  any  kind  of  wood  successively  in  alcohol, 
water,  and  dilute  muriatic  acid,  until  all  the  substances  soluble  in  these 
menstrua  are  removed. 

Lignin  has  neither  taste  nor  odour,  undergoes  no  change  by  keep- 
ing, and  is  insoluble  in  alcohol,  water,  and  the  dilute  acids.  By  diges- 
tion in  a concentrated  solution  of  pure  potassa,  it  is  converted,  accord- 
ing to  M.  Braconnot,  into  a substance  similar  to  ulmin.  Mixed  with 
strong  sulphuric  acid,  it  suffers  decomposition,  and  is  changed  into  a 
matter  resembling  gum;  and  on  boiling  the  liquid  for  some  time  the  mu- 
cilage disappears,  and  a saccharine  principle  like  the  sugar  of  grapes 
is  generated.  M.  Braconnot  finds  that  several  other  substances 
which  consist  chiefly  of  woody  fibre,  such  as  straw,  bark,  or  linen, 
yield  sugar  by  a similar  treatment.  (An.  de  Ch.  et  de  Ph.  vol.  xii.) 


COLOURING  MATTER.  507 

Digested  in  nitric  acid,  lignin  is  converted  into  the  oxalic,  malic,  and 
acetic  acids. 

When  the  woody  fibre  is  heated  in  close  vessels,  it  yields  a large 
quantity  of  impure  acetic  acid  (pyroligneous  acid),  and  charcoal  of 
great  purity  remains  in  the  retort.  During  this  process  a peculiar  spir- 
ituous liquid  is  formed,  which  was  discovered  in  1812  by  Mr.  P.  Taylor,* 
and  has  been  examined  by  MM.  Macaire  and  Marcetj-j-  who  proposed  for 
it  the  name  of  pyroxylic  spirit.  This  liquid  is  similar  to  alcohol  in  sev- 
eral of  its  properties,  but  differs  from  it  essentially  in  not  yielding  ether 
by  the  action  of  sulphuric  acid.  It  has  a strong,  pungent,  ethereal 
odour,  with  a flavour  like  the  oil  of  peppermint.  It  boils  at  150^  F., 
and  its  density  is  0.828.  It  burns  with  a blue  flame,  and  without  re- 
sidue. The  pyroacetic  spirit,  obtained  by  Mr.  Chenevix  by  distilling 
the  acetates  of  manganese,  zinc,  and  lead,  differs  from  pyroxylic  spirit, 
not  only  in  composition,  but  in  burning  with  a yellow  flame,  and  in 
being  miscible  in  all  proportions  with  oil  of  turpentine.  Pyroxylic 
spirit,  according  to  the  analysis  of  Macaire  and  Marcet,  consists  of  car- 
bon, oxygen,  and  hydrogen,  very  nearly  in  the  proportion  of  six  equiv- 
alents of  the  first,  four  of  the  second,  and  seven  of  the  third;  and 
pyroacetic  spirit,  of  four  equivalents  of  carbon,  two  of  oxygen,  and 
three  of  hydrogen.  Pyroacetic  spirit  appears  very  similar,  if  not  idem 
tical  with  the  pyroacetic  ether  of  Derosne;  and,  like  pyroxylic  spirit, 
differs  essentially  from  alcohol  in  not  yielding  ether  by  the  action  of 
sulphuric  acid.  (Page  494. ) 

The  ligneous  fibre  was  found  by  Gay-Lussac  and  Thenard  to  consist 
of  carbon  51.43,  oxygen  42.73,  and  hydrogen  5.82.  According  to  Dr. 
Prout  it  contains  50  per  cent,  of  carbon. 


SECTION  V. 

SUBSTANCES  WHICH,  SO  FAR  AS  IS  KNOWN,  DO  NOT  BE- 
LONG TO  EITHER  OF  THE  PRECEDING  SECTIONS. 

Colouring  Matter. 

Infin-ite  diversity  exists  in  the  colour  of  vegetable  substances;  but 
the  prevailing  tints  are  red,  yellow,  blue,  and  green,  or  mixtures  of 
these  colours.  The  colouring  matter  rarely  or  never  occurs  in  an  insu- 
lated state,  but  is  always  attached  to  some  other  proximate  principle, 
such  as  mucilaginous,  extractive,  farinaceous,  or  resinous  substances, 
by  which  some  of  its  properties,  and  in  particular  that  of  solubility,  are 
greatly  influenced.  Nearly  all  kinds  of  vegetable  colouring  matter  are 
decomposed  by  the  combined  agency  of  the  sun^s  rays  and  a moist  at- 
mosphere; and  they  are  all,  without  exception,  destroyed  by  chlorine. 
(Page  206.)  Heat,  likewise,  has  a similar  effect,  even  without  being 
very  intense;  for  a temperature  between  300®  or  400®  F.,  aided  by 
moist  air,  destroys  the  colouring  ingredient.  Acids  and  alkalies  com- 
monly change  the  tint  of  vegetable  colours,  entering  into  combination 
with  them,  so  as  to  form  new  compounds. 


* Quarterly  Journal,  vol.  xiv.  p.  436. 
f Annals  of  Philosophy,  N.  S.  yol.  viii.  p.  69, 


508 


COLOURING  MATTER. 


Several  of  the  metallic  oxides,  and  especially  alumina  and  the  oxides 
of  iron  and  tin,  form  with  colouring*  matter  insoluble  compounds,  to 
which  the  name  of  lakes  is  applied.  Lakes  are  commonly  obtained  by 
mixing  alum  or  pure  muriate  of  tin  with  a coloured  solution,  and  then 
by  means  of  an  alkali  precipitating*  the  oxide  which  unites  with  the 
colour  at  the  moment  of  separation.  On  this  property  are  founded 
many  of  the  processes  in  dyeing  and  calico-printing.  The  art  of  the 
dyer  consists  in  giving  a uniform  and  permanent  colour  to  cloth.  This 
is  sometimes  effected  merely  by  immersing  the  cloth  in  the  coloured 
solution;  whereas  in  other  instances  the  affinity  betxyeen  the  colour  and 
the  fibre  of  the  cloth  is  so  slight,  that  it  only  receives  a stain  which  is 
removed  by  washing  with  water.  In  this  case  some  third  substance  is 
requisite,  which  has  an  affinity  both  for  the  cloth  and  colouring  matter, 
and  which,  by  combining  at  the  same  time  with  each,  may  cause  the 
dye  to  be  permanent.  A substance  of  this  kind  was  formerly  called  a 
mordant;  but  the  term  hasisy  introduced  by  the  late  Mr.  Henry  of  Man- 
chester, is  now  more  generally  employed.  The  most  important  bases, 
and  indeed  the  only  ones  in  common  use,  arfe  alumina,  oxide  of  iron, 
and  oxide  of  tin.  The  two  former  are  exhibited  in  combination  either 
with  the  sulphuric  or  acetic  acid,  and  the  latter  most  commonly  as  the 
muriate.  Those  colouring  substances  that  adhere  to  the  cloth  without 
a basis  are  called  substantive  colours,  and  those  which  require  a basis, 
adjective  colours. 

Various  as  are  the  tints  observable  in  dyed  stuffs,  they  may  all  be  pro- 
duced by  the  four  simple  ones,  blue,  red,  yellow,  and  black;  and 
hence  it  will  be  convenient  to  treat  of  colouring  matters  in  that  order. 

Blue  Dyes. — Indigo  is  chiefly  obtained  from  an  American  and  Asiatic 
plant,  the  Indigofera,  several  species  of  which  are  cidtivated  for  the 
purpose.  It  is  likewise  extracted  from  the  Nerium  tinctorium;  and  an 
inferior  sort  is  prepared  from  the  Isatis  tinctorial  or  woad,  a native  of 
Europe.  Two  different  methods  are  employed  for  its  extraction.  In 
one,  the  recent  plant,  cut  a short  time  before  its  flowering,  is  placed, 
in  bundles  in  a steeping  vat,  where  it  is  kept  down  wdth  cross  bars  of 
wood,  and  covered  to  the  depth  of  an  inch  or  two  with  water.  In  a 
short  time  fermentation  sets  in,  carbonic  acid  gas  is  freely  disengaged, 
and  a yellow  solution  is  formed.  In  the  course  of  ten  or  twelve  hours, 
when  its  surface  begins  to  look  green  from  the  mixture  of  blue  indigo 
with  the  yellow  solution,  it  is  drawn  off  into  the  beating  vat,  where  it 
is  agitated  with  paddles,  until  all  the  colouring  matter  is  oxidized  by 
absorbing  oxygen  from  the  atmosphere,  and  is  deposited  in  the  form  of 
blue  insoluble  indigo.  The  other  method  consists  in  drying  the  leaves 
like  hay,  renioving  the  leaf  from  its  stalk  by  threshing,  and  grinding 
the  former  into  powder,  in  which  state  it  is  preserved  for  use.  The 
dye  is  then  extracted  either  by  maceration  in  water  at  the  temperature 
of  tlie  air,  and  fermentation;  or  by  digestion  in  water  at  150®  or  180® 
F.,  without  being  fermented.  In  either  case  it  is  beaten  with  paddles 
as  before.  (Ure  in  .lourn.  of  Science,  N.  S.  vi.  259.)  The  process  of 
fermciitation,  by  some  thought  essential,  may  be  dispensed  with.  Ac- 
cording to  Mr.  Weston,  however,  the  dye,  as  contained  in  the  plant,  is 
insoluble  in  cold  water;  but  l)y  exposure  to  the  air  it  undergoes  a change, 
in  which  oxygen  acts  a part,  and  by  which  it  is  rendered  soluble  in 
water,  (.lourn.  of  Science,  N.  S.  v.  296.) 

The  indigo  of  commerce,  which  occurs  in  cakes  of  a deep  blue  col- 
our and  earthy  aspect,  is  a mixed  substance,  containing,  in  addition 
to  salts  of  magnesia  and  lime,  the  four  following  ingredients: — 1.  a 
glutinous  matter;  2.  indigo-brown;  3*  indigo-red;  4.  indigo-blue.  (Ber- 
zelius in  Lehrbuch,  iii.  679.) 


COLOURING  MATTER. 


509 


1.  The  gluten  is  obtained  by  digesting  finely  pulverized  indigo  in 
dilute  sulphuric  acid,  neutralizing  with  chalk,  and  evaporating  the  fil- 
tered solution  to  dryness.  The  gluten  is  then  taken  up  by  alcohol,  and 
on  evaporation  is  left  with  the  appearance  of  a yellow  or  yellowish- 
brown,  transparent,  shining  varnish.  Its  odour  is  similar  to  that  of 
broth,  and  it  contains  nitrogen  as  one  of  its  elements.  It  differs,  how- 
ever, from  common  gluten  in  its  free  solubility  both  in  alcohol  and 
water. 

2.  Indigo-brown  has  not  been  obtained  in  a perfectly  pure  state,  ow- 
ing to  its  tendency  to  unite  both  with  acids  and  alkalies.  With  the 
former  it  yields  in  general  sparingly  soluble,  and  with  the  latter  very 
soluble  compounds,  which  have  a deep  brown  colour.  From  indigo, 
freed  from  gluten  by  dilute  acid,  it  is  separated  by  a strong  solution  of 
potassa  aided  by  gentle  heat;  and  after  dilution  with  water,  without 
which  it  passes  with  difficulty  through  paper,  the  liquid  is  filtered. 
The  solution  has  a green  tint,  owing  to  some  indigo-blue  being  dissolv- 
ed, and  with  sulphuric  acid  yields  a bulky  semi-gelatinous  precipitate  of 
a blackish  colour.  By  dissolving  it  in  solution  of  carbonate  of  ammo- 
nia, evaporating  to  dryness,  and  removing  the  soluble  parts  by  a small 
quantity  of  water,  the  brown  matter  is  freed  from  indigo-blue  and  sul- 
phuric acid.  It  still,  however,  contains  ammonia,  and  though  this 
alkali  may  be  expelled  by  means  of  hydrated  lime  or  baryta,  the  indigo- 
brown  retains  some  of  the  earth  in  combination.  Like  indigo-gluten,  it 
contains  a considerable  quantity  of  nitrogen  as  one  of  its  elements.  The 
indigo  green  of  Chevreul  is  probably  a mixture  of  this  substance  with 
indigo-blue. 

3.  Indigo-red  is  obtained  by  boiling  indigo,  previously  purified  by 
potassa,  in  successive  portions  of  strong  alcohol  as  long  as  a red  solution 
is  obtained.  The  alcoholic  solutions  are  then  concentrated  by  evapora- 
tion, during  which  the  indigo-red  is  deposited  as  a blackish -brown  pow- 
der. The  concentrated  solution,  of  a deep  red  colour, ' yields  by  eva- 
poration a compound  of  indigo-red  and  indigo-brown  with  alkali,  which 
is  soluble  in  water. 

Indigo-red  is  insoluble  in  water  and  alkalies;  but  it  is  soluble,  though 
sparingly,  in  hot  alcohol,  and  rather  more  freely  in  ether.  It  dissolves 
in  strong  sulphuric  acid,  and  forms  a dark  yellow  liquid;  and  with  nitric 
acid  it  yields  a beautiful  purple  solution,  which  speedily  becomes  yellow 
by  decomposition.  When  heated  in  vacuo  it  yields  a gray  crystalline 
sublimate,  which,  when  purified  by  a second  sublimation,  is  obtained 
sn  minute  transparent  needles,  shining,  and  white.  This  substance, 
in  its  relation  to  reagents,  resembles  indigo-red;  and  especially  by  yield- 
ing with  nitric  acid  a similar  purple-red  solution,  which  subsequently 
becomes  yellow. 

4.  Indigo-hlue. — I'his  term  is  applied  to  the  real  colouring  matter  of 
indigo,  which  is  left,  though  not  quite  pure,  after  acting  on  common  in- 
digo with  dilute  acid,  potassa,  and  alcohol.  It  is  conveniently  prepar- 
ed from  the  greenish-yellow  solution,  which  dyers  make  by  mixing  in- 
digo with  green  vitriol,  hydrate  of  lime,  and  water;  when  the  indigo  is 
deoxidized  by  the  protoxide  of  iron,  and  yields  a soluble  compound 
with  lime.  On  pouring  this  solution  into  an  excess  of  muriatic  acid, 
while  freely  exposed  to  the  air,  oxygen  gas  is  absorbed,  and  the  indigo 
is  obtained  in  the  form  of  a blue  powder.  It  may  also  be  procured  in  a 
state  of  great  purity  by  sublimation;  but  this  process  is  one  of  delicacy, 
from  the  circumstance  that  the  subliming  and  decomposing  points  of 
indigo  are  very  near  each  other;  and  minute  directions  have  been  given 
by  Mr.  Crum  for  conducting  it  with  success.  (An.  of  FhiL  N.  S.  v. ) 
To  be  sure  of  obtaining  it  c[uite  pure  by  either  process,  the  indiga 


510 


COLOURING  MATTER. 


should  first  be  purified  by  the  action  of  dilute  acid,  potassa,  and 
alcohol. 

Pure  indigo  sublimes  at  550^  F.,  forming  a violent  vapour  with  a tint 
of  red,  and  condensing  into  long  flat  acicular  crystals  which  appear  red 
by  reflected,  and  blue  by  transmitted  light.  It  has  neither  taste  nor 
odour,  and  it  is  insoluble  in  water,  alkalies,  and  ether.  Roiling 
alcohol  takes  up  a trace  of  it,  and  acquires  a blue  tint;  but  it  is 
generally  deposited  again  on  standing.  Nitric  acid  produces  a change 
which  has  already  been  described.  (Page  474.)  Concentrated  sulphuric 
acid,  especially  that  of  Nordhausen,  dissolves  it  readily,  forming  an  in- 
tensely deep  blue  solution,  commonly  termed  sulphate  of  indigOy  which 
is  employed  by  dyers  for  giving  the  Saxon  blue.  The  indigo  during 
solution  undergoes  a change,  and  in  this  modified  state  it  has  received 
tlie  name  of  cerulin  from  Mr.  Crum,  who  regards  it  as  a compound  of 
one  equivalent  of  indigo  and  four  of  water.  According  to  Berzelius 
the  solution  is  of  a more  complicated  nature,  and  contains  the  three 
following  substances;  1.  indigo-purple ; 2.  sulphate  of  indigo;  3.  hypo- 
sulpliate  of  indigo. 

Indigo-purple  is  chiefly  formed  when  indigo  is  dissolved  in  English 
oil  of  vitriol,  and  subsides  when  the  solution  is  diluted  with  from  30  to 
50  times  its  weight  of  water.  It  was  first  described  under  the  name  of 
pheneciny  from  ^o7v/|,  purple,  by  Mr.  Crum,  who  considers  it  a hydrate 
of  indigo  with  two  equivalents  of  water.  Into  the  dilute  solution,  after 
phenecin  is  separated,  Berzelius  inserts  fragments  of  carefully  washed 
flannel,  until  all  the  colour  is  withdrawn  from  the  liquid.  The  dyed 
flannel,  after  the  adhering  acid  is  entirely  removed,  is  digested  in  water 
with  a little  carbonate  of  ammonia,  by  which  means  a blue  solution  is 
obtained  consisting  of  ammonia  in  combination  with  sulphate  and  hypo- 
sulphate  of  indigo.  The  solution  is  evaporated  to  dryness  at  140°  F., 
and  to  the  residue  is  added  alcohol  of  0.833,  which  dissolves  only  the 
hyposulphate. 

The  compounds  of  indigo  with  sulphuric  and  hyposulphuric  acid  are 
considered  by  Berzelius,  not  as  salts  in  which  indigo  acts  as  a base,  but 
as  distinct  acids  of  which  indigo  is  an  essential  ingredient.  Indigo-sul- 
phuric acidy  as  sulphate  of  indigo  may,  therefore,  be  called,  is  prepared 
by  mixing  indigo-sulphate  of  ammonia  with  acetate  of  lead,  when  indigo- 
sulphate  of  lead  subsides.  This  salt  is  suspended  in  water,  and  decom- 
posed by  sulphuretted  hydrogen:  the  sulphuret  of  lead  is  collected  on 
a filter;  and  the  filtered  solution,  at  first  colourless  or  nearly  so,  owing 
to  deoxidation  of  indig'o  by  sulphuretted  hydrogen,  but  which  soon 
becomes  blue  by  the  action  of  the  air,  is  evaporated  at  a temperature 
not  exceeding  122°  F.  The  acid  is  left  as  a dark  blue  solid,  of  a sour 
astringent  taste,  soluble  in  water  and  alcohol,  and  capable  of  forming  a 
distinct  group  of  salts  with  alkalies.  Indigo-hyposulphuric  acid  may  be 
prepared  by  a similar  process. 

()ne  of  the  most  remarkable  characters  of  indigo-blue  is  its  suscepti- 
bility of  being  deoxidized,  and  thus  returning  to  the  state  in  which  it 
appears  to  exist  in  the  plant,  and  of  again  recovering  its  blue  tint  by 
subsequent  oxidation,  'file  change  is  effected  by  various  deoxidizing 
agents,  such  as  sulpliurctted  hyclrogen,  hydrosulphuret  of  ammonia, 
hydrated  j)i'otoxide  of  iron,  or  solution  of  orpiment  in  potassa.  In  the 
deoxidized  state  it  readily  unites  with  alkaline  substances,  such  as  po- 
tassa or  lime,  and  forms  compounds  which  are  very  soluble  in  water. 
'Die  method  by  whicli  dyers  prepare  their  blue  vat  is  founded  on  these 
properties.  A portion  of  indigo  is  put  into  a tub  with  about  three  times 
its  weight  ol'  green  vitriol  and  an  equal  quantity  of  slaked  lime,  and 
water  is  added.  The  protoxide  of  iron,  precipitated  by  lime,  gradually 


COLOURING  MATTER. 


511 


deoxidizes  the  indigo,  and  in  the  course  of  a day  or  two  a yellow  solution 
is  obtained.  When  cotton  cloth  is  moistened  with  this  liquid  and  ex- 
posed to  the  air,  it  speedily  becomes  green  from  the  mixture  of  colours, 
and  then  blue;  and  as  the  blue  indigo  is  insoluble,  and  U4pites  chemically 
with  the  fibre  of  the  cloth,  the  dye  is  permanent. 

Deoxidized  indigo  has  been  obtained  in  a separate  state  by  Liebig. 
A mixture  is  made  with  1.5  parts  of  indigo,  2 of  green  vitriol,  2.5  of 
hydrate  of  lime,  and  50  or  60  of  water;  and  after  an  interval  of  24  hours 
the  yellow  solution  is  carefully  drawn  off  by  a syphon,  and  mixed  with 
dilute  muriatic  acid.  A thick  white  precipitate  falls,  which  remains 
without  change  if  carefully  excluded  from  oxygen,  and  may  even  be 
exposed  to  the  air  when  quite  dry;  but  it  rapidly  becomes  blue  by  ex- 
posure to  the  atmosphere  while  moist,  or  by  being  covered  with  aerated 
water.  To  this  substance  Liebig  has  applied  the  name  of  mdigogene^ 
and  he  has  ascertained  that,  in  passing  into  blue  indigo,  it  absorbs  11.5 
per  cent  of  oxygen.  The  necessity  for  perfectly  excluding  every  source 
of  oxygen,  renders  the  preparation  of  indigogene  difficult.  All  the 
vessels  employed  in  the  process  should  be  filled  with  hydrogen  gas,  the 
water  be  freed  from  air  by  boiling,  and  as  a further  protection  a little 
sulphite  of  ammonia  is  added  both  to  the  acid  by  which  the  precipitate 
is  made,  and  to  the  water  with  which  it  is  washed. 

From  the  analytical  researches  of  Mr.  Crum,  it  appears  that  indigo 
is  composed  of  nitrogen,  oxygen,  hydrogen,  and  carbon,  in  the  propor- 
tion of  one  equivalent  of  the  first  element,  two  of  the  second,  four  of 
the  third,  and  sixteen  of  the  fourth.  This  would  make  its  atomic  weight 
130;  but  it  admits  of  doubt  whether  the  indigo  analyzed  by  Mr.  Crum 
was  absolutely  pure. 

Red  Dyes. — The  chief  substances  which  are  employed  for  the  red 
dye  are  cochineal,  lac,  archil,  madder,  Brazil  wood,  logwood,  and  saf- 
flower, all  of  which  are  adjective  colours.  The  cochineal  is  obtained 
from  an  insect  which  feeds  upon  the  leaves  of  several  species  of  the 
CactuSi  and  which  is  supposed  to  derive  this  colouring  matter  from  its 
food.  It  is  very  soluble  in  water,  and  is  fixed  on  cloth  by  means  of 
alumina  or  oxide  of  tin.  Its  natural  colour  is  crimson;  but  when  bitar- 
trate of  potassa  is  added  to  the  solution,  it  yields  a rich  scarlet  dye. 
The  beautiful  pigment  called  carmine  is  a lake  made  of  cochineal  and 
alumina,  or  oxide  of  tin. 

The  dye  called  archil  is  obtained  from  a peculiar  kind  of  lichen, 
{Lichen  roccella,)  which  grows  chiefly  in  the  Canary  Islands,  and  is  em- 
ployed by  the  Dutch  in  forming  the  blue  pigment  called  litmus  or  turn- 
sol.  The  colouring  ingredient  of  litmus  is  a compound  of  the  red 
colouring  matter  of  the  lichen  and  an  alkali;  and  hence,  on  the  addition 
of  an  acid,  the  colouring  matter  is  set  free,  and  the  red  tint  of  the  plant 
is  restored.  Litmus  is  not  only  used  as  a dye,  but  is  employed  by 
chemists  for  detecting  the  presence  of  a free  acid. 

The  colouring  principle  of  logwood  has  been  procured  in  a separate 
state  by  M.  Chevreul,  who  has  applied  to  it  the  name  of  hematin.  (An. 
de  Ch.  vol.  Ixxxi.)  It  is  obtained  in  crystals  by  digesting  the  aqueous 
extract  of  logwood  in  alcohol,  and  allowing  the  alcoholic  solution  to 
evaporate  spontaneously. 

Safflower  is  the  dried  flowers  of  the  Carthamus  tinctorius,  which  is 
cultivated  in  Egypt,  Spain,  and  in  some  parts  of  the  Levant.  The  pig- 
ment called  rouge  is  prepared  from  this  dye. 

Madder,  extensively  employed  in  dyeing  the  Turkey  redy  is  the  root 
of  the  Ruhia  tinctorum.  A red  substance,  supposed  to  be  the  chief 
colouring  principle  of  the  plant,  has  been  obtained  in  an  insulated  state  by 
Robiquet  and  Colin,  who  have  termed  \\.  alizarinCy  from  ali-zariy  the  com- 


512 


TANNIN. 


mercial  name  by  which  madder  is  known  in  the  Levant.  Their  pro- 
cess has  received  the  following-  modification  by  Zenneck.  Ten  parts  of 
madder  are  dig-estedin  four  of  sulphuric  ether,  the  solution  is  evaporated 
to  the  consistence  of  syrup,  and  then  allowed  to  became  dry  by  sponta- 
neous evaporation.  The  residue  is  pulverized,  and  sublimed  by  a g*entle 
heat  from  a. watch  glass:  The  sublimate,  which  is  collected  by  covering 
the  watch  glass  with  a cone  of  paper,  is  deposited  in  the  form  of  yel- 
lowish-red, bi'illiant,  diaphonous,  acicular  crystals,  which  are  soft,  flexi- 
ble, and  heavier  than  water.  They  soften  when  heated,  and  sublime  at 
a temperature  between  500  and  600®  F.,  causing  an  aromatic  odour. 
They  are  nearly  insoluble  in  cold  and  very  sparingly  soluble  in  hot  water. 
They  require  for  solution  210  times  their  weight  of  alcohol,  and  160  of 
ether  at  60®  F.  According  to  Zenneck  the  acidity  of  alizarine  is  very 
decisive,  both  in  its  sour  taste,  and  its  power  of  neutralizing  alkalies.  It 
consists,  in  100  parts,  of  18  of  carbon,  20  of  hydrogen,  and  62  of  oxygen 
(Journal  of  Science,  N.  S.  v.  198.) 

Yellotv  Dyes, — The  chief  yellow  dyes  are  quercitron  bark,  turmeric, 
wild  American  hiccory,  fustic,  and  saffron;  all  of  which  are  adjective 
colours.  Quercitron  bark,  which  is  one  of  the  most  important  of  the 
yellow  dyes,  was  introduced  into  notice  by  Dr.  Bancroft.  With  a basis 
of  alumina,  the  decoction  of  this  bark  gives  a bright  yellow  dye.  With 
oxide  of  tin  it  communicates  a variety  of  tints,  which  may  be  made  to 
vary  from  a pale  lemon  coloiir  to  deep  orange.  With  oxide  of  iron  it 
gives  a drab  colour. 

Turmeric  is  the  root  of  the  Curcuma  loiiga,  a native  of  the  East  Indies. 
Paper  stained  with  a decoction  of  this  substance  constitutes  the  turmeric 
or  curcuma  paper,  employed  by  chemists  as  a test  of  free  alkali,  by  the 
action  of  which  it  receives  a brown  stain. 

The  colouring  ingredient  of  saffron  {Crocus  sativus)  is  soluble  in 
water  and  alcohol,  has  a bright  yellow  colour,  is  rendered  blue  and 
then  lilac  by  sulphuric  acid,  and  receives  a green  tint  on  the  addition  of 
nitric  acid.  From  the  great  diversity  of  colours  which  it  is  capable 
of  assuming  under  different  circumstances,  MM.  Bouillon  Lagrange 
and  Vogel  have  proposed  for  it  the  name  of  polychroite.  (An.  de  Ch. 
vol.  Ixxx. ) . 

Black  Dyes.  —The  black  dye  is  made  of  the  same  ingredients  as  writ- 
ing ink,'  and,  therefore,  consists  essentially  of  a compound  of  oxide  of 
iron  with  gallic  acid  and  tannin.  From  the  addition  of  logwood  and 
acetate  of  copper,  the  black  receives  a shade  of  blue. 

By  the  dexterous  combination  of  the  four  leading  colours,  blue,  red, 
yellow,  and  black,  all  other  shades  of  colour  may  be  procured.  Thus 
green  is  communicated  by  forming  a blue  ground  with  indigo,  and  then 
adding  a yellow  by  means  of  quercitron  bark. 

The  reader  who  is  desirous  of  studying  the  details  of  dyeing  and 
calico-printing,  a subject  which  does  not  fall  within  the  plan  of  this 
work,  may  consult  Berthollet’s  EUmens  de  VArt  de  la  Teinture;  the  trea- 
tise of  Dr.  Bancroft  on  Permanent  Colours;  a paper  by  Mr.  Henry  in 
the  tliird  volume  of  the  Manchester  Memoirs;  and  the  Essay  of  Thenard 
and  Board  in  the  74th  volume  of  tlie  Annalesde  Chimie. 

Tannin. 

Tannin  exists  in  large  quantity  in  tlie  excrcvscences  of  several  species 
of  the  oak,  called  gall-nuts;  in  tlie  bark  of  most  trees;  in  some  inspis- 
sated juices,  such  as  kino  and  catechu;  in  the  leaves  of  the  tea-plant, 
sumacli,  and  whortleberry  {IJvaursi)-,  and  in  all  astringent  plants,  be- 
ing the  chief  cause  of  the  astringency  of  vegetable  matter.  It  is  fre- 
quently associated  with  gallic  acid,  as  for  example  in  gall-nuts,  most 


TANNIN. 


513 


kinds  of  bark,  and  in  tea;  but  In  kino,  catechu,  and  cinchona  bark,  no 
gallic  acid  is  present.  In  some  instances  tannin  appears  to  be  converted 
into  gallic  acid.  Thus  on  exposing  an  infusion  of  gall-nuts  for  some 
time  to  the  air,  nearly  all  the  tannin  disappears,  and  a quantity  of  gallic 
acid  is  found  in  the  liquid  much  greater  than  that  which  it  had  original- 
ly contained.  (Page  470.) 

Several  methods  have  been  proposed  for  preparing  tannin;  but  the 
following  process  of  Berzelius,  modified  in  the  first  part  by  my  assistant 
Mr.  Warrington,  is  the  most  convenient.  Gall-nuts,  in  coarse  powder, 
are  digested  in  water  so  as  to  form  a rather  concentrated  solution,  and 
the  decanted  liquid  is  treated  with  a little  white  of  eggs  until  the  colour 
changes  from  a brown  to  a pale  yellow,  when  it  is  filtered.  When 
cold,  concentrated  sulphuric  acid  is  added  as  long  as  a precipitate  falls; 
and  by  preserving  the  solution  for  a few  days  an  additional  quantity  is 
obtained.  The  precipitate,  of  a yellowish- white  colour,  consisting  of 
sulphuric  acid  and  tannin,  is  then  washed  with  dilute  sulphuric  acid, 
pressed  in  folds  of  bibulous  paper,  dissolved  in  pure  water,  and  ma- 
cerated with  cartronate  of  lead  in  fine  powder.  Sulphate  of  lead  is  thus 
formed,  and  is  separated  by  filtration  from  the  pale  yellow  solution  of 
tannin,  which  should  be  evaporated  in  vacuo  with  a vessel  of  sulphuric 
acid.  A hard  yellowish-brown  extract  remains;  and  on  dissolving  the 
soluble  portions  in  ether,  and  evaporating  spontaneously,  pure  tannin 
is  left. 

Another  process,  recommended  by  Berzelius,  is  to  precipitate  tannin 
with  a concentrated  solution  of  carbonate  of  potassa,  avoiding  an  ex- 
cess of  the  al]sali  which  would  redissolve  the  precipitate.  The  white 
compound  of  tannin  and  potassa  is  washed  with  ice-Cold  water,  dissolv- 
ed in  dilute  acetic  acid,  filtered,  and  mixed  with  acetate  of  lead.  The 
precipitate,  which  consists  of  oxide  of  lead  and  tannin,  is  carefully 
washed,  suspended  in  water,  and  decomposed  by  sulphuretted  hydro- 
gen. The  filtered  solution  of  tannin  is  then  evaporated  and  purified  by 
ether,  as  already  ntentioned. 

Pure  tannin  is  colourless  and  inodorous,  has  an  astringent  tete,  V* 
unchangeable  in  the  air,  and  may  be  rubbed  into  powder.  It  is  soluble 
in  water,  and  the  solution  reddens  litmus.  It  is  dissolved  also  by  ether, 
and  with  the  aid  of  heat  by  absolute  alcohol.  By  exposure  to  the  air  it 
becomes  yellow,  yellowish-browm,  and  dark-brown;  and  when  evapor- 
ated to  the  consistence  of  an  extract,  a portion  of  it  is  rendered  insol- 
uble. The  infusion  of  gall-nuts  owes  its  colour  chiefly  to  this  cause; 
and  the  foregoing  directions  to  evaporate  in  vacuo  are  given  with  the 
view  of  avoiding  the  agency  of  air.  With  acids,  it  forms  compounds 
of  sparing  solubility,  which,  when  saturated,  are  purely  astringent  in 
taste,  without  any  acidity.  Alkaline  bases  have  a similar  effect.  Tannin 
is  precipitated,  for  example,  by  the  carbonates  of  potassa  and  ammonia, 
by  the  alkaline  earths,  by  alumina,  and  many  of  the  oxides  of  the  com^ 
mon  metals.  Nitric  acid  and  chlorine  decompose  tannin,  producing  a 
change,  the  nature  of  which  is  not  well  understood. 

The  most  characteristic  property  of  tannin  is  its  action  on  a salt  of 
iron  and  a solution  of  gelatin.  With  peroxide  of  iron,  or  still  better 
with  the  protoxide  and  peroxide  mixed,  tannin  forms  a black-coloured 
compound,  which,  together  with  gallate  of  iron,  constitutes  the  basis 
of  writing  ink  and  the  black  dyes.  (Page  471.)  Mixed  with  a solution 
of  gelatin,  a yellowish  flocculent  precipitate  subsides,  wliich  is  insolu- 
ble in  water,  resists  putrefaction  powerfully,  and  on  drying  becomes 
hard  and  tough.  This  substance,  to  which  the  name  pf  tanno-gelatin 
has  been  applied,  is  the  essential  basis  of  leather,  being  always  formed 
when  skins  are  macerated  in  an  infusion  of  bark.  The  composition  of 


514 


VEGETABLE  ALBUMEN. 


tanno-g*elatin  is  not  always  uniform,  having  been  found  by  Ur.  Duncan, 
jun.,  and  Dr.  Bostock,  to  vary  with  the  proportions  employed.  If  the 
gelatin  is  added  in  slight  excess  only,  the  resulting  compound  consists, 
according  to  Sir  H.  Davy,  of  54  parts  of  gelatin  and  46  of  tannin;  so 
that  the  quantity  of  tannin  contained  in  any  fluid  may  in  this  way  be  de- 
termined with  tolerable  precision.  Tanno-gelatin  is  soluble  to  a consi- 
derable extent  in  an  excess  of  gelatin. 

From  an  analysis  of  the  compound  of  tannin  and  oxide  of  lead,  Ber- 
zelius states  that  100  parts  of  tannin  are  composed  of  carbon  52.69, 
oxygen  43.45,  and  hydrogen  3.86. 

From  the  experiments  of  Sir  H.  Davy,  it  appears  that  the  inner  cor- 
tical layers  of  barks  are  the  richest  in  tannin.  The  quantity  is  greatest 
in  the  beginning  of  spring,  at  the  time  the  buds  begin  to  open,  and 
smallest  during  winter.  Of  all  the  varieties  of  bark  which  he  examin- 
ed, that  of  the  oak  contains  the  gi’eatest  quantity  of  tannin. 

By  processes  similar  to  those  above  described  tannin  may  be  obtained 
from  cinchona  bark,  catechu,  kino,  and  other  sources.  These  various 
kinds  of  tannin  correspond  in  most  respects,  but  in  some  points  a dif- 
ference is  observable.  This  may  be  traced  in  their  action  on  the  salts 
of  iron,  with  which,  instead  of  striking  a black  or  bluish-black  tint,,  as 
solution  of  gall-nuts  or  oak-bark  does,  some  varieties  of  tannin  give  a 
green  colour. 

Jirtijidal  Tannin. — This  interesting  substance  was  discovered  twenty 
years  ago  by  Mr.  Hatchett,  who  gave  a full  description  of  it  in  the  Phi- 
losophical Transactions  for  1805  and  1806.  The  best  method  of  pre- 
paring it  is  by  the  action  of  nitric  acid  on  charcoal.  For  this  purpose 
100  grains  of  charcoal  in  fine  powder  are  digested  in  an  ounce  of  nitric 
acid,  of  density  1.4,  diluted  with  two  ounces  of  water.  The  mixture 
is  exposed  to  a gentle  heat,  which  is  to  be  continued  until  all  the  char- 
coal is  dissolved.  The  reddish-brown  solution  is  then  evaporated  to  dry- 
ness, in  order  to  expel  the  pure  acid,  the  temperature  being  carefully 
regulated  towards  die  close  of  the  process,  so  that  the  product  may 
not  be  decomposed. 

Artificial  tannin  is  a brown  fusible  substance,  of  a resinous  fracture, 
and  astringent  taste.  It  is  soluble  even  in  cold  water  and  in  alcohol.  It 
reddens  litmus  paper,  probably  from  adhering  nitric  acid.  With  a salt 
of  iron  and  solution  of  gelatin,  it  acts  precisely  in  the  same  manner  as 
natural  tannin.  It  differs,  however,  from  that  substance  in  not  being 
decomposed  by  the  action  of  strong  nitric  acid. 

Artificial  tannin  may  be  prepared  in  Several  ways.  Thus  it  is  gen- 
erated by  the-  action  of  nitric  acid,  both  on  animal  or  vegetable  char- 
coal, and  on  pit-coal,  asphaltum,  jet,  indigo,  common  resin,  and  sev- 
eral other  resinous  substances.  It  is  also  procured  by  treating  common 
resin,  elemi,  assafa*tida,  camphor,  balsams,  &c.  first  with  sulphuric 
acid,  and  then  with  alcohol. 

Vegetable,  Mbunien.  Gluten*  Yeast. 

Vcgctahle  Albumen. this  name  is  (listinguished  a vegetable 
principle  which  has  a close  resemblance  to  animal  albumen,  especially 
in  the  characteristic  property  of  being  coagulable  by  heat.  This  sub- 
stance was  found  by  Vogel  in  the  bitter  almond,  and  in  the  sweet  al- 
mond by  Bmdlay:  it  appears  to  be  an  ingredient  of  emulsive  seeds  gen- 
erally; and  it  exists  in  the  sap  of  many  plants.  Einholf  detected  it  in 
wheat,  rye,  barley,  i)cas,  and  beans.  Vegetable  albumen  is  soluble  in 
cold  water,  but  by  a boiling  temperature  it  is  coagulated,  and  thus 
completely  deprived  of  its  solubility.  It  is  insoluble  in  alcohol,  and 
very  sparingly  soluble  in  acids.  Alkalies  dissolve  it  readily,  and  it  may 
be  precipitated  from  them  by  acids;  but  the  albumen  falls  in  combina^ 


GLUTEN. 


515 


tion  with  a portion  of  the  acid.  Ferrocyanate  of  potassa  and  corrosive 
sublimate  act  upon  it  as  on  solutions  of  animal  albumen. 

Vegetable  albumen  contains  nitrogen  as  one  of  its  elements,  and  is 
very  prone,  when  kept  in  the  moist  state,  to  undergo  the  putrefactive 
fermentation,  emitting  an  offensive  odour,  with  disengagement  of 
ammonia  and  formation  of  acetate  of  ammonia.  During  a certain  period 
of  putrefaction  it  has  the  odour  of*old  cheese.  (Berzelius.) 

Gluten. — In  the  separation  of  starch  from  wheat  flour,  as  already 
described  (page  503),  a gray  viscid  substance  remains,  fibrous  in  its  tex- 
ture, and  elastic.  Beccaria,  who  first  carefully  examined  its  properties, 
was  struck  with  its  analogy  to  glue,  both  in  its  viscidity  as  w^ell  as  its 
tendency  to  putrefy  like  animal  matter,  and  gave  it  the  name  of  vegetable 
gluten.  Einhof  has  since  shown  that  this  gluten  is  a mixed  substance, 
containing  gluten  and  vegetable  albumen. 

Pure  gluten  is  obtained  by  washing  dough  in  water  until  the  starch 
and  soluble  parts  are  removed,  and  treating- the  residue  with  boiling 
alcohol.  On  mixing  the  alcoholic  solution  with  water,  and  distilling  off 
the  spirit,  the  gluten  is  deposited  in  large  coherent  flakes.  As  thus  ob- 
tained it  has  a pale  yellow  colour,  and  a peculiar  odour,  but  no  taste; 
adheres  tenaciously  to  the  fingers  when  handled,  and  has  considerable 
elasticity.  It  is  insoluble  in  water  and  ether,  but  dissolves  readily  in 
hot  alcohol,  apparently  without  any  change  of  property;  but  if  the  al- 
coholic solution  is  evaporated  to  dryness,  the  ghiten  is^left  as  a transpa- 
rent varnish.  It  swells  up  and  softens  with  acetic  acid,  forming  a com- 
pound which  is  soluble  in  water.  It  unites  also  with  the  mineral  acids; 
and  these  compounds,  excepting  that  with  sulphuric  acid,  dissolve  rea- 
dily in  pure  water,  but  are  insoluble  when  there  is  an  excess  of  acid.  It 
is  dissolved  by  dilute  solution  of  potassa,  apparently  without  being  de- 
composed; for  the  gluten,  after  being  thrown  down  by  the  mineral 
acids,  retains  its  viscidity.  In  this  state,  however,  it  is  combined  with 
some  of  the  acid.  (Berzelius.) 

When  gluten  is  kept  in  a warm  moist  situation  it  ferments,  and  an 
acid  is  formed;  but  in  a few  days  putrefaction  ensues,  and  an  offensive 
odour,  like  that  of  putrefying  animal  matter,  is  emitted.  According  to 
I*roust,  who  made  these  spontaneous  changes  a particular  object  of  study, 
the  process  is  divisible  into  two  distinct  periods.  In  the  first,  carbonic 
acid  and  hydrogen  gases  are  evolved;  and  in  the  second,  besides  acetic 
and  phosphoric  acids  and  ammonia,  two  new  compounds  are  generated, 
for  which  he  proposed  the  names  of  caseic  «cidand  caseous  oxide.  These 
are  the  same  principles  which  are  generated  during  the  fermentation  of 
the  curd  of  milk,  and  their  real  nature  Will  be  considered  in  the  section 
on  milk.  It  is  apparent  from  these  circumstances  that  gluten  contains 
nitrogen  as  one  of  its  elements,  and  that  it  approaches  closely  to  the 
nature  of  animal  substances.  It  has  hence  been  called  a vegeto-animal 
principle. 

If  gluten  is  dried  by  a gentle  heat,  it  contracts  in  volume,  becomes 
hard  and  brittle,  and  may  in  this  state  be  preserved  without  change. 
Exposed  to  a strong  heat,  it  yields,  in  addition  to  the  usual  inflamma- 
ble gases/  a thick  fetid  oil,  and  carbonate  of  ammonia. 

Gluten  is  present  in  most  kinds  of  grain,  such  as  wheat,  barley,  rye, 
oats,  peas,  and  beans;  but  the  first  contains  it  in  by  far  the  largest  pro- 
portion. This  is  the  reason  that  wheaten  bread  is  more  nutritious  than 
’ that  made  with  other  kinds  of  flour;  for  of  all  vegetable  substances 
gluten  appears  to  be  the  most  nutritive.  It  is  to  the  presence  of  gluten 
that  wheat  flour  owes  its  property  of  forming  a tenacious  paste  with 
water.  To  the  same  cause  is  owing  the  formation  of  light  spongy  bread;, 
the  carbonic  acid  which  is  disengaged  during  the  fermentation  of  dough 


516 


A SPAR  AGIN. 


being’  detained  by  the  viscid  gluten,  distends  the  whole  mass,  and  thus 
produces  the  rising  of  the  dough.  From  the  experiments  of  Sir  H.  Davy, 
it  appears  that  good  wheat  flour  contains  from  19  to  24  per  cent  of 
gluten.  The  wheat  grown  in  the  south  of  Europe  is  richer  in  gluten 
than  that  of  colder  climates. 

M.  Taddey,  an  Italian  chemist,  has  given  an  account  of  two  principles 
separable  from  the  gluten  of  Beccaria  by  means  of  boiling  alcohol.  To 
the  substance  soluble  in  alcohol  he  has  applied  the  name  of  gliadine^ 
from  y>iicty  gluten;  and  to  the  other  that  of  zymome,  from  ^vfJL^ , a fer- 
ment. (An.  of  Phil.  XV.)  For  the  latter  he  has  discovered  a delicate 
test  in  the  powder  of  guaiacum,  which  when  rubbed  in  a mortar  with 
moist  zymome,  instantly  strikes  a beautiful  blue  colour;  and  the  same  tint 
appears,  though  less  rapidly,  when  it  is  kneaded  with  gluten  or  dough  made 
with  good  wheat  flour.  But  with  bad  flour,  the  gluten  of  which  has  suf- 
fered spontaneous  decomposition,  the  blue  tint  is  scarcely  visible;  and  ac- 
cordin^y  M.  Taddey  conceives  that  useful  inferences  as  to  the  quality 
of  flour  may  be  drawn  from  the  action  of  g'uaiacum. 

These  views  have  been  lately  criticised  by  Berzelius,  who  declares 
that  the  substances  described  by  Taddey  are  nothing  else  than  the  gluten 
and  vegetable  albumen  already  described;  and  the  habitual  accuracy 
of  Berzelius  leaves  little  chance  of  error  in  his  statement.  The  blue 
tint,  above  alluded  to,  must  have  arisen  from  the  action  of  guaiacum 
either  on  vegetable  albumen  itself,  or  on  some  substance  by  which  it  is 
accompanied  in  wheat.  (An.  of  Phil.  iv.  69,  orLehrbuch,  iii.  362.) 

Yeast. — This  subst-ance  is  always  generated  during  the  vinous  fermen- 
tation of  vegetable  juices  and  decoctions,  rising  to  the  surface  in  the 
form  of  a frothy,  flocculent,  somewhat  viscid  matter,  the  nature  and 
composition  of  which  are  unknown.  It  is  insoluble  in  water  and  alcohol, 
and  in  a warm,  moist  atmosphere  gradually  putrefies,  a sufficient  proof 
that  nitrogen  is  one  of  its  elements.  Submitted  to  a moderate  heat,  it 
becomes  dry  and  hard,  and  may  in  this  state  be  preserved  without  change. 
Heated  to  redness  in  close  vessels,  it  yields  products  similar  to  those 
procured  under  the  same  circumstances  from  gluten.  To  this  substance, 
indeed,  yeast  is  supposed  by  some  chemists  to  be  very  closely  allied. 

The  most  remarkable  property  of  yeast  is  that  of  exciting  fermenta- 
tion. By  exposure  for  a few  minutes  to  the  heat  of  boiling  water,  it 
loses  this  property,  but  after  some  time  again  acquires  it  Nothing  con- 
clusive is  known  concerning  either  the  nature  of  these  changes,  or  the 
mode  in  which  yeast  operates  in  establishing  the  fermentative  process. 

Jlsparagin^  Bassorin,  Caffein^  Cathartin^  Fungirij  Su- 
beriuy  Ulmin^  Lupulin,  Inuliri^  M^dullin^  Polleyiin^ 
Piper  in.,  Olivile^  Sarcocollj  Rhubarbariuj  Rfi6in^ 
Colocyntin^  Bitter  Principle.,  Extractive  Matter^ 
Plumbagin,  Chlorophyle, 

Asparagin. — This  principle  was  discovered  by  MM.  Vauquelin  and 
Uobic[uet  in  the  juice  of  the  asparagus,  from  which  it  is  deposited  in 
crystals  by  evaporation.  The  form  of  its  crystals  is  a rectangular  octo- 
hedron,  six-sided  i)rism,  or  right  rhombic  prism.  Its  taste  is  cool  and 
slightly  nauseous,  it  is  soluble  in  water,  and  has  neither  an  acid  nor  afta- 
line  reaction.  (Ann.  de  Ch.  Ivii.  88.)  f 

A.sparagin  is  contained  also  in  the  root  of  marsh-mallow  and  liquorifce. 
Robiquet,  who  first  ol)tained  it  from  the  juice  of  the  recent  liquorice 
root,  doubted  its  identity  with  asparagin,  and  gave  it  the  name  of  flge- 
doiit;  but  the  mistake  has  been  corrected  by  M.  Plisson. 

Plisson  has  noticed  that  when  asparagin  is  boiled  for  some  time  :with 


BASSORIN,  ULMTN. 


517 


hydrate  of  lead  or  mag’nesia,  it  is  resolved  into  ammonia  and  a new  acid 
called  the  aspartic.  On  decomposing*  aspartate  of  lead  by  sulphuretted 
hydrog’en,  and  evaporating*  the  filtered  solution,  the  acid  is  obtained  as  a 
colourless  powder  composed  of  minute  prismatic  crystals.  It  has  little 
taste,  is  sparingly  soluble  in  cold  water,  and  still  less  so  in  alcohol.  Its 
aqueotis  solution  is  not  precipitated  by  the  soluble  salts  of  baryta,  lime, 
lead,  magnesia,  copper,  mercury,  or  silver.  I'he  aspartates,  when  the 
taste  of  the  base  does  not  interfere,  have  the  taste  of  the  juice  of  meat. 

It  yields  ammonia  when  decomposed  by  heat.  (An.  de  Ch.  et  de  Ph. 
XXXV.  175,  and  xl.  309.) 

Bassorin  was  first  noticed  in  gum  hussora  by  Vauquelin.  According 
to  Gehlen  and  Bucholz,  it  is  contained,  together  with  common  gum,  in 
gum  tragacanth;  and  John  found  it  in  the  gum  of  the  cherry-tree.  Sa- 
lop, from  the  experiments  of  Caventou,  appears  to  consist  almost  totally 
of  bassorin. 

Bassorin  is  characterized  by  forming  with  cold  water  a bulky  jelly, 
which  is  insoluble  in  that  menstruum,  as  well  as  in  alcohol  and  ether. 
Boiling  water  does  not  dissolve  it,  except  by  long-continued  ebullition, 
w^hen  the  bassorin  at  length  disappears,  and  is  converted  into  a substance 
similar  to  gvim  arable. 

Caffein  was  discovered  in  coffee  by  Robiquet  in  the  year  1821,  and 
was  soon  after  obtained  from  the  same  source  by  Pelletier  and  Caven- 
tou, w’ithout  a knowledge  of  the  discovery  of  Robiquet.  It  is  a white 
crystalline  volatile  matter,  which  is  soluble  in  boiling  water  and  alco- 
hol, and  is  deposited  on  cooling  in  the  form  of  silky  filaments  like 
arhianthus;  Pelletier,  contrary  to  tlie  opinion  of  Robiquet,  at  first  re- 
garded it  as  an  alkaline  base;  but  he  now  admits  that  it  does  not  affect 
the  vegetable  blue  colours,  nor  combine  with  acids.  (Journal  de  Phar- 
macie  for  May  1826.) 

Hitherto  the  properties  of  caffein  have  not  been  fully  described. 
From  the  analysis  of  Pelletier  and  Dumas,  100  parts  of  it  consist  of 
carbon  46.51,  nitrogen  21.54,  hydrogen  4.81,  and  oxygen  27.14. 
Though  it  contains  more  nitrogen  than  most  animal  substances,  it 
does  not,  under  any  circumstances,  undergo  the  putrefactive  ferment- 
ation. 

Caihariin, — This  name  has  been  applied  by  MM.  Lassaigne  and 
Feneulle  to  the  active  principle  of  senna.  (An.  de  Ch.  et  de  Ph.  voL 
xvi.) 

Fun^in. — This  name  is  applied  by  M.  Braconnot  to  the  fleshy  sub- 
stance of  the  mushroom.  It  is  procured  in  a pure  state  by  digestion  in 
hot  water,  to  wliich  a little  alkali  is  added.  Fungin  is  nutritious  in  a 
high  degree,  and  in  composition  is  very  analogous  to  animal  sub- 
stances, Like  flesh,  it  yields  nitrogen  gas  when  digested  in  dilute  ni- 
tric acid. 

Suherin. — This  name  has  been  applied  by  Chevreul  to  the  cellular 
tissue  of  the  common  cork,  the  outer  bark  of  the  cork-oak,  {quercus 
suber),  after  the  astringent,  oily,  rcsinou.s,  and  other  soluble  matters 
have  been  removed  by  the  action  of  w’ater  and  alcohol.  Suherin  differs 
from  all  other  veg'etable  principles  by  yielding  the  suberic  when  treated 
by  nitric  acid.  I 

Uimin,  discovered  by  Klaproth,  is  a substance  which  exudes  spon-  | 
taneously  from  the  elm,  oak,  chestnut,  and  other  trees;  and,  accord-  1 
ing  to  Berzelius,  is  a constituent  of  most  kinds  of  bark.  It  may  be 
prepared  by  acting  upon  elm-bark  by  liot  alcohol  and  cold  water,  and  | 
then  digesting  the  residue  in  water,  which  contains  an  alkaline  carbo-  j 
nate  in  solution.  On  neutralizing  the  alkali  with  an  acid,  the  ulmin  is 
precipitated. 


44 


518 


LUPULIN,  SAIICOCOLL. 


Ulmin  is  a dark  brown,  nearly  black  substance,  is  insipid  and  inodo^ 
rous,  and  is  very  sparing*ly  soluble  in  water  and  alcohol.  It  dissolves 
freely,  on  the  contrary,  in  the  solution  of  an  alkaline  carbonate,  and  is 
thrown  down  by  an  acid.  Ulmin  is  regarded  as  an  acid  b}^  M.  P.  Boul- 
lay,  who  has  proposed  for  it  the  name  of  ulmic  acid.  He  found  that 
100  parts  of  it  contain  56.7  of  carbon,  and  43.3  of  oxygen  and  hydro- 
gen in  the  proportion  to  form  water.  According  to  him  it  is  an  ingre- 
dient of  vegetable  mould  and  turf,  and  contributes  much  to  the  growth 
of  plants.  The  black  matter  deposited  during  the  decomposition  of 
prussic  acid,  supposed  by  Gay-Lussac  to  be  a carburet  of  nitrogen,  is 
an  acid  very  similar  to  the  ulmic,  and  to  which  he  has  given  the  nanle 
of  azw/wzcacid.  (An.  de  Ch.  et  de  Ph.  xliii.  273.) 

Lupulin  is  the  name  applied  by  Dr.  Ives  to  the  active  principle  of  the 
hop,  but  which  has  not  yet  been  obtained  in  a state  of  purity. 

Inulin  is  a white  powder  like  starch,  which  is  spontaneously  deposit- 
ed from  a decoction  of  the  roots  of  the  Inula  Jielenium  or  elecampane . 
This  substance  is  insoluble  in  cold,  and  soluble  in  hot  water,  and  is  de- 
posited from  the  latter  as  it  cools,  a character  which  distinguislies  it 
from  starch.  With  iodine  it  forms  a greenish-yellow  compound  of  a 
perishable  nature.  Its  solution  is  somewhat  mucilaginous;  but  inulin  is 
distinguished  from  gum  by  insolubility  in  cold  water,  and  in  not  yielding 
the  saccholactic  when  digested  in  nitric  acid. 

Medullin. — This  name  was  applied  by  John  to  the  pith  of  the  sun- 
flower, but  its  existence  as  an  independent  principle  is  somewhat  du- 
bious. The  term  pollenin  has  been  given  by  the  same  chemist  to  the 
pollen  of  tulips. 

Piperin  is  the  name  which  is  applied  to  a white  crystalline  substance 
extracted  from  black  pepper.  It  is  tasteless,  and  is  quite  free  from 
pungency,  the  stimulating  property  of  the  pepper  being  found  to  re- 
side in  a fixed  oil.  (Pelletier,  in  An.  de  Ch.  et  de  Ph.  vol.  xvi.) 

A process  lately  recommended  for  its  preparation  by  Vogel  consists 
in  digesting,  for  two  days,  16  ounces  of  black  pepper  in  coarse  powder 
in  twice  its  weight  of  water,  five  times  in  succession;  and  digesting  the 
insoluble  parts,  previously  well  pressed  and  dried,  for  three  days  in  24 
ounces  of  alcohol.  The  solution  is  pressed  through  linen  cloth,  filtered, 
and  evaporated  to  the  consistence  of  syrup;  and  the  impure  crystals  of 
piperin,  deposited  by  cooling,  are  freed  from  adhering  resinous  matter 
by  ether,  and  purified  by  animal  charcoal  and  a second  crystallization 
from  alcohol. 

Piperin  crystallizes  in  four-sided  prisms,  which  have  commonly  a 
yellow  colour,  owing  to  adhering  oil  or  resin.  It  is  insoluble  in  cold, 
and  sparingly  soluble  in  hot  water;  but  it  is  very  soluble  in  alcohol,  and 
less  so  in  ether.  Acetic  acid  also  dissolves  it,  and  leaves  it  by  evapora- 
tion in  feathery  crystals.  It  fuses  at  212®,  and  consists  of  carbon,  oxy- 
gen, and  hydrogen. 

Olivile. — When  the  gum  of  the  olive  tree  is  dissolved  in  alcoliol,  and 
the  solution  is  allowed  to  evaporate  spontaneously,  a peculiar  substance, 
apparently  different  from  the  other  proximate  principles  hitherto  ex- 
amined, is  deposited  either  in  flattened  needles  or  as  a brilliant  amyla- 
ceous powder.  To  this  M.  Pelletier,  its  discoverer,  has  given  the  name 
of  olivile.  (An.  of  Phil.  vol.  xii.) 

SarcocoU  h the  concrete  juice  of  the  Fencea  sarcocolla,  phuit  which 
grows  in  the  northern  ])arts  of  Africa.  It  is  imported  in  the  form  of 
small  grains  of  a yellowish  or  reddish  colour  like  gum  arabic,  to  which 
its  properties  arc  similar.  It  has  a sweetish  taste,  dissolves  in  the  mouth 
like  gum,  and  forms  a mucilage  with  water.  It  is  distinguished  ^om 
gum,  however,  by  its  solubility  in  alcohol,  and  by  its  aqueous  solution 


RHUBARBAIUN,  PLUMBAGIN. 


519 


being  precipitated  by  tannin.  Dr.  Thomson,  who  has  given  a full  ac- 
count of  sarcocoll  in  his  System  of  Chemistry,  considers  it  closely  allied 
to  the  saccharine  matter  of  liquorice. 

Rhuharharin  is  the  name  employed  by  Pfaff  to  designate  the  princi- 
ple in  which  the  purgative  property  of  the  rhubarb  resides.  M.  Nani 
of  Milan  regards  the  active  principle  of  this  plant  as  a vegetable  alkali; 
but  he  has  not  given  any  proof  of  its  alkaline  nature.  (Journal  of 
Science,  xvi.  172.) 

Rhein. — M.  Vaudin  has  applied  this  name  to  a substance  which  he 
obtained  by  gently  heating  rhubarb  in  powder  with  eight  times  its  weight 
of  nitric  acid  of  1.375,  evaporating  to  the  consistence  of  syrup,  and 
diluting  with  cold  water.  Rhein,  which  is  then  deposited,  is  inodorous, 
has  a slightly  bitter  taste,  and  an  orange  colour.  It  is  sparingly  soluble 
in  cold  water;  but  it  dissolves  in  alcohol,  ether,  and  hot  water,  and  its 
solutions  are  rendered  pale  yellow  by  acids,  and  rose-red  by  alkalies.  It 
may  be  extracted  from  rhubarb  by  ether,  a fact  which  proves  that  it 
exists  ready  formed  in  the  plant;  and  its  mode  of  preparation  shows 
that  it  possesses  unusual  permanence,  powerfully  resisting  the  action  of 
nitric  acid. 

Colocyntin. — This  name  was  applied  by  Vauquelin  to  a bitter  resin- 
ous matter  extracted  from  colocynth  by  the  action  of  alcohol,  and  left 
by  evaporation  as  a brittle  substance  of  a golden-yelloW  colour.  It  is 
slightly  soluble  in  water,  is  freely  dissolved  by  alcohol  and  alkalies, 
and  possesses  the  purgative  properties  of  colocynth.  (Journ.  of  Science, 
xviii.  400.) 

Bitter  Principle. — This  name  was  formerly  applied  to  a substance 
supposed  to  be  common  to  bitter  plants,  and  to  be  the  cause  of  their 
peculiar  taste.  The  recent  discoveries  in  vegetable  chemistry,  how- 
ever, have  shown  that  it  can  no  longer  be  regarded  as  a uniform  un- 
varying principle.  The  bitterness  of  the  nux  vomica,  for  example,  is 
owing  to  strychnia,  that  of  opium  to  morphia,  that  of  cinchona  bark  to 
cinch onia  and  quinia,  &c.  The  cause  of  the  bitter  taste  in  the  root  of 
the  squill  is  different  from  that  of  the  hop  or  of  gentian.  The  term 
bitter  principle,  when  applied  to  any  one  principle  common  to  bitter 
plants,  conveys  an  erroneous  idea,  and  should  therefore  be  aban- 
doned. 

Extractive  Matter. — This  expression,  if  applied  to  one  determinate 
principle  supposed  to  be  the  same  in  different  plants,  is  not  less  vague 
than  the  foregoing.  It  is  indeed  true  that  most  plants  yield  to  water  a 
substance  which  differs  from  gum,  sugar,  or  any  proximate  principle  of 
vegetables,  which  therefore  constitutes  a part  of  what  is  called  an  ex- 
tract  in  pharmacy,  and  which,  for  want  of  a more  precise  term,  may  be 
expressed  by  the  name  of  extractive.  It  must  be  remembered,  how- 
ever, that  this  matter  is  always  mixed  with  other  proximate  principles, 
and  that  there  is  no  proof  whatever  of  its  being  identical  in  different 
plants.  I'he  solution  of  saffron  in  hot  water,  said  to  afford  pure  ex- 
tractive matter  by  evaporation,  contains  the  colouring  matter  of  the 
plant,  together  with  all  the  other  vegetable  principles  of  saffron,  which 
happen  to  be  soluble  in  the  menstruum  employed. 

Plumbagin,  extracted  by  Dulong  from  the  root  of  the  Plumbago  Eu- 
ropaea,  is  soluble  in  water,  alcohol,  and  ether,  and  crystallizes  from 
its  solutions  in  acicular  crystals  of  a yellow  colour.  Its  aqueous  solu- 
tion is  made  cherry-red  by  alkalies,  subacetate  of  lead,  and  permuriate 
of  iron;  but  acids  restore  the  yellow  tint,  and  the  plumbagin  is  found 
unaltered,  its  taste  is  at  first  sweet,  but  is  subsequently  sharp  and 
acrid,  extending  to  the  throat.  (Journal  of  Sciepce,  N.  S.  vi.  191.) 


520 


SACCriAUlNE  FERMENTATION. 


Chlorophyle. — This  name  lias  been  applied  by  Pelletier  and  Caventou 
to  the  green  colouring  matter  of  leaves.  It  is  prepared  by  bruising 
green  leaves  into  a pulp  with  water,  pressing  out  all  the  liquid,  and 
boiling  the  pulp  in  alcohol.  The  solution  is  mixed  with  water,  and  the 
spirit  driven  off*  by  distillation,  when  the  chlorophyle  is  left  floating  on 
the  surface  of  the  water.  As  thus  obtained,  it  appears  to  be  wax  stained 
with  the  green  colour  of  the  leaves;  and  from  some  late  observations  of 
M.  Macaire  Prlnsep,  the  wax  may  be  removed  by  ether,  and  the  colour- 
ing matter  left  in  a pure  state.  The  red  tiutumnal  tint  of  the  leaves, 
according  to  the  same  observer,  is  the  effect' of  an  acid  generated  in  the 
leaf.  The  green  tint  may  be  restored  by  the  action  of  an  alkali. 


SECTION  VI. 

ON  THE  SPONTANEOUS  CHANGES  OF  VEGETABLE  MATTER. 

Vegetable  substances,  for  reasons  already  explained  in  the  remarks 
introductory  to  the  study  of  organic  chemistry,  are  very  liable  to  spon- 
taneous decomposition.  So  long,  indeed,  as  they  remain  in  connexion 
with  the  living  plant  by  which  they  were  produced,  the  tendency  of 
their  elements  to  form  new  combinations  is  controlled;  but  as  soon  as 
the  vital  principle  is  extinct,  of  whose  agency  no  satisfactory  explana- 
tion can  at  present  be  afforded,  they  become  subject  to  the  unrestrained 
influence  of  chemical  affinity.  To  the  spontaneous  changes  which  they 
then  experience  from  the  operation  of  this  power,  the  term  fermentation 
is  applied. 

As  might  be  expected  from  the  difference  in  the  constltiitlbn  of  dif- 
ferent vegetable  compounds,  they  are  not  all  equally  prone  to  fermenta- 
tion; nor  is  the  nature  of  the  change  the  same  in  all.  Thus  alcohol, 
oxalic,  acetic,  and  benzoic  acids,  probably  the  vegetable  alkalies,  and 
pure  naphtlia,  may  be  kept  for  years  without  change,  and  some  of  them 
appear  unalterable;  while  others,  such  as  gluten,  sugar,  starch,  and 
mucilaginous  substances,  are  very  liable  to  decomposition.  In  like  man- 
ner, the  spontaneous  change  sometimes  terminates  in  the  formation  of 
sugar,  at  another  time  in  that  of  alcohol,  at  a third  in  that  of  acetic 
acid,  and  at  a fourth  in  the  total  dissolution  of  the  substance.  This  has 
led  to  the  division  of  the  fermentative  processes  into  four  distinct  kinds, 
namely,  the  saccharine^  vinous,  acetous,  and  jow/re/flc/fre  fermentation. 

Sa cchari ne  Ferment ation. 

The  only  substance  known  to  be  subject  to  the  first  kind  of  fermen- 
tation is  starch.  Wlieq  gelatinous  starch,  or  amidine,  is  kept  in  a moist 
state  for  a considerable  length  of  time,  a change  gradually  ensues,  and 
a quantity  of  sugar,  equal  to  about  half  the  weight  of  tlie  starch  em- 
ployed, is  generated.  J'kxposure  to  the  atmosphere  is  not  necessary  to 
this  cliange,  buttiie  quantity  of  sugar  is  increased  by  access  of  air.' 

The  germination  of  seeds,  as  exemplilied  in  the  malting  of  barley,  is 
likewise  an  instance  of  tlie  saccharine  fermentation;  but  as  it  differs  in 
some  respects  from  the  process  above  mentioned,  being  probably  modi- 
fied by  the  vitality  of  the  germ,  it  may  with  greater  propriety  be  dis- 
cussed in  the  following  section. 


VINOUS  FERMENTATION. 


521 


The  ripening*  of  fruit  has  also  been  reg*arded  as  an  example  of  the 
saccharine  fermentation,  especially  since  some  fruits,  such  as  the  pear 
and  apple,  if  gathered  before  their  maturity,  become  sweeter  by  keep- 
ing. I cannot,  however,  adopt  this  opinion.  The  process  of  ripening 
If  appears  to  consist  in  the  conversion,  not  of  starch,  but  of  acid  into  sugar. 
Such  at  least  is  the  view  deducible  from  the  experiments  of  Proust, 
who  examined  the  unripe  grape  in  its  different  stages  towards  matu- 
rity. He  found  that  the  green  fruit  contains  a large  quantity  of  free 
acid,  chiefly  the  citric,  which  gradually  disappears  as  the  grape  ripens, 
while  its  place  is  occupied  by  sugar.  It  is  hence  probable  that  the 
elements  of  the  acid  itself,  as  the  result  of  a vital  process,  are  made  to 
enter  into  a new  arrangement,  by  which  sugar  is  generated.  The  for- 
mation of  an  acid  may  be  regarded  as  one  step  towards  the  production 
of  saccharine  matter,  a view  which  will  account  for  the  strong  acidity  of 
many  fruits,  such  as  the  gooseberry  and  currant,  just  before*they  begin 
to  ripen. 

Vinous  Fermentation, 

The  conditions  which  are  required  for  establishing  the  vinous  fermen- 
tation are  four  in  number;  namely,  the  presence  of  sugar,  water,  yeast 
or  some  ferment,  and  a certain  temperature.  The  best  mode  of  study- 
ing this  process,  so  as  to  observe  the  phenomena  and  determine  the 
nature  of  the  change,  is  to  place  five  parts  of  sugar  with  about  twenty  of 
water  in  a glass  flask  furnished  with  a bent  tube,  the  extremity  of 
which  opens  under  an  inverted  jar  full  of  water  or  mercury;  and  after 
adding  a little  yeast,  to  expose  the  mixture  to  a temperature  of  about 
60®  or  70®  Fahr.  In  a short  time  bubbles  of  gas  begin  to  collect  in  the 
vicinity  of  the  yeast,  and  the  liquid  is  soon  put  into  brisk  motion,  in 
consequence  of  the  formation  and  disengagement  of  a large  quantity  of 
gaseous  matter;  the  solution  becomes  turbid,  its  temperature  rises,  and 
froth  collects  upon  its  surface.  After  continuing  for  a few  days,  the 
evolution  of  gas  begins  to  abate,  and  at  length  ceases  altogether;  the 
impurities  gradually  subside,  and  leave  the  liquor  clear  and  transparent. 

The  only  appreciable  changes  which  are  found  to  have  occurred  du- 
ring the  process  are  the  disappearance  of  the  sugar,  and  the  formation 
of  alcohol,  which  remains  in  the  flask,  and  of  carbonic  acid  gas,  which 
is  collected  in  the  pneumatic  apparatus.  A small  portion  of  yeast  is  in- 
deed decomposed;  but  the  quantity  is  so  minute  that  it  may  without 
inconvenience  be  left  out  of  consideration.  The  yeast  indeed  appears 
to  operate  only  in  exciting  the  fermentation,  without  further  con- 
tributing to  the  products.  The  atmospheric  air,  it  is  obvious,  has  no 
share  in  the  phenomena,  since  it  may  be  altogether  excluded  without, 
affecting  the  result.  Tlie  theory  of  the  process  is  founded  on  the  fact 
that  the  sugar,  which  disappears,  is  almost  precisely  equal  to  the  united 
weights  of  the  alcohol  and  carbonic  acid;  and  hence  the  former  is  sup- 
posed to  be  resolved  into  the  two  latter.  The  mode  in  which  this 
change  is  conceived  to  take  place  has  been  ably  explained  by  Gay-Lus- 
sac, an  explanation  which  will  be  easily  understood  by  comparing  the 
composition  of  sugar  with  that  of  alcohol.  The  elements  of  sugar, 
which  consist  of  carbon,  hydrogen,  and  oxygen,  in  the  ratio  of  one 
equivalent  of  each,  (page  502,)  are  multiplied  by  three,  in  order  to 
equalize  the  quantity  of  hydrogen  contained  in  the  two  compounds^ 
(An.  de  Ch.  xcv.  3170 


44* 


522  VINOUS  FEUMENTATION. 

By  weight. 

By  volume. 

Sugar. 

Alcohol. 

Sugar. 

Alcohol. 

Carbon,  18  or  three  equiv. 

12  or  two  equiv. 

Vap.  of  carbon, 

3 

2 

Hydrogen,  3 or  three  equiv. 

3 or  three  equiv. 

Hydrogen, 

3 

3 

Oxygen,  24  or  three  equiv. 

8 or  one  equiv. 

Oxygen, 

i 

45 

23 

Now  on  inspecting*  this  table,  and  remembering  that  carbonic  acid 
consists  of  one  equivalent  of  carbon,  or  one  volume  of  its  vapour,  and 
two  equivalents  or  one  volume  of  oxygen,  it  will  be  apparent  that  the 
elements  of  sugar  are  n such  proportion  as  to  form  one  equivalent  of 
alcohol,  or  one  volume  of  its  vapour,  and  one  equivalent  or  one  volume 
of  carbonic  acid.  Therefore  45  parts  of  sugar  are  capable  of  furnishing 
23  parts  of  alcohol  and  22  of  carbonic  acid. 

It  admits  of  doubt  whether  any  substance  besides  sugar  is  capable  of 
undergoing  the  vinous  fermentation.  The  only  other  principle  which 
is  supposed  to  possess  this  property  is  starch,  and  this  opinion  chiefly 
rests  on  the  two  following  facts.  First,  it  is  well  known  that  potatoes 
which  contain  but  little  sugar,  yield  a large  quantity  of  alcohol  by  fer- 
mentation, during  which  the  starch  disappears.  And  secondly,  M.  Cle- 
ment procured  the  same  quantity  of  alcohol  from  equal  w'eights  of 
malted  and  umnalted  barley.  (/Vn.  de  Ch.  et  de  Ph.  v.  422.)  Nothing 
conclusive  can  be  inferred,  how^ever,  from  these  data;  for,  from  the  fa- 
cility with  which  starch  is  converted  into  sugar,  it  is  probable  that  the 
saccharine  may  precede  the  vinous  fermentation.  This  view  is,  indeed, 
justified  by  the  practice  of  distillers,  who  do  not  ferment  with  unmalted 
barley  only,  but  are  obliged  to  mix  with  it  a certain  proportion  of  malt, 
w^hich  appears  to  act  as  a Ferment  to  the  unmalted  grain. 

Though  a solution  of  pure  sugar  is  not  susceptible  of  the  vinous  fer- 
mentation without  being  mixed  with  yeast,  or  some  such  ferment;  yet 
the  saccharine  juices  of  plants  do  not  require  the  addition  of  that  sub- 
stance, or  in  other  w'ords,  they  contain  some  principle  which,  like  yeast, 
excites  the  fermentative  process.  Thus,  must  or  the  juice  of  the  grape 
ferments  spontaneously;  but  Gay-Lussac  has  observed  that  these  juices 
cannot  begin  to  ferment  unless  they  are  exposed  to  the  air.  By  heating 
must  to  212^  F.,  and  then  corking  it  carefully,  the  juice  may  be  pre- 
served without  change;  but  if  it  be  exposed  to  the  air  for  a few  seconds 
only,  it  absorbs  oxygen,  and  fermentation  takes  place.  From  this  it 
would  appear  that  the  must  contains  a principle  which  is  convertible 
into  yeast,  or  at  least  acquires  the  characteristic  property  of  that  sub- 
stance, by  absorbing  oxygen. 

It  appears  from  the  experiments  of  M.  Colin,  that  various  substances 
are  capable  of  acting  as  a ferment.  This  property  is  possessed  by  glu- 
ten and  vegetable  albumen,  caseous  matter,  albumen,  fibrin,  gelatin, 
blood,  and  urine.  In  general  they  act  most  efficaciously  after  the  com- 
mencement of  putrefaction;  and  indeed  exposure  to  oxygen  gas  seems 
equally  necessary  for  enabling  these  substances  to  act  as  ferments,  as 
to  the  principle  contained  in  the  juice  of  the  fruit. 

7'he  v.arious  kinds  of  stimulating  fluids,  prepared  by  means  of  th-c 
vinous  fermentation,  are  divisible  into  wines  which  are  formed  from  the 
juices  of  saccharine  fruits,  and  the  various  kinds  of  ale  and  beer  pro- 
duced from  a decoction  of  the  nutritive  grains  previously  malted: 

The  j»iice  of  the  grape  is  superior,  for  the  ])urpo.se  of  making  wine, 
to  that  of  all  other  fruits,  not  merely  in  containing  a larger  proportion 
of  saccharine  matter,  since  this  deficiency  may  be  supplied  artificially, 
but  in  the  nature  of  its  acid.  I'he  chief  or  only  acidulous  piinciple  of 
tlic  mature  grape,  ripened  in  a warm  climate,  such  as  Spain,  Portugal, 


ACETOUS  FERMENTATION. 


523 


or  Madeira,  is  bitartrate  of  potassa.  As  this  salt  is  insoluble  in  alcohol, 
the  greater  part  of  it  is  deposited  during  the  vinous  fermentation;  and 
an  additional  quantity  subsides,  constituting  the  cm^r,  during  the  pro- 
gress of  wine  towards  its  point  of  highest  perfection.  The  juices  of 
other  fruits,  on  the  contrary,  such  as  the  gooseberry  or  currant,  con- 
tain malic  and  citric  acids,  which  are  soluble  both  in  water  an.d  alcohol, 
and  of  which,  therefore,  they  can  never  be  deprived.  Consequently 
these  wines  are  only  rendered  palatable  by  the  presence  of  free  sugar, 
which  conceals  the  taste  of  the  acid;  and  hence  it  is  necessary  to  arrest 
the  progress  of  fermentation  long  before  the  whole  of  the  saccharine 
matter  is  consumed.  For  the  same  reason,  these  wines,  unless  made 
very  sweet,  do  not  adniit  of  being  long  kept;  for  as  soon  as  the  free 
sugar  is  converted  into  alcohol  by  the  slow  fermentative  process,  which 
may  be  retarded  by  the  addition  of  brandy  but  cannot  be  prevented,  the 
wine  acquires  a strong  sour  taste. 

Ale  and  beer  differ  from  wine  in  containing  a large  quantity  of  mu- 
cilaginous and  extractive  matters,  derived  from  the  malt  with  which  they 
are  made.  From  the  presence  of  these  substances  they  always  contain 
a free  acid,  and  are  greatly  disposed  to  pass  into  the  acetous  fermenta- 
tion. The  sour  taste  is  concealed  partly  by  free  sugar,  and  partly  by 
the  bitter  flavour  of  the  hop,  the  presence  of  which  diminishes  the 
tendency  to  the  formation  of  an  acid. 

The  fermentative  process  which  takes  place  in  dough  mixed  with 
yeast,  and  oh  which  depends  the  formation  of  good  bread,  has  been 
supposed  to  be  of  a peculiar  kind,  and  is  sometimes  designated  by  the 
name  of  'panary  fermentation.  The  late  ingenious  researches  of  Dr. 
Colquhoun,  however,  leave  little  or  no  doubt  that  the  phenomena  are 
to  be  ascribed  to  the  saccharine  matter  of  the  flour  undergoing  the  vi- 
nous fermentation,  by  which  it  is  resolved  into  alcohol  and  carbonic 
acid.  (Brewster’s  Journal,  vi.)  Indeed  Mr.  Graham  has  actually  pro- 
cured alcohol  by  distillation  from  fermented  dough. 

Jlcetous  Fermentation. 

When  any  liquid  which  has  undergone  the  vinous  fermentation,  or 
even  pure  alcohol  diluted  with  water,  is  mixed  with  yeast,  and  exposed 
in  a warm  place  to  the  open  air,  an  intestine  movement  speedily  com- 
mences, heat  is  developed,  the  fluid  becomes  turbid  from  the  deposi- 
tion of  a peculiar  filamentous  matter,  oxygen  is  absorbed  from  the  at- 
mosphere, and  carbonic  acid  is  disengaged.  These  changes,  after  con- 
tinuing a certain  time,  cease  spontaneously;  the  liquor  becomes  clear, 
and  instead  of  alcohol,  it  is  now  found  to  contain  acetic  acid.  This 
process  is  called  the  acetous  fermentation. 

The  vinous  may  easily  be  made  to  terminate  in  the  acetous  fermenta- 
tion; nay,  the  transition  takes  place  so  easily,  that  in  many  instances, 
in  which  it  is  important  to  prevent  it,  this  is  with  difficulty  effected.  It 
is  the  uniform  result  if  the  fermenting  liquid  be  exposed  to  a warm  tem- 
perature and  to  the  open  air;  and  the  means  by  which  it  is  avoided  is  by 
, excluding  the  atmosphere,  or  by  exposure  to  cold. 

For  the  acetous  fermentation  a certain  degree  of  warmth  is  indispen- 
sable. It  takes  place  tardily  below  60®  F.;  at  50®  it  is  very  sluggish; 
and  at  32®,  or  not  quite  so  low,  it  is  wholly  arrested.  It  proceeds 
with  vigour,  on  the  contrary,  when  the  thermometer  ranges  between 
60®  and  80®,  and  is  even  promoted  by  a temperature  somewhat  higher. 
The  presence  of  water  is  likewise  essential;  and  a portion  of  yeast,  or 
some  analogous  substance,  by  which  the  process  may  be  established, 
must  also  be  present. 

The  information  contained  in  chemical  works,  relative  to  the  sub- 


524 


PUTREFACTIVE  FERMENTATION. 


stances  susceptible  of  the  acetous  fermentation,  is  somewhat  confused, 
a circumstance  which  appears  to  have  arisen  from  phenomena  of  a to- 
tally different  nature  being  included  under  the  same  name.  It  seems 
necessary  to  distinguish  between  the  mere  formation  of  acetic  acid,  and 
the  acetous  fermentation.  Several  or  perhaps  most  vegetable  substances 
yield  acetic  acid  when  they  undergo  spontaneous  decomposition.  Mu- 
cilaginous substances  in  particular,  though  excluded  from  the  air,  gra- 
dually become  sour;  and  consistently  with  this  fact,  inferior  kinds  of 
ale  and  beer  are  known  to  acquire  acidity  in  a short  time,  even  when 
confined  in  well-corked  bottles.  In  like  manner,  a solution  of  sugar, 
mixed  with  water  in  which  the  gluten  of  wheat  has  fermented,  and  kept 
in  close  vessels,  was  found  by  Fourcroy  and  Vauquelin  to  yield  acetic 
acid.  All  these  processes,  however,  appear  essentially  different  from 
the  proper  acetous  fermentation  above  described,  being  unattended  with 
visible  movement  in  the  liquid,  with  absorption  of  oxygen,  or  disen- 
gagement of  carbonic  acid. 

The  acetous  fermentation,  in  this  limited  sense,  consists  in  the  con- 
version of  alcohol  into  acetic  acid.  That  this  change  docs  really  take 
place  is  inferred,  not  only  from  the  disappearance  of  alcohol  and  the 
simultaneous  production  of  acetic  acid,  but  also  from  the  quantity  of 
the  latter  being  precisely  proportional  to  that  of  the  former.  The  na- 
ture of  the  chemical  action,  however,  is  at  j)resent  exceedingly  ob- 
scure. Indeed  the  only  probable  explanation  which  has  been  offered  is 
the  following.  Since  alcohol  contains  a greater  proportional  quantity 
of  carbon  and  hydrogen  than  acetic  acid,  it  has  been  supposed  that  the 
oxygen  of  the  atmosphere,  the  presence  of  which  is  indispensable,  ab- 
stracts so  much  of  those  elements,  by  giving  rise  to  the  formation  of 
carbonic  acid  and  water,  as  to  leave  the  remaining  carbon,  hydrogen, 
and  oxygen  of  the  alcohol  in  the  precise  ratio  for  forming  acetic  acid. 
The  experiments  of  Saussure,  however,  are  incompatible  with  this 
view.  According  to  his  researches,  the  quantity  of  carbonic  acid 
generated  during  the  acetous  fermentation  is  precisely  equal  in  vol- 
ume to  the  oxygen  which  is  absorbed;  and  hence  it  is  inferred,  that  this 
gas  unites  exclusively  with  the  carbon  of  the  alcohol.  This  result  is 
different  from  what  might  have  been  anticipated,  and  requires  confir- 
mation. 

The  acetous  fermentation  is  conducted  on  a large  scale  for  yielding 
the  common  vinegar  of  commerce.  In  France  it  is  prepared  by  expos- 
ing weak  wines  to  the  air  during  warm  weather;  and  in  this  country  it 
is  made  from  a solution  of  brown  sugar  or  molasses,  or  an  infusion  of 
malt.  The  vinegar  thus  obtained  always  contains  a large  quantity  of 
mucilaginous  and  other  vegetable  matters,  the  presence  of  which  ren- 
ders it  liable  to  several  ulterior  changes. 

Putrefactive,  Fermentation, 

By  this  term  is  implied  a process  which  is  not  attended  with  the  phe- 
nomena of  the  saccharine,  vinous,  or  acetous  fermentation,  biit  during 
which  the  vegetable  matter  is  completely  decomposed.  All  proximate 
principles  are  not  equally  liable  to  this  kind  of  dissolution.  "I  hose  in 
which  charcoal  and  hydrogen  prevail,  such  as  the  oils,  resins,  and  al- 
cohol, do  not  undergo  the  ])utrefactive  fermentation;  nor  do  acids,  which 
contain  a considerable  excess  of  oxygen,  manifest  a tendency  to  suffer 
this  change.  'I'hosc  substances  alone  are  disposed  to  putrefy,  the  oxy- 
gen and  hydrogen  of  which  are  in  proportion  td  form  water;  and  such,> 
in  particular,  as  contain  nitrogen.  Among  these,  however,  a singular 
difference  is  observable.  Caff’ein  evinces  no  tendency  to  spontaneous* 
decomposition;  while  gluten,  which  certainly  must  contain  a less  pro 


PUTREFACTIVE  FERMENTATION. 


525 


portlonal  quantity  of  nitrogen,  putrefies  with  great  facility.  It  is  dif- 
ficult to  assign  the  precise  cause  of  this  difference;  but  it  most  probably 
depends  partly  upon  the  mode  in  which  the  ultimate  elements  of  bodies 
are  arranged,  and  partly  on  their  cohesive  power;— those  substances, 
the  texture  of  which  is  the  most  loose  and  soft,  being,  ca^teiris  paribus, 
the  most  liable  to  spontaneous  decomposition. 

The  conditions  which  are  required  for  enabling  the  putrefactive  pro- 
cess to  take  place,  are  moisture,  air,  and  a certain  temperature. 

The  presence  of  a certain  degree  of  moisture  is  absolutely  necessary; 
and  hence  vegetable  substances,  which  are  disposed  to  putrefy  under 
favourable  circumstances,  may  be  preserved  for  an  indefinite  period  if 
carefully  dried,  and  protected  from  humidity.  Water  acts  apparently 
by  softening  the  texture,  and  thus  counteracting  the  agency  of  cohe- 
sion; and  a part  of  the  effect  may  also  be  owing  to  its  affinity  for  some 
of  the  products  of  putrefaction.  It  is  not  likely  that  this  liquid  is  act- 
ually decomposed,  since  water  appears  to  be  a uniform  product. 

The  air  cannot  be  regarded  as  absolutely  necessary,  since  putrefac- 
tion is  found  to  be  produced  by  the  concurrence  of  the  two  other  con- 
ditions only;  but  the  process  is  without  doubt  materially  promoted  by 
free  exposure  to  the,  atmosphere.  Its  operation  is  of  course  attributable 
to  the  oxygen  combining  with  the  carbon  and  hydrogen  of  the  decaying 
substance. 

The  temperature  most  favourable  to  the  putrefactive  process  is  be- 
tween 60®  and  100®  Fahr.  A strong  heat  is  unfavourable,  by  expelling 
moisture;  and  a cold  of  32®  F.,  at  which  water  congeals,  arrests  its 
progress  altogether.  The  mode  in  which  caloric  acts  is  the  same  as  in 
all  similar  cases,  namely,  by  tending  to  separate  elements  from  one  an- 
other which  are  already  combined. 

The  products  of  the  putrefactive  fermentation  may  be  divided  into 
the  solid,  liq^uid,  and  gaseous.  The  liquid  are  chiefly  water,  together 
with  a little  acetic  acid,  and  probably  oil.  The  gaseous  products  are 
light  carburetted  hydrogen,  carbonic  acid,  and,  when  nitrogen  is  pre- 
sent, ammonia.  Pure  hydrogen,  and  probably  nitrogen,  are  sometimes 
disengaged.  Thus  hydrogen  and  carbonic  acid,  according  to  Proust, 
are  evolved  from  putrefying  gluten;  and  Saussure  obtained  the  same 
gases  from  the  putrefaction  of  wood  in  close  vessels.  Under  ordinary 
circumstances,  however,  the  chief  gaseous  product  of  decaying  plants 
is  light  carburetted  hydrogen,  which  is  generated  in  great  quantity  at 
the  bottom  of  stagnant  pools  during  summer  and  autumn.  (Page  241.) 
Another  elastic  principle,  supposed  to  arise  from  putrefying  vegetable 
remains,  is  the  noxious  miasm  of  marshes.  The  origin  of  these  miasms, 
however,  is  exceedingly  obscure.  Every  attempt  to  obtain  them  in  an 
insulated  state  has  hitherto  proved  abortive;  and,  therefore,  if  they  are 
really  a distinct  species  of  matter,  they  must  be  regarded,  like  the 
effluvia  of  contagious  fevers,  as  of  too  subtile  a nature  for  being  sub- 
jected to  chemical  analysis. 

When  the  decay  of  leaves  or  other  parts  of  plants  has  proceeded  so 
far  that  all  trace  of  organization  is  effaced,  a dark  pulverulent  sub- 
stance remains,  consisting  of  charcoal  combined  with  a little  oxygen 
and  hydrogen.  This  compound  is  vegetable  mould,  which,  when  mix- 
ed with  a proper  quantity  of  earth,  constitutes  the  soil  necessary  to  the 
growth  of  plants.  Saussure,  in  his  excellent  Recherches  Chimiques  sur 
la  Vegetation,  has  described  vegetable  mould  as  a substance  of  uniform 
composition;  and  on  heating  it  to  redness  in  close  vessels,  he  procured 
carburetted  hydrogen  and  carbonic  acid  gases,  water  holding  acetate  or 
carbonate  of  ammonia  in  solution,  a minute  quantity  of  empyreumatic 


526 


GERMINATION. 


oil,  and  a larg’e  residue  of  charcoal  mixed  with  saline  and  earthy  ingre- 
dients. On  exposing  vegetable  mould  to  the  action  of  light,  air,  and 
moisture,  a chemical  change  ensues,  the  effect  of  which  is  to  render  a 
portion  of  it  soluble  in  water,  and  thus  applicable  to  the  nutrition  and 
growth  of  plants. 


SECTION  VII. 

ON  THE  CHEMICAL  PHENOMENA  OF  GERMINATION  AND 
VEGETATION. 

Germination. 

Germination  is  the  process  by  which  a new  plant  originates  from 
seed.  A seed  consists  essentially  of  two  parts,  the  gtrm  of  the  future 
plant,  endowed  with  a principle  of  vitality,  and  the  cotyledons  or  seed- 
lohesy  both  of  which  are  enveloped  in  a common  covering  of  cuticle. 
In  the  germ,  two  parts,  the  radicle  and  plumulay  may.  be  distinguished, 
the  former  of  which  is  destined  to  descend  into  the  earth  and  constitute 
the  root,  the  latter  to  rise  into  the  air  and  form  the  stem  of  the  plant. 
The  office  of  the  seed-lobes  is  to  afford  nourishment  to  the  young  plant, 
until  its  organization  is  so  far  advanced,  that  it  may  draw  materials  for 
its  growth  from  extraneous  sources.  For  this  reason  seeds  are  composed 
of  highly  nutritious  ingredients.  The  chief  constituent  of  most  of  them 
is  starch,  in  addition  to  which  they  frequently  contain  gluten,  gum, 
vegetable  albumen  or  curd,  and  sugar. 

The  conditions  necessary  to  germination  are  three-fold;  namely, 
moisture,  a certain  temperature,  and  the  presence  of  oxygen  gas. 
The  necessity  of  moisture  to  this  process  has  been  proved  by  exten- 
sive observation.  It  is  well  known  that  the  concurrence  of  other  con- 
ditions cannot  enable  seeds  to  germinate  provided  they  are  kept  quite 
dry. 

A certain  degree  of  warmth  is  not  less  essential  than  moisture.  Ger- 
mination cannot  take  place  at  32®  F.:  and  a strong  heat,  such  as  that  of 
boiling  water,  prevents  it  altogether  by  depriving  the  germ  of  the  vital 
principle.  The  most  favourable  temperature  ranges  from  60®  to  80®, 
the  precise  degree  varying  with  the  nature  of  the  plant,  a circumstance 
that  accounts  for  the  difference  in  the  season  of  the  year  at  which  dif- 
ferent seeds  begin  to  germinate. 

That  the  presence  of  air  is  necessary  to  germination  was  demonstrat- 
ed by  several  philosophers,  such  as  Ray,  Boyle,  Muschenbroeck,  and 
Boerhaave,  before  the  chemical  nature  of  tlie  atmosphere  was  discov- 
ered; and  Sclieele,  soon  after  the  discovery  of  oxygen,  proved  that 
beans  do  not  germinate  without  exposure  to  that  gas.  Achard  after- 
wards demonstrated  the  same  fact  with  respect  to  seeds  in  general,  and 
his  experiments  have  been  fully  confirmed  by  subsequent  observers.  It 
has  even  been  shown  by  Humboldt,  that  a dilute  solution  of  chlorine, 
owing  to  the  tendency  of  that  gas  to  decompose  water  and  set  oxygen 
at  liberty,  promotes  the  germination  of  seeds.  These  circumstances 
account  for  the  fact  that  seeds,  when  buried  deep  in  the  earth,  are  un- 
able to  germinate. 


GERMINATION. 


527 


It  is  remarkable  that  the  influence  of  light,  which  is  so  favourable  to 
^ all  the  subsequent  stages  of  vegetation,  is  injurious  to  the  process  of 
j germination.  Ingenhoiisz  and  Sennebier  have  proved  that  a seed  ger- 
i minates  more  rapidly  in  the  shade  than  in  light,  and  in  diffused  daylight 
I quicker  than  when  exposed  to  the  direct  solar  rays, 
j From  the  preceding  remarks  it  is  apparent  that  when  a seed  is  placed 
an  inch  or  two  under  the  surface  of  the  ground  in  spring,  and  is  loosely 
covered  with  earth,  it  is  in  a state  every  way  conducive  to  germination. 
The  ground  is  warmed  by  absorbing  the  solar  rays,  and  is  moistened  by 
occasional  showers;  the  earth  at  the  same  time  protects  the  seed  from 
light,  but  by  its  porosity  gives  free  access  to  the  air. 

The  operation  of  malting  barley,  in  which  the  grain  is  made  to  germi- 
nate by  exposure  to  warmth,  air,  and  humidity,  affords  the  best  means 
of  studying  the  phenomena  of  germination.  In  preparing  malt,  the 
grain  passes  through  four  distinct  stages,  called  steepingy  couching, 
flooring,  and  kiln-drying.  In  the  first  it  is  steeped  in  water  for  about 
two  days,  when  it  absorbs  moisture,  softens,  and  swells  considerably. 
It  is  then  removed  to  the  couch-frame,  where  it  is  laid  in  heaps  30 
inches  in  depth  for  from  26  to  30  hours.  In  this  situation  the  grain  be- 
comes warm  and  acquires  a disposition  to  germinate;  but  as  the  temper- 
ature, in  such  large  heaps,  would  rise  very  unequally,  and  germination 
consequently  be  rapid  in  some  portions  and  slow  in  others,  the  process 
of  flooring  is  employed.  This  consists  in  laying  the  grain  in  strata  a 
few  inches  thick  on  large  airy  but  shaded  floors,  where  it  remains  for 
about  12  or  14  dilys,  until  germination  has  advanced  to  the  extent  desir- 
ed by  the  maltster.  During  this  interval  the  grain  is  frequently  turned, 
in  order  that  the  temperature  of  the  whole  mass  should  be  uniform, 
that  each  grain  should  be  duly  exposed  to  the  air,  and  that  the  radicles 
. of  contiguous  grains  should  not  become  entangled  with  each  other.  As 
soon  as  saccharine  matter  is  freely  developed,  germination  must  be  ar- 
rested; since  otherwise,  being  taken  up  as  nutriment  by  the  young 
plant,  it  would  speedily  disappear.  Accordingly,  the  grain  is  removed 
to  the  kiln,  where  it  is  exposed  to  a temperature  gradually  rising  from 
100®  to  160®,  or  rather  higher;  the  object  being,  first,  to  dry  the  grain 
completel}^,  and  then  to  provide  against  any  recurrence  of  germination 
by  destroying  the  vitality  of  the  plant.  The  most  convenient  mode  of 
applying  the  heat  is  to  place  the  grain  on  a metallic  net-work,  through 
which  passes  hot  air  issuing  from  a fire  made  with  good  coke.  The  pro- 
cess of  malting  is  liot  conducted  during  summer,  because  in  hot  weather 
the  grain  is  apt  to  become  mouldy. 

The  difference  between  malted  and  unmalted  barley  is  readily  per- 
ceived by  the  taste;  but  it  will  be  more  correctly  appreciated  by  inspect- 
ing the  result  of  Proust’s  comparative  analysis  of  malted  and  unmalted 
barley.  (An.  de  Ch.  et  de  Ph.  v.) 

InlQO 


Resin 

parts  of  Barley, 

parts  of 

1 

Gum 

4 

. 15 

Sugar 

. . 5 

.15 

Gluten 

3 

1 

Starch 

. 32 

. 56 

Hordein  . 

. 55 

. 12 

It  is  hence  apparent  that  during  germination,  the  hordein  is  converted 
into  starch,  gum,  and  sugar;  so  that  from  an  insoluble  material,  which 
could  not  in  that  state  be  applied  to  the  uses  of  the  young  plant,  two 


528 


GROWTH  OF  PI.ANTS. 


soluble  and  highly  nutritive  principles  result,  >vliich  by  being  dissolved 
in  water  are  readily  absorbed  by  the  radicle. 

The  chemical  changes  which  take  place  during  germination  have  been 
ably  investigated  by  Saussure,  whose  experiments  are  detailed  in  the 
work  to  whicli  I have  already  referred,  i’he  leading  facts  which  he  de- 
termined are  the  following; — that  oxygen  gas  is  consumed,  that  carbon- 
ic acid  is  evolved,  and  that  the  volume  of  the  latter  is  precisely  equal 
to  that  of  the  former.  Now  since  carbonic  acid  gas  contains  its  own 
volume  of  oxygen,  it  follows  that  this  gas  must  have  united  exclusively 
With  carbon.  It  is  likewise  obvious  that  the  grain  must  weigh  less  after 
than  before  germination,  provided  it  is  brought  to  the  same  state  of  dry- 
ness in  both  instances.  Saussure  indeed  found  that  the  loss  is  greater 
than  can  be  accounted  for  by  the  carbon  of  the  carbonic  acid  which  is 
evolved;  and  hence  he  concluded  that  a portion  of  water,  generated 
at  the  expense  of  the  grain  itself,  is  dissipated  in  drying.  According 
to  Proust,  the  diminution  in  weight  is  about  a third;  but  Dr.  Thom- 
son affirms  that  in  fifty  processes,  conducted  on  a large  scale  under  his 
inspection,  the  average  loss  did  not  exceed  one-fifth. 

On  the  Growth  of  Pla?its. 

While  a plant  differs  from  an  animal  in  exhibiting  no  signs  of  percep- 
tion or  voluntary  motion,  and  in  possessing  no  stomach  to  serve  as  a re- 
ceptacle for  its  food,  there  exists  between  them  a close  analogy  both  of 
parts  and  functions,  which,  though  not  discerned  at  first,  becomes  striking 
on  a near  examination.  The  stem  and  branches  act  as  a frame-work  or 
skeleton  for  the  support  and  protection  of  the  parts  necessary  to  the 
life  of  the  individual.  The  root  serves  the  purpose  of  a stomach  by 
imbibing  nutritious  juices  from  the  soil,  and  thus  supplying  the  plant 
with  materials  for  its  growth.  The  sap  or  circulating  fluid,  composed 
of  water  holding  in  solution  saline,  extractive,  mucilaginous,  saccharine, 
and  other  soluble  substances,  rises  upwards  through  the  wood  in  a dis- 
tinct system  of  tubes  called  the  common  vessels^  which  correspond  in 
their  office  to  the  lacteals  and  pulmonary  arteries  of  animals,  and  are 
distributed  in  minute  ramifications  over  the  surface  of  the  leaves.  In 
its  passage  through  this  organ,  which  may  be  termed  the  lungs  of  a 
plant,  the  sap  is  fully  exposed  to  the  agency  of  light  and  air,  experiences 
a change  by  which  it  is  more  completely  adapted  to  the  wants  of  the 
vegetable  economy,  and  then  descends  through  the  inner  layer  of  the 
bark  in  another  system  of  tubes  called  the  proper  vessels^  yielding  in  its 
course  all  the  juices  and  principles  peculiar  to  the  plant. 

The  chemical  changes  which  take  place  during  the  circulation  of  the 
sap  are  in  general  of  such  a complicated  nature,  and  so  much  under  the 
control  of  the  vital  principle,  as  to  elude  the  sagacity  of  the  chemist. 
One  part  of  the  subject,  however,  namely,  the  reciprocal  agency  of  the 
atmosphere  and  growing  vegetables  on  each  other,  falls  within  the  reach 
of  chemical  inquiry,  and  has  accordingly  been  investigated  by  several 
philosophers. 

For  the  leading*  facts  relative  to  what  is  called  the  respiration  of  plants, 
or  the  chemical  changes  which  the  leaves  of  growing  vegetables  pro- 
duce on  the  atmosphere,  we  are  indebted  to  Priestley  and  Ingenhousz, 
the  former  of  whom  discovered  that  ])lants  absorb  carbonic  acid  from 
the  air  under  certain  circumstances  and  emit  oxygen  in  return;  and  the 
latter  ascertained  that  this  change  occurs  only  during  exposure  to  the 
direct  rays  of  the  sun.  When  a healthy  plant,  the  roots  of  which  are 
supplied  with  proper  nourishment,  is  exposed  to  the  direct  solar  beams 
in  a given  quantity  of  atmospheric  air,  the  carbonic  acid  after  a certain 
interval  is  removed,  and  an  equal  volume  of  oxygen  is  substituted  for  it. 


GROWTH  OF  PLANTS. 


529 


If  a fresh  portion  of  carbonic  acid  is  supplied,  the  same  result  will 
ensue.  In  like  manner,  Sennebier  and  Woodhouse  observed,  that  when 
the  leaves  of  a plant  are  immersed  in  water,  and  exposed  to  the  rays  of 
the  sun,  oxygen  gas  is  disengaged.  That  the  evolution  of  oxygen  in 
this  experiment  is  accompanied  with  a proportional  absorption  of  car- 
bonic acid,  is  proved  by  employing  water  deprived  of  carbonic  acid  by 
boiling,  in  which  case  no  oxygen  is  procured. 

Such  are  the  changes  induced  by  plants  when  exposed  to  sunshine; 
but  in  the  dark  an  opposite  effect  ensues.  Carbonic  acid  gas  is  not  ab- 
sorbed under  these  circumstances,  nor  is  oxygen  gas  evolved;  but  on 
the  contrary,  oxygen  disappears,  and  carbonic  acid  gas  is  disengaged. 
In  the  dark,  therefore,  vegetables  deteriorate  rather  than  purify  the  air, 
producing  the  same  effect  as  the  respiration  of  animals. 

From  several  of  the  preceding  facts,  it  is  supposed  that  the  oxygen 
emitted  by  plants  while  under  the  influence  of  light  is  derived  from  the 
carbonic  acid  which  they  absorb,  and  that  the  carbon  of  that  gas  is  ap- 
plied to  the  purposes  of  nutrition.  Consistently  with  this  view  it  has 
been  observed  that  plants  do  not  thrive  when  kept  in  an  atmosphere  of 
pure  oxygen;  and  it  was  found  by  Dr.  Percival  and  Mr.  Henry,  that  the 
presence  of  a little  carbonic  acid  is  even  favourable  to  their  growth. 
Saussure,  who  examined  this  subject  minutely,  ascertained  that  plants 
grow  better  in  an  atmosphere  which  contains  about  one-twelfth  of  car- 
bonic acid  than  in  common  air,  provided  they  are  exposed  to  sunshine; 
but  if  that  gas  be  present  in  a greater  proportion,  its  influence  is  preju- 
dicial. In  an  atmosphere  consisting  of  one-half  of  its  volume  of  carbon- 
ic acid,  the  plants  perished  in  seven  days;  and  they  did  not  vegetate  at 
all  when  that  gas  was  in  the  proportion  of  two-thirds.  In  the  shade, 
the  presence  of  carbonic  acid  is  always  detrimental.  He  likewise  ob- 
served that  the  presence  of  oxygen  is  necessary,  in  order  that  a plant 
should  derive  benefit  from  admixture  with  carbonic  acid. 

Saussure  is  of  opinion  that  plants  derive  a large  quantity  of  their 
carbon  from  the  carbonic  acid  of  the  atmosphere,  an  opinion  which  re- 
ceives great  weight  from  the  two  following  comparative  experiments.  On 
causing  a plant  to  vegetate  in  pure  water,  supplied  with  common  air, 
exposed  to  light,  the  carbon  of  the  plant  increased  in  quantity;  but 
when  supplied  with  common  air,  in  a dark  situation,  it  even  lost  a portion 
of  the  carbon  which  it  had  previously  possessed. 

Light  is  necessary  to  the  colour  of  plants.  The  experiments  of  Sen- 
nebier and  Mr.  Gough  have  shown  that  the  green  colour  of  the  leaves  is 
not  developed,  except  when  they  are  in  a situation  to  absorb  oxygen 
and  give  out  carbonic  acid. 

Though  the  experiments  of  different  philosophers  agree  as  to  the  in- 
fluence of  vegetation  on  the  air  in  sunshine  and  during  the  night,  con- 
siderable uncertainty  prevails  both  as  to  the  phenomena  occasioned  by 
diffused  daylight,  and  concerning  the  total  effect  produced  by  plants  on 
the  constitution  of  the  atmosphere.  Priestley  found  that  air,  vitiated  by 
combustion  or  the  respiration  of  animals,  and  left  in  contact  for  several 
days  and  nights  with  a sprig  of  mint,  was  gradually  restored  to  its 
original  purity;  and  hence  he  inferred  that  the  oxygen  gas,  consumed 
during  these  and  various  other  processes,  is  restored  to  the  mass  of  the 
atmosphere  by  the  agency  of  growing  vegetables. 

This  doctrine  receives  confirmation  from  the  researches  of  Ingenhousz 
and  Saussure,  who  were  led  to  adopt  the  opinion  that  the  quantity  of 
oxygen  gas  evolved  from  plants  by  day,  exceeds  that  of  carbonic  acid 
emitted  during  the  night.  The  conclusions  of  Mr.  Ellis,  on  the  contra- 
ry, are  precisely  the  reverse.  From  an  extensive  series  of  experiments 
contrived  with  much  sagacity,  Mr.  Ellis  inferred  that  growing  plants 


530 


FOOD  OF  PLANTS. 


give  out  oxygen  only  in  direct  sunsliine,  while  at  all  other  times  they  ab- 
sorb it;  that  when  exposed  to  the  ordinary  vicissitudes  of  sunshine  and 
shade,  light  and  darkness,  they  form  more  carbonic  acid  in  the  period 
of  a day  and  night,  than  they  destroy;  and,  consequently,  that  the 
general  effect  of  vegetation  on  the  atmosphere  is  the  same  as  that  pro- 
duced by  animals.  (Ellis’s  Researches  and  farther  Inquiries  on  Vegeta- 
tion, &c.) 

This  question  has  been  ably  discussed  by  Sir  H.  Davy  in  his  Elements 
of  Agricultural  Chemistry.  Sir  H.  Davy  was  of  opinion  that  the  ex- 
periments of  Mr.  Ellis  cannot  be  regarded  as  decisive,  havings  been 
conducted  under  circumstances  unfavourable  to  accuracy  of  result.  He 
considers  the  original  experiments  of  Priestley  as  unexceptionable,  and 
adduces  others  made  by  himself  in  support  of  the  same  doctrine. 

On  the  Food  of  Plants, 

The  chief  source  from  which  plants  derive  the  materials  for  their 
growth  is  the  soil.  However  various  the  composition  of  the  soil,  it 
consists  essentially  of  two  parts,  so  far  as  its  solid  constituents  are  con- 
cerned. One  is  a certain  quantity  of  earthy  matters,  such  as  siliceous 
earth,  clay,  lime,  and  sometimes  magnesia;  and  the  other  is  formed 
from  the  remains  of  animal  and  vegetable  substances,  which,  when 
mixed  with  the  former,  constitute  common  mould.  A mixture  of  this 
kind,  moistened  by  rain,  affords  the  proper  nourishment  of  plants. 
The  water,  percolating  through  the  mould,  dissolves  the  soluble  salts 
with  which  it  comes  in  contact,  together  with  the  gaseous,  extractive, 
and  other  matters  which  are  formed  during  the  decomposition  of  the 
animal  and  vegetable  remains.  In  this  state  it  is  readily  absorbed  by  the 
roots,  and  conveyed  as  sap  to  the  leaves,  where  it  undergoes  a process 
f assimilation. 

But  though  this  is  the  natural  process  by  which  plants  obtain  the 
greater  part  of  their  nourishment,  and  without  which  they  do  not  arrive 
at  perfect  maturity,  they  may  live,  grow,  and  even  increase  in  weight, 
when  wholly  deprived  of  nutrition  from  this  source.  Thus  in  the  ex- 
periment of  Saussure,  already  described,  sprigs  of  peppermint  were 
found  to  vegetate  in  distilled  water;  and  it  is  well  known  that  many 
plants  grow  when  merely  suspended  in  the  air.  In  the  hot-houses  of 
the  botanical  garden  of  Edinburgh,  for  example,  there  are  two  plants, 
species  of  the  fig-tree,  the  Ficus  australis  and  Ficus  elastica,  the  latter 
of  which,  as  Dr.  Graham  infoi^ms  me,  has  been  suspended  for  six,  and 
the  former  for  nearly  twelve  years,  during  which  time  they  have  con- 
tinued to  send  out  shoots  and  leaves. 

Before  scientific  men  had  learned  to  appreciate  the  influence  of  at- 
mospheric air  on  vegetation^  the  increase  of  carbonaceous  matter,  which 
occurs  in  some  of  these  instances,  was  supposed  to  be  derived  from 
water,  an  opinion  naturally  suggested  by  the  important  offices  perform- 
ed by  this  fluid  in  the  vegetable  economy.  Without  water,  plants 
speedily  wither  and  die.  It  gives  the  soft  parts  that  degree  of  succu- 
lence necessary  for  the  performance  of  their  functions; — it  affords  two 
elements,  oxygen  and  hydrogen,  which  either  as  water,  or  under  some 
other  form,  are  contained  in  all  vegetable  products; — and,  lastly,  the 
roots  absorb  from  tlie  soil  those  substances  only,  which  are  dissolved  or 
suspended  in  water.  So  carefully,  indeed,  has  nature  provided  against 
the  chance  of  deficient  moisture,  that  the  leaves  are  endowed  with  a 
j)ropei’ty  both  of  absorbing  aqueous  vapour  directly  from  the  atmos- 
phere, and  of  lowering  their  temperature  during  the  night  by  radiation, 
so  as  to  cause  a deposition  of  dew  upon  their  surface,  in  consequence 
of  which,  during  the  driest  seasons  and  in  the  warmest  climates,  they 


FOOD  OF  PLANTS. 


531 


frequently  continue  to  convey  this  fluid  to  the  plant,  when  it  can  no 
longer  be  obtained  in  sufficient  quantity  from  the  soil.  But  necessary 
as  is  this  fluid  to  vegetable  life,  it  cannot  yield  to  plants  a principle 
which  it  does  not  possess.  The  carbonaceous  matter  which  accumulates 
in  plants,  under  the  circumstances  above  mentioned,  may,  with  every 
appearance  of  justice,  be  referred  to  the  atmosphere;  since  we  know 
that  carbonic  acid  exists  there,  and  that  growing  vegetables  have  the 
property  of  taking  carbon  from  that  gas. 

When  plants  are  incinerated,  their  ashes  are  found  to  contain  saline 
and  earthy  matters,  the  elements  of  which,  if  not  the  compounds 
themselves,  are  supposed  to  be  derived  from  the  soil.  Such  at  least  is 
the  view  deducible  from  the  researches  of  Saussure,  and  which  might 
have  been  anticipated  by  reasoning  on  chemical  principles.  The  ex- 
periments of  M.  Schrader,  however,  lead  to  a different  conclusion. 
He  sowed  several  kinds  of  grain,  such  as  barley,  wheat,  rye,  and  oats, 
in  pure  flowers  of  sulphur,  and  supplied  the  shoots  as  they  grew  with 
nothing  but  air,  light,  and  distilled  water.  On  incinerating  the  plants, 
thus  treated,  they  yielded  a greater  quantity  of  saline  and  earthy  mat- 
ters than  were  originally  present  in  the  seeds. 

These  results,  supposing  them  accurate,  may  be  accounted  for  in 
two  ways.  It  may  be  supposed,  in  the  first  place,  that  the  foreign 
matters  were  introduced  accidentally  from  extraneous  sources,  as  by 
fine  particles  of  dust  floating  in  the  atmosphere;  or,  secondly,  it  may 
be  conceived,  that  they  were  derived  from  the  sulphur,  air,  and  water, 
with  which  the  plants  wei’e  supplied.  If  the  latter  opinion  be  adopted, 
we  must  infer  either  that  the  vital  principle,  which  certainly  controls 
chemical  affinity  in  a surprising  manner,  and  directs  this  power  in  the 
production  of  new  compounds  from  elementary  bodies,  may  likewise 
convert  one  element  into  another;  or  that  some  of  the  substances,  sup- 
posed by  chemists  to  be  simple,  such  as  oxygen  and  hydrogen,  are 
compounds,  not  of  two,  but  of  a variety  of  different  principles.  As 
these  conjectures  are  without  foundation,  and  are  utterly  at  variance 
with  the  facts  and  principles  of  the  science,  I do  not  hesitate  in  adopt- 
ing the  more  probable  opinion,  that  the  experiments  of  M.  Schrader 
were  influenced  by  some  source  of  error  which  escaped  detection. 


ANIMAL  CHEMISTRY 


All  distinct  compounds,  which  are  derived  from  the  bodies  of  ani- 
mals, are  cdWo-d  proximate  animal  principles.  They  are  distinguished 
from  inorganic  matter  by  the  characters  stated  in  the  introduction  to  or- 
ganic chemistry.  The  circumstances  which  serve  to  distinguish  them 
from  vegetable  matter  are,  the  presence  of  nitrogen,  their  strong  ten- 
dency to  putrefy,  and  the  highly  offensive  products  to  which  their  spon- 
taneous decomposition  gives  rise.  It  should  be  remembered,  however, 
that  nitrogen  is  likewise  a constituent  of  many  vegetable  substances; 
though  few  of  these,  the  vegeto-animal  principles  excepted,  (page  515,) 
are  prone  to  suffer  the  putrefactive  fermentation.  It  is  likewise  remark- 
able that  some  compounds  of  animal  origin,  such  as  cholesterine  and 
the  oils,  do  not  contain  nitrogen  as  one  of  their  elements,  and  are  not 
disposed  to  putrefy. 

The  essential  constituents  of  animal  compounds  are  carbon,  hydrogen, 
oxygen,  and  nitrogen,  besides  which  some  of  them  contain  phosphorus, 
sulphur,  iron,  and  earthy  and  saline  matters  in  small  quantity.  Owing 
to  the  presence  of  sulphur  and  phosphorus,  the  process  of  putrefac- 
tion, which  wdll  be  particularly  described  hereafter,  is  frequently  at- 
tended with  the  disengagement  of  sulphuretted  and  phosphuretted  hy- 
drogen gases.  When  heated  in  close  vessels,  they  yield  water,  car- 
bonic oxide,  carburetted  hydrogen,  probably  free  nitrogen  and  hydro- 
gen, carbonate  and  hydrocyanate  of  ammonia,  and  a peculiarly  fetid 
thick  oil.  The  carbonaceous  matter  left  in  the  retort  is  less  easily  burn- 
ed, and  is  more  effectual  as  a decolorizing  agent,  than  charcoal  derived 
from  vegetable  matter. 

The  principle  of  the  method  of  analyzing  animal  substances  has 
already  been  mentioned.  (Page  455.) 

In  describing  the  proximate  animal  principles,  the  number  of  which 
is  far  less  considerable  than  the  vegetable  compounds,  the  arrangement 
suggested  by  Gay-Lussac  and  Thenard  in  their  Recherches  Physico-chi- 
miquesy  and  followed  by  Thenard  in  his  System  of  Chemistry,  has  been 
adopted.  Tlie  animal  compounds  are  accordingly  arranged  in  three 
sections.  The  first  contains  substances  which  are  neither  acid  nor  olea- 
ginous; the  second  comprehends  the  animal  acids;  and  the  third  in- 
cludes the  animal  fats.  Several  of  the  principles  belonging  to  the  first 
division,  such  as  fibrin,  albumen,  gelatin,  caseous  matter,  and  urea, 
were  shown  by  Gay-I^ussac  and  Thenard  to  have  several  points  of  simi- 
larity in  their  composition.  They  all  contain,  for  example,  a large 
quantity  of  carbon,  and  their  hydrogen  is  in  such  proportion  as  to  con- 
vert all  their  oxygen  into  water,  and  their  nitrogen  into  ammonia.  No 
general  laws  have  been  established  relative  to  the  constitution  of  the 
compounds  comprised  in  the  other  sections. 


FIBRIN. 


533 


SECTION  I. 

SUBSTANCES  WHICJI  ARE  NEITHER  ACID  NOR  OLEA- 
GINOUS. 

Fibrin. 

Fibrin  enters  larg*ely  into  the  composition  of  the  blood,  and  is  the 
basis  of  the  muscles:  it  may  be  regarded,  therefore,  as  one  of  the 
most  abundant  of  the  animal  pi'inciples.  It  is  most  conveniently  pro- 
cured by  stirring  recently  drawn  blood  with  a stick  during  its  coagula- 
tion, and  then  washing  the  adhering  fibres  with  water  until  they  are 
perfectly  white.  It  may  also  be  obtained  from  lean  beef  cut  into  small 
slices,  the  soluble  parts  being  removed  by  digestion  in  several  successive 
portions  of  water. 

Fibrin  is  solid,  white,  insipid,  and  inodorous.  When  moist  it  is 
somewhat  elastic,  but  on  drying  it  becomes  hard,  brittle,  and  semi- 
transparent. In  a moist  warm  situation  it  readily  putrefies.  It  is  insol- 
uble in  water  at  common  temperatures,  and  is  dissolved  in  very  minute 
quantity  by  the  continued  action  of  boiling  water.  Alcohol,  of  specific 
gravity  0. 81,  converts  it  into  a fatty  adipocirous  matter,  which  is  soluble 
in  alcohol  and  ether,  but  is  precipitated  by  water. 

The  action  of  acids  on  fibrin  has  been  particularly  described  by  Ber- 
zelius.* Digested  in  concentrated  acetic  acid,  fibrin  swells  and  be- 
comes a bulky  tremulous  jelly,  which  dissolves  completely,  with  di^ 
engagement  of  a little  nitrogen,  in  a considerable  quantity  of  hot 
water. 

By  the  action  of  nitric  acid,  of  specific  gravity  1.25,  aided  by  heat 
on  fibrin,  a yellow  solution  is  formed  with  disengagement  of  a large 
quantity  of  nearly  pure  nitrogen,  in  which  Berzelius  could  not  detect 
the  least  trace  of  the  deutoxide  of  nitrogen.  After  digestion  for  twenty- 
four  hours,  a pale  yellow  pulverulent  substance  is  deposited,  which 
Fourcroy  and  Vauquelin  described  as  a new  acid  under  the  name  of 
yellow  acid.  According  to  Berzelius,  however,  it  is  a compound  of 
modified  fibrin  xind  nitric  acid,  together  with  some  malic  and  nitrous 
acids.  It  likewise  contains  some  fatty  matter,  which  may  be  removed 
by  alcohol.  The  origin  of  the  nitrogen  which  is  disengaged  in  the  be- 
ginning of  the  process  is  somewhat  obscure.  From  the  total  absence  of 
deutoxide  of  nitrogen,  it  is  probable  that  in  the  early  stages  very  little, 
if  any,  of  the  nitric  acid  is  decomposed,  and  that  the  nitrogen  gas  is 
solely  or  chiefly  derived  from  the  fibrin. 

Dilute  muriatic  acid  hardens  without  dissolving  fibrin,  and  the  strong 
acid  decomposes  it.  The  action  of  sulphuric  acid,  according  to  Bra- 
connot,  is  very  peculiar.  When  fibrin  is  mixed  with  its  own  weight  of 
concentrated  sulphuric  acid,  a perfect  solution  ensues,  without  change 
of  colour,  or  disengagement  of  sulphurous  acid.  On  diluting  with 
water,  boiling  for  nine  hours,  and  separating  the  acid  by  means  of 
chalk,  the  filtered  solution  was  found  to  contain  a peculiar  white 
matter,  to  which  Braconnot  has  applied  the  name  of  leucine.  (An.  de 


* Medico-chirurgical  Transactions,  vol.  iii.  p.  201,  et  seq. 
45* 


534 


ALBUMEN. 


Ch.  et  de  Ph.  xlii.)  Digested  in  strong  sulphuric  acid,  a dark  reddish- 
brown,  nearly  black,  solution  is  formed,  and  the  fibrin  is  carbonized 
and  decomposed. 

Fibrin  is  dissolved  by  pure  potassa,  and  is  thrown  down  when  the 
solution  is  neutralized.  The  fibrin  thus  precipitated,  however,  is  par- 
tially changed,  since  it  is  no  longer  soluble  in  acetic  acid.  It  is  soluble 
likewise  in  ammonia. 

According  to  the  analysis  of  Gay-Lussac  and  Thenard,  100  parts  of 
fibrin  are  composed  of  carbon  53.36,  hydrogen  7.021,  oxygen  19.685, 
and  nitrogen  19.934.  From  these  numbers  fibrin  may  be  regarded  as 
an  atomic  compound  of  eighteen  equivalents  of  carbon,  fourteen  of 
hydrogen,  five  of  oxygen,  and  three  of  nitrogen. 

Albumen. 

Albumen  enters  largely  into  the  composition  both  of  animal  fluids  and 
solids.  Dissolved  in  water  it  forms  an  essential  constituent  of  the  serum 
of  the  blood,  the  liquor  of  the  serous  cavities,  and  the  fluid  of  dropsy; 
and  in  a solid  state  it  is  contained  in  several  of  the  textures  of  the 
body,  such  as  the  cellular  membrane,  the  skin,  glands,  and  vessels. 
From  this  it  appears  that  albumen  exists  under  two  forms,  liquid  and 
solid. 

Liquid  albumen  is  best  procured  from  the  white  of  eggs,  which  con- 
sists almost  solely  of  this  principle,  united  with  water  and  free  soda, 
and  mixed  with  a small  quantity  of  saline  matter.  In  this  state  it  is  a 
thick  glairy  fluid,  insipid,  inodorous,  and  easily  miscible  with  cold 
water,  in  a sufficient  quantity  of  which  it  is  completely  dissolved. 
When  exposed  in  thin  layers  to  a current  of  air  it  dries,  and  becomes 
a solid  and  transparent  substance,  which  retains  its  solubility  in  water, 
and  may  be  preserved  for  any  length  of  time  without  change;  but  if 
kept  in  its  fluid  condition  it  readily  putrefies.  From  the  free  soda 
which  they  contain,  albuminous  liquids  have  always  an  alkaline  re- 
actio  w. 

Liquid  albumen  is  coagulated  by  heat,  alcohol,  and  the  stronger 
acids.  Undiluted  albumen  is  coagulated  by  a temperature  of  160^,  and 
when  diluted  with  water  at  212*^  F.  Water  which  contains  only 
1-lOOOth  of  its  weight  of  albumen  is  rendered  opake  by  boiling.  (Bos- 
tock. ) On  this  property  is  founded  the  method  of  clarifying  by  means 
of  albuminous  solutions;  for  the  albumen  being  coagulated  by  heat,  en- 
tangles in  its  substance  all  the  foreign  particles  which  are  not  actually 
dissolved,  and  carries  them  with  it  to  the  surface  of  the  liquid.  The 
character  of  being  coagulated  by  hot  water  distinguishes  albumen  from 
all  otlier  animal  fluids. 

The  acids  differ  in  their  action  on  albumen.  The  sulphuric,  muri- 
atic, and  nitric  acids  coagulate  it;  and  in  each  case,  according  to  The- 
nard, some  of  the  acid  is  retained  by  the  albumen.  It  is  precipitated 
also  by  pyrophosphoric  acid,  but  not  by  the  phosphoric,  a character, 
as  already  mentioned,  by  which  these  acids  may  be  distinguished  from 
each  other.  (Page  195.)  The  solution  of  albumen  is  not  precipitated 
at  all  by  acetic  acid.  By  maceration  in  dilute  nitric  acid  for  a month, 
it  is  converted,  according  to  Mr.  Hatchett,  into  a substance  soluble  in 
liot  water,  and  possessed  of  the  leading  properties  of  gelatin.  Digest- 
ed in  strong  sulphuric  acid,  tlic  coagulum  is  dissolved,  and  a dark  sol- 
ution is  formed  similar  to  that  produced  by  the  same  acid  on  fibrin;  but 
if  tlie  heat  be  applied  very  cautiously;  the  liquid  assumes  a bqp:i(itiful 
red  colour.  This  property  was  discovered  some  years  ago  by  Dr/Hdpe, 
who  informs  me  that  the  experiment  does  not  always  succeedi  the  re- 
sult being  influenced  by  very  slight  causes. 


ALBUMEN. 


535 


Albumen  is  precipitated  by  several  reagents,  especially  by  metallic 
salts.  This  effect  is  produced  by  muriate  of  tin,  subacetate  of  lead, 
muriate  of  gold,  and  solution  of  tannin.  Corrosive  sublimate  is  a very 
delicate  test  of  the  presence  of  albumen,  causing  a milkiness  when  the 
albumen  is  diluted  with  2000  parts  of  water.  The  nature  of  the  pre- 
cipitate has  already  been  explained.  (Page  379.)  Ferrocyanate  of 
potassa  is  equally  if  not  still  more  delicate,  provided  a little  acetic  acid 
is  previously  added  to  neutralize  the  free  soda. 

When  an  albuminous  liquid  is  exposed  to  the  agency  of  galvanism, 
pure  soda  makes  its  appearance  at  the  negative  wire,  and  the  albumen  coa- 
gulates around  that  which  is  in  connexion  with  the  positive  pole  of  the 
battery.  Mr.  Brande,*  who  first  observed  this  phenomenon,  ascribes 
it  to  the  separation  of  free  soda,  upon  which  he  supposes  the  solubility 
of  albumen  in  water  to  depend;  but  M.  Lassaignef  attributes  it  to  the 
decomposition  of  muriate  of  soda,  the  acid  of  which  coagulates  the 
albumen.  However  this  may  be,  galvanism  is  one  of  the  most  elegant 
and  delicate  tests  which  we  possess  of  the  presence  of  albumen  in  ani- 
mal fluids. 

Chemists  are  not  agreed  as  to  the  cause  of  the  coagulation  of  albu- 
men. When  it  is  coagulated  by  different  chemical  agents,  such  as  tan- 
nin and  metallic  salts,  the  albumen  is  thrown  down  in  consequence  of 
forming  an  insoluble  compound  with  the  substance  employed;  and  per- 
haps this  is  also  the  mode  by  which  acids  coagulate  it.  With  respect  to 
the  agency  of  heat,  alcohol,  and  probably  of  acids,  a different  view 
must  be  adopted.  The  explanation  usually  given  is  that  proposed  by 
Dr.  Thomson,  who  ascribes  the  solubility  of  albumen  to  the  presence 
of  free  soda,  and  its  coagulation  to  the  removal  of  the  alkali.  To  this 
hypothesis  Dr.  Bostock  objects,  and  with  every  appearance  of  justice, 
that  albuminous  liquids  do  not  contain  a sufficient  quantity  of  free  al- 
kali for  the  purpose.  (Medico-chir.  Trans,  vol.  ii.  p.  175.)  Were  [to 
hazard  an  opinion  on  this  subject,  it  would  be  the  following: — that  al- 
bumen combines  directly  with  water  at  the  moment  of  being  secreted, 
at  a time  when  its  particles  are  in  a state  of  minute  division;  but  as  its 
affinity  for  that  liquid  is  very  feeble,  the  compound  is  decomposed  by 
slight  causes,  and  for  the  same  reason  the  albumen  becomes  quite  in- 
soluble, as  soon  as  it  is  rendered  solid  by  coagulation.  Silica  aftbrds  an 
instance  of  a similar  phenomenon.  (Page  319.) 

Albumen  coagulates  without  appearing  to  undergo  any  change  of 
composition,  but  it  is  quite  insoluble  in  water,  and  is  less  liable  to  pu- 
trefy than  in  its  liquid  state.  It  is  dissolved  by  alkalies  with  disengage- 
ment of  ammonia,  and  is  precipitated  from  its  solution  by  acids.  In  the 
coagulated  state,  it  bears  a very  close  resemblance  to  fibrin,  and  is  with 
difficulty  distinguished  from  it.  Alcohol,  ether,  acids,  and  alkalies,  ac- 
cording to  Berzelius,  act  upon  each  in  the  same  manner.  He  observes, 
however,  that  acetic  acid  and  ammonia  dissolve  fibrin  more  easily  than 
coagulated  albumen.  According  to  Thenard,  they  are  readily  distin- 
guished by  means  of  deutoxide  of  hydrogen,  from  which  fibrin  causes 
evolution  of  oxygen,  while  albumen  has  no  action  upon  it. 

Albumen  has  been  analyzed  by  Gay-Lussac  and  Thenard,  and  Dr. 
Prout,  with  the  following  results: — 


* Philosophical  Transactions  for  1809. 
f An.  de  Ch.  et  de  Ph.  vol.  xx. 


536 


GELATIN. 


Gay-Lussac  and  Thenard. 

Carbon,  52.883,  seventeen  equi^ 

Hydrogen,  7.540,  thirteen  equiv. 

Oxygen,  23.872,  six  equiv. 

Nitrogen,  15.705,  two  equiv. 

100.000 

Gelatin* 

Gelatin  exists  abundantly  in  many  of  the  solid  parts  of  the  body,  es- 
pecially in  the  skin,  cartilages,  tendons,  membranes,  and  bones.  Ac- 
cording to  Berzelius,  it  is  not  contained  in  any  of  the  healthy  animal 
fluids;  and  Dr.  Bostock,  with  respect  to  the  blood,  has  demonstrated 
the  accuracy  of  this  statement.  (Medico-chir.  Trans,  vol.  i.  and  ii.) 

^ Gelatin  is  distinguished  from  all  animal  principles  by  its  ready  solu- 
bility in  boiling  water,  and  by  the  solution  forming  a bulky,  semi-trans- 
parent, tremulous  jelly  as  it  cools.  Its  tendency  to  gelatinize  is  such, 
that  one  part  of  gelatin,  dissolved  in  100  parts  of  water,  becomes 
solid  in  cooling.  This  jelly  is  a hydrate  of  gelatin,  and  contains  so  much 
water,  that  it  readily  liquefies  when  warmed.  On  expelling  the  water 
by  a gentle  heat,  a brittle  mass  is  left,  which  retains  its  solubility  in  hot 
water,  and  may  be  preserved  for  any  length  of  time  without  change. 
Jelly,  on  the  contrary,  soon  becomes  acid  by  keeping,  and  then  putre- 
fies. 

The  common  gelatin  of  commerce  is  the  well  known  cement  called 
gluCy  which  is  prepared  by  boiling  in  water  the  cuttings  of  parchment, 
or  the  skins,  ears,  and  hoofs  of  animals,  and  evaporating  the  solution. 
Isinglass,  which  is  the  purest  variety  of  gelatin,  is  prepared  from  the 
sounds  of  fish  of  the  genus  acipenser^  especially  from  the  sturgeon.  The 
animal  jelly  of  the  confectioners  is  made  from  the  feet  of  calves,  the 
tendinous  and  ligamentous  parts  of  which  yield  a large  quantity  of 
gelatin. 

Gelatin  is  insoluble  in  alcohol,  but  is  dissolved  readily  by  most  of  the 
diluted  acids,  which  form  an  excellent  solvent  for  it.  Mixed  with  twice 
its  weight  of  concentrated  sulphuric  acid,  it  dissolves  without  being 
charred;  and  on  diluting  the  solution  with  water,  boiling  for  several 
hours,  separating  the  acid  by  means  of  chalk,  and  evaporating  the  fil- 
tered liquid,  a peculiar  saccharine  principle  is  deposited  in  crystals. 
This  substance  has  a sweet  taste,  somewhat  like  that  of  the  sugar  of 
grapes,  is  soluble  in  water,  though  less  so  than  common  sugar,  and  is 
insoluble  in  alcohol.  When  heated  to  redness,  it  yields  ammonia  as  one 
of  the  products,  a circumstance  which  shows  that  it  contains  nitrogen. 
Mixed  with  yeast,  its  solution  does  not  undergo  the  vinous  fermentation; 
and  it  combines  directly  with  nitric  acid.  It  is  hence  apparent  that, 
though  possessed  of  a sweet  taste,  it  differs  entirely  from  sugar.  This 
substance  was  discovered  by  M.  Braconnot.  (An.  de  Ch.  et  de  Ph.  vol. 
xiii.) 

Gelatin  is  dissolved  by  the  liquid  alkalies,  and  the  solution  is  not  pre- 
cipitated by  acids. 

Gelatin  manifests  little  tendency  to  unite  with  metallic  oxides.  -Cor- 
roswe  sublimate  and  subacetate  of  lead  do  not  occasion  any  precipitate 
in  a solution  of  gelatin,  and  the  salts  of  tin  and  silver  affect  it  very 
slightly.  The  best  precipitant  for  it  is  tannin.  By  means  of  an  infu- 
sion of  gall-nuts.  Dr.  Bostock  detected  the  presence  of  gelatin  when 
mixed  with  5000  times  its  weight  of  water;  and  its  quantity  may  even 
be  estimated  approximately  by  this  reagent.  (Page  513.)  But  since 


Dr.  Prout 


50.  fifteen  equiv. 

7.78,  fourteen  equiv. 

26.67,  six  equiv. 

15.55,  two  equiv. 

100.00 


UREA. 


537 


other  animal  substances,  as  for  example  albumen,  are  precipitated  by 
tannin,  it  cannot  be  relied  on  as  a test  of  gelatin.  The  best  character  for 
this  substance  is  that  of  solubility  in  hot  water,  and  of  forming  a jelly 
as  it  cools. 

According  to  the  analysis  of  gelatin  by  Gay-Lussac  and  Thenard,  100 
parts  of  this  substance  consist  of  carbon  47.881,  hydrogen  7.914,  oxy- 
gen 27.207,  and  nitrogen  16.998.  From  these  numbers  it  appears  that 
its  composition,  as  to  the  relative  quantity  of  its  elements,  is  identical 
with  that  of  albumen  as  determined  by  Dr.  Prout. 

Urea. 

Pure  urea  is  procured  by  evaporating  fresh  urine  to  the  consistence 
of  a syrup,  and  then  gradually  adding  to  it,  when  quite  cold,  pure  con- 
centrated nitric  acid,  which  should  be  free  from  nitrous  acid,  till  the 
whole  becomes  a dark-coloured  crystallized  mass,  which  is  to  be  re- 
peatedly washed  with  ice-cold  water,  and  then  dwed  by  .pressure  be- 
tween folds  of  bibulous  paper.  To  the  nitrate  of  urea,  thus  procured, 
a pretty  strong  solution  of  carbonate  of  potassa  or  soda  is  added,  until 
the  acid  is  neutralized;  and  the  solution  is  afterwards  concentrated  by 
evaporation,  and  set  aside,  in  order  that  the  nitre  may  separate  in  crys- 
tals. Dr.  Prout  recommends  that  the  residual  liquid,  which  is  an  im- 
pure solution  of  urea,  should  be  made  up  into  a thin  paste  with  animal 
charcoal,  and  be  allowed  to  remain  in  that  state  for  a few  hours.  The 
paste  is  then  mixed  with  cold  water,  which  takes  up  the  urea,  while  the 
colouring  matter  is  retained  by  the  charcoal;  and  the  colourless  solution 
is  evaporated  to  dryness  at  a low  temperature.  The  residue  is  then 
boiled  in  pure  alcohol,  by  which  the  urea  is  dissolved,  and  from  which  it 
is  deposited  in  crystals  on  cooling.  (Medico-chir.  Trans,  viii.  529.)  In 
order  to  obtain  them  quite  colourless,  it  is  necessary  to  redissolve  in  al- 
cohol, and  crystallize  a second  or  even  a third  time. 

The  crystals  of  pure  urea  are  transparent  and  colourless,  of  a slight  pearly 
lustre,  and  have  commonly  the  form  of  a four-sided  prism.  It  leaves  a 
sensation  of  coldness  on  the  tongue  like  nitre,  and  its  smell  is  faint  and 
peculiar,  but  not  urinous.  Its  specific  gravity  is  about  1.35.  It  does 
not  aflfect  the  colour  of  litmus  or  turmeric  paper.  In  a moist  atmosphere 
it  deliquesces  slightly;  but  otherwise  undergoes  no  change  on  exposure 
to  the  air.  (Prout. ) It  is  fused  at  248®  F. , and  at  a rather  higher  tem- 
perature it  is  decomposed,  being  resolved  chiefly  into  carbonate  of  ammo- 
nia and  cyanic  acid,  the  latter  of  which,  if  the  heat  be  not  incautiously 
raised,  is  left  in  the  retort.  (Wohler.) 

Water  at  60®  dissolves  more  than  its  own  weight  of  urea,  and  boiling 
water  takes  up  an  unlimited  quantity.  It  requires  for  solution  about 
five  times  its  weight  of  alcohol  of  specific  gravity  0.816  at  60^  F.,  and 
rather  less  than  its  own  weight  at  a boiling  temperature.  The  aqueous 
solution  of  pure  urea  may  be  exposed  to  the  atmosphere  for  several 
months,  or  be  heated  to  the  boiling  point,  without  change;  but,  on  the 
contrary,  if  the  other  constituents  of  urine  are  present,  it  putrefies  with 
rapidity,  and  is  decomposed  by  a temperature  of  212®  F.,  being  almost 
entirely  resolved  into  carbonate  of  ammonia  by  continued  ebullition. 

The  pure  fixed  alkalies  and  alkaline  earths  decompose  urea,  espe- 
cially by  the  aid  of  heat,  carbonate  of  ammonia  being  the  chief  product. 

Though  urea  has  not  any  distinct  alkaline  properties,  it  unites  with  ‘ 
the  nitric  and  oxalic  acids,  forming  sparingly  soluble  compounds,  which 
crystallize  in  scales  of  a pearly  lustre.  This  property  affords  an  excel- 
lent test  of  the  presence  of  urea.  Both  compounds  have  an  acid  reac- 
tion, and  the  nitrate  consist  of  54  parts  or  one  equivalent  of  nitric  acid, 
and  60  parts  or  two  equivalents  of  urea. 


538 


UREA. 


The  constituents  of  urea,  according*  to  the  analysis  of  Dr.  Prout,  are 
in  the  proportion  of  one  equivalent  of  carbon,  two  of  hydrogen,  one 
of  ojxygen,  and  one  of  nitrogen.  Its  atomic  weight,  therefore,  is  30. 

A singular  instance  of  the  artificial  production  of  urea  has  been  no- 
ticed by  Wohler.  It  is  formed  by  the  action  of  ammonia  on  cyanogen, 
as  also  by  direct  contact  of  cyanous  acid  and  ammonia;  but  the  best 
mode  of  prepai’ing  it  is  by  decomposing  cyanite  of  silver  with  muriate 
of  ammonia,  or  acting  on  cyanite  of  lead  with  ammonia.  In  the  last 
case,  oxide  of  lead  is  set  free,  and  the  only  other  product  appears  in 
colourless,  transparent,  four-sided,  rectangular  crystals.  These  crys- 
tals, judging  by  the  mode  of  preparation,  must  be  cyanite  of  ammonia; 
but  yet  no  ammonia  is  evolved  from  them  by  the  action  of  potassa:  the 
stronger  acids  do  not,  as  with  other  cyanites,  cause  an  evolution  of 
carbonic  and  cyanous  acids;  nor  do  they  yield  precipitates  with  salts  of 
lead  and  silver.  In  fact,  though  procured  by  the  mutual  action  of  cyan- 
ous acid  and.  ammonia,  the  characters  above  mentioned  do  not  indicate 
the  presence  of  either;  but  on  the  contrary  the  crystals  agree  with  urea 
obtained  from  urine  in  composition  and  in  all  their  chemical  properties.* 
(Journal  of  Science,  N.  S.  iii.  491.)  The  cyanous  acid  above  referred 
to  is  that  discovered  by  Wohler.  (Page  265.) 


* This  identity  of  composition  between  the  cyanite  of  ammonia  and 
urea  does  not  obtain,  unless  it  be  assumed  that  the  cyanite  contains  one 
equivalent  of  water.  Thus  the  protohydrated  cyanite  of  ammonia  would 
consist  of 


Cyanous  acid. 

Ammonia, 

Water, 


Carbon, 

Nitrogen, 

Oxygen, 


C Nitrogen, 

C Hydrogen, 
C Oxygen, 

C Hydrogen, 


12  or  two  equivalents. 

14  or  one 

8 or  one — — 

14  or  one 

3 or  three 

8 or  one — 

1 or  one 


These  proportions  are  equivalent  to 
Carbon, 

Nitrogen, 

Oxygen, 

Hydrogen, 


Now  the  composition  of  urea  is. 
Carbon, 
Nitrogen, 
Oxygen, 
Hydrogen, 


60 

12  or  two  equivalents. 

28  or  two 

16  or  two  — — 

4 or  four 

60 

6 or  one  equivalent. 

14  or  one 

8 or  one 

2 or  two - 


30 

Here  it  is  apparent  that  the  proportions  in  which  the  elements  are 
united  in  the  two  substances  are  precisely  the  same;  and  that  two  equiv- 
alents of  urea  are  exactly  equal  to  one  equivalent  of  the  hydrated  cyan- 
ite of  ammonia.  JVorl/i  American  Med,  and  Surg.  Journaly  for  Jan,  1829, 
from  the  Journ,  de  Chimie  M^d,  B. 


ANIMAL  ACIDS. 


539 


Sugar  of  Milk^  and  Sugar  of  Diabetes, 

Sugar  of  Milk. — The  saccharine  principle  of  milk  is  obtained  from 
whey  by  evaporating*  that  liquid  to  the  consistence  of  syrup,  and  allow- 
ing* it  to  cool.  It  is  afterwards  purified  by  means  of  albumen  and  a se- 
cond crystallization. 

The  sugar  of  milk  has  a sweet  taste,  though  less  so  than  the  sugar  of 
the  cane,  from  which  it  differs  essentially  in  several  other  respects. 
Thus  it  requires  seven  parts  of  cold  and  four  of  boiling  water  for  solu- 
tion, and  is  insoluble  in  alcohol.  It  is  not  susceptible  of  undergoing 
the  vinous  fermentation;  and  when  digested  with  nitric  acid,  it  yields 
saccholactic  acid,  a property  first  noticed  by  Scheele,  and  which  dis- 
tinguishes the  saccharine  principle  of  milk  from  every  other  species  of 
sugar.  Like  starch,  it  is  convertible  into  real  sugar  by  being  boiled  in 
water  acidulated  with  sulphuric  acid. 

Sugar  of  milk  contains  no  nitrogen,  and,  according  to  the  analysis  of 
Gay-Lussac  and  Thenard,  is  very  analogous  to  common  sugar  in  the 
proportion  of  its  elements. 

Sugar  of  Diabetes.  — In  the  disease  called  diabetes,  the  urine  contains 
a peculiar  saccharine  matter,  which,  when  properly  purified,  appears 
identical  both  in  properties  and  composition  with  vegetable  sugar,  ap- 
proaching nearer  to  the  sugar  of  grapes  than  that  from  the  sugar-cane. 
This  kind  of  sugar  is  obtained  in  an  irregularly  crystalline  mass  by  eva- 
porating diabetic  urine  to  the  consistence  of  syrup,  and  keeping  it  in  a 
warm  place  for  several  days.  It  is  purified  by  washing  the  mass  with 
alcohol,  either  cold  or  at  most  gently  heated,  till  that  liquid  comes  off 
colourless,  and  then  dissolving  it  in  hot  alcohol.  By  repeated  crystalli- 
zation it  is  thus  rendered  quite  pure.  (Front.) 

A few  other  principles  yet  remain  to  be  considered,  such  as  the  col- 
ouring principles  of  the  blood,  caseous  matter,  and  mucus;  but  these 
will  be  more  conveniently  studied  in  subsequent  sections. 


SECTION  II. 

ANIMAL  ACIDS. 

In  animal  bodies  several  acids  are  found,  such  as  the  sulphuric,  mu- 
riatic, phosphoric,  acetic,  &c.,  which  belong  equally  to  the  mineral  or 
vegetable  kingdom,  and  which  have  consequently  been  described  in 
other  parts  of  the  work.  In  this  section  are  included  those  acids  only 
which  are  believed  to  be  peculiar  to  animal  bodies. 

Uric^  Purpuric^  Rosacicy  FormiCy  and  Lactic  Acidsy  fyc. 

Uric  or  LithicAcid. — This  acid  is  a common  constituent  of  urinary  and 
gouty  concretions,  and  is  always  present  in  healthy  urine,  combined 
with  ammonia  or  some  other  alkali.  The  urine  of  birds  of  prey,  such 
as  the  eagle,  and  of  the  boa  constrictor  and  other  serpents,  consists  al- 
most solely  of  urate  of  ammonia,  from  which  pure  uric  acid  may  be  pro- 
cured by  a very  simple  process.  For  this  purpose  the  solid  urine  of  the 


540 


ANIMAL  ACIDS. 


hoa  constrictor  is  reduced  to  a fine  powder,  and  dig’ested  in  a solution  of 
pure  potassa,  in  which  it  is  readily  dissolved  with  diseng'ag’ement  of 
ammonia.  The  urate  of  potassa  is  then  decomposed  by  adding  acetic, 
muriatic,  or  sulphuric  acid  in  slight  excess,  when  the  uric  acid  is  thrown 
down,  and,  after  being  washed,  is  collected  on  a filter.  On  its  first 
separation  from  the  alkali,  it  is  in  the  form  of  a gelatinous  liydrate,  but 
in  a short  time  this  compound  is  decomposed  spontaneously,  and  the 
uric  acid  subsides  in  small  crystals. 

Pure  uric  acid  is  white,  tasteless,  and  inodorous.  It  is  insoluble  in 
alcohol,  and  is  dissolved  very  sparingly  by  cold  or  hot  water,  requiring 
about  10,000  times  its  weight  of  that  fluid  at  60^  F.  for  solution. 
(Prout.)  It  reddens  litmus  paper,  and  unites  with  alkalies,  forming 
salts  which  are  called  urates  or  litliates.  The  uric  acid  does  not  effer- 
vesce with  alkaline  carbonates;  but  Dr.  Thomson  affirms  that  when  boil- 
ed for  some  time  with  carbonate  of  soda,  the  whole  of  the  carbonic  acid 
is  expelled.  A current  of  carbonic  acid,  on  the  contrary,  throws  down 
the  uric  acid  when  dissolved  by  potassa.  This  acid  undergoes  no  change 
by  exposure  to  the  air. 

Of  the  acids  none  exert  any  peculiar  action  on  the  uric  excepting 
nitric  acid.  When  a few  drops  of  nitric  acid,  slightly  diluted,  are  mix- 
ed on  a watch-glass  with  uric  acid,  and  the  liquid  is  evaporated  to  dry- 
ness, a beautiful  purple  colour  comes  into  view,  the  tint  of  which  is 
improved  by  the  addition  of  water.  This  character  affords  an  unequiv- 
ocal test  of  the  presence  of  uric  acid.  The  nature  of  the  change  will 
be  considered  immediately. 

Uric  acid  is  decomposed  by  chlorine.  Liebig  has  observed,  that 
when  dry  uric  acid  is  heated  with  dry  chlorine,  an  enormous  quantity  of 
cyanic  and  muriatic  acid  is  generated.  If  the  uric  acid  is  moist,  chlo- 
rine then  gives  rise  to  the  disengagement  of  carbonic  and  cyanous  acids; 
while  in  solution  there  remain  muriatic  acid,  ammonia,  and  much  oxalic 
acid. 

Uric  acid  has  been  repeatedly  analyzed  by  Dr.  Prout,  and  its  constit- 
uents, according  to  his  latest  analysis,  (Medico-chir.  Trans,  vol.  ix.) 
are  in  the  following  proportions: — 


Carbon, 

36 

Hydrogen, 

2 

Oxygen, 

24 

Nitrogen, 

28 

90 

or  six  equivalents, 
or  two  equivalents, 
or  three  equivalents, 
or  two  equivalents. 


The  crystallized  acid,  as  analyzed  by  Dr.  Prout,  is  supposed  by  most 
chemists  to  be  anhydrous;  but  Dr.  Thomson  maintains  that  on  exposing 
90  parts  of  it  to  a temperature  of  400°  F.  it  loses  18  parts,  or  two  equiv- 
alents of  water,  and  that  the  residue  is  anhydrous  uric  acid,  composed 
of  six  equivalents  of  carbon,  one  of  oxygen,  and  two  of  nitrogen.  On 
this  view  the  atomic  weight  of  uric  acid  is  72,  a number  which  Dr. 
Tliomson  has  deduced  from  his  analysis  of  urate  of  soda. 

The  salts  of  uric  acid  have  been  described  by  Dr.  Henry.  (Manches- 
ter Memoirs,  vol.  ii.  N.  S. ) The  only  ones  of  importance  are  the  urates 
of  ammonia,  potassa,  and  soda.  Urate  of  ammonia  is  soluble  to  a con- 
siderable extent  in  boiling,  but  more  sparingly  in  cold  water.  The  urates 
of  soda  and  potassa,  if  neutral,  arc  of  very  sparing  solubility;  but  an 
excess  of  eitl)er  alkali  takes  up  a large  quantity  of  the  acid.  The  for- 
mer was  found  by  Dr.  Wollaston  to  be  the  chief  constituent  of  gouty 
concretions. 

When  uric  acid  is  heated  in  a retort,  carbonate  and  hydrocyanate  of 


ANIMAL  ACIDS. 


541 


ammonia  are  g-eneratecl,  and  a volatile  acid  sublimes,  called  pyro-uric 
acid,  which  was  formerly  described  by  Dr.  lleory,  and  has  since  been 
studied  by  Chevallier  and  Lassaigne,  Liebig-,  and  Wblder.  'i'he  two 
latter  chemists  have  noticed  that  pyro-uric  is  identical  with  cyanic  acid 
(page  264);  and  Wohler  linds  that  urea,  as  well  as  cyanic  acid,  is  an 
essential  product  of  the  destructive  distillation  of  uric  acid. 

Purpuric  Acid. — This  compound  was  fii’st  recognized  as  a distinct 
acid  by  Dr.  Prout,  and  was  described  by  him  in  the  Philosophical  Trans- 
actions for  1818.  Though  colourless  itself,  it  has  a remarkable  tenden- 
cy to  form  red  or  purple  coloured  salts  with  alkaline  bases,  a character 
by  which  it  is  distinguished  from  all  other  substances,  and  to  which  it 
owes  the  name  of  purpuric  acid,  suggested  by  Dr.  Wollaston.  Thus 
the  purple  residue  above  mentioned,  as  indicative  of  the  presence  of 
uric  acid,  is  purpurate  of  ammonia,  which  is  always  generated  when  the 
uric  is  decomposed  by  nitric  acid. 

Purpuric  acid  may  be  prepared  by  the  following  process,  for  the  out- 
line of  which  I am  indebted  to  directions  kindly  given  me  by  Dr.  Prout. 
Let  200  grains  of  uric  acid,  prepared  from  the  urine  of  the  hoa  constric- 
tor, be  dissolved  in  3C0  grains  of  pure  nitric  acid  diluted  with  an  equal 
weight  of  water,  the  uric  acid  being  added  gradually  in  order  that  the 
heat  m.ay  not  be  excessive.  Effervescence  ensues  after  each  addition, 
nitrous  acid  fumes  appear,  heat  is  evolved,  and  a colourless  solution  is 
formed,  which,  on  standing  in  a cool  place  for  some  hours,  yields  col- 
ourless cry.stals,  which  have  the  outline  of  an  oblique  rhomboidal  prism. 
By  gentle  evaporation  an  additional  quantity  may  be  obtained.  They 
contain  nitric  and  purpuric  acid  and  ammonia,  should  be  dissolved  in 
water,  and  be  exactly  neutralized  by  pure  ammonia;  and  the  liquid  is 
then  digested  in  a solution  of  potassa  until  the  ammonia  is  wholly 
expelled.  On  pouring  this  solution  into  dilute  sulphuric  acid,  pur- 
puric acid  is  set  free,  and,  being  insoluble  in  water,  subsides  as  a gran- 
ular powder,  of  a white  colour  if  pure,  but  commonly  of  a yellowish- 
white  tint. 

Considerable  uncertainty  prevails  as  to  the  nature  of  purpuric  acid. 
Vauqueliii  denied  that  its  salts  have  a purple  colour,  attributing  that 
tint  to  some  impurity,  and  I.assaigne  is  inclined  to  the  same  opinion. 
(An.  de  Ch.  et  de  Ph.  xxii.  334.);  but  from  the  intense  colour  given 
even  by  a very  minute  quantity  of  purpuric  acid,  the  opinion  of  Dr. 
Prout  appears  to  be  the  more  probable..  The  composition  of  the  acid  is, 
likewise,  unsettled;  for  Dr.  Prout  has  expressed  a doubt  of  the  accu- 
racy of  the  analysis  which  he  formerly  published. 

The  name  of  erythric  acid  (from  , to  redden)  was  applied 

by  Brugnatelli  to  a substance  which  he  procured  by  the  action  of  nitric 
on  uric  acid.  It  obviously  contains  purpuric  acid,  and  Dr.  Prout  thinks 
it  proba!)Ie  that  it  is  a supersalt,  consisting  of  purpuric  and  nitric 
acids,  and  ammonia,  being  probably  identical  with  the  crystals  above 
mentioned. 

Rosacic  Acid. — This  name  was  applied  by  Proust  to  a peculiar  acid 
supposed  to  exivt  in  the  red  matter,  commonly  called  by  medical  practi- 
tioners the  later itious sediment,  which  is  deposited  from  the  urine  in  some 
stages  of  fever.  PTom  the  experiment  of  Vogel  it  appears  to  be  uric 
acid,  either  combined  with  an  alkali,  or  modified  by  the  presence  of 
animal  matter.  Dr.  Prout  is  of  opinion  that  it  contains  some  purpurate 
of  ammonia;  and,  as  he  has  detected  the  presence  of  nitric  acid  in  the 
urine  from  which  such  sediments  were  deposited,  he  thinks  it  probable 
that  the  purpurate  may  be  generated  by  the  reaction  of  the  uric  and  ni- 
tric acids  on  each  other  in  tlie  urinary  passages. 


542 


ANIMAL  ACIDS. 


Hippuric  Acid,  Under  this  name,  derived  from  a horse  and 
urine,  Liebig*  has  lately  described  a peculiar  compound,  wliich  is  depos- 
ited from  the  urine  of  the  horse,  when  it  is  mixed  with  muriatic  acid 
in  excess.  7'he  deposite,  which  is  crystalline  and  of  a yellowish-brown 
tint,  is  boiled  with  milk  of  lime,  to  which  small  quantities  of  chloride 
of  lime  are  added,  until  the  urinous  odour  ceases.  It  is  then  digested 
with  animal  charcoal;  and  on  mixing  the  hot  filtered  solution  with  a 
large  excess  of  muriatic  acid,  hippuric  acid  is  deposited  in  cooling 
in  rather  large  prisms,  tw^o  or  three  inches  in  length,  and  beautifully 
white. 

The  claim  of  hippuric  acid  to  be  regarded  as  a proximate  principle  is 
doubtful,  since  it  is  closely  allied  to  benzoic  acid.  Liebig,  indeed, 
conceives  that  Fourcroy  and  Yauquelin,  who  report  benzoic  acid  to 
exist  in  the  urine  of  the  cow  and  some  other  animals,  were  deceived  by 
hippuric  acid;  and  he  considers  that  the  latter  is  clearly  distinguished 
from  the  former  by  its  form,  by  the  character  of  its  salts,  in  being  less 
soluble  in  w’ater,  and  in  containing  nitrogen.  But  when  hippuric  acid 
is  heated,  partial  decomposition  takes  place,  and  benzoic  acid  is  sublim- 
ed; and  a similar  conversion  is  effected  by  the  action  of  sulphuric  and 
nitric  acid.  These  facts  render  it  probable  that  hippuric  acid  is  a com- 
pound of  benzoic  acid  with  some  animal  matter,  by  which  its  proper- 
ties are  modified.  (An.  de  Ch.  et  de  Ph.  xliii.  188.) 

Formic  Acid. — The  acid  extracted  from  ants  was  for  sometime  sus- 
pected, chiefly  on  the  authority  of  Fourcroy  and  Vauquelin,  to  be  a 
mixture  of  acetic  and  malic  acids;  but  the  experiments  of  Suersen, 
Gehlen,  Berzelius,  and  Dobereiner  leave  no  doubt  of  its  being  a dis- 
tinct compound.  In  volatility  and  odour  it  does,  indeed,  resemble  the 
acetic  acid;  but  in  composition  it  is  entirely  different.  According  to 
the  analysis  of  formate  of  lead  by  Berzelius,  the  atomic  weight  of  for- 
mic acid  is  inferred  to  be  37;  and  it  is  composed  of  carbon  12  parts  or 
two  equivalents,  hydrogen  1 or  one  equivalent,  and  24  parts  or  three 
equivalents  of  oxygen.  It  hence  differs  from  oxalic  acid,  only  in  con- 
taining one  equivalent  of  hydrogen.  According  to  Dobereiner  it  is  re- 
solved into  carbonic  oxide  and  water  by  the  action  of  strong  sulphuric 
acid.  The  same  ingenious  chemist  has  succeeded  in  preparing  formic 
acid  artificially,  by  applying  a gentle  heat  to  a mixture  of  tartaric 
acid,  water,  and  peroxide  of  manganese.  The  tartaric  acid  is  convert- 
ed into  water,  carbonic  acid,  and  formic  acid.  (An.  of  Phil.  vol.  iv.  N. 
S.  311.) 

Liebig  and  Gmelin  have  found  that  several  other  substances,  such  as 
sugar,  starch,  sugar  of  milk,  and  ligneous  fibre,  may  be  substituted  for 
tartaric  acid;  but  the  formic  acid  is  then  accompanied  by  some  foreign 
matter,  which  may  be  removed  by  neutralizing  wdth  an  alkali,  and  de- 
composing the  formate  by  sulphuric  acid.  Even  alcohol  may  be  used; 
but  it  must  be  employed  in  a dilute  state,  in  order  to  prevent  the  pro- 
duction of  sulphuric  or  formic  ether. 

Lactic  Acid. — The  existence  of  this  acid,  though  described  by  Ber- 
zelius,  and  found  by  him  in  sour  milk  and  in  many  animal  fluids,  was 
never  demonstrated  in  a satisfactory  manner.  Berzelius  himself  now 
admits  it  to  be  acetic  acid  disguised  by  animal  matter,  an  opinion 
which  is  confirmed  by  Ticdemann  and  Gmelin  in  their  experimental 
Essay  on  Digestion.  (Die  Yerdauung  nach  Ycrsuche.  Heidelberg, 
1826.) 

The  amniotic  is  a weak  acid  which  was  discovered  by  Buniva  and  Yaii- 
quelin  in  the  liquor  of  the  amnios  of  the  cow,  from  which  it  is  deposit- 
ed by  gentle  evaporation  in  the  form  of  white  acicular  crystals.  It  is 


ANIMAL  OILS  AND  FATS. 


543 


very  sparingly  soluble  in  water,  but  yields  with  the  alkalies  soluble 
compounds  which  are  decomposed  by  most  of  the  acids. 

Several  other  animal  acids,  such  as  the  stearic,  oleic,  margaric,  and 
others,  should  also  be  mentioned  here;  but  as  they  are  closely  allied  to 
the  fatty  principles  from  which  they  are  derived,  they  will  be  more  con- 
veniently described  in  the  following  section. 


SECTION  III. 

OLEAGINOUS  SUBSTANCES. 

Animal  Oils  and  Fats. 

The  fatty  principles  derived  from  the  bodies  of  animals  are  very 
analogous  in  composition  and  properties  to  the  vegetable  fixed  oils; 
and  in  Britain,  where  the  latter  are  comparatively  expensive,  the  for- 
mer are  employed,  both  for  the  purpose  of  giving  light,  and  for  the 
manufacture  of  soap.  Their  ultimate  elements  are  carbon,  hydrogen, 
and  oxygen;  and  most  of  them,  like  the  fixed  oils,  consist  of  stearine 
and  elaine. 

From  a curious  experiment  of  Berard,  it  appears  that  a substance 
very  analogous  to  fat  may  be  made  artificially.  On  mixing  together  one 
measure  of  carbonic  acid,  ten  measures  of  carburetted  hydrogen,  and 
twenty  of  hydrogen,  and  transmitting  the  mixture  through  a red-hot 
tube,  several  white  crystals  were  obtained,  which  were  insoluble  in 
water,  soluble  in  alcohol,  and  fusible  by  heat  into  an  oily  fluid. — (An. 
of  Ph.  xii.  41.)  Dbbereiner  ^prepared  an  analogous  substance  from  a 
mixture  of  coal  gas  and  aqueous  vapour. 

Train  OIL — Train  oil  is  obtained  by  means  of  heat  from  the  blubber 
of  the  whale,  and  is  employed  extensively  in  making  oil  gas,  and  for 
burning  in  common  lamps.  It  is  generally  of  a reddish  or  yellow  colour, 
emits  a strong  unpleasant  odour,  and  has  a considerable  degree  of  vis- 
cidity, properties  which  render  it  unfit  for  being  burned  in  Argand 
lamps,  and  which  are  owing  partly  to  the  heat  employed  in  its  extrac- 
tion, and  partly  to  the  presence  of  impurities.  By  purification,  in- 
deed, it  may  be  rendered  more  limpid,  and  its  odour  less  offensive; 
but  it  is  always  inferior  to  spermaceti  oil. 

Spermaceti  oil  is  obtained  from  an  oily  matter  lodged  in  a bony  cavity 
in  the  head  of  physeter  macrocephaluSi  or  spermaceti  wliale.  On 
subjecting  this  substance  to  pressure  in  bags,  a quantity  of  pure 
limpid  oil  is  expressed;  and  the  residue,  after  being  melted,  strained, 
and  washed  with  a weak  solution  of  potassa,  is  sold  under  the  name  of 
spermaceti. 

Animal  Oil  of  Dippel. — This  name  is  applied  to  a limpid  volatile  oil, 
which  is  entirely  different  from  the  oils  above  mentioned,  and  is  a pro- 
duct of  the  destructive  distillation  of  animal  matter,  especially  of  albu- 
minous and  gelatinous  substances.  When  purified  by  distillation,  it  is 
clear  and  transparent.  It  was  formerly  much  used  in  medicine,  but  is 
now  no  longer  employed. 

Hogslard  and  Suet, — The  most  common  kinds  of  fat  are  hogslard  and 
suet,  which  differ  from  each  other  chiefly  in  consistence.  The  latter 


544 


ANIMAL  OILS  AND  FATS. 


when  separated  by  fusion  from  tlie  membrane  in  which  it  occurs,  is 
called  tallow,  wliich  is  extensively  employed  in  the  manufacture  of  soap 
and  candles.  ^ Both  these  varieties  of  fat,  as  well  as  train  and  sperma- 
ceti oil,  consist  almost  entirely  of  stearine  and  elai'ne;  and  when  con* 
verted  into  soap,  underg*o  the  same  change  as  the  fixed  oils,  yielding 
margaric  and  oleic  acids,  and  the  mild  principle  of  oils  called  glficerine. 
Stearic  acid  is  also  a constituent  of  soap  made  from  these  animal  fats. 

The  method  of  preparing  stearine  and  elaine  from  the  vegetable  oils 
has  already  been  detailed  (Page  485);  and  the  same  process,  which 
originated  with  M.  Braconnot,  is  also  applicable  to  hogslard.  'Phe  mode 
by  which  M.  Chevreul  obtains  these  principles  is  by  treating  hogslard  in 
successive  portions  of  hot  alcohol.  'I'he  spirit  in  cooling  deposites  the 
stearine  in  the  form  of  white  crystalline  needles,  which  are  brittle,  and 
have  the  aspect  of  wax,  fuse  readily^  when  heated,  and  are  insoluble  in 
water.  I’he  alcoholic  solution,  when  evaporated,  leaves  an  oily  fluid 
which  is  elaine.  They  may  be  then  rendered  quite  pure  by  re-solution 
in  boiling  alcohol. 

For  a full  account  of  the  acids  generated  during  the  formation  of  soap 
by  the  action  of  alkaline  substances  on  oil  or  fat,  I refer  to  the  treatise 
of  M.  Chevreul  Sur  les  Corps  Gras.  Margaric  and  oleic  acids  are  best 
prepared  from  soap  made  with  potassa  and  fluid  vegetable  oil.  This 
soap,  after  being  dried  as  much  as  possible,  is  treated  by  successive  por- 
tions of  cold  alcohol  of  specific  gravity  0.821,  in  which  the  oleate  of 
potassa  is  soluble,  and  the  margarate  insoluble.  I'he  two  salts  being 
thus  separated,  are  decomposed  by  means  of  an  acid. 

Margaric  acid,  so  named  from  its  pearly  lustre  (from  fJLctpyotp  irrt^ 
a pearl)  is  insoluble  in  water,  and  is  hence  precipitated  by  acids  from 
the  solution  of  its  salts.  It  is  abundantly  dissolved  by  hot  alcohol,  and 
is  deposited  from  the  saturated  solution,  in  cooling,  in  a crystalline  mass 
of  a pearly  lustre.  At  140^  F.  it  is  fused,  and  shoots  into  brilliant  white 
acicular  crystals  as  it  cools.  It  has  an  acid  reaction,  and  its  salts,  those 
of  the  alkalies  excepted,  are  very  sparingly  soluble  in  water.  The 
crystallized  acid  contains  3.4  per  cent  of  water,  and  the  acid  itself  con- 
sists of  79  parts  of  carbon,  12  of  hydrogen,  and  9 of  oxygen. 

Oleic  acid  is  best  prepared  from  soap  made  with  linseed  oil  and  po- 
tassa, since  the  greater  part  of  it  consists  of  oleate  of  potassa.  This 
salt  is  first  separated  from  margarate  of  potassa  by  cold  alcohol,  and  the 
oleic  acid  then  precipitated  from  an  aqueous  solution  of  the  oleate  by 
means  of  an  acid.  At  the  mean  temperature,  oleic  acid  is  a colourless 
oily  fluid,  which  congeals  wlien  it  is  cooled  to  near  zero.  It  has  a slightly 
rancid  odour  and  taste,  and  reddens  litmus  paper.  Its  specific  gravity 
is  0.898.  It  is  insoluble  in  water,  but  is  dissolved  in  every  proportion 
by  alcoliol.  Of  the  neutral  oleates  hitherto  examined,  those  of  soda  and 
potassa  are  alone  soluble  in  water.  In  its  pure  state  it  contains  3.8  per 
cent  of  water,  and  consists,  the  water  abstracted,  of  80.94  parts  of  car- 
bon, 11.36  of  hydrogen,  and  7.7  of  oxygen. 

Stearic  Jlcid. — This  acid  is  best  prepared  from  soap  made  with  potassa 
and  suet  or  hogslard,  and  exists  in  this  soap,  together  with  mai’garic  and 
oleic  acids,  d’lie  soap  is  dissolved  in  6 times  its  weight  of  warm  water, 
then  mixed  with  40  or  50  ])arls  of  cold  water,  and  the  mixture  .*  et  a^de 
in  a place  the  tcm]:)cratiire  of  which  is  about  56^.  A precipitate  of  a 
pearly  hnstre  gradually  collects,  consisting  of  the  bimargarate  and  bi- 
stcaratc  of  [)Otassa,  which  are  to  be  collected  and  well  washed  upon  a 
filter.  'I'lie  two  salts  are  then  separated  by  repeated  solut.on  in  about 
20  times  their  weight  of  boiling  alcohol,  from  which  on  cooling  the 
whole  of  the  bisteai'ate  is  deposited,  while  ])art  of  the  bimarg-arate  on 
each  occasion  is  retained  in  solution.  The  former  is  considered  pure 


ANIMAL  OILS  AND  FATS. 


545 


when  the  stearic  acid,  separated  from  the  potassa  by  means  of  another 
acid,  requires  a temperature  of  153®  F.  for  fusion. 

'Stearic  acid  is  very  similar  in  its  appearance  and  properties  to  mar- 
garic  acid,  and  the  chief  ground  of  distinction  between  them  is  in  the 
latter  being  rather  more  fusible,  and  containing  rather  more  oxygen 
than  the  former. 

Sebadc  Acid. — Thenard  has  applied  this  name  to  an  acid  which  is  ob- 
tained by  the  distillation  of  hogslard  or  suet,  and  is  found  in  the  reci- 
pient mixed  with  acetic  acid  and  fat,  partially  decomposed.  It  is  sepa- 
rated from  the  latter  by  means  of  boiling  water,  and  from  the  former  by 
acetate  of  lead.  The  sebate  of  lead,  which  subsides,  is  subsequently 
decomposed  by  sulphuric  acid. 

Sebacic  acid  reddens  litmus  paper,  dissolves  freely  in  alcohol,  and  is 
more  soluble  in  hot  than  in  cold  water.  It  melts  like  fat  when  heated, 
and  crystallizes  in  small  white  needles  in  cooling.  It  is  not  applied  to 
any  use. 

Bulyrine.^^wVi&v  differs  from  the  common  animal  fats  in  containing 
a peculiar  oleaginous  matter,  which  is  quite  fluid  at  70®  F.,  and  to 
which  Chevreul  has  applied  the  name  of  hutyrine.  When  converted 
into  soap,  it  yields,  in  addition  to  the  usual  products,  three  volatile  odo- 
riferous compounds,  namely,  the  butyric,  caproic,  and  capric  acids. 

Phocenine  is  a peculiar  fatty  substance  contained  in  the  oil  of  the 
porpoise  (^delphinum  phococna)  mixed  with  ela'inc.  When  converted 
into  soap,  it  yields  a volatile  odoriferous  acid,  called  the  phocenic  acid* 
(Chevreul.) 

Hircine  is  contained  in  the  fat  of  the  goat  and  sheep,  and  yields  the 
hircic  acid  when  converted  into  soap.  (Chevreul.) 

Other  acids  more  or  less  analogous  to  those  above  described  are  formed 
during  the  conversion  of  other  oleaginous  substances  into  soap.  Thus, 
castor  oil  yields  three  acids,  to  wliich  MM.  Bussy  and  Lecanu  have  ap- 
plied the  names  of  margaric,  ricinic,  and  elaiodic  acid.  The  cevadic  acid 
was  prepared  in  a similar  manner  by  Pelletier  and  Caventou  from  oil 
derived  from  the  seeds  of  the  Veratrum  sabadilla;  and  the  same  che- 
mists have  given  the  name  of  jatrophic  acid  (more  properly  crotonic)  to 
the  acid  of  the  soap  made  from  croton  oil.  This  oil  is  derived  from  the 
seeds  of  the  Croton  tiglium. 

The  sweet  principle  of  oils,  glycerine  of  Chevreul,  was  discovered  by 
Scheele.  It  was  originally  obtained  in  the  formation  of  common  plaster 
by  boiling  oil  with  oxide  of  lead  and  a little  water;  and  Chevreul  found 
that  it  is  produced  during  the  saponification  of  fatty  substances  in  gen- 
eral. In  preparing  soap  by  means  of  potassa,  the  glycerine  is  left  in  the 
mother  liquor;  and  on  neutralizing  the  free  alkali  with  sulphuric  acid, 
evaporating  to  the  consistence  of  syrup,  and  treating  the  residue  with 
alcohol,  it  is  dissolved.  The  alcoholic  solution,  when  evaporated, 
yields  glycerine  in  the  form  of  an  uncrystallizable  syrup.  It  is  soluble 
in  water  and  alcohol,  and  has  a sweet  taste,  but  is  not  susceptible  either 
of  the  vinous  or  acetous  fermentation.  According  to  the  analysis  of 
Chevreul,  glycerine,  of  the  specific  gravity  of  1.^  contains  40.071 
parts  of  carbon,  8.925  of  hydrogen,  and  51.004  of  oxygen. 

Spermaceti. — This  inflammable  substance,  which  is  prepared  from  the 
spermaceti  whale  as  above  mentioned,  commonly  occurs  in  crystalline 
plates  of  a white  colour  and  silvery  lustre.  It  is  brittle,  and  feels  soft 
and  slightly  unctuous  to  the  touch.  It  has  no  taste,  and  scarcely  any 
odour.  It  is  insoluble  in  water,  but  dissolves  in  about  thirteen  times 
its  weight  of  boiling  alcohol,  from  which  the  greater  part  is  deposited 
on  cooling  in  the  form  of  brilliant  scales.  It  is  still  more  soluble  in 
ether.  It  is  exceedingly  fusible,  liquefying  at  a temperature  which  U 

4 6* 


^46 


ANIMAL  OILS  AND  TATS. 


distinctly  below  212^  F.  Dig*ested  with  pure  potassa  it  is  converted 
into  soap,  and  tlie  acid  then  generated  has  received  from  Chevreul  the 
name  of  cctic  acid^ 

The  spermaceti  of  commerce  always  contains  some  fluid  oil,  from 
which  it  may  be  purified  by  solution  in  boiling  alcohol.  To  the  white 
crystalline  scales  deposited  from  the  spirit  as  it  cools,  and  which  is  sper- 
maceti in  a state  of  perfect  purity,  Chevreul  has  given  the  name  of 
cetine. 

Mipocire. — When  apiece  of  fresh  muscle  is  exposed  for  some  time 
to  the  action  of  water,  or  is  kept  in  moist  earth,  the  fibrin  entirely  dis- 
appears, and  a fatty  matter  called  adipocire  remains,  which  has  some  re- 
semblance to  spermaceti.  I'he  fibrin  was  formerly  thought  to  be  really 
converted  into  adipocire;  but  Gay-I.ussac*  and  Chevreul  maintain  that 
this  substance  proceeds  entirely  from  the  fat  originally  present  in  the 
muscle,  and  that  the  fibrin  is  merely  destroyed  by  ])utrefaction.  Dr. 
'I'homson  maintains,  however,  that  tlie  conversion  of  fibrin  into  fat  does 
occur  in  some  instances,  and  has  related  a remarkable  case  in  proof  of 
his  opinion.  (Ann.  of  Phil.  vol.  xii.  ]).  41.)  According  to  M.  Chev- 
reul, the  adipocire  is  not  a pure  fatty  principle,  but  a species  of  soap, 
chiefly  consisting  of  margaric  acid  in  combination  with  ammonia  gener- 
ated during  the  decomposition  of  the  fibrin. 

Cholcstcrine.\ — 'fliis  name  is  applied  by  Chevreul  to  the  crystalline 
matter  which  constitutes  the  basis  of  most  of  the  biliary  concretions 
formed  in  the  human  subject.  Fourcroy,  regarding  it  as  identical 
with  spermaceti  and  the  fatty  matter  just  described,  comprehended 
all  these  substances  under  tlie  general  appellation  of  adipocire;  but 
Chevreul  has  shown  that  it  is  an  independent  principle,  wholly  different 
from  spermaceti. 

Cholesterine  is  a white  brittle  solid  of  a crystalline  lamellated  struc- 
ture and  brilliant  lustre,  very  much  resembling  spermaceti;  but  it  is 
distinguished  from  that  substance  by  requiring  a temperature  of  278® 
F.  for  fusion,  and  by  not  being  convertible  into  soap  when  digested  in  a 
solution  of  potassa.  It  is  free  from  taste  and  odour,  and  is  insoluble  in 
water.  It  dissolves  freely  in  boiling  alcohol,  from  which  it  is  deposited 
on  cooling  in  white  pearly  scales.  According  to  the  analysis  of  Chev- 
reul it  is  composed  of  85.095  parts  of  carbon,  11.88  of  hydrogen,  and 
3.025  of  oxygen. 

When  heated  with  its  own  weight  of  concentrated  nitric  acid, 
cholesterine  is  dissolved  with  disengagement  of  nitric  oxide  gas;  and 
in  cooling  a yellow  matter  subsides,  an  additional  quantity  of  which 
may  be  obtained  by  dilution  with  water.  I'his  substance  possesses  the 
])roperties  of  acidity,  and  is  called  cholesteric  acid.  It  is  insoluble  in 
water,  but  dissolves  freely  in  alcohol,  especially  with  the  aid  of  heat, 
its  taste  is  slightly  styptic,  and  its  odour  somewhat  like  that  of  buttery 
it  is  lighter  than  water,  and  fusible  at  136^  F.  In  mass  it  is  of  an 
orange-yellow  tint;  but  when  the  alcoholic  solution  is  evaporated  spon- 
taneously, it  is  deposited  in  acicular  crystals  of  a white  colour.  It  red- 
dens litmus  paper,  and  neutralizes  alkaline  bases.  The  cholesterates  of 
potassa  and  soda  arc  delique.scent  and  very  soluble  in  water,  but  insolu- 
l>lc  in  alcohol  and  ether.  'I  he  cholesterates  of  the  earths  and  other 
metallic  oxides  arc  either  sparingly  dissolved  by  water  or  altogether  in- 
Boluble.  Its  salts  are  precipitated  by  the  mineral  and  most  of  the  vege- 
table acids;  but  are  not  decomposed  by  carbonic  acid.  For  these  flicts 


♦ An.  de  Ch.  et  de  Fh.  vol.  iv. 

-j-  From  bile  and  solid-, 


ON  THE  BLOOD. 


547 


respecting'  the  formation  and  properties  of  cholesteric  acid,  we  are  in* 
debted  to  the  experiments  of  Pelletier  and  Caventou.  (Journal  de  Phar- 
niacie,  iii.  292.) 

Cholesterine  has  been  detected  in  the  bile  of  man,  and  of  several  of 
the  lower  animals,  such  as  the  ox,  dog*,  pig',  and  bear.  This  interest- 
ing discovery  was  made  about  the  same  time  by  Chevreul  in  Paris,  and 
by  Tiedemann  and  Gmelin  in  Heidelberg.  Lassaigne  has  likewise  found 
it  in  the  biliary  calculus  of  a pig.  (An.  de  Ch.  et  de  Ph.  xxxi.)  It  is 
frequently  formed  in  parts  of  the  body  quite  unconnected  with  the 
hepatic  circulation,  and  appears  to  be  a common  product  of  deranged 
.vascular  action.  Caventou,  in  the  Journal  de  Pharmacie  for  October 
1825,  states  that  the  contents  of  an  abscess,  formed  under  the  jaw  ap- 
parently in  consequence  of  a carious  tooth,  were  found  by  him  to  con- 
sist almost  entirely  of  cholesterine.  In  the  article  Calcul  of  the  Nouveau 
Dictionnaire  de  Medecine^  M.  Breschet  observes  that  cholesterine  has 
been  found  in  cancer  of  the  intestines,  and  in  the  fluid  of  hydrocele 
and  ascites  in  the  human  subject;  and  adds  that  M.  Barruel  procured  it 
in  large  quantity  from  an  ovarian  cyst  in  a mare,  and  in  the  fluid  drawn 
off‘  from  the  ovary  of  a woman,  and  scrotum  of  a man.  Breschet  has 
found  it  also  in  a tumour  under  the  tongue.  Dr.  Christison  found  it  in 
the  fluid  of  hydrocele,  taken  from  a patient  in  the  Royal  Infirmary  of 
Edinburgh  by  the  late  Dr.  William  Cullen,  in  an  osseous  cyst  into  which 
the  kidneys  of  another  patient  were  converted,  and  in  the  membranes 
of  the  brain  of  an  epileptic  patient. 

The  best  method  of  preparing  pure  cholesterine  is  to  treat  human 
biliary  concretions,  reduced  to  powder,  with  boiling  alcohol,  and  to 
filter  the  hot  solution  as  rapidly  as  possible.  As  the  liquid  cools, 
the  greater  part  of  the  cholesterine  subsides.  In  this  way  it  is  freed 
from  the  colouring  matter,  with  which  it  is  commonly  associated  in  the 
gall-stone. 

Ambergris. — This  substance  is  found  floating  on  the  surface  of  the 
sea  near  the  coasts  of  India,  Africa,  and  Brazil,  and  is  supposed  to  be 
a concretion  formed  in  the  stomach  of  the  spermaceti  whale.  It  has 
commonly  been  regarded  as  a resinous  principle;  but  its  chief  constit- 
uent is  a substance  very  analogous  to  cholesterine,  and  to  which  Pelle- 
tier and  Caventou  have  given  the  name  of  ambreine.  By  digestion  in 
nitric  acid,  ambreine  is  converted  into  a peculiar  acid  called  the  ambreit 
acid.  (An.  of  Phil.  vol.  xvi.) 


ON  THE  MORE  COMPLEX  ANIMAL  SUBSTANCES,  AND 
SOME  FUNCTIONS  OP  ANIMAL  BODIES. 


SECTION  1. 

ON  THE  BLOOD,  RESPIRATION,  AND  ANIMAL  HEAT. 

The  blood,  while  circulating  in  the  vessels  of  living  animals,  is  fluid, 
and  of  a florid-red  colour  in  the  arteries,  and  of  a dark  purple  colour 
in  the  veins.  Its  taste  is  slightly  saline,  its  odour  peculiar,  and  to  the 
touch  it  seems  somewhat  unctuous.  Its  specific  gravity  is  variable,  but 
most  commonly  is  near  1.05;  and  in  man  its  temperature  is  about  98?  or 


548 


ON  THE  BLOOD. 


100®  Fahr.  When  recently  drawn,  it  appears  to  the  naked  eye  as  a 
uniform  homog-eneous  fluid;  but  if  examined  with  a microscope  of  suf- 
ficient power,  numerous  red  particles  of  a globular  form  are  seen  float- 
ing in  a colourless  fluid.  The  compound  nature  of  the  blood  is  render- 
ed still  more  apparent  by  the  process  of  coagulation,  during  which  it 
separates  spontaneously  into  two  distinct  portions,  a yellowish  liquid 
called  the  serum,  of  the  blood,  and  a red  solid,  known  by  the  name 
of  the  c/o/,  cruor,  or  crassamenium.  The  proportion  of  these  parts  is 
variable,  the  latter  being  more  abundant  in  healthy  vigorous  animals 
than  in  those  which  have  been  debilitated  by  depletion,  low  living,  op 
disease. 

The  serum  is  somewhat  unctuous  to  the  touch,  of  a saline  taste,  and 
of  slightly  alkaline  reaction,  owing  to  the  presence  of  a little  free  soda. 
Its  average  specific  gravity  is  about  1.029.  Like  other  albuminous  li- 
quids, it  is  coagulated  by  heat,  acids,  alcohol,  and  all  other  substances 
which  coagulate  albumen.  On  subjecting  the  coagulum  prepared  by 
heat  to  gentle  pressure,  a small  quantity  of  a colo\irless  limpid  fluid, 
called  the  serosliy,  oozes  out,  which  contains  according  to  Dr.  Bostock 
about  l-50th  of  its  weight  of  animal  matter,  together  with  a little  mu- 
riate of  soda.  Of  this  animal  matter  a portion  is  albumen,  which  may 
easily  be  coagulated  by  means  of  galvanism;  but  a small  quantity  of 
some  other  principle  is  present,  winch  differs  both  from  albumen  and 
gelatin.  (Medico-chir.  Trans,  ii.  166.) 

From  the  analysis  of  the  late  Dr.  Marcet,  1000  parts  of  the  serum  of 
human  blood  are  composed  of  water  900  parts,  albumen  86.8,  muriate 
of  potassa  and  soda  6.6,  muco-extractive  matter  4,  carbonate  of  soda 
1.65,  sulphate  of  potassa  0.35,  and  of  earthy  phosphates  0.60.  This 
result  agrees  very  nearly  with  that  obtained  by  Berzelius,  who  states 
that  the  extractive  matter  of  Marcet  is  lactate  (acetate)  of  soda  united 
with  animal  matter.  (Medico-chir.  Trans,  iii.  231.) 

The  serum,  instead  of  being  transparent  as  it  commonly  is,  has  some- 
times a cloudy  appearance  like  whey,  and  in  some  more  rare  instances 
is  perfectly  opake  and  white,  as  if  it  had  been  mixed  with  milk.  The 
cause  of  the  opacity  has  been  experimentally  examined  by  Drs.  Traill 
and  Christison,  who  have  traced  it  to  the  presence  of  oleaginous  matter, 
which  the  latter  has  shown  to  contain  both  stearine  and  elai’ne,  and  to 
be  very  similar  to  human  fat.  The  milkiness  may,  therefore,  be  ascrib- 
ed to  fat  being  mechanically  diffused  through  the  serum  like  oil  in  an 
emulsion.  It  may  be  easily  separated  by  agitating  the  serum  in  a tube 
with  half  its  bulk  of  sulphuric  ether,  when  the  adipose  matter  is  in- 
stantly dissolved,  the  opacity  in  consequence  disappears,  and  on  eva- 
porating the  clear  ethereal  solution,  which  rises  to  the  surface  of  the 
mixture,  the  fat  is  obtained  in  a separate  state.  By  this  means  he  pro- 
cured on  one  occasion  five  per  cent,  of  fat  from  milky  serum,  and  one 
per  cent,  from  serum  which  had  the  aspect  of  whey.  Dr.  Christison 
has  detected  traces  of  fat  in  perfectly  transparent  serum;  so  that  adipose 
matter  in  small  quantity  appears  to  be  frequently  contained  in  the  blood. 
(Edin.  Med.  and  Surg.  Journal,  April,  1830.) 

The  crassamentuin  or  clot  of  the  blood  consists  of  two  parts,  the 
fibrin  and  colouring  principle.  The  latter  resides  in  distinct  particles 
which,  according  to  Prevost  and  Dumas,  are  elliptical  in  birds  and  cold- 
blooded animals,  and  assume  the  globular  form  in  mammiferous  animals. 
These  globules  are  insoluble  in  serum;  but  their  colour  is  dissolved  by 
pure  water,  acids,  alkalies,  and  alcohol.  Much  uncertainty  prevails 
among  chemists  relative  to  the  cause  of  the  colour  of  the  red  globules. 
As  soon  as  the  blood  was  known  to  contain  iron,  the  peroxide  of  which 
has  a red  tint,  the  colour  of  the  red  globules  was  ascribed  to  the  pre- 


ON  THE  BLOOD. 


549 


sence  of  that  metal,  and  some  chemists  supposed  it  to  be  in  the  form  of 
siibphosphate  of  iron.  This  opinion  was  adopted  by  Foiircroy  and 
Vauquelin,  who  affirmed  that  phosphate  of  iron  may  be  dissolved  in 
serum  by  means  of  an  alkali,  and  that  the  colour  of  the  solution  is  ex- 
actly similar  to  that  of  the  blood. 

This  subject  was  investig’ated  in  the  year  1806  by  Berzelius,  who 
showed  that  subphosphate  of  iron  cannot  be  dissolved  in  serum,  in  the 
way  supposed  by  Foiircroy  and  Vauquelin,  except  in  very  minute  quan- 
tity; and  that  this  salt,  even  when  rendered  soluble  by  pliosphoric  acid, 
communicates  a tint  quite  different  from  that  of  the  red  g'lobules.  On 
comparing*  together  the  composition  of  the  three  principal  ingredients 
of  the  blood,  viz.  fibrin,  albumen,  and  colouring  matter,  he  found  that 
the  ashes  of  the  last  always  yielded  oxide  of  iron  in  the  proportion  of 
1.200th  of  the  original  mass,  while  the  oxide  was  entirely  wanting  in 
the  two  former.  From  this  it  was  a probable  inference  that  iron  is 
somehow  or  other  concerned  in  the  production  of  the  red  colour;  but 
the  experiments  of  Berzelius  did  not  make  known  the  state  which 
that  metal  exists  in  the  blood.  He  could  not  detect  its  presence  by  any 
of  the  liquid  tests.  (Medico-chir.  Trans,  iii.  213.) 

In  a series  of  experiments  published  in  1812,  (Philos.  Trans.)  Mr. 
Brande  obtained  results  quite  contrary  to  those  of  Berzelius.  He  de- 
tected iron  in  the  ashes  of  the  serum  and  fibrin  as  well  as  those  of  the 
red  globules;  and  in  each  it  was  present  in  such  minute  quantity,  that 
no  effect  as  a colouring  agent  could  be  expected  from  it.  Mr.  Brande 
supposed  that  the  tint  of  the  red  globules  is  produced  by  a peculiar 
animal  colouring  principle,  capable,  like  other  substances  of  a similar 
nature,  of  combining  with  metallic  oxides.  lie  succeeded  in  obtaining 
a compound  of  the  colouring  matter  of  the  blood  with  oxide  of  tin;  but 
its  best  precipitants  are  nitrate  of  mercury  and  corrosive  sublimate. 
Woollen  cloths  impregnated  with  either  of  these  compounds,  on  being 
dipped  into  an  aqueous  solution  of  the  colouring  matter,  acquired  a 
permanent  red  dye,  unchangeable  by  washing  with  soap. 

The  conclusions  of  Brande,  relative  to  the  presence  of  iron  in  the 
albumen  and  fibrin  of  the  blood,  received  additional  support  from  the 
researches  of  Vauquelin  (An.  de  Ch.  et  de  Ph.  i.);  but  the  question 
has  been  finally  decided  by  Dr.  Engelhart,  a young  German  chemist  of 
great  promise,  who  gained  the  prize  offered  in  the  year  1825  by  the 
Medical  Faculty  of  Gottingen  for  the  best  essay  on  the  nature  of  the 
colouring  matter  of  the  blood.  (Edin.  ,Med.  and  Surg.  Journ.  for  Janu- 
ary, 1827.)  He  demonstrated  that  the  fibrin  and  albumen  of  tlie  blood, 
when  carefully  separated  from  colouring  particles,  do  not  contain  a 
trace  of  iron;  and,  on  the  contrary,  he  procured  iron  from  the  red 
globules  by  incineration.  But  he  has  likewise  succeeded  in  proving  the 
existence  of  iron  in  the  colouring  matter  of  the  blood  by  the  liquid 
tests;  for,  on  transmitting  a current  of  chlorine  gas  through  a solution 
of  the  red  globules,  the  colour  entirely  disappeared,  white  flocks  were 
thrown  down,  and  a transparent  solution  remained,  in  which  peroxide 
of  iron  was  discovered  by  all  the  usual  reagents.  I'he  results  obtained 
by  Dr.  Engelhart  relative  to  the  quantity  of  the  iron,  correspond  with 
those  of  Berzelius,  'fhese  facts  have  been  since  confirmed  by  Rose, 
who  has  accounted  in  a satisfactory  manner  for  the  failure  of  former 
chemists  in  detecting  iron  in  the  blood  while  in  a fluid  state.  He  finds 
that  oxide  of  iron  cannot  be  precipitated  by  the  alkalies,  hydrosulphuret 
of  ammonia,  or  infusion  of  galls,  if  it  is  dissolved  in  a solution  which 
contains  albumen  or  other  soluble  organic  principles. 

From  the  presence  of  iron  in  the  red  globules,  and  its  total  absence 
in  the  other  principles  of  the  blood,  it  is  probable  that  this  metal. 


550 


ON  THE  BLOOD. 


though  its  quantity  does  not  exceed  one-half  per  cent.,  is  essential  to 
the  production  of  the  red  colour.  The  experiments  of  Dr.  Engelhart, 
however,  have  not  determined  the  manner  in  which  it  acts,  nor  in  what 
state  it  exists  in  the  blood,  though  it  is  most  probably  in  the  form  of  an 
oxide.  It  is  a singular  coincidence  that  sulphocyanic  acid,  which  forms  i 
with  peroxide  of  iron  a colour  exactly  like  that  of  venous  blood,  has 
been  detected  in  the  saliva.  The  existence  of  tliis  acid  in  the  blood  it- 
self is,  therefore,  a circumstance  by  no  means  improbable. 

Dr.  Engelhart  is  likewise  the  first  chemist  who  has  procured  the  col- 
ouring matter  of  blood  in  a state  of  perfect  purity.  I'he  method  for- 
merly recommended  is  that  of  Berzelius,  whose  process  consists  in  al- 
lowing the  clot  cut  into  thin  slices  to  drain  as  much  as  possible  on  bi- 
bulous paper,  triturating  it  with  water,  and  then  evaporating  the  solu- 
tion at  a temperature  not  exceeding  122^^  F.  As  thus  prepared,  the 
colouring  matter  retains  all  its  properties,  but  is  mixed  with  a little 
serum.  The  method  of  Dr.  Pingelhart  is  founded  on  the  fact,  that 
serum,  when  much  diluted,  does  not  coagulate  by  heat,  while  the  red 
particles  are  coagulated,  and  fall  down  in  the  form  of  brown  flocks. 
Serum  diluted  with  ten  parts  of  water  does  not'coagulate  at  160®  F.; 
but  the  colouring  matter,  dissolved  in  fifty  parts  of  water,  begins  to 
coagulate  at  149®  F. 

The  colouring  particles,  when  prepared  in  this  way,  are  no  longer  of 
a bright-red  colour,  and  their  nature  is  somewhat  modified,  in  conse- 
quence of  which  they  are  insoluble  in  water.  When  half  dried,  they 
form  a brownish-red,  granular,  friable  mass;  and  when  completely  dried 
at  a temperature  between  167®  and  190®,  the  mass  is  tough,  hard,  bril- 
liant, black  with  reflected,  and  garnet-red  with  transmitted  light.  Ex- 
cept in  their  insolubility,  they  have  all  the  properties  of  the  red  parti- 
cles obtained  by  the  method  of  Berzelius.  The  caustic  alkalies  with  the 
aid  of  heat  dissolve  them  entirely,  and  the  solution  acquires  a dark 
blood-red  colour. 

The  fibrin  of  the  blood  may  easily  be  obtained  in  a pure  state  by 
washing  the  clot  in  cold  water  until  the  colouring  matter  is  entirely  re- 
moved. While  circulating  in  the  animal  body  it  is  either  in  a fluid  state, 
or  suspended  in  the  serum  in  the  form  of  minute  colourless  globules; 
but  when  removed  from  the  vessels,  and  set  at  rest,  it  becomes  solid  in 
the  course  of  a few  minutes,  giving  rise  to  what  is  called  the  coagula- 
tion of  the  blood.  The  time  required  for  coagulation  is  influenced  by 
temperature,  being  promoted  by  heat,  and  retarded  by  cold.  Dr. 
Scudamore  finds  that  blood  which  begins  to  coagulate  in  four  minutes 
and  a half  in  an  atmosphere  of  53®  F.,  undergoes  the  same  change  in 
two  minutes  and  a half  at  98®;  and  that  which  coagulates  in  four  min- 
utes at  98®  will  become  solid  in  one  minute  at  120®.  On  the  contrary, 
blood  which  coagulates  firmly  in  five  minutes  at  60®  will  remain  quite 
fluid  for  twenty  minutes  at  the  temperature  of  40®,  and  requires 
upwards  of  an  hour  for  complete  coagulation.  (Scudamore  on  the 
Blood.) 

The  process  of  coagulation  is  influencGd  by  exposure  to  the  air.  If 
atmospheric  air  be  excluded,  as  by  filling  a bottle  completely  with  re- 
cently drawn  blood,  ai\d  closing  the  orifice  with  a good  stopper,  coag- 
ulation is  retarded.  It  is  singular,  however,  that  if  blood  be  confined 
within  the  exliaiistcd  receiver  of  an  air-pump,  the  coagulation  is  accel- 
erated. (Scudamore.) 

Itccently  drawm  blood,  owing  doubtless  to  its  temperature,  is  known 
to  give  off  a portion  of  acpieous  vapovir,  which  has  a peculiar  odour, 
indicative  of  the  presence  of  some  peculiar  principle,  but  in  which 
nothing  but  water  can  be  detected.  Physiologists  are  not  agreed  upon 


ON  THE  BLOOB. 


551 


the  question  whether  the  act  of  coagulation  is  or  is  not  accompanied 
with  disengagement  of  gaseous  matter.  In  the  experiments  of  Vogel, 
Brande,  and  Scudamore,  blood  coagulating  in  the  vacuum  of  an  air- 
pump  was  found  to  emit  carbonic  acid,  and  Dr.  Scudamore  even  infer- 
red that  the  evolution  of  this  gas  constitutes  an  essential  part  of  the  pro- 
cess. Other  experimentalists,  however,  obtained  a different  result. 
Dr.  John  Davy  and  Dr.  Duncan,  jun.,  failed  in  their  attempts  to  pro- 
cure carbonic  acid  from  blood  during  coagulation;  and  Dr.  Christison, 
in  an  experiment  performed  four  years  ago  in  my  laboratory,  was  not 
more  successful.  These  facts  appear  conclusive  against  the  opinion  of 
Dr.  Scudamore,  and  they  receive  additional  weight  from  the  considera- 
tion, that  the  appearance  of  carbonic  acid  in  the  experiments  above 
mentioned  might  easily  have  been  occasioned  by  casual  exposure  to  the 
atmosphere  previous  to  the  blood  being  placed  under  the  receiver. 

Coagulation  is  influenced  by  the  rapidity  with  which  the  blood  is 
removed  from  the  body.  Dr.  Scudamore  observed,  that  blood  slowly 
drawn  from  a vein  coagulates  more  rapidly  than  when  taken  in  a full 
stream. 

Experiments  are  still  wanting  to  show  the  influence  of  different  gases 
on  coagulation.  Oxygen  gas  accelerates  coagulation,  and  carbonic  acid 
retards,  but  cannot  prevent  it. 

Caloric  is  evolved  during  the  coagulation  of  the  blood.  The  late 
Dr.  Gordon  estimated  the  rise  of  the  thermometer  at  six  degrees;  and 
Dr.  Davy,  on  the  other  hand,  regards  the  increase  of  temperature  from 
this  cause  as  very  slight.  Dr.  Scudamore  finds  that  the  rate  at  which 
blood  cools  is  distinctly  slower  than  it  would  be  were  no  caloric  disen- 
gaged, and  he  observed  the  tiiermometer  to  rise  one  degree  at  the  com- 
mencement of  coagulation. 

Some  substances  prevent  the  coagulation  of  the  blood.  This  effect 
is  produced  by  a saturated  solution  of  muriate  of  soda,  muriate  of  am- 
monia, or  nitre,  and  a solution  of  potassa.  The  coagulation,  on  the 
contrary,  is  promoted  by  alum,  and  the  sulphates  of  zinc  and  copper. 
The  blood  of  persons  who  have  died  a sudden  violent  death,  by  some 
kinds  of  poison,  or  from  mental  emotion,  is  usually  found  in  a fluid 
state.  Lightning  is  said  to  have  a similar  effect;  but  Dr.  Scudamore 
declares  this  to  be  an  error.  Blood,  through  which  electric  dis- 
charges were  transmitted,  coagulated  as  quickly  as  that  which  was 
not  electrified;  and  in  animals  killed  by  the  discharge  of  a powerful 
galvanic  battery,  the  blood  in  the  veins  was  always  found  in  a solid 
state. 

The  cause  of  the  coagulation  of  the  blood  has  been  the  subject  of 
much  speculation  to  physiologists.  The  tendency  of  this  fluid  to  pre- 
serve the  liquid  form  while  contained  in  a living  animal,  cannot  be  as- 
scribed  to  the  motion  to  which  it  is  continually  subject  within  the  ves- 
sels. It  is  a familiar  fact  that  blood,  though  continually  stirred  out  of 
the  body,  is  not  prevented  from  coagulating;  and  it  has  been  noticed, 
that  the  coagulation  of  blood,  which  is  set  at  rest  within  its  proper 
vessels  by  the  application  of  ligatures,  or  which  has  been  accidentally 
extravasated  within  the  body,  is  materially  retarded.  It  has,  indeed, 
been  hitlierto  found  impossible  to  account  in  a satisfactory  manner  for 
the  blood  retaining  its  fluidity  from  the  influence  cf  motion,  tempera- 
ture, or  the  operation  of  any  physical  or  chemical  laws;  and,  conse- 
quently, it  is  generally  ascribed  to  the  agency  of  the  vital  principle. 
The  blood  is  supposed  either  to  be  endowed  with  a principle  of  vitality, 
or  to  receive  from  the  living  parts  with  which  it  is  in  contact  a certain 
vital  impression,  which,  together  with  constant  motion,  counteracts  its 
tendency  to  coagulate. 


55^ 


RESPIRATION. 


The  clot  of  blood  drawn  from  an  individual  in  a state  of  health  is  red 
throiig'liout  its  whole  substance,  ’ cause  tlie  fibrin  coiig*ulales  before 
the  red  globules  have  had  timet  subside.  In  inflaminaloiy  diseases, 
on  the  contrary,  the  blood  under,^oes  a peculiar  change,  in  consecjucnce 
of  which  tlie  red  globules  sink  to  the  bottom  before  the  fibrin  has  be- 
come solid,  and  thus  leave  the  upper  surface  of  the  latter  of  its  natural 
pale  colour.  This  appearance  is  familiarly  known  by  the  name  of  huffy 
coat.  Its  formation  must  obviously  depend  either  on  the  coagulation 
being  unusually  slow,  so  that  the  red  globules  have  full  leisure  to 
subside;  or  on  the  coagulation  taking  place  in  the  ordinary  period, 
wdiile  tlie  red  globules  subside  with  unusual  rapidity.  The  nature 
of  the  change  which  gives  rise  to  the  buffy  coat  is  altogether  un- 
known. 

In  addition  to  the  constituents  of  the  blood  already  enumerated,  M. 
Barrutl  declares  that  this  fluid  contains  a volatile  ])rinciple,  peculiar  to 
each  species  of  animal.  This  principle  has  an  odour  resembling  that  of 
the  cutaneous  or  pulmonary  exhalation  of  the  animal,  and  serves  as  a 
distinctive  character  by  which  the  blood  of  different  animals  may  be 
recognize*].  It  is  dissolved  in  the  blood,  and  its  odour  may  be  perceiv- 
ed when  the  blood  or  its  scrum  is  mixed  with  strong  sulphuric  acid. 
The  odour  is  commonly  stronger  in  the  male  than  in  the  female.  In 
man  it  resembles  the  human  perspiration;  in  the  ox,  it  smells  like  oxen 
or  a cow-house;  and  the  odour  from  horses’  blood  is  similar  to  that  of 
its  perspiration.  (Journ.  of  Science,  vi.  N.  S.  187.)  Should  the  accu- 
racy of  these  observations  be  confirmed,  they  may  be  advantageously 
applied  in  some  cases  of  legal  medicine. 

Eespiraiion, 

When  venous  blood  is  brought  into  contact  with  atmospheric  air,  its 
surface  passes  from  a dark-purple  to  a florid-red  colour,  oxygen  disap- 
pears, and  carbonic  acid  gas  is  emitted.  I'liese  changes  take  place 
more  speeddy  when  air  is  agitated  with  blood;  they  are  still  more  rapid 
when  pure  oxy  gen  is  substituted  for  atmospheric  air;  and  they  do  not 
occur  at  all  when  oxygen  is  entirely  excluded.  It  is  hence  inferred 
that  the  pi-ocess  of  arterialization,  as  it  is  called,  or  the  conversion  of 
venous  ir.to  arterial  blood,  depends  entirely  on  the  presence  of  oxygen. 
It  is  also  presumed  that  the  alternating  shades  of  colour  are  caused  by 
the  red  pai  tides  undergoing*  certain  chemical  changes,  the  nature  of 
which,  however,  is  at  present  quite  inexplicable. 

The  saine  changes  that  occur  out  of  the  body  are  continually  taking 
place  within  it.  During  respiration,  venous  blood  is  exposed  in  the 
lungs  to  ihe  agency  of  the  air  and  is  arterialized,  oxygen  gas  disap- 
pears, and  carbonic  acid  is  evolved;  and  it  is  remaikable  that  these 
phenomena  ensue  not  only  during  life,  but  even  after  death,  provided 
the  respiratoiy  process  be  preserved  artificially.  Since,  therefore,  the 
essential  ])henomeiia  of  artcrializatlon,  according  to  the  best  data  we 
possess,  are  the  same  in  a living  and  in  a dead  animal,  and  whether  the 
blood  is  or  is  not  contained  in  the  body,  it  seems  legitimate  to  infer,  that 
this  process  is  not  necessarily  dependent  on  the  vital  principle,  but  is 
solely  determined  by  the  laws  of  chemical  action. 

In  studying  the  sulqcct  of  respiration  the  hrst  object  is  to  determine 
the  precise  cliangc  ])roduced  in  the  constitution  of  the  air  which  is  in- 
haled. Dr.  lilack  was  the  first  to  notice  that  the  air  exhaled  from  the 
lungs  contains  a considerable  quantity  of  carbonic  acid,  which  may  be 
detected  by  transmission  through  lime-water.  Priestley,  some  years 
after,  observed  that  air  is  rendered  unfit  for  supporting  flame  or  animal 


RESPIRATION. 


553 


life  by  the  process  of  respiration,  from  which  it  was  probable  that  oxy- 
g*en  is  consumed?  and  Lavoisier  subsequently  established  the  fact,  that 
during"  respiration  oxygen  gas  disappears,  and  carbonic  acid  is  disen- 
gaged. The  chief  experimentalists  who  have  since  cultivated  this  de- 
partment of  chemical  physiology  are  Priestley,  Scheele,  Lavoisier, 
Seguin,  Crawford,  Goodwin,  Davy,  Ellis,  Allen  and  Pepys,  Edwards 
and  Despretz.  Of  these  the  results  obtained  by  Messrs.  Allen  and 
Pepys,*  and  Dr.  Edwards,-}^  are  the  most  conclusive  and  satisfactory, 
their  researches  having  been  conducted  with  great  care,  and  aided  by 
all  the  resources  of  modern  chemistry. 

One  of  the  chief  objects  of  Messrs.  Allen  and  Pepys,  in  their  exper- 
iments, was  to  ascertain  if  any  uniform  relation  exists  between  the 
oxygen  consumed  and  the  carbonic  acid  evolved.  They  found  in  gen- 
eral that  the  quantity  of  the  former  exceeds  that  of  the  latter?  but  as 
the  difference  was  very  trifling,  they  inferred  that  the  carbonic  acid  of 
the  expired  air  is  exactly  equal  to  the  oxygen  which  disappears.  The 
experiments  of  Dr.  Edwards  were  attended  with  a remarkable  result, 
which  accounts  very  happily  for  some  of  the  discordant  statements  of 
preceding  inquirers.  He  found  the  ratio  between  the  gases  to  vary 
with  the  animal.  In  some  animals  it  might  be  regarded  as  nearly  equal? 
while  in  others  the  loss  of  oxygen  considerably  exceeded  the  gain  of 
carbonic  acid,  so  that  the  respired  air  suffered  a material  diminution  in 
volume.  With  respect  to  the  human  subject,  the  statement  of  Allen 
and  Pepys  seems  very  near  the  truth. 

The  quantity  of  oxygen  withdrawn  from  the  atmosphere,  and  of 
carbonic  acid  disengaged,  is  variable  in  different  individuals,  and  in  the 
same  individual  at  different  times.  It  is  estimated  by  Allen  and  Pepys, 
that  in  every  minute  during  the  calm  respiration  of  a healthy  man  of 
ordinary  stature,  26.6  cubic  inches  of  carbonic  acid  of  the  temperature 
of  50®  F.  are  .emitted,  and  an  equal  volume  of  oxygen  witlidrawn  from 
the  atmosphere.  From  these  data  it  has  been  calculated,  that  in  an  in- 
terval of  twenty-four  hours  not  less  than  eleven  ounces  of  carbon  are 
given  off  from  the  lungs  alone, — an  estimate  which  must  surely  be  in- 
accurate, the  quantity  being  so  great  as  sometimes  to  exceed  the  weight 
of  carbon  contained  in  the  food.  The  same  observers  have  lately  found 
the  production  of  carbonic  acid  in  a pigeon,  breathing  freely  in  atmos- 
pheric air,  to  be  such  that,  supposing  the  same  rate  to  continue,  the 
bird  must  have  thrown  off  96  grains  of  carbon  in  the  space  of  24  hours. 
From  the  observations  of  Dr.  Prout,  it  appears  that  the  quantity  of 
carbonic  acid  emitted  from  the  lungs  is  variable  at  particular  periods  of 
the  day,  and  in  particular  states  of  the  system.  It  is  more  abundant 
during  the  day  than  the  night?  about  daybreak  it  begins  to  increase, 
continues  to  do  so  till  about  noon,  and  then  decreases  until  sunset. 
During  the  night  it  seems  to  remain  uniformly  at  a minimum?  and  the 
maximum  quantity  given  off*  at  noon,  exceeds  the  minimum  by  about 
one-fifth  of  the  whole.  The  quantity  of  carbonic  acid  is  diminished 
by  any  debilitating  causes,  such  as  low  diet,  depressing  passions,  and 
the  like.  (An.  of  Phil.  xiii.  269.)  The  experiments  of  Dr.  Fyfe,  pub- 
lished in  his  Inaugural  Dissertation,  are  confirmatory  of  those  above 
mentioned. 

Messrs.  Allen  and  Pepys  have  shown  that  atmospheric  air,  when 
drawn  into  the  lungs,  returns  charged  in  the  succeeding  expiration  with 
from  8 to  6 per  cent,  of  carbonic  acid  gas.  They  found  also,  that  when 


• Philosophical  Transactions  for  1808. 
t De  Pinfluence  des  Agens  Physiques  sur  la  Vie.  1824. 
4r 


554 


RESPIRATION. 


an  ammal  is  confined  in  the  same  quantity  of  air,  death  ensues  before 
all  the  oxygen  is  consumed;  that  when  the  same  portion  of  air  is  re- 
peatedly  respired  until  it  can  no  longer  support  life,  it  then  contains 
only  10  per  cent,  of  carbonic  acid. 

Although  in  respiration,  the  arterialization  of  tlie  blood  by  means  of 
free  oxygen  is  the  essential  change,  without  the  due  performance  of 
which  the  life  of  warm-blooded  animals  cannot  be  preserved  beyond  a 
few  minutes,  and  which  is  likewise  necessary  to  the  lowest  of  the  insect 
tribe,  it  is  important  to  determine  whetlier  the  nitrogen  of  the  atmos- 
phere has  any  influence  in  the  function.  The  results  of  different  in- 
quirers differ  considerably.  In  the  experiments  of  Priestley,  Davy, 
Humboldt,  Henderson,  and  Pfaff,  there  appeared  to  be  absorption  of 
nitrogen,  a less  quantity  of  that  gas  being  exhaled  than  was  inspired. 
Nysten,  Berthollet,  and  Despretz,  on  the  contrary,  remarked  an  in- 
crease in  the  bulk  of  the  nitrogen;  and  from  the  researches  of  Seguiri 
and  Lavoisier,  Vauquelin,  Ellis,  Dalton,  and  Spallanzani,  it  was  infer- 
red that  there  is  neither  absorption  nor  exiialation  of  nitrogen,  the 
quantity  of  that  gas  undergoing  no  change  during  its  passage  through 
the  air-cells  of  the  lungs.  Messrs.  Allen  and  Pepys  arrived  at  a similar 
conclusion;  and  since  the  appearance  of  their  essay,  the  opinion  has 
prevailed  very  generally  among  physiologists,  that  in  respiration  the 
nitrogen  of  the  air  is  altogether  passive. 

The  facts  ascertained  by  Dr.  Edwards  relative  to  this  subject  are 
novel  and  of  peculiar  interest.  This  acute  physiologist  has  reconciled 
the  discordant  results  of  prt>ceding  experimenters,  by  showing  that, 
during  the  respiration  even  of  the  same  animal,  the  quantity  of  nitro- 
gen may  one  while  be  increased,  at  another  time  diminished,  and  at  a 
third  wholly  unchanged.  He  has  traced  these  phenomena  to  the  influ- 
ence of  the  seasons;  and  he  suspects,  as  indeed  is  most  probable,  that 
other  causes,  independently  of  season,  have  a share  in  their  produc- 
tion. In  nearly  all  the  lower  animals  which  were  made  the  subjects  of 
experiment,  an  augmentation  of  nitrogen  was  observable  during  sum- 
mer. Sometimes,  indeed,  it  was  so  slight  that  it  might  be  disregarded. 
But  in  many  other  instances,  it  was  so  great  as  to  place  the  fact  be- 
yond the  possibility  of  doubt;  and  on  some  occasions  it  almost  equalled 
the  whole  bulk  of  the  animal.  Such  continued  to  be  the  result  of  his 
inquiries  until  the  close  of  October,  when  he  observed  a sensible  dim- 
inution of  nitrogen,  and  the  same  continued  throughout  the  whole  of 
winter  and  the  beginning  of  spring. 

There  are  two  modes  of  accounting  for  these  phenomena.  Accord- 
ing to  one  view,  the  nitrogen  which  disappears  is  ascribed  to  the  ab- 
sorption of  what  was  inhaled,  and  its  increase  to  direct  exhalation,  the 
opposite  processes  of  absorption  and  exhalation  being  supposed  not  to 
occur  at  the  same  moment.  According  to  the  other  view,  both  these 
processes  are  always  going  on  at  the  same  time,  and  the  result  depends 
on  the  preponderance  of  one  over  the  other.  When  absorption  pre- 
vails, a smaller  quantity  of  nitrogen  is  exhaled  than  was  inspired;  when 
exhalation  exceeds  absorption,  increase  of  nitrogen  takes  place;  but 
when  absorption  and  exhalation  are  equal,  the  bulk  of  the  inspired  air, 
so  far  as  concerns  nitrogen,  is  unchanged.  The  latter  opinion,  which 
is  adopted  by  Dr.  Edwards,  is  supported  by  two  decisive  experiments 
performed  by  Messrs.  Allen  and  Pepys,  in  one  of  which  a guinea-pig 
was  confined  in  a vessel  of  oxygen  gas,  and  in  the  other  in  an  atmos- 
phere composed  of  21  measures  of  oxygen  and  79  of  hydrogen.  In 
both  cases  the  residual  air  contained  a quantity  of  nitrogen  greater  than 
the  bulk  of  the  animal  itself;  and  in  the  latter  a portion  of  hydrogen 


RESPIUA.TION. 


555 


had  disappeared.  Hence  it  follows  that  nitrogen  may  be  exhaled  from 
the  lungs,  and  that  hydrogen  may  be  absorbed. 

An  account  of  some  interesting  researches  on  the  respiration  of  birds, 
bearing  directly  on  this  subject,  was  published  last  year  by  Messrs.  Al- 
len and  Pepys  (Phil.  Trans.  1829).  The  subject  of  inquiry  was  the  pi- 
geon, and  the  phenomena  attending  its  respiration  were  observed  un- 
der three  different  circumstances,  namely,  in  atmospheric  air,  in  oxy- 
gen gas,  and  in  a mixture  of  oxygen  and  hydrogen,  in  which  the  former 
amounted,  as  in  the  amosphere,  to  20  per  cent.  In  each  case  the  bulk 
of  the  gaseous  mixture  remained  without  change.  In  the  experiments 
with  atmospheric  air,  the  oxygen  which  disappeared  was  equal  to  the 
carbonic  acid  evolved;  the  nitrogen  was  unaffected,  except  on  one  oc- 
casion when  the  bird  appeared  uneasy,  and  then  there  was  a slight  loss 
of  nitrogen.  In  oxygen  gas  the  production  of  carbonic  acid  was  about 
half  the  quantity  emitted  when  the  pigeon  breathed  common  air;  and 
the  decrease  in  oxygen  was  exactly  equal  to  the  united  volumes  of  the 
carbonic  acid  and  nitrogen  which  were  disengaged.  When  the  pigeon 
was  placed  in  mixed  oxygen  and  hydrogen  gases,  the  production  of  car- 
bonic acid  was  rather  more  abundant  than  in  atmospheric  air,  and  its 
volume  equalled  exactly  the  loss  in  oxygen;  nitrogen,  as  before,  was 
given  out  with  considerable  freedom,  and  its  bulk  precisely  correspond- 
ed to  the  decrease  in  hydrogen.  In  the  two  latter  series  of  experi- 
ments, especially  in  the  last,  the  respiration  of  the  pigeon  was  at  times 
laborious.  The  experiments,  however,  are  decisive  of  the  fact,  that 
Carbonic  acid  and  nitrogen  gases  may  be  thrown  off  from  the  lungs,  and 
that  oxygen  and  hydrogen  gases  may  be  absorbed. 

Two  theories  have  been  proposed  to  explain  the  phenomena  of  res- 
piration. According  to  one  theory,  the  carbonic  acid  found  in  the  res- 
pired air  is  actually  generated  in  the  lungs  themselves;  while,  according 
to  the  other,  this  gas  is  thought  to  exist  ready  formed  in  the  blood,  and 
to  be  merely  thrown  off  from  that  liquid  during  its  distribution  through 
the  lungs.  The  former  theory,  which  appears  to  have  originated  with 
Priestley,  has  received  several  modifications.  Priestley  imagined  that 
the  phenomena  of  respiration  are  owing  to  the  disengagement  of  phlo- 
giston from  the  blood,  and  its  combination  with  the  air.  Dr.  Crawford 
modified  this  doctrine  in  the  following  manner.  (Crawford  on  Animal 
Heat.)  He  was  of  opinion  that  venous  blood  contains  a peculiar  com- 
pound of  carbon  and  hydrogen,  termed  hydro-carhon^  the  elements  of 
which  unite  in  the  lungs  with  the  oxygen  of  the  air,  forming  water  with 
the  one,  and  carbonic  acid  with  the  other;  and  that  the  blood,  thus  pu- 
rified, regains  its  florid  hue,  and  becomes  fit  for  the  purposes  of  the 
animal  economy. 

The  hypothesis  of  Crawford,  however,  is  not  merely  liable  to  the  ob- 
jection  that  the  supposed  hydro  carbon,  as  respects  the  blood,  is  quite 
imaginary;  but  it  was  found  at  variance  with  the  leading  facts  establish- 
ed by  Messrs.  Allen  and  Pepys.  By  the  elaborate  researches  of  these 
chemists  it  was  established,  that  carbonic  acid  gas  contains  its  own  vol- 
ume of  oxygen;  and  they  also  concluded  that  air  inhaled  into  the  lungs, 
returns  charged  with  a quantity  of  carbonic  acid,  almost  exactly  equal 
in  bulk  to  the  oxygen  which  disappears— an  inference  which,  as  applied 
to  man  and  some  of  the  lower  animals,  seems  very  near  the  truth.  A 
review  of  these  circumstances  induced  them  to  adopt  the  opinion,  that 
the  oxygen  of  the  air  combines  in  the  lungs  exclusively  with  carbon; 
and  that  the  watery  vapour,  which  is  always  contained  in  the  breath,  is 
an  exhalation  from  minute  pulmonary  vessels.  They  conceived  that 
the  fine  animal  membrane  interposed  between  the  blood  and  the  air 
does  not  prevent  chemical  action  from  taking  place  between  them. 


556 


ANIMAL  HEAT. 


This  view  has  been  further  modified  by  Mr.  Ellis,  who  supposes  that 
the  carbon  is  separated  from  the  venous  blood  by  a process  of  secretion, 
and  that  then,  coming*  into  direct  contact  with  oxygen,  it  is  converted 
into  carbonic  acid.  (Inquiry,  &c.  Parts  I.  and  II.) 

^ The  circumstance  which  led  Mr.  Ellis  to  this  opinion,  was  a disbelief 
in  the  possibility  of  oxygen  acting  upon  the  blood  through  the  animal 
membrane  in  which  it  is  confined.  The  experiments  adduced  in  proof 
of  the  impermeability  of  membranous  substances  are  not,  however,  quite 
satisfactory;  while,  on  the  contrary,  the  facts  noticed  by  several  accurate 
observers  appear  to  leave  no  doubt  that  moist  animal  membranes,  even 
in  the  living  body,  are  in  some  way  or  other  permeable  to  substances  in 
a gaseous  form*. 

According  to  the  second  theory,  which  was  supported  by  La  Grange 
and  Hassenfratz,  and  has  lately  been  adopted  by  Dr.  Edwards,  carbonic 
acid  generated  during  the  course  of  the  circulation  is  given  off  from 
venous  blood  in  the  lungs,  and  oxygen  gas  is  absorbed.  This  doctrine, 
though  generally  regarded  hitherto  as  less  probable  than  the  preceding, 
is  supported  by  very  powerful  arguments.  The  experiments  and  ob- 
servations  of  Dr.  Edwards  seem  to  leave  no  doubt  that  the  blood,  while 
circulating  through  the  lungs,  is  capable  of  absorbing  hydrogen,  nitro- 
gen, and  oxygen  gases,  and  of  emitting  nitrogen;  and  he  has  gone  very 
far  towards  proving  that  the  carbonic  acid  is  derived  from  the  same 
source.  On  confining  frogs  and  snails  for  some  time  in  an  atmosphere 
of  hydrogen,  the  residual  air  was  found  to  contain  a quantity  of  carbonic 
acid,  which  was  in  some  instances  even  greater  than  the  bulk  of  the  ani- 
mal; and  a similar  result  was  obtained  with  young  kittens. 

The  confined  limits  of  the  present  work  do  not  admit  of  an  examina- 
tion into  the  respective  advantages  and  disadvantages  of  these  two 
theories.  It  will,  therefore,  suffice  to  observe  that,  in  the  present  stage 
of  the  inquiry,  the  deficiency  of  precise  data  prevents  the  establishment 
of  one  of  them  in  preference  to  the  other;  but  that  the  arguments  pre- 
ponderate in  favour  of  the  last. 

The  conversion  of  venous  into  arterial  blood  appears  not  to  be  confin- 
ed to  the  lungs.  The  disengagement  of  carbonic  acid  from  the  surface 
of  the  skin,  and  the  corresponding  disappearance  of  oxygen  gas,  was 
demonstrated  by  the  experiments  of  Jurine  and  Abernethy;  and  although 
the  accuracy  of  their  results  has  been  doubted  by  some  persons,  it  haa 
been  confirmed  by  others.  However  this  may  be  in  the  human  subject, 
the  fact  with  respect  to  many  of  the  lower  animals  is  unquestionable. 
Spallanzani  proved  that  some  animals  possessed  of  lungs,  such  as  ser- 
pents, lizards,  and  frogs,  produce  the  same  change  on  the  air  by  means 
of  their  skin,  as  by  their  proper  respiratory  organs;  and  Dr.  Edwards, 
in  a series  of  masterly  experiments,  has  shown  that  this  function  compen- 
sates so  fully  for  the  want  of  respiration  by  the  lungs,  as  to  enable  these 
animals,  in  the  winter  season,  to  live  for  an  almost  unlimited  period  un- 
der the  surface  of  water. 

Animal  Heat. 

The  striking  analogy  between  the  processes  of  combustion  and  res- 
piration, in  both  of  which  oxygen  gas  disappears,  and  an  oxidized  body 
is  substituted  for  it,  led  Dr.  Black  to  infer  tliat  the  caloric  generated  -in 
the  animal  system,  by  means  of  which  the  more  perfect  animals  preserve 


• See  some  judicious  remarks  on  this  subject  in  the  Essay  on  Respira- 
tion and  Animal  Heat,  by  Dr.  Williams,  in  the  Medico-chir.  Trans,  of 
Edinburgh,  vol.  ii, 


ANIMAL  HEAT. 


557 


their  temperature  above  that  of  the  surrounding*  medium,  is  derived 
from  the  changes  going  forward  in  the  lungs.  But  this  opinion  is  not 
founded  on  analogy  alone;  many  circumstances  conspire  to  show  that 
the  development  of  animal  heat  is  dependent  on  the  function  of  respira- 
tion, although  the  mode  by  which  the  effect  is  produced  has  not  hither- 
to been  satisfactorily  determined.  Thus,  in  all  animals  whose  respira- 
tory organs  are  small  and  imperfect,  and  which,  therefore,  consume  but 
a comparatively  minute  quantity  of  oxygen,  and  generate  little  carboriic 
acid,  the  temperature  of  the  blood  varies  with  that  of  the  medium  in 
which  they  live.  In  warm-blooded  animals,  on  the  contrary,  in  which 
tlie  respiratory  apparatus  is  larger,  and  the  chemical  changes  more  com- 
plicated, the  temperature  is  almost  uniform;  and  those  have  the  highest 
temperature  whose  lungs,  in  proportion  to  the  size  of  their  bodies,  are 
largest,  and  which  consume  the  greatest  quantity  of  oxygen.  The 
temperature  of  the  same  animal  at  different  times  is  connected  with  the 
state  of  the  respiration.  When  the  blood  circulates  sluggishly,  and  the 
the  temperature  is  low,  the  quantity  of  oxygen  consumed  is  compara- 
tively small;  but,  on  the  contrary,  a large  quantity  of  that  gas  disappears 
when  the  circulation  is  brisk,  and  the  power  of  generating  heat  ener- 
getic. It  has  also  been  observed,  especially  by  Crawford  and  De  Laroche, 
that  when  an  animal  is  placed  in  a very  warm  atmosphere,  so  as  to  re- 
quire little  heat  to  be  generated  within  his  own  body,  the  consumption 
of  oxygen  is  unusually  small,  and  the  blood  within  the  veins  retains  the 
arterial  character.  ^ 

The  connexion  between  the  power  of  generating  heat  and  respiration 
has  been  illustrated  in  a very  pointed  manner  by  Dr.  Edwards.  Some 
young  animals,  such  as  puppies  and  kittens,  require  so  small  a quantity 
of  oxygen  for  supporting  life,  that  they  may  be  deprived  of  that  gas  al- 
together for  twenty  minutes  without  material  injury;  and  it  is  remarkable 
that  so  long  as  they  possess  this  property,  the  temperature  of  their 
bodies  sinks  rapidly  by  free  exposure  to  the  air.  But  as  they  grow  older 
they  become  able  to  maintain  their  own  temperature,  and  at  the  same 
time  their  power  to  endure  the  privation  of  oxygen  ceases.  The  same 
observation  applies  to  young  sparrows,  and  other  birds  which  ai'e  naked 
when  hatched;  while  young  partridges,  which  are  both  fledged  and  able 
to  retain  their  own  temperature  at  the  period  of  quitting  the  shell,  die 
when  deprived  of  oxygen  as  rapidly  as  an  adult  bird. 

The  first  consistent  theory  of  the  production  of  animal  heat  was  pro- 
posed by  Dr.  Crawford.  This  theory  was  founded  on  the  assumption  that 
the  carbonic  acid  contained  in  the  breath  is  generated  in  the  lungs,  and 
that  its  formation  is  accompanied  with  disengagement  of  caloric.  But 
since  the  temperature  of  the  lungs  is  not  higher  than  that  of  other  in- 
ternal organs,  and  arterial  very  little  if  at  all  warmer  than  venous  blood, 
it  follows  that  the  greater  part  of  the  caloric,  instead  of  becoming  free, 
must  in  some  way  or  other  be  rendered  insensible.  Accordingly,  on 
comparing  the  specific  caloric  of  arterial  and  venous  blood.  Dr.  Craw- 
ford found  the  capacity  of  the  former  to  exceed  that  of  the  latter  in  the 
ratio  of  1030  to  892.  He,  therefore,  inferred  that  the  dark  blood  within 
the  veins,  at  the  moment  of  beijig  arterialized,  acquires  an  increase  of 
insensible  caloric;  and  that  while  circulating  through  the  body,  and 
gradually  resuming  the  venous  character,  it  sufiers  a diminution  of  ca- 
pacity,  and  evolves  a proportional  degree  of  heat. 

Unfortunately  for  the  hypothesis  of  Crawford,  one  of  the  leading  facts 
on  which  it  is  founded  has  been  called  in  question;  Dr.  Davy  maintain- 
ing, on  the  authority  of  his  own  experiments,  that  there  is  little  or  no 
diflierence  between  the  capacity  of  venous  and  arterial  blood.  (Philos. 
Trans,  for  1814.)  If  this  be  true,  the  hypothesis  itself  necessarily  falls 


558 


ANIMAL  HEAT. 


to  the  ground.  One  part  of  the  doctrine  of  Crawford  may,  however, 
in  a modified  form,  be  applied  to  the  theory  of  respiration  advocated  by 
Dr.  Edwards.  For  if  oxyg*en  be  absorbed  by  the  blood  in  its  passage 
through  the  lungs,  and  carbonic  acid,  ready  formed,  be  emitted  in  re- 
turn, it  follows  that  this  gas  must  be  generated  during  the  course  of  the 
circulation;  and  it  may  be  inferred  that  the  heat  developed  in  cqpse- 
quence  of  this  chemical  change  is  at  once  communicated  to  the  adja- 
cent organs.  In  this  way  the  question  concerning  the  capacity  of  the 
blood  for  caloric  may  be  entirely  disregarded. 

While  some  physiologists  have  been  disposed  to  refer  the  source  of 
animal  heat  entirely  to  the  alternate  changes  of  venous  to  arterial,  and 
of  arterial  to  venous  blood,  others  have  denied  its  agency  altogether, 
ascribing  the  evolution  of  caloric  solely  to  the  influence  of  the  nervous 
system.  The  chief  foundation  for  this  opinion  is  in  the  experiments  of 
Mr.  Brodie,  who  inflated  the  lungs  of  animals  recently  killed  by  nar- 
cotic poisons  or  division  of  the  spinal  marrow.  (Phil.  Trans,  for  1811 
and  1812.)  In  an  animal  so  treated,  the  blood  continued  to  circulate, 
the  phenomena  of  arterialization  took  place  with  regularity,  oxygen  gas 
disappeared,  and  carbonic  acid  was  evolved;  but  nothwithstanding  the 
concurrence  of  all  these  circumstances,  the  temperature  fell  with  equal 
if  not  greater  rapidity  than  in  another  animal  killed  at  the  same  time, 
but  in  which  artificial  respiration  was  not  performed. 

Were  these  experiments  rigidly  exact,  they  would  lead  to  the  opi- 
nion that  no  caloric  is  evolved  by  the  mere  process  of  arterialization. 
This  inference,  however,  cannot  be  admitted  for  two  reasons: — first, 
because  other  physiologists,  in  repeating  the  experiments  of  Brodie, 
have  found  that  the  process  of  cooling  is  retarded  by  artificial  respira- 
tion; and,  secondly,  because  it  is  difficult  to  conceive  why  the  formation 
of  carbonic  acid,  which  uniformly  gives  rise  to  increase  of  temperature 
in  other  cases,  should  not  be  attended  within  the  animal  body  with  a 
similar  effect.  It  may  hence  be  inferred,  that  this  is  one  of  the  sources 
of  animal  heat.  It  is  certain,  however,  that  the  heat  of  animals  cannot 
be  maintained  by  the  sole  process  of  arterialization.  Consistently  with 
this  fact,  the  researches  of  Dulong  and  Despretz  agree  in  proving,  in 
opposition  to  the  results  obtained  by  Lavoisier  and  Crawford,  that  a 
healthy  animal  imparts  to  the  surrounding  bodies  a quantity  of  heat  con- 
siderably greater  than  can  be  accounted  for  by  the  combustion  of  the 
carbon  thrown  off*  during  the  same  interval  from  the  lungs  in  the  form 
of  carbonic  acid.  (An.  de  Ch.  et  de  Ph.  26.) 

Though  the  influence  of  the  nervous  system  over  the  development  of 
animal  heat  is  no  longer  doubtful,  physiologists  are  not  agreed  as  to  the 
mode  by  which  it  operates.  Its  action  may  be  either  direct  or  indirect; 
that  is,  the  nerves  may  possess  some  specific  power  of  generating  heat, 
or  they  may  excite  certain  operations  by  which  the  same  effect  is  occa- 
sioned. It  is  far  from  improbable,  that  the  nerves  act  more  by  the  latter 
than  the  former  mode;  that  the  infinite  number  of  chemical  phenomena 
going  on  in  the  minute  arterial  branches  during  the  processes  of  secre- 
tion and  nutrition,  processes  which  are  entirely  dependent  on  the  ner- 
vous system,  are  attended  with  disengagement  of  caloric.  This  view 
has,  at  least,  been  ably  defended  by  Dr.  Williams  in  the  essay  to  which 
1 have  already  referred. 


SALIVA 


559 


SECTION  IL 


ON  THE  SECRETED  FLUIDS  SUBSERVIENT  TO  DIGESTION. 

Saliva,  Pancreatic  and  Gastric  Jtiices, 

Saliva. — The  saliva  is  a slightly  viscid  liquor,  secreted  by  the  salivary 
glands.  When  mixed  with  distilled  water,  a flaky  matter  subsides 
which  is  mucus,  derived  apparently  from  the  lining  membrane  of  the 
mouth.  The  clear  solution,  when  exposed  to  the  agency  of  galvanism, 
yields  a coagulum,  and  is  hence  inferred  by  Mr.  Brande  to  contain  al- 
bumen; but  the  quantity  of  this  principle  is  so  very  small  that  its  pres- 
ence cannot  be  demonstrated  by  any  other  reagent.  The  greater  part 
of  the  animal  matter  remaining  in  the  liquid  is  peculiar  to  the  saliva, 
and  m^y  termed  salivary  matter.  It  is  soluble  in  water,  insoluble  in 
alcohol,  and,  when  freed  from  the  accompanying  salts,  is  not  precipi- 
tated by  subacetate  of  lead,  corrosive  sublimate,  or  infusion  of  gall- 
nuts.  The  saliva  likewise  contains  a small  quantity  of  animal  matter, 
which  is  soluble  both  in  alcohol  and  water,  and  which  is  supposed  by 
Tiedemann  and  Gmelin  to  be  osmazome. 

The  solid  contents  of  the  saliva,  according  to  Berzelius,  do  not  ex- 
ceed 7 in  1000  parts,  the  rest  being  water.  From  the  recent  analysis 
of  Tiedemann  and  Gmelin,  the  chief  saline  constituent  is  muriate  of 
potassa;  but  several  other  salts,  such  as  the  sulphate,  phosphate,  ace- 
tate, carbonate,  and  sulphocyanate  of  potassa,  are  likewise  present  in 
small  quantity.  The  saliva  of  the  human  subject,  according  to  the 
same  authority,  contains  very  little  soda.  The  property  which  the  saliva 
possesses  of  striking  a red  colour  with  a persalt  of  iron  is  owing  to 
sulphocyanate  of  potassa.  Sulphocyanic  acid  exists  also  in  the  saliva  of 
the  sheep;  but  it  has  not  been  found  in  that  of  the  dog.  The  saliva 
of  the  sheep  contains  so  much  carbonate  of  soda,  that  it  effervesces 
with  acids. 

The  only  known  use  of  the  saliva  is  to  form  a soft  pulpy  mass  with 
the  food  during  mastication,  so  as  to  reduce  it  into  a state  fit  for  being 
swallowed  with  facility,  and  for  being  more  readily  acted  on  by  the 
juices  of  the  stomach. 

Concretions  are  sometimes  found  in  the  salivary  glands  and  ducts.  A 
stone  contained  in  the  salivary  gland  of  an  ass  was  found  by  M.  Caven- 
tou  to  contain  91.6  parts  of  carbonate  of  lime,  4.8  of  phosphate  of 
lime,  and  3.6  of  animal  matter.  A salivary  concretion  of  a horse  was 
found  by  M.  Henry,  jun.  to  consist  of  carbonate  of  lime  85.52,  car- 
bonate of  magnesia  7.56,  phosphate  of  lime  4.40,  and  2.48  of  ani- 
mal matter.  Carbonate  of  lime  is  the  chief  ingredient  of  salivary  con- 
cretions. 

Pancreatic  Juice. — This  fluid  is  commonly  supposed  to  be  analogous 
to  the  saliva,  but  it  appears  from  the  analysis  of  Tiedemann  and  Gmelin 
that  it  is  essentially  different.  The  chief  animal  matters  are  albumen, 
and  a subst?mce  like  curd;  but  it  also  contains  a small  quantity  of  sal- 
ivary matter  and  osmazome.  It  reddens  litmus  paper,  owing  to  the 
presence  of  free  acid,  which  is  supposed  to  be  the  acetic.  Its  salts  are 


560 


GASTRIC  JUICE. 


nearly  the  same  as  those  contained  in  the  saliva,  except  that  sulpho' 
cyanic  acid  is  wanting*.  The  uses  of  this  fluid  are  entirely  unknown. 

Gastric  Juice. — The  gastric  juice,  collected  from  the  stomach  of  an 
animal  killed  while  fasting,  is  a transparent  fluid  which  has  a saline 
taste,  and  has  neither  an  acid  nor  alkaline  reaction.  During  the  pro- 
cess of  digestion,  on  the  contrary,  it  is  found  to  be  distinctly  acid. 
Thus  free  muriatic  acid  was  detected  under  these  circumstances  by  Dr. 
Prout*  in  tlie  stomach  of  the  rabbit,  hare,  horse,  calf,  and  dog;  and 
he  has  discovered  the  same  acid  in  the  sour  matter  ejected  from  the 
stomach  of  persons  labouring  under  indigestion,  a fact  which  has  since 
been  confirmed  by  Mr.  Children.  Messrs.  Tiedemann  and  Gmelin  have 
observed  that  the  secretion  of  acid  commences  as  soon  as  the  stomach 
receives  the  stimulus  of  food  or  any  foreign  body.  This  effect  is  oc- 
casioned, for  example,  by  the  presence  of  flint  stones  or  other  indiges- 
tible matters;  but  it  is  produced  in  a still  greater  degree  by  substances 
of  a stimulating  nature.  According  to  their  observation,  the  acidity  is 
owing  to  the  secretion  of  free  muriatic  and  acetic  acids. 

The  gastric  juice  coagulates  milk,  and  it  is  generally  supposed  to 
produce  this  effect  quite  independently  of  the  presence  of  an  acid. 
According  to  the  experiments  of  Spallanzani  and  Stevens  it  is  highly 
antiseptic,  not  only  preventing  putrefaction,  but  rendering  meat  fresh 
after  it  is  tainted.  But  of  all  the  properties  of  the  gastric  juice,  its 
solvent  virtue  is  the  most  remarkable,  being  that  on  which  depends  the 
first  stage  of  the  process  of  digestion.  When  the  food  is  introduced 
into  the  stomach,  it  is  there  intimately  mixed  with  the  gastric  juice,  by 
the  agency  of  which  it  is  dissolved,  and  converted  into  a semi-fluid 
matter  called  chyme.  That  this  change  is  really  owing  to  the  solvent 
power  of  the  gastric  juice  fully  appears  from  the  researches  of  Spallan- 
zani, Reaumur,  and  Stevens.  In  the  experiments  of  Dr.  Stevens,  de- 
scribed in  his  Inaugural  Dissertation,  the  common  articles  of  food  were 
enclosed  in  hollow  silver  spheres  perforated  with  holes,  and  after  re- 
maining for  some  time  within  the  stomach,  completely  protected  from 
pressure  and  trituration,  the  alimentary  substances  were  found  to  have 
* been  entirely  dissolved.  A similar  effect  takes  place  when  nutritious 
matters,  out  of  the  body,  are  mixed  with  the  gastric  fluid,  and  the 
mixture  is  exposed  to  a temperature  of  100°  Fahr.  So  great,  indeed, 
is  the  solvent  power  of  this  fluid,  that  it  has  been  known,  to  dissolve  the 
coats  of  the  stomach  itself;  at  least  the  corrosions  of  this  organ,  some- 
times witnessed  in  persons  who  have  died  suddenly  while  fasting  and  in 
good  health,  were  ascribed  by  the  celebrated  physiologist,  John  Hun- 
ter, to  this  cause. 

No  department  of  chemical  physiology  is  more  obscure  than  that  of 
digestion.  There  appears  so  little  connexion  between  the  properties 
and  composition  of  the  gastric  juice,  that  physiologists  are  quite  at  a 
loss  in  wliat  way  to  account  for  its  solvent  power.  An  attempt  has 
lately  been  made  by  I'iedemann  and  Gmelin  to  explain  the  phenomena 
on  chemical  principles.  They  ascribe  its  solvent  action  to  the  dilute 
muriatic  and  acetic  acids,  which  they  maintain  to  be  always  secreted 
during  tlie  digestive  process,  and  which,  according  to  their  observa- 
tion, arc  capable  of  dissolving  most  or  all  of  tlie  substances  employed 
as  food.  They  have  not  shown,  however,  that  the  gastric  juiCe  in  -its 
neutral  state,  or  wlien  neutralized  by  an  alkali,  is  devoid  of  solvent  prop- 
erties, a circumstance  which  requires  investigation  before  a decisive 
ojiinion  can  be  formed  of  the  accuracy  of  their  view^s. 


rhilosophical  Transactions  for  1824. 


BILE. 


561 


Bile  and  Biliary  Concretions. 

The  bile  is  a yellow  or  greenish-yellow  coloured  fluid,  of  a peculiar 
sickening  odour,  and  of  a taste  at  first  sweet  and  then  bitter,  but  ex- 
ceedingly nauseous.  Its  consistence  is  variable,  being  sometimes  lim- 
pid, but  more  commonly  viscid  and  ropy.  It  is  rather  denser  than 
water,  and  may  be  mixed  with  that  liquid  in  every  proportion.  It  con- 
tains a minute  quantity  of  free  soda,  and  is,  therefore,  slightly  alkaline; 
but  owing  to  the  colour  of  the  bile  itself,  its  action  on  test  paper  is 
scarcely  visible.. 

Of  the  chemists  who  have  of  late  years  investigated  the  composition 
of  the  bile,  Thenard,  Berzelius,  and  Tiedemann  and  Gmelin  deserve 
particular  mention.  In  an  elaborate  essay  published  in  the  Memoires 
d^Jlrcudl,  vol.  i.  Thenard  endeavoured  to  show  that  the  bile  of  the  ox 
consists  of  three  distinct  animal  principles,  a yellow  colouring  matter, 
a species  of  resin,  and  a peculiar  substance,  to  which,  from  its  sweetish 
bitter  taste,  he  applied  the  name  of  picromel.  According  to  his  ana- 
l3^sis,  800  parts  of  bile  consist  of  water  700  parts,  resin  15,  picromel 
69,  yellow  matter  about  4,  soda  4,  phosphate  of  soda  2,  muriates  of 
soda  and  potassa  3.5,  sulphate  of  soda  0.8,  phosphate  of  lime  and  per- 
haps magnesia  1.2,  and  a trace  of  oxide  of  iron.  He  supposed  the  res- 
in to  be  combined  with  the  picromel  and  soda,  and  ascribes  its  solu- 
bility in  water  to  this  cause. 

Berzelius  takes  a totally  different  view  of  the  constitution  of  the  bile. 
He  denies  that  this  fluid  contains  any  resinous  principle,  and  regards 
the  yellow  matter,  resin,  and  picromel  of  Thenard,  as  one  and  the 
same  substance,  to  which  he  applies  the  name  of  biliary  matter,  (Med- 
ico-chir.  Trans,  vol.  hi.)  Tiedemann  and  Gmelin,  however,  in  their 
recent  work  on  digestion,  admit  the  existence  of  picromel  and  resin  as 
the  chief  constituents  of  bile;  although  it  appears  from  their  experi- 
ments that  the  substance  described  by  Thenard  as  picromel  was  not 
pure,  but  contained  a portion  of  resin.  According  to  the  analysis  of 
these  chemists,  tlie  bile  of  the  ox  is  a very  complex  fluid,  consisting  of 
the  following  ingredients: — water  to  the  extent  of  91.5  percent.;  a 
volatile  odoriferous  principle;  cholesterine;  resin;  asparagin;  picromel; 
yellow  colouring  matter;  a peculiar  azotized  substance  soluble  in  water 
and  alcohol;  a substance  which  is  soluble  in  hot  alcohol,  but  insoluble 
in  water,  supposed  to  be  gluten;  osmazome;  a principle  which  emits 
a urinous  odour  when  heated;  a substance  analogous  to  albumen  or 
caseous  matter;  and  mucus.  The  salts  of  the  bile  are  the  margarate, 
oleate,  acetate,  cholate^  bicarbonate,  phosphate,  sulphate,  and  mu- 
riate of  soda,  together  with  a little  phosphate  of  lime.  The  cholic  is 
a peculiar  animal  acid,  which  crystallizes  in  needles,  reddens  litmus 
paper,  and  is  distinguished  from  analogous  compounds  by  having  a 
sweet  taste. 

The  flaky  precipitate  which  is  occasioned  by  adding  acids  to  bile 
from  the  ox,  consists  of  several  substances.  At  first  the  caseous  and 
colouring  matters,  along  with  mucus,  are  thrown  down;  and,  after- 
wards, the  margaric  acid,  and  a compound  of  picromel  and  resin  with 
the  acid  employed,  are  precipitated.  When  acetate  of  lead  is  mixed 
with  this  fluid,  a white  precipitate  falls,  which  consists  of  oxide  of  lead 
combined  with  the  phosphoric,  sulphuric,  and  several  other  acids,  to- 
gether with  a small  quantity  of  the  compound  of  picromel  and  resin. 
On  adding  subacetate  of  lead  to  the  clear  liquid,  a copious  precipitate 
ensues,  consisting  chiefly  of  picromel,  resin,  and  oxide  of  lead.  If 
this  compound  be  suspended  in  water,  through  which  a current  of  sul- 


562 


BILE. 


phurettecl  hydrogen  gas  is  transmitted,  sulphuret  of  lead  and  the  resin 
subside,  while  the  picromel  remains  in  solution.  By  collecting  and 
drying  the  precipitate,  and  digesting  it  in  alcohol,  the  resin  is  dissolved, 
and  may  be  obtained  by  evaporation.  The  aqueous  solution,  when  evap- 
orated, yields  the  picromel  of  Thenard;  but  according  to  Tiedemann 
and  Gmelin,  it  still  contains  a portion  of  resin.  The  chief  difficulty, 
indeed,  of  preparing  pure  picromel  arises  from  its  tendency  to  dissolve 
the  resin;  and  the  only  mode  of  separation  is  by  throwing  them  down 
repeatedly  by  means  of  subacetate  of  lead.  By  this  process  the  affinity 
of  the  picromel  and  resin  for  each  other  is  gradually  lessened,  until  at 
length  the  separation  is  rendered  complete. 

Pure  picromel  occurs  in  opake  rounded  crystalline  particles,  is  solu- 
ble in  water  and  alcohol,  but  is  insoluble  in  ether.  Its  taste  is  sweet 
without  any  bitterness;  but  it  cannot  be  regarded  as  a species  of  sugar, 
because  a large  quantity  of  nitrogen  enters  into  its  composition.  Its 
aqueous  solution  is  not  precipitated  by  acids,  nor  by  acetate  and  sub- 
acetate of  lead.  When  digested  with  the  resin  of  bile,  a portion  of  the 
latter  is  dissolved,  and  a solution  is  obtained,  which  has  both  a bitter 
and  sweet  taste,  and  yields  a precipitate  with  subacetate  of  lead  and 
the  stronger  acids.  This  is  the  compound  which  causes  the  peculiar 
taste  of  the  bile. 

The  bile  of  the  human  subject  has  not  been  studied  so  minutely  as 
that  of  the  ox.  According  to  Thenard  it  consists,  besides  salts,  of  wa- 
ter, colouring  matter,  albumen,  and  a species  of  resin.  Chevallier  has 
since  detected  picromel,  and  Chevreul  cholesterine,  in  human  bile; 
and  both  these  discoveries  have  been  confirmed  by  the  observations  of 
Tiedemann  and  Gmelin. 

The  derangement  which  takes  place  in  the  system  when  the  secretion 
of  bile  or  its  passage  into  the  intestines  is  arrested,  is  a sufficient  indica- 
tion of  the  importance  of  this  fluid.  It  acts  as  a stimulus  to  the  intesti- 
nal canal  generally,  and  produces  on  the  chyme  some  peculiar  change, 
which  is  essential  to  its  conversion  into  chyle. 

Biliary  Calculi, — The  concretions  which  are  sometimes  formed  in  the 
human  gall-bladder  have  been  particularly  examined  by  Fourcroy,  The- 
nard, and  Chevreul.  Fourcroy  found  that  they  consist  chiefly  of  a pe- 
culiar fatty  matter,  resembling  spermaceti,  which  he  included  under 
the  name  of  adipocire,  (page  546);  and  the  experiments  of  Thenard 
tended  to  confirm  this  view.  According  to  Chevreul,  however,  biliary 
concretions  in  general  are  composed  of  the  yellow  colouring  matter  of 
the  bile  and  cholesterine,  the  latter  predominating,  and  being  some- 
times in  a state  of  purity;  and  I have  had  frequent  opportunities  of  sa- 
tisfying myself  of  the  accuracy  of  this  observation.  These  substances 
may  easily  be  separated  from  each  other  by  boiling  alcohol,  which  dis- 
solves the  cholesterine,  and  leaves  the  colouring  matter;  or  by  digestion 
in  dilute  potassa,  in  wliich  the  colouring  matter  is  dissolved,  wliile  the 
cliolesterine  is  insoluble. 

Gall-stones  sometimes  contain  a portion  of  inspissated  bile;  and  in 
some  rare  instances  tlie  cholesterine  is  entirely  wanting. 

The  concretions  found  in  the  gall-bladder  of  the  ox  consist  almost 
entirely  of  the  yellow  biliary  colouring  matter,  which,  from  the  beauty 
and  permanence  of  its  tint,  is  much  valued  by  painters.  This  substance 
is  readily  distinguished  by  its  yellow  or  brown  colour,  by  insolubility 
in  water  and  alcohol,  and  by  being  readily  dissolved  by  a solution  of 
potassa.  The  solution  has  at  lirst  a yellowish-brown  colour,  which 
gradually  ac([uires  a green  lint,  and  is  precipitated  in  green  flocks  by 
muriatic  acid.  According  to  the  observation  of  Tiedemann  and  Gmelin, 
the  colouiing  matter  is  influenced  by  the  presence  of  oxygen  gas. 


CHYLE. 


563 


The  yellowish  precipitate,  occasioned  by  adding  muriatic  acid  to  bile, 
absorbs  oxygen  by  exposure  to  the  air,  and  its  colour  changes  to 
green.  The  action  of  nitric  acid  is  still  more  remarkable.  By  suc- 
cessive additions  of  this  acid,  the  tint  of  the  colouring  matter  may 
be  converted  into  green,  blue,  violet,  and  red,  in  the  course  of  a few 
seconds. 

Erythrogen. — This  substance  was  discovered  in  1821  by  M.  Bizio  of 
Venice  in  a peculiar  fluid,  quite  different  from  bile,  which  was  found 
in  the  gall-bladder  of  a person  who  had  died  of  jaundice.  It  is  of  a 
green  colour,  transparent,  tasteless,  and  of  the  odour  of  putrid  fish. 
It  is  unctuous  to  the  touch,  may  be  scratched  or  cut  with  facility,  and 
has  a specific  gravity  of  1.57.  It  does  not  affect  the  colour  of  litmus 
or  turmeric  paper.  At  110®  F.  it  fuses,  having  the  appearance  of  oil, 
and  crystallizes  when  slowly  cooled;  and  at  122®  F.  it  rises  in  the  form 
of  vapour.  It  is  insoluble  in  water  and  ether,  but  is  dissolved  readily 
by  hot  alcohol;  and  the  solution,  by  partial  evaporation  and  cooling, 
yields  crystals  in  the  form  of  rhomboidal  parallelopipedons. 

When  erythrogen  is  put  into  nitric  acid  of  the  temperature  of  about 
120®  or  140®  Fahr.  its  green  tint  disappears,  effervescence,  owing  to 
the  escape  of  oxygen  gas,  ensues,  and  the  solution  acquires  a deep 
purple  colour.  A similar  phenomenon  takes  place,  with  disengagement 
of  hydrogen  gas,  when  erythrogen  is  digested  in  a solution  of  ammo- 
nia; and  when  volatilized  in  the  open  air,  it  yields  a purple-coloured 
vapour.  M.  Bizio  is  of  opinion  that  the  erythrogen,  under  all  these 
circumstances,  unites  with  nitrogen,  and  that  the  product  is  identical 
with  the  colouring  matter  of  the  blood.  The  production  of  the  red 
compound  is  characteristic  with  erythrogen,  and  suggested  the  name 
by  which  this  substance  is  designated.  ruber.)  (Journal  of 

Science,  vol.  xvi.) 

Erythrogen  has  not  been  discovered  either  in  bile  or  in  any  of  the 
animal  fluids. 


SECTION  III. 

CHYLE.  MILK.  EGGS. 

Chyle. — The  fluid  absorbed  by  the  lacteal  vessels  from  the  small  In- 
testines during  the  process  of  digestion  is  known  by  the  name  of  chyle^ 
Its  appearance  varies  in  different  animals;  but  as  collected  from  the 
thoracic  duct  of  a mammiferous  animal  three  or  four  hours  after  a meal, 
it  is  a white  opake  fluid  like  milk,  having  a sweetish  and  slightly  saline 
taste.  . In  a few  minutes  after  removal  from  the  duct  it  becomes  solid, 
and  in  the  course  of  twenty-four  hours  separates  into  a firm  coagulum, 
and  a limpid  liquid,  which  may  be  called  the  serum  of  the  chyle.  The 
coagulum  is  an  opake  white  substance,  of  a slightly  pink  hue,  insolu- 
ble in  water,  but  soluble  easily  in  the  alkalies  and  alkaline  carbonates. 
Vauquelin*  regards  it  as  fibrin  in  an  imperfect  state,  or  as  intermediate 
between  that  principle  and  albumen;  but  Mr.  Brandef  considers  it 
more  closely  allied  to  the  caseous  matter  of  milk  than  to  fibrin. 


• An.  de  Ch.  vol.  xxxi. 


\ Philos.  Trans,  for  1812. 


564 


MILK. 


The  serum  of  chyle  is  rendered  turbid  by  heat,  and  a few  flakes  of 
albumen  are  deposited;  but  when  boiled  after  being*  mixed  with  acetic 
acid,  a copious  precipitation  ensues.  To  this  substance,  which  thus 
differs  slightly  from  albumen.  Dr.  Prout  has  applied  the  name  of  in- 
cipient albumen.  The  same  chemist  has  made  a comparative  analysis  of 
the  chyle  of  two  dogs,  one  of  which  was  fed  on  animal  and  the  other  on 
vegetable  substances,  and  the  result  of  his  inquiry  is  as  follows:— (An- 
nals of  Philos,  vol.  xiii.  p.  25.) 


Water,  .... 

Vegetable 

Food, 

93,6 

Animal 

Food, 

89.2 

Fibrin,  .... 

0.6 

0.8 

Incipient  albumen.? 

4.6 

4.7 

Albumen,  with  a little  red  colouring  matter. 

0.4 

4.6 

Sugar  of  milk?  .... 

. a trace 

Oily  matter,  .... 

. a trace 

a trace 

Saline  matters,  .... 

0.8 

0.7 

100.0 

100.0 

Milk. — This  well-known  fluid,  secreted  by  the  females  of  the  class 
mammalia  for  the  nourishment  of  their  young,  consists  of  three  distinct 
parts,  the  cream,  curd,  and  whey,  into  which  by  repose  it  spontaneously 
separates.  The  cream,  which  collects  upon  its  surface,  is  an  unctuous 
yellowish-white  opake  fluid,  of  an  agreeable  flavour.  According  to 
Berzelius  100  parts  of  cream,  of  specific  gravity  1.0244,  consist  of  but- 
ter 4.5,  caseous  matter  3.5,  and  whey  92.  By  agitation,  as  in  the  pro- 
cess of  churning,  the  butter  assumes  the  solid  form,  and  is  thus  obtained 
in  a separate  state.  During  the  operation  there  is  an  increase  of  tem- 
perature amounting  to  about  three  or  four  degrees,  oxygen  gas  is  absorb- 
ed, and  an  acid  is  generated;  but  the  absorption  of  oxygen  cannot  be  an 
essential  part  of  the  process,  since  butter  may  be  obtained  by  churning, 
even  when  atmospheric  air  is  entirely  excluded. 

After  the  cream  has  separated  spontaneously,  the  milk  soon  becomes 
sour,  and  gradually  separates  into  a solid  coagulum  called  curd,  and  a 
limpid  fluid  which  is  whey.  The  coagulation  is  occasioned  by  free 
acetic  acid,  and  it  may  be  produced  at  pleasure  either  by  adding  a free 
acid,  or  by  means  of  the  fluid  known  by  the  name  of  rennet,  which  is 
made  by  infusing  the  inner  coat  of  a calPs  stomach  in  hot  water.  When 
an  acid  is  employed,  the  curd  is  found  to  contain  some  of  it  in  combi- 
nation, and  may,  therefore,  be  regarded  as  an  insoluble  compound  of  an 
acid  with  the  caseous  matter  of  milk;  but  nothing  certain  is  known  re- 
specting the  mode  by  which  the  gastric  fluid,  the  active  principle  of 
rennet,  produces  its  effect. 

The  curd  of  skim  milk,  made  by  means  of  rennet,  and  separated  from 
the  whey  by  washing  with  water,  is  generally  considered  to  be  caseous 
matter,  or  the  basis  of  cheese  in  a state  of  purity.  In  this  state,  it  is  a 
white  insipid,  inodorous  substance,  insoluble  in  water,  but  readily  solu- 
ble in  the  alkalies,  especially  in  ammonia.  By  alcohol  it  is  converted, 
like  albumen  and  fibrin,  into  an  adipocirous  substance  of  a fetid  odour; 
and,  like  the  same  substances,  it  may  be  dissolved  by  a sufficient  quan- 
tity of  acetic  acid. 

In  a recent  essay  Braconnot  maintains  that  caseum,  in  its  coagulated 
state,  is  always  combined  with  some  foreign  substance,  generally  an 
earthy  salt  or  an  acid,  on  which  its  insolubility  depends;  and  that  when 
pure,  it  is  soluble  both  in  hot  and  cold  water,  is  not  coagulated  either 
by  heat  or  air,  and  when  concentrated  becomes  viscid  like  mucilage, 


MILK. 


565 


bein^  so  highly  adhesive  that  it  may  be  usefully  employed  as  a cement. 
Soluble  caseum  may  be  obtained  from  curd,  spontaneously  formed  in 
milk  as  it  becomes  sour,  in  which  state  it  is  combined  with  acetic  acid, 
by  washing  the  curd,  and  digesting  it  with  water,  to  which  so  much 
carbonate  of  potassa  is  added,  as  is  sufficient  to  unite  with  the  acetic 
acid.  Acetate  of  potassa  is  generated  with  disengagement  of  carbonic 
acid,  and  the  caseum  is  dissolved.  In  order  to  separate  it  from  the  ac- 
companying acetate,  the  solut;ion,  after  separating  the  cream  which  col- 
lects on  its  surface  by  repose,  is  mixed  with  a little  sulphuric  acid;  and 
the  precipitated  sulphate  of  caseum,  carefully  washed,  is  dissolved  in 
water  by  means  of  the  smallest  possible  quantity  of  carbonate  of  potassa. 
If  alcohol  is  then  freely  employed,  the  caseum  itself  is  thrown  down; 
but  if  the  solution  is  mixed  with  about  its  own  volume  of  alcohol,  a de- 
posite  of  sulphate  of  potassa  with  some  curd  and  cream  takes  place,  and 
the  filtered  liquor  contains  caseum  in  a state  of  great  purity. 

Caseum,  as  thus  prepared,  still  contains  a little  potassa;  but  Bracon- 
not  considers  its  solubility  as  not  dependent  on  the  presence  of  the  al- 
kali. When  evaporated  to  dryness,  it  forms  a diaphanous  mass  which 
strongly  resembles  gum  arabic,  may  be  long  preserved  without  change, 
and  still  retains  its  solubility  in  water.  It  has  an  acid  reaction,  and  com- 
bines readily  with  the  alkalies,  forming  very  soffible  compounds.  With 
other  metallic  oxides,  as  well  as  with  their  salts,  it  forms  sparingly  sol- 
uble compounds.  It  affinity  for  acids  is  equally  marked,  and  it  is  pre- 
cipitated by  all  the  mineral  acids,  except  the  phosphoric.  Braconnot 
conceives  that  soluble  caseum  may  be  advantageously  employed  in  a 
commercial  point  of  view.  Its  adhesiveness  fits  it. as  a cement  for  glass, 
porcelain,  wood,  and  paper.  Its  solution,  flavoured  with  sugar  and 
aromatics,  may  be  serviceable  to  convalescents  as  an  article  of  food.  It 
may  be  taken  in  its  dry  state  in  long  voyages,  forming  together  with 
water,  butter,  and  sugar,  an  excellent  substitute  for  milk.  (An.  de 
Ch.  et  de  Ph.  xliii.  337.) 

Caseum  is  commonly  considered  to  have  a close  resemblance  to  ani- 
mal albumen,  and  the  analogy  is  supported  by  its  being  coagulated  by 
acids.  In  other  respects,  if  the  remarks  of  Braconnot  prove  correct,  it 
resembles  gum  rather  than  albumen.  It  differs  from  both,  however,  in 
the  nature  of  the  spontaneous  changes  to  which  it  is  subject;  for  when 
kept  in  a moist  state,  it  undergoes  a species  of  fermentation  precisely 
analogous  to  that  experienced  by  gluten  under  the  same  circumstances. 
(Page  515.)  The  accuracy  of  the  remarks  made  by  Proust  on  this  sut)- 
ject  has  been  questioned  by  Braconnot.  (Brewster’s  Journal,  viii.  369.) 
The  latter  states  that,  in  his  experiments,  the  curd  from  spontaneously 
coagulated  skim  milk,  covered  with  water,  and  kept  at  a temperature 
of  about  75®  F.,  underwent  complete  putrefaction  in  the  space  of  a 
month.  The  soluble  parts  were  then  filtered,  and  by  evaporation  yield- 
ed a product  of  a very  fetid  odour,  acetate  of  ammonia,  and  acetic  of 
acid.  The  residue,  after  being  reduced  to  the  consistence  of  syrup, 
concreted  on  cooling  into  a granulated  reddish  mass  like  honey,  but  of 
a saline  bitter  taste,  and  was  separated  by  the  action  of  alcohol  into  two 
parts,  one  soluble  and  the  other  insoluble.  The  former  is  the  caseate 
of  ammonia  of  Proust,  and  the  latter  is  his  caseous  oxide. 

In  order  to  obtain  caseous  oxide  quite  pure,  it  must  be  washed  care- 
fully with  alcohol,  treated  with  animal  charcoal,  and  dissolved  repeated- 
ly in  boiling  water,  from  which  it  is  separated  by  evaporation.  In  this 
state  it  is  a beautiful  white  powder,  inodorous,  and  of  a slight  bitter  taste. 
It  is  heavier  than  water,  and  soluble  in  14  parts  of  that  fluid  at  72^  F. 
On  allowing  the  solution  to  evaporate  spontaneously,  it  crystallizes 


566 


EGGS. 


either  in  the  form  of  elegant  dendritic  ramifications,  or  in  rings  com- 
posed of  delicate  acicular  crystals  of  a silky  lustre. 

Caseous  oxide  is  almost  entirely  insoluble  even  in  boiling  alcohol. 

Its  aqueous  solution  yields  a white  flaky  precipitate  with  infusion  of 
gall-nuts,  soluble  in  excess  of  the  precipitant;  and  subacetate  of  lead 
likewise  throws  down  a white  precipitate.  The  crystals,  if  suddenly 
heated,  volatilize  without  change;  but  if  the  heat  is  gradually  raised, 
decomposition  ensues,  and  a large  quantity  of  carbonate  and  hydrosul- 
phate of  ammonia  is  generated.  When  strongly  heated  in  open  vessels 
it  takes  fire,  and  burns  with  flame  without  residue. 

The  composition  of  caseous  oxide  has  not  been  determined;  but  from 
the  facility  with  which  its  aqueous  solution  putrefies,  Braconnot  regards 
it  as  a highly  azotized  animal  principle.  It  contains  sulphur  also.  He 
believes  it  to  be  a product  of  the  putrefaction  of  all  animal  substances, 
and  proposes  for  it  the  name  of  aposepediney  from  and  (n^Tre^m, 
result  of  putrefaction,  as  more  appropriate  than  caseous  oxide. 

Braconnot  denies  the  existence  of  caseic  acid.  Proust’s  caseate  of 
ammonia  consist  of  various  substances,  such  as  free  acetic  acid,  aposep- 
edine,  animal  matter,  resin,  several  salts,  and  a yellow  pungent  oil, 
which  is  the  chief  cause  of  the  pungency  of  old  cheese. 

From  750  parts  of  curd  completely  putrefied  were  obtained  36  of  dry 
matter  insoluble  in  water.  These  consisted  of  14.92  of  margarate  of 
lime,  2.57  of  margaric  acid,  and  18.51  of  oleic  acid,  retaining  margaric 
acid  and  a brown  animal  matter. 

According  to  the  analysis  of  Gay-Lussac  and  Thenard,  100  parts  of 
the  caseous  matter  are  composed  of  carbon  59.781,  hydrogen  7.429, 
oxygen  11.409,  and  nitrogen  21.381.  It  yields  by  incineration  a white 
ash  amounting  to  6.5  per  cent,  of  its  weight,  the  greater  part  of  which 
is  phosphate  of  lime,  a circumstance  which  renders  caseous  matter  an 
article  of  food  peculiarly  proper  for  young  animals. 

Milk  carefully  deprived  of  its  cream  has  a specific  gravity  of  about 
1.033;  and  1000  parts  of  it,  according  to  Berzelius,  are  thus  constitut- 
ed:— water  928.75,  caseous  matter  with  a trace  of  butter  28;  sugar  of 
milk  35;  muriate  and  phosphate  of  potassa  L95;  lactic  (acetic)  acid, 
acetate  of  potassa,  and  a trace  of  lactate  of  iron  6;  and  earthy  phos- 
phates 0.30.  Subtracting  the  caseous  matter,  the  remaining  substances 
constitute  whey. 

Eggs. — The  composition  of  the  recent  egg  and  the  changes  which  it 
undergoes  during  the  process  of  incubation,  have  been  ably  investigat- 
ed by  Dr.  Prout.  (Phil.  Trans,  for  1822.)  New-laid  eggs  are  rather 
heavier  than  water;  but  they  become  lighter  after  a time,  in  conse- 
quence of  water  evaporating  through  the  pores  of  the  shell,  and  air 
being  substituted  for  it.  An  egg  of  ordinary  size  yields  to  boiling  water 
about  three-tenths  of  a grain  of  saline  matter,  consisting  of  the  sul- 
phates, carbonates,  and  phosphates  of  lime  and  magnesia,  together 
with  animal  matter  and  a little  free  alkali. 

Of  an  egg  which  weighs  1000  grains,  the  shell  constitutes  106.9,  the 
white  604.2,  and  the  yelk  288.9  grains.  The  shell  contains  about  two 
per  cent,  of  animal  matter,  one  per  cent,  of  the  phosphates  of  lime 
and  magnesia,  and  the  residue  is  carbonate  of  lime  with  a little  carbo- 
nate of  magnesia. 

When  the  yelk  of  a hard  boiled  egg  is  repeatedly  digested  in  alcohol 
of  specific  gravity  0.807,  until  that  fluid  comes  off  colourless,  there  re- 
mains a white  pulvcnilcnt  residuum,  possessed  of  many  of  the  proper- 
ties of  albumen,  but  distinguished  from  that  principle  by  containing  a 
large  quantity  of  pho.sphorus  in  some  unknown  state  of  combination. 
The  alcoholic  solution  is  of  a deep  yellow  colour,  and  on  cooling  de- 


LIQUIDS  OF  SEROUS  AND  MUCOUS  SURFACES.  567 


posltes  crystals  of  a sebaceous  matter,  and  a portion  of  yellow  semi- 
fluid oil.  On  distilling  off  the  alcohol,  the  oil  is  left  in  a separate  state. 
When  the  yelk  is  dried  and  burned,  the  phosphorus  is  converted  into 
phosphoric  acid,  which  melting  into  a glass  upon  the  surface  of  the 
charcoal,  protects  it  from  complete  combustion.  In  the  white  of  the 
egg,  which  consists  chiefly  of  albumen,  sulphur  is  present. 

The  obvious  use  of  the  phosphorus  contained  in  the  yelk  is  to  supply 
phosphoric  acid  for  forming  the  bones  of  the  chick;  but  Dr.  Prout  was 
unable  to  discover  any  source  of  the  lime  with  which  that  acid  unites  to 
form  the  earthy  part  of  bone.  It  cannot  be  discovered  in  the  soft  parts 
of  the  egg;  and  hitherto  no  vascular  connexion  has  been  traced  between 
the  chick  and  its  shell. 


SECTION  IV, 

ON  THE  LIQUIDS  OF  SEROUS  AND  MUCOUS  SURFACES,  &c., 
AND  ON  PURULENT  MATTER. 

The  surface  of  the  cellular  membrane  is  moistened  with  a peculiar 
limpid  transparent  fluid  called  lymph,  which  is  in  very  small  quantity 
during  health,  but  collects  abundantly  in  some  dropsical  affections. 
Mr.  Brande  collected  it  from  the  thoracic  duct  of  an  animal  which  had 
been  kept  without  food  for  twenty-four  hours.  Its  chief  constituent  is 
water,  besides  which  it  contains  muriate  of  soda  and  albumen,  the  latter 
being  in  such  minute  quantity  that  it  is  coagulated  only  by  the  action  of 
galvanism.  Lymph  does  not  affect  the  colour  of  test  paper;  but  when 
evaporated  to  dryness,  the  residue  gives  a green  tint  to  the  syrup  of 
violets. 

The  fluid  secreted  by  serous  membranes  in  general,  such  as  the  peri- 
cardium, pleura,  and  peritoneum,  is  very  similar  to  lymph.  Accord- 
ing to  Dr.  Bostock,  100  parts  of  the  liquid  of  the  pericardium  consist 
of  water  92  parts,  albumen  5.5,  mucus  2,  and  muriate  of  soda  0.5. 
The  serous  fluid  exhaled  within  the  ventricles  of  the  brain  in  hydroce- 
phalus internus  is  composed,  in  1000  parts,  of  water  988.3,  albumen 
1.66,  muriate  of  potassa  and  soda  7.09,  lactate  (acetate)  of  soda  and 
its  animal  matter  2.32,  soda  0.28,  and  animal  matter  soluble  only  in 
water,  with  a trace  of  phosphates,  0.35.  (Berzelius  in  Medico-chir. 
Trans,  vol.  hi.  p.  252.) 

The  liquor  of  the  amnios,  or  the  fluid  contained  in  the  membrane 
which  foetus  in  utero,  differs  in  different  animals.  That 

of  the  human  female  was  found  by  Vauquelin  and  Bunlva  to  contain  a 
small  quantity  of  albumen,  soda,  muriate  of  soda,  phosphate  and  car- 
bonate of  lime,  and  a matter  like  curd  which  gives  it  a milky  appear- 
ance. That  of  the  cow,  according  to  the  same  authority,  contains  the 
substance  already  described  under  the  name  of  amniotic  acid;  but  sev- 
eral other  chemists,  such  as  Prout,  Dulong,  Labillardiere,  and  Lassaigne, 
have  been  unable  to  detect  it.  Lassaigne  states,  that  this  acid  exists  in 
the  fluid  of  the  allantois  of  the  cow.  Dr.  Prout  found  some  sugar  of 
milk  in  the  amnios  of  a woman.  (Ann.  of  Phil.  v.  417.) 

Humours  of  the  Eye. — The  aqueous  and  vitreous  humours  of  the  eye 
contain  rather  more  than  80  per  cent,  of  water.  The  other  constitu- 


568  LIQUIDS  OF  SEROUS  AND  MUCOUS  SURFACES. 


ents  are  a small  quantity  of  albumen,  muriate  and  acetate  of  soda,  pure 
soda,  though  scarcely  sufficient  to  affect  the  colour  of  test  paper,  and 
animal  matter  soluble  only  in  water,  but  which  is  not  gelatin.  (Berze- 
lius.) The  crystalline  lens,  besides  the  usual  salts,  contains  36  per 
cent,  of  a peculiar  animal  matter,  very  analogous  to  albumen  if  not 
identical  with  it.  In  cold  water  it  is  soluble,  but  is  coagulated  by  boil- 
ing. The  coagulum,  according  to  Berzelius,  has  all  the  properties  of 
the  colouring  matter  of  the  blood  excepting  its  colour. 

The  tears  are  limpid  and  of  a saline  taste,  dissolve  freely  in  water, 
and,  owing  to  the  presence  of  free  soda,  communicate  a green  tint  to 
the  blue  infusion  of  violets.  Their  chief  salts  are  the  muriate  and  phos- 
phate of  soda.  According  to  Fourcroy  and  Vauquelin  the  animal  mat- 
ter of  the  tears  is  mucus;  but  it  is  more  probably  either  albumen,  or 
some  analogous  principle.  Its  precise  nature  has  not,  however,  been 
satisfactorily  determined. 

Mucus. — The  term  mucus  has  been  employed  in  very  different  signi- 
fications. Dr.  Bostock  applies  it  to  a peculiar  animal  matter  which  is 
soluble  both  in  hot  and  cold  water,  is  not  precipitated  by  corrosive 
sublimate  or  solution  of  tannin,  is  not  capable  of  forming  a jelly,  and 
which  yields  a precipitate  with  subacetate  of  lead.  The  existence  of 
this  principle  has  not,  however,  been  fully  established;  for  the  pre- 
sence of  muriatic  and  phosphoric  acids,  the  latter  of  which  is  frequent- 
ly contained  in  animal  fluids,  and  the  former  scarcely  ever  absent,  suf- 
ficiently accounts  for  the  precipitates  occasioned  in  them  by  the  salts  of 
lead  or  silver.  But  even  supposing  the  opinion  of  Dr.  Bostock  to  be 
correct,  it  would  be  advisable  to  give  some  new  name  to  his  princi- 
ple, and  apply  the  term  mucus  solely  to  the  fluid  secreted  by  mucous 
surfaces. 

The  properties  of  mucus  vary  somewhat  according  to  the  source  from 
which  it  is  derived;  but  its  leading  characters  are  in  all  cases  the  same, 
and  ai’e  best  exemplified  in  mucus  from  the  nostrils.  Nasal  mucus,  ac- 
cording to  Berzelius,  has  the  following  properties.  Immersed  in  water, 
it  imbibes  so  much  of  that  fluid  as  to  become  transparent,  with  the  ex- 
ception of  a few  particles  which  remain  opake.  When  dried  on  blot- 
ting paper,  it  loses  its  transparency,  but  again  acquires  it  when  moist- 
ened. It  is  not  coagulated  or  rendered  horny  by  being  boiled  in  water; 
but  as  soon  as  the  ebullition  has  ceased,  it  collects  unchanged  at  the 
bottom  of  the  vessel.  It  is  dissolved  by  dilute  sulphuric  acid.  Nitric 
acid  at  first  coagulates  it;  but  by  continued  digestion,  the  mucus  grad- 
ually softens  and  is  finally  dissolved,  forming  a clear  yellow  liquid. 
Acetic  acid  hardens  mucus,  and  does  not  dissolve  it  even  at  a boiling 
temperature.  Pure  potassa  at  first  renders  it  more  viscid,  but  after* 
wards  dissolves  it.  By  tannin  mucus  is  coagulated,  both  when  soften- 
ed by  the  absorption  of  water,  and  when  dissolved  either  in  an  acid  or 
an  alkali. 

Fus. — Purulent  matter  is  the  fluid  secreted  by  an  inflamed  and  ul- 
cerated surface.  Its  properties  vary  according  to  the  nature  of  the  sore 
from  which  it  is  discharged.  The  purulent  matter  formed  by  an  ill- 
conditioned  ulcer  is  a thin,  transparent,  acrid,  fetid  ichor;  whereas  a 
healing  sore  in  a sound  constitution  yields  a yellowish-white  coloured 
liquid,  of  the  consistence  of  cream,  which  is  described  as  bland,  opake, 
and  inodorous.  This  is  termed  healthy  pus,  and  is  possessed  of  the 
following  properties.  Though  it  appears  homogeneous  to  the  naked 
eye,  when  examined  by  the  microscope  it  is  found  to  consist  of  minute 
globules  floating  in  a transparent  liquid.  Its  specific  gravity  is  about 
1.03.  It  is  insoluble  in  water;  and  is  thickened,  but  not  dissolved  by 
alcohol.  AVhen  recent  it  does  not  affect  the  colour  of  test  paper;  but 


URINE. 


569 


by  exposure  to  the  air  it  becomes  acid.  The  dilute  acids  have  little 
effect  upon  it;  but  strong*  sulphuric,  nitric,  and  muriatic  acids  dissolve 
it,  and  the  pus  is  thrown  down  by  dilution  with  water.  Ammonia  re- 
duces it  to  a transparent  jelly,  and  gradually  dissolves  a considerable 
portion  of  it.  With  the  fixed  alkalies,  it  forms  a whitish  ropy  fluid, 
which  is  decomposed  by  water. 

The  composition  of  pus  l]ias  not  been  ascertained  with  precision;  but 
its  characteristic  ingredient  is  more  closely  allied  to  albumen  than  the 
other  animal  principles. 

Several  attempts  have  been  made  to  discover  a chemical  test  for  dis- 
tinguishing pus  from  mucus.  When  these  fluids  are  in  their  natural 
state,  the  appearance  of  each  is  so  characteristic  that  the  distinction 
cannot  be  attended  with  any  difficulty;  but  on  the  contrary,  when  a 
mucous  surface  is  inflamed,  its  secretion  becomes  opake,  and,  as  some- 
times happens  in  some  pulmonary  diseases,  acquires  more  or  less  of 
the  aspect  of  pus.  Mr.  Charles  Darwin,  who  examined  this  subject, 
pointed  out  three  grounds  of  distinction  between  them.  1.  When  the 
solution  of  these  liquids  in  sulphuric  acid  is  diluted,  the  pus  subsides  to 
the  bottom,  and  the  mucus  remains  suspended  in  the  water.  2.  When 
pus  and  catarrhal  mucus  are  diffused  through  water,  the  former  sinks, 
and  the  latter  floats.  3.  Pus  is  precipitated  from  its  solution  in  potassa 
by  water,  while  the  solution  of  mucus  is  not  decomposed  by  similar 
treatment.  Dr.  Thomson,  in  his  system  of  chemistry,  has  given  the 
following  test  on  the  authority  of  Grasmeyer.  The  substance  to  be  ex- 
amined, after  being  triturated  with  its  own  weight  of  water,  is  mixed 
with  an  equal  quantity  of  a saturated  solution  of  carbonate  of  potassa. 
If  it  contain  pus,  a transparent  jelly  forms  in  a few  hours;  but  this  does 
not  happen  if  mucus  only  is  present.  Dr.  Young,  in  his  work  on  Con- 
sumptive Diseases,  has  given  a very  elegant  character  for  distinguishing 
pus,  founded  on  its  optical  properties.  But  the  practical  utility  of  tests 
of  any  kind  is  rendered  very  questionable  by  the  fact  that  inflamed 
mucous  membranes  may  secrete  genuine  pus  without  breach  of  sur- 
face, and  that  the  natural  passes  into  purulent  secretion  by  insensible 
shades. 

Sweat — Watery  vapour  is  continually  passing  off  by  the  skin  in 
the  form  of  insensible  perspiration;  but  when  the  external  heat  is  con- 
siderable, or  violent  bodily  exercise  is  taken,  drops  of  fluid  collect 
upon  the  surface,  and  constitute  what  is  called  sweat.  This  fluid  con- 
sists chiefly  of  water;  but  it  contains  some  muriate  of  soda  and  free 
acetic  acid,  in  consequence  of  which  it  has  a saline  taste  and  an  acid 
reaction. 


SECTION  V. 

ON  THE  URINE  AND  URINARY  CONCRETIONS. 

The  urine  differs  from  most  of  the  animal  fluids  which  have  been 
described  by  not  serving  any  ulterior  purpose  in  the  animal  economy. 
It  is  merely  an  excretion  designed  for  ejecting  from  the  system  sub- 
stances, which,  by  their  accumulation  within  the  body,  would  speedily 


570 


URINE. 


prove  fatal  to  health  and  life.  The  sole  office  of  the  kidneys,  indeed, 
appears  to  consist  in  separating  from  the  blood  the  superfluous  matters 
that  are  not  required  or  adapted  for  nutrition,  or  which  have  already 
formed  part  of  the  body,  and  been  removed  by  absorption.  The  sub- 
stances  which  in  particular  pass  off  by  this  organ  are  nitrogen,  in  the 
form  of  highly  azotized  products,  and  various  saline  and  earthy  com- 
pounds. This  sufficiently  accounts  for  the  great  diversity  of  different 
substances  contained  in  the  urine. 

The  quantity  of  the  urine  is  affected  by  various  causes,  especially  by 
the  nature  and  quantity  of  the  liquids  received  into  the  stomach;  but 
on  an  average  a healthy  person  voids  between  thirty  and  forty  ounces 
daily.  The  quality  of  this  fluid  is  likewise  influenced  by  the  same  cir- 
cumstances, being  sometimes  in  a very  dilute  state,  and  at  others  high- 
ly concentrated.  The  urine  voided  in  the  morning  by  a person  who 
has  fed  heartily,  and  taken  no  more  fluids  than  is  sufficient  for  satisfying 
thirst,  may  be  regarded  as  affording  the  best  specimen  of  natural  heal- 
thy urine. 

The  urine  in  this  state  is  a transparent  limpid  fluid  of  an  amber  col- 
our, having  a saline  taste,  and  while  warm  emitting  an  odour  which  is 
slightly  aromatic,  and  not  at  all  disagreeable.  Its  specific  gravity  in  its 
most  concentrated  form  is  about  1.030.  It  gives  a red  tint  to  litmus 
paper,  a circumstance  which  indicates  the  presence  either  of  a free 
acid  or  of  a supersalt.  Though  at  first  quite  transparent,  an  insoluble 
matter  is  deposited  on  standing;  so  that  urine,  voided  at  night,  is  found 
to  have  a light  cloud  floating  in  it  by  the  following  morning.  This  sub- 
stance consists  in  part  of  mucus  from  the  urinary  passages,  and  partly 
of  superurate  of  ammonia,  which  is  much  more  soluble  in  warm  than  in 
cold  water. 

I'he  urine  is  very  prone  to  spontaneous  decomposition.  When  kept 
for  two  or  three  days  it  acquires  a strong  urinous  smell;  and  as  the  pu- 
trefaction proceeds,  the  disagreeable  odour  increases,  until  at  length  it 
becomes  exceedingly  offensive.  As  soon  as  thes6  changes  commence, 
the  urine  ceases  to  have  an  acid  reaction,  and  the  earthy  phosphates 
are  deposited.  In  a short  time,  a free  alkali  makes  its  appearance, 
and  a large  quantity  of  carbonate  of  ammonia  is  gradually  gener- 
ated. Similar  changes  may  be  produced  in  recent  urine  by  con- 
tinued boiling.  In  both  cases  the  phenomena  are  owing  to  the  decom- 
position of  urea,  which  is  almost  entirely  resolved  into  carbonate  of 
ammonia. 

The  composition  of  the  urine  has  been  studied  by  several  chemists, 
but  the  most  recent  and  elaborate  analysis  of  this  fluid  is  by  Berzelius. 
According  to  the  researches  of  this  indefatigable  chemist,  1000  parts  of 
urine  are  composed  of 


Water,  ------ 

Urea,  ------ 

Uric  acid,  - - - - • 

Free  lactic  acid,  lactate  of  ammonia,  and  animal  matter  not 
separable  from  them,  - - - - 

Mucus  of  the  bladder,  . - - - 

Sulphate  of  potassa,  - - - - 

Sulphate  of  soda,  . - - - 

phosphate  of  soda,  - . - - 

Pliosphate  of  ammonia,  , . - - 

Muriate  of  soda,  . - . - 

Muriate  of  ammonia,  - - - 

Earthy  matters,  with  a trace  of  fluate  of  lime, 

Siliceous  earth,  - - . - - 


933.00 

30.10 

1.00 

17.14 

0.32 

3.71 

3.T6 

2.94 

1.65 

4.45 

1.50 

1.00 

0.03 


URINE. 


571 


Besides  the  ingredients  included  in  the  preceding  list,  the  urine  con- 
tains several  other  substances  in  small  quantity.  From  the  property 
this  fluid  possesses  of  blackening  silver  vessels  in  which  it  is  evaporat- 
ed, owing  to  the  formation  of  sulphuret  of  silver,  Proust  inferred  the 
presence  of  unoxidized  sulphur;  and  Dr.  Front,  from  the  odour  of  phos- 
phuretted  hydrogen,  which  he  thinks  he  has  perceived  in  putrefying 
urine,  suspects  that  phosphorus  is  likewise  present.  The  urine  also 
contains  a peculiar  yellow  colouring  matter  which  has  not  hitherto  been 
obtained  in  a separate  state.  From  the  precipitate  occasioned  in  urine 
by  the  infusion  of  gall-nuts,  the  presence  of  gelatin  has  been  inferred; 
but  this  effect  appears  owing  to  the  presence  not  of  gelatin  but  of  a 
small  portion  of  albumen. 

According  to  Scheele,  the  urine  of  infants  sometimes  contains  ben- 
zoic acid,  a compound  which,  when  present,  may  be  easily  procured 
by  evaporating  the  urine  nearly  to  the  consistence  of  syrup,  and  adding 
muriatic  acid.  The  precipitate,  consisting  of  uric  and  benzoic  adds, 
is  digested  in  alcohol,  which  dissolves  the  benzoic  acid. 

Notwithstanding  the  high  authority  of  Berzelius,  it  is  very  doubtful 
if  any  free  acid  be  present  in  healthy  urine.  Dr.  Prout,  with  every 
appearance  of  justice,  maintains  that  the  acidity  of  recent  urine  is  oc- 
casioned by  supersalts,  and  not  by  uncombined  acid.  He  is  of  opinion 
that  the  acid  reaction  is  chiefly,  if  not  wholly,  to  be  ascribed  to  the 
superphosphate  of  lime  and  superurate  of  ammonia,  salts  which  he 
finds  may  co-exist  in  a liquid  without  mutual  decomposition.  A very 
strong  argument,  which  to  me  indeed  appears  conclusive,  in  favour  of 
this  view,  is  derived  from  the  fact,  that  on  adding  muriatic  acid  to  re- 
cent urine,  minute  crystals  of  uric  acid  are  gradually  deposited,  as 
always  happens  when  this  acid  subsides  slowly  from  a state  of  solu- 
tion; but,  on  the  contrary,  if  no  free  acid  is  added,  an  amorphous 
sediment,  which  Dr.  Prout  regards  as  superurate  of  ammonia,  is  ob- 
tained. 

Such  is  a general  view  of  the  composition  of  human  urine  in  its  na- 
tural healthy  state.  But  this  fluid  is  subject  to  a great  variety  of  mor- 
bid conditions,  which  arise  either  from  the  deficiency  or  excess  of  cer- 
tain principles  which  it  ought  to  contain,  or  from  the  presence  of  others 
wholly  foreign  to  its  composition.  As  the  study  of  these  affections  af- 
fords an  interesting  example  of  the  application  of  chemistry  to  pathol- 
ogy and  the  practice  of  medicine,  I shall  briefly  mention  some  of  the 
most  important  morbid  states  of  this  fluid,  referring  for  more  ample  de- 
tails to  the  excellent  treatise  of  Dr.  Prout.* 

Of  the  substances  which,  though  naturally  wanting,  are  sometimes 
contained  in  the  urine,  the  most  remarkable  is  sugar,  which  is  secreted 
by  the  kidneys  in  diabetes.  (Page  539.)  Diabetic  urine  has  a sweet 
taste,  and  yields  a syrup  by  evaporation,  is  almost  always  of  a pale  straw 
colour,  and  in  general  has  a greater  specific  gravity  than  ordinary  urine. 
It  contains  a remarkably  small  proportion  of  azotized  substances,  so 
that  it  has  no  tendency  to  putrefy;  but  the  presence  of  sugar  renders  it 
susceptible  of  undergoing  the  vinous  fermentation. 

The  acidifying  process  which  is  constantly  going  forward  in  the  kid- 
neys, as  evinced  by  the  formation  of  sulphuric,  phosphoric,  and  uric 
acids,  sometimes  proceeds  to  a morbid  extent,  in  consequence  of  which 
two  acids,  the  oxalic  and  nitric,  are  generated,  neither  of  which  exists 
in  healthy  urine.  The  former,  by  uniting  with  lime,  gives  rise  to  one  of 
the  worst  kinds  of  urinary  concretions;  and  the  latter,  in  the  opinion  of 


Inquiry  into  the  Nature  and  Treatment  of  Gravel,  Calculus,  &c. 


572 


URINE. 


T 


Dr.  Prout,  leads  to  the  production  of  purpurate  of  ammonia  by  reactinir 
on  uric  acid.  ^ 

In  severe  cases  of  jaundice,  tlie  bile  passes  from  the  blood  into  the 
kidneys,  and  communicates  a yello\v  colour  to  the  urine.  The  most  del- 
icate test  of  its  presence  is  muriatic  acid,  which  causes  a ^I’een  tint. 

Though  albumen  is  contained  in  very  minute  quantity  in  healthy 
urine,  in  some  diseases  it  is  present  in  large  proportion.  According  to 
Dr.  Blackall,  it  is  characteristic  of  certain  kinds  of  dropsy,  accompanied 
with  an  inflammatory  diathesis,  as  in  that  which  supervenes  in  scarlet 
fever;  and  Dr.  Prout  has  described  two  cases  of  albuminous  urine,  in 
which,  without  any  febrile  symptoms,  albumen  existed  in  such  quantity 
that  spontaneous  coagulation  took  place  within  the  bladder.  From  the 
Medical  Reports  lately  published  by  Dr.  Bright,  it  appears  that  drop- 
sical effusions  are  sometimes  owing  to  an  inflammatory  or  diseased  state 
of  the  kidneys;  and  in  these  cases  the  urine  commonly  contains  so  much 
albumen  as  to  be  rendered  turbid  by  heat.  So  regular  indeed  is  its  oc- 
currence, that  Dr.  Bright  considers  albuminous  urine,  in  dropsical  pa- 
tients, to  be  a sign  of  i*enal  disease. 

In  the  blood  of  patients  suffering  under  this  malady,  Dr.  Bostock  de- 
tected a crystalline  substance  resembling  urea;  and  Dr.  Christison,  pur- 
suing the  inquiry,  obtained  urea  with  all  its  characteristic  properties. 
(Edinb.  Med.  and  Surg.  Journ.  Oct.  1829.) 

In  certain  states  of  the  system  urea  is  generated  in  an  unusually  small 
proportion.  This  occurs  especially  in  diabetes  melUtus,  and  in  acute  and 
chronic  inflammation  of  the  liver,  diseases  in  which  urea  is  said  some- 
times to  be  wholly  wanting;  but  the  experience  of  Dr.  Prout  has  led 
him  to  doubt  if  it  is  ever  entirely  absent.  Dr.  Henry  has  shown  that 
urea,  when  mixed  with  a considerable  proportion  of  sugar,  cannot  be 
discovered  by  the  usual  lest  of  nitric  acid;  and,  consequently,  that 
though  present  in  diabetic  urine,  it  may  be  easily  overlooked.  The  me- 
thod by  which  he  has  succeeded  in  detecting  it  in  such  cases  is  by  distil- 
lation, urea  being  the  only  known  animal  principle  which  is  converted 
into  carbonate  of  ammonia  at  a boiling  temperature.  (Medico-chir. 
Trans,  ii.  127.)  During  the  hysteric  paroxysm,  also,  the  animal  matters 
of  the  urine  are  deficient,  while  its  saline  ingredients  are  secreted  in 
unusual  quantity.  An  excess  of  urea  occasionally  exists.  The  mode 
by  which  Dr.  Prout  estimates  the  proportion  of  this  principle  is  by  put- 
ting the  urine  in  a watch-glass,  and  carefully  adding  to  it  nearly  an  equal 
quantity  of  nitric  acid,  in  such  a manner  that  the  acid  may  collect  at  the 
bottom.  If  spontaneous  crystallization  ensue,  an  excess  of  urea  is  indi- 
cated; and  the  degree  of  excess  may  be  inferred  approximately  by 
marking  the  time  which  elapses  before  the  effect  takes  place.  Undi- 
luted healthy  urine  yields  crystals  only  after  an  interval  of  half  an  hour; 
but  the  nitrate  crystallizes  within  that  interval  when  the  urea  is  in  ex- 
cess. 

An  unusually  abundant  secretion  of  uric  acid  is  a circumstance  by  no 
means  uncommon.  In  some  instances  this  acid  makes  its  appearances  in 
a free  state;  but  happily  it  generally  occurs  in  combination  with  an 
alkali,  especially  with  soda  or  ammonia.  As  the  urates  are  much  more 
soluble  in  warm  than  in  cold  water,  the  urine  in  which  they  abound  is 
quite  clear  at  the  moment  of  being  voided,  but  deposites  a copious  sedi- 
ment in  cooling.  The  undue  secretion  of  these  salts,  if  temporary,  oc- 
casions scarcely  any  inconvenience,  and  arises  from  such  slight  causes, 
that  it  frequently  takes  place  without  being  noticed.  This  affection  is 
generally  produced  by  errors  in  diet,  whether  as  to  quantity  or  quality, 
and  by  all  causes  which  interrupt  the  digestive  process  in  any  of  its 
stages,  or  render  it  imperfect.  Dr.  Prout  specifies  unfermented  heavy 


URINARY  CONCRETIONS. 


S7i 


bread,  and  hard  boiled  puddings  or  dumplings,  as  in  particular  dispos- 
ing to  the  formation  of  the  urates.  These  sediments  have  commonly  a 
yellowish  tint,  which  is  communicated  by  the  colouring  matter  of  the 
urine ^ or  when  they  are  deposited  in  fevers,  forming  the  lateritous  sedi- 
ment, they  are  red,  in  consequence  of  the  colouring  matter  of  the  urine 
being  then  more  abundant.  In  fevers  of  an  imtable  natui*e,  as  in  hec- 
tic, the  sediment  has  a pink  colour,  which  is  ascribed  by  Ur.  Prout  to 
the  presence  of  purpurate  of  ammonia,  and  by  Proust  to  rosacic  acid. 
(Page  541.) 

So  long  as  uric  acid  remains  in  combination  with  a base,  it  never 
yields  a crystalline  deposite;  but  when  this  acid  is  in  excess  and  in  a 
free  state,  its  very  sparing*  solubility  causes  it  to  separate  in  minute 
crystals,  even  within  the  bladder,  giving  rise  to  two  of  the  most  dis- 
tressing complaints  to  which  human  nature  is  subject, — to  gi’avel  when 
the  crystals  are  detached  from  one  another,  and  when  agglutinated  by 
animal  matter  into  concrete  masses,  to  the  disease  called  the  stone. 
These  diseases  may  arise  either  from  uric  acid  being  directly  secreted 
by  the  kidneys,  or,  as  Dr.  Prout  suspects,  from  the  formation  of  some 
other  acid,  by  which  the  urate  of  ammonia  is  decomposed.  The  ten- 
dency of  urine  to  contain  free  acid  occurs  most  frequently  in  dyspeptic 
persons  of  a gouty  habit,  and  is  familiarly  known  by  the  name  of  the 
uric  or  lithic  acid  diathesis.  In  these  individuals  the  disposition  to  undue 
acidity  of  the  urine  is  superadded  to  that  state  of  the  system  which  leads 
to  an  unusual  supply  of  the  urates. 

A deficiency  of  the  acid  in  urine  is  not  less  injurious  than  its  excess. 
As  phosphate  of  lime  in  its  neutral  state  is  insoluble  in  water,  this  salt 
cannot  be  dissolved  in  urine  except  by  being  in  the  form  of  a superphos- 
phate. Hence  it  happens  that  healthy  urine  yields  a precipitate,  when 
it  is  neutralized  by  an  alkali;  and  if,  by  the  indiscriminate  employment 
of  alkaline  medicines,  or  from  any  other  cause,  the  urine,  while  yet 
within  the  bladder,  is  rendered  neutral,  the  earthy  phosphates  are  ne- 
cessarily deposited,  and  an  opportunity  afforded  for  the  formation  of  a 
stone. 

Urinary  Concretions. 

The  first  step  towards  a knowledge  of  urinary  calculi  was  made  in  the 
year  1776  by  Scheele,  who  showed  that  many  of  the  concretions  formed 
in  the  bladder  consist  of  uric  or  lithic  acid.  The  subject  was  afterwards 
successfully  investigated  by  Drs.  Wollaston  and  Pearson  in  this  country, 
and  by  Fourcroy  and  Vauquelin  in  France;  but  the  merit  of  having  first 
ascertained  the  composition  and  chemical  characters  of  most  of  the 
species  of  urinary  calculi  at  present  known,  belongs  to  Dr.  Wollaston. 
(Phil.  Trans,  for  1797.)  The  chemists  who  have  since  materially  con- 
tributed to  advance  our  knowledge  of  this  department  of  science,  are 
Dr.  Henry,  Mr.  Brande,  Dr.  Prout,  and  the  late  Dr.  Marcet,  to  whose 
“ Essay  on  the  Chemical  History  and  Medical  Treatment  of  Calculous 
Disorders,’’  I may  refer  the  reader  who  is  desirous  of  studying  this  im- 
portant subject. 

The  most  common  kinds  of  urinary  concretions  may  be  conveniently 
divided  into  six  species:  1.  The  uric  acid  calculus;  2.  The  bone-earth 
calculus,  principally  consisting  of  phosphate  of  lime;  3.  The  ammoniaco- 
magnesian  phosphate;  4.  The  fusible  calculus,  being  a mixture  of  the 
two  preceding  species;  5.  The  mulberry  calculus,  composed  of  oxalate 
of  lime;  and,  lastly.  The  cystic  oxide  calculus.  (Marcet.) 

1.  The  uric  acid  forms  a hard  inodorous  concretion,  commonly  of  an 
oval  form,  of  a brownish  or  fawn-colour,  and  smooth  surface.  These 
calculi  consist  of  layers  arranged  concentrically  around  a central  nu^ 


574 


URINARY  CONCRETIONS. 


cleus,  the  laminae  being-  distinguished  from  each  other  by  a slight  dif- 
ference in  colour,  and  sometimes  by  the  interposition  of  some  other 
substance. 

This  species  is  readily  distinguished  by  the  following  characters.  It 
Is  very  sparingly  soluble  in  water  and  muriatic  acid.  Digested  in  pure 
potassa  it  quickly  disappears,  and  on  adding  an  acid  to  the  solution,  the 
uric  acid  is  precipitated.  It  is  dissolved  with  effervescence  by  nitric 
acid,  and  the  solution  yields  purpurate  of  ammonia  when  evaporated. 
Before  the  blowpipe  it  becomes  black,  emits  a peculiar  animal  odour, 
and  is  gradually  consumed,  leaving  a trace  of  white  ash,  which  has  an 
alkaline  reaction. 

As  a variety  of  this  species  may  be  mentioned  urate  of  ammonia,  a 
rare  kind  of  calculus  first  noticed  by  Fourcroy.  Mr.  Brande  and  Dr. 
Marcet  expressed  a doubt  of  its  ever  forming  an  independent  concre- 
tion; but  its  existence,  as  such,  has  been  established  by  Dr.  Prout.  The 
calculus  of  urate  of  ammonia  has  the  same  general  chemical  charac- 
ters as  that  composed  of  uric  acid,  from  which  it  is  distinguished  by  its 
solubility  in  boiling  water,  when  reduced  to  powder,  and  by  its  solution 
in  potassa  being  attended  with  the  disengagement  of  ammonia.  It  de- 
flagrates remarkably  before  the  blow-pipe.  (Medico-chir.  Trans,  x. 
389.) 

2.  The  bone-earth  calculus,  first  correctly  analyzed  by  Dr.  Wollaston, 
consists  of  phosphate  of  lime.  The  surface  of  these  calculi  is  of  a pale 
brown  colour,  and  quite  smooth  as  if  they  had  been  polished.  When 
sawed  through  the  middle,  they  are  found  to  be  laminated  in  a very  re- 
gular manner,  and  the  layers  in  general  adhere  so  slightly  that  they  may 
be  separated  with  ease  into  concentric  crusts.  Dr.  Yellowly,  in  several 
bone-earth  concretions,  has  detected  small  quantities  of  carbonate  of 
lime,  which  appears  to  have  been  overlooked  by  others. 

This  calculus,  when  reduced  to  powder,  dissolves  with  facility  in  di- 
lute nitric  or  muriatic  acid,  but  is  insoluble  in  potassa.  Before  the  blow- 
pipe it  first  assumes  a black  colour,  from  the  decomposition  of  a little 
animal  matter,  and  then  becomes  quite  white,  undergoing  no  further 
change  unless  the  heat  be  very  intense,  when  it  is  fused. 

3.  Phosphate  of  ammonia  and  magnesia  was  first  described  as  a con- 
stituent of  urinary  calculi  by  Dr.  Wollaston.  It  rarely  exists  quite  alone, 
because  the  same  state  of  urine  which  leads  to  the  formation  of  this  spe- 
cies, favours  the  deposition  of  phosphate  of  lime;  but  it  is  frequently  the 
prevailing  ingredient.  It  often  appears  in  the  form  of  minute  sparkling 
crystals,  diffused  over  the  surface  or  between  the  interstices  of  other 
calculous  laminse. 

Calculi,  in  which  this  salt  prevails,  are  generally  white,  and  less  com- 
pact than  the  foregoing  species.  When  reduced  to  powder  they  are 
dissolved  by  cold  acetic  acid,  and  still  more  easily  by  the  stronger  acids, 
the  salt  being  thrown  down  unchanged  by  ammonia.  Digested  in  pure 
potassa  it  emits  an  ammoniacal  odour,  but  it  is  not  dissolved.  Before 
the  blowpipe,  a smell  of  ammonia  is  given  out,  it  diminishes  in  size, 
and  melts  into  a white  pearl  with  rather  more  facility  than  phosphate  of 
lime. 

4.  The  fusible  calculus,  the  nature  of  which  was  first  determined  by 
Dr.  Wollaston,  is  a mixture  of  the  two  preceding  species.  It  is  com- 
monly of  a white  colour,  and  its  fracture  is  usually  ragged  and  uneven. 
It  is  more  friable  than  any  of  the  other  kinds  of  calculus,  separates 
easily  into  layers,  and  leaves  a white  dust  on  the  fingers.  These  con- 
cretions are  very  common,  and  sometimes  attain  a large  size. 

The  fusible  calculus  is  characterized  by  the  facility  with  which  it 
melts  into  a pearly  globule,  which  is  sometimes  quite  transparent. 


URINARY  CONCRETIONS. 


575 


When  reduced  to  powder,  and  put  into  cold  acetic  acid,  the  phosphate 
of  ammonia  and  magnesia  is  dissolved,  and  the  phosphate  of  lime,  al- 
most the  whole  of  which  is  left,  dissolves  readily  in  muriatic  acid, 

5,  The  mulberry  calculus,  so  named  from  its  resemblance  to  the  fruit 
of  the  mulberry,  was  first  proved  to  consist  of  oxalate  of  lime  by  Dr. 
Wollaston.  This  concretion  is  sufficiently  characterized  by  its  dark-co- 
loured tuberculated  surface;  but  it  may  also  be  distinguished  chemically 
by  the  following  properties.  Heated  before  the  blowpipe,  the  oxalic 
acid  is  decomposed,  and  pure  lime  remains,  which  gives  a strong  brown 
stain  to  moistened  turmeric  paper.  It  is  insoluble  in  the  alkalies;  but  by 
digestion  in  carbonate  of  potassa  it  is  decomposed,  and  the  insoluble 
carbonate  of  lime  is  left.  When  reduced  to  powder  and  digested  in 
muriatic  or  nitric  acid,  a perfect  solution  is  effected.  It  is  not  dissolved 
by  acetic  acid,  a circumstance  which  distinguishes  it  from  the  ammo- 
niaco-magnesian  phosphate;  and  it  is  distinguished  from  phosphate  of 
lime  by  being  insoluble  in  phosphoric  acid. 

6.  The  cystic  oxide  was  described  by  its  discoverer  Dr.  Wollaston 
in  the  Philosophical  Transactions  for  1810.  This  concretion  is  not  lam- 
inated, but  appears  as  one  uniform  mass,  confusedly  crystallized 
through  its  whole  substance,  having  somewhat  the  appearance  of  the 
ammoniaco-magnesian  phosphate,  though  more  compact.  Before  the 
blowpipe  it  emits  a peculiarly  fetid  smell,  quite  distinct  from  that  of 
uric  acid,  and  is  consumed.  It  is  characterized  by  the  great  variety  of 
reagents  in  which  it  is  soluble.  It  is  dissolved  abundantly  by  the  mu- 
riatic, nitric,  sulphuric,  and  oxalic  acids;  by  potassa,  soda,  ammonia,  and 
lime-water;  and  even  by  the  neutral  carbonates  of  soda  and  potassa.  It 
is  insoluble  in  water,  alcohol,  bicarbonate  of  ammonia,  and  in  the  tar- 
taric, citric,  and  acetic  acids. 

From  the  similarity  which  this  substance  bears  to  certain  oxides  in 
uniting  both  with  acids  and  alkalies.  Dr.  Wollaston  termed  it  an  oxide, 
and  gave  it  the  name  of  cystic,  on  the  supposition  of  its  being  peculiar 
to  the  bladder.  Dr.  Marcet,  however,  has  found  it  in  the  kidney. 

Cystic  oxide  is  a rare  species  of  calculus.  In  this  country  seven  spe- 
cimens only  have  been  found; — two  by  Dr.  Wollaston,  two  by  Dr. 
Henry,  and  three  by  Dr.  Marcet.  Professor  Stromeyer  has  met  with 
two  instances  of  it  in  one  family,  and  in  one  of  the  cases  the  cystic 
oxide  was  also  detected  in  the  urine.  M.  Lassaigne  has  likewise  found 
it  in  a stone  taken  from  the  bladder  of  a dog.  From  the  analysis  of  this 
chemist,  100  parts  of  cystic  oxide  are  composed  of  carbon  36.2,  hydro- 
gen 12.8,  oxygen  17,  and  nitrogen  34, 

Jt  is  remarkable  that  cystic  oxide  is  never  accompanied  with  the  mat- 
ter of  any  other  concretion;  whereas  the  other  species  are  frequently 
met  with  in  the  same  stone.  They  are  sometimes  so  intimately  mixed 
that  they  can  be  separated  from  one  another  only  by  chemical  analysis, 
forming  what  is  called  a compound  calculus;  but  more  frequently  the 
concretion  consists  of  two  or  more  different  species  aiTanged  in  distinct 
alternate  layers.  This  is  termed  the  alternating  calculus. 

Besides  the  calculi  just  mentioned,  a few  other  species  have  been 
noticed.  Two  were  described  by  Dr.  Marcet  under  the  names  of 
xanthic  oxide  and  fibrinous  calculus,  both  of  which  are  exceedingly  rare. 
Xanthic  oxide  is  of  a reddish  or  yellow  colour,  is  soluble  both  in  acids 
and  alkalies,  and  its  solution  in  nitric  acid,  when  evaporated,  assumes  a 
bright  lemon-yellow  tint,  a property  to  which  it  owes  its  name,  and  by 
which  it  is  characterized,  (^ctvdog  yellow.)  The  fibrinous  calculus  de- 
rives its  name  from  fibrin,  to  which  its  properties  are  closely  analogous. 
The  third  species  consists  chiefly  of  carbonate  of  lime,  and  is  likewise 
of  rare  occurrence.  It  is  probable  that  in  some  very  uncommon  cases. 


576 


SOLID  PARTS  OF  ANIMALS. 


ilica  forms  the  principal  ingredient  of  a stone;  at  least  siliceous  matter 
wlis  found  by  Mr.  Venables  to  be  voided  in  one  if  not  in  two  cases  of 
gravel.  (Journal  of  Science,  N.  S.  vi.  234.)  ^ 

From  the  solubility  of  urinary  concretions  in  chemical  menstrua, 
hopes  were  once  entertained  that  reagents  might  be  introduced  into  the 
urine  through  the  medium  of  the  blood,  or  be  at  once  injected  into  the 
bladder,  so  as  to  dissolve  urinary  calculi,  and  thus  supersede  the  neces- 
sity of  a painful  and  dangerous  operation.  It  has  been  found,  however, 
that,  for  this  purpose,  it  would  be  necessary  to  employ  acid  or  alkaline 
solutions  of  greater  strength  than  may  safely  be  introduced  into  the 
bladder;  and  consequently  all  attempts  of  the  kind  have  been  abandoned. 
The  last  suggestion  of  this  nature  was  made  by  Messrs.  Prevost  and  Du- 
mas, who  proposed  to  disunite  the  elements  of  calculi  by  means  of  gal- 
vajusm.  This  agent,  however,  though  it  may  produce  this  effect  out 
of  the  body,  will  scarcely,  I conceive,  be  found  admissible  in  practice. 


SECTION  VI. 

ON  THE  SOLID  PARTS  OF  ANIMALS. 

Bone^  Horrij  Membranes^  Tendons^  Ligaments^ 
Muscles^  fyc. 

Rones  consist  of  earthy  salts  and  animal  matter  intimately  blended; 
the  former  of  which  are  designed  for  giving  solidity  and  hardness,  and 
the  latter  for  agglutinating  the  earthy  particles.  The  animal  substances 
are  chiefly  cartilage,  gelatin,  and  a peculiar  fatty  matter  called  marrow. 
On  reducing  bones  to  powder,  and  digesting  them  in  water,  the  fat  rises 
and  swims  upon  its  surface,  while  the  gelatin  is  dissolved.  By  digest- 
ing bones  in  dilute  muriatic  acid,  both  the  gelatin  and  earthy  salts  are 
dissolved,  and  the  pure  cartilage  is  left,  which  is  flexible,  but  retains 
the  original  figure  of  the  bone.  The  cartilage  of  bones  is  formed  be- 
fore the  earthy  matter,  and  constitutes  the  nidus  in  which  the  latter  is 
deposited.  In  its  chemical  properties,  it  is  very  analogous  to  coagulated 
albumen. 

When  bones  are  heated  in  close  vessels,  a large  quantity  of  car- 
bonate of  ammonia,  some  fetid  empyreumatic  oil,  and  the  usual  in- 
flammable gases,  pass  over  into  the  recipient;  while  a mixture  of 
charcoal  and  earthy  matter,  called  animal  charcoal,  remains  in  the  re- 
tort. If,  on  the  contrary,  they  are  heated  to  redness  in  an  open  fire, 
the  charcoal  is  consumed,  and  a pure  white  friable  earth  is  the  sole 
residue. 

According  to  the  analysis  of  Berzelius,  100  parts  of  dry  human  bones 
consist  of  animal  matters  33.3,  phosphate  of  lime  51.04,  carbonate  of 
lime  11.30,  fluate  of  lime  2,  phosphate  of  magnesia  1.16,  and  soda, 
muri  te  of  soda,  and  water  1.2.  Mr.  Hatchett  found,  also,  a small  quan- 
tity of  sulphate  of  lime;  and  Fourcroy  and  Vauquelin  discovered  traces 
of  ah  imina,  silica,  and  the  oxides  of  iron  and  manganese. 

Teeth  are  composed  of  the  same  materials  as  bone;  but  the  enamel 
dissolves  completely  in  dilute  nitric  acid,  and  therefore  is  free  from  car- 
tilage. From  the  analysis  of  Mr.  Pepys,  the  enamel  contains  78  per 


SOLID  PARTS  OF  ANIMALS. 


srr 

cent  of  phosphate  and  6 of  carbonate  of  lime,  the  residue  being  pro- 
bably gelatin.  The  composition  of  ivory  is  similar  to  that  of  the  bony 
matter  of  teeth  in  general. 

The  shells  of  eggs  and  the  covering  of  crustaceous  animals,  such 
as  lobsters,  crabs,  and  the  starfish,  consist  of  carbonate  and  a little 
phosphate  of  lime,  and  animal  matter.  The  shells  of  oysters,  muscles, 
and  other  molluscous  animals  consist  almost  entirely  of  carbonate  of 
lime  and  animal  matter,  and  the  composition  of  pearl  and  mother  of 
pearl  is  similar. 

Horn  differs  from  bone  in  containing  only  a trace  of  earth.  It  con- 
sists chiefly  of  gelatin  and  a cartilaginous  substance  like  coagulated 
albumen.  The  composition  of  the  nails  and  hoofs  of  animals  is  sim- 
ilar to  that  of  horn 5 and  the  cuticle  belongs  to  the  same  class  of  sub- 
stances. 

Tendons  appear  to  be  composed  almost  entirely  of  gelatin;  for  they 
are  soluble  in  boiling  water,  and  the  solution  yields  an  abundant  jelly 
on  cooling.  The  composition  of  the  true  skin  is  nearly  the  same  as  that 
of  tendons.  Membranes  and  ligaments  are  composed  chiefly  of  gelatin, 
but  they  also  contain  some  substance  which  is  insoluble  in  water,  and  is 
similar  to  coagulated  albumen. 

According  to  the  analysis  of  Vauquelin,  the  principal  ingredient  of 
hair  is  a peculiar  animal  substance,  insoluble  in  water  at  212®  F.,  but 
which  may  be  dissolved  in  that  liquid  by  means  of  Papin’s  digester,  and 
is  soluble  in  a solution  of  potassa.  Besides  this  substance,  hair  contains 
oil,  sulphur,  silica,  iron,  manganese,  and  carbonate  and  phosphate  of 
lime.  The  colour  of  the  hair  depends  on  that  of  its  oil;  and  the  effect 
of  metallic  solutions,  such  as  nitrate  of  silver,  in  staining  the  hair,  is 
owing  to  the  presence  of  sulphur. 

The  composition  of  wool  and  feathers  appears  analogous  to  that  of 
hair.  The  quill  part  of  the  feather  was  found  by  Mr.  Hatchett  to  con- 
sist of  coagulated  albumen. 

Silk  is  covered  with  a peculiar  varnish  which  is  soluble  in  boiling 
water  and  in  alkaline  solutions,  and  amounts  to  about  23  per  cent,  of 
the  raw  material.  By  digestion  in  alcohol  it  is  also  deprived  of  a por- 
tion of  wax.  The  remaining  fibrous  structure  has  been  examined  in  a 
very  imperfect  manner.  By  the  action  of  nitric  acid,  it  is  converted 
into  a yellow  crystalline  substance  of  a bitter  taste. 

The  flesh  of  animals,  ovmuscle,  consists  essentially  of  fibrin;  but  in- 
dependently of  this  principle,  it  contains  several  other  ingredients,  such 
as  albumen,  gelatin,  a peculiar  extractive  matter  called  osmazome,  fat, 
and  salts,  substances  which  are  chiefly  derived  from  the  blood,  vessels, 
and  cellular  membrane,  dispersed  through  the  muscles.  On  macerat- 
ing flesh,  cut  into  small  fragments,  in  successive  portions  of  cold  wa- 
ter, the  albumen,  osmazome,  and  salts  are  dissolved;  and  on  boiling 
the  solution,  the  albumen  is  coagulated.  From  the  remaining  liquid, 
the  osmazome  may  be  procured  in  a separate  state  by  evaporating  to 
the  consistence  of  an  extract,  and  treating  it  with  cold  alcohol.  By  the 
action  of  boiling  water,  the  gelatin  of  the  muscle  is  dissolved,  the  fat  melts 
and  rises  to  the  surface  of  the  water,  and  pure  fibrin  remains. 

The  characteristic  odour  and  taste  of  soup  are  owing  t6  the  osma- 
zome.  This  substance  is  of  a yellowish-brown  colour,  and  is  distin- 
guished from  the  other  animal  principles  by  solubility  in  water  and  alco- 
hol, whether  cold  or  at  a boiling  temperature,  and  by  not  forming  a 
jelly  when  its  solution  is  concentrated  by  evaporation.  Like  gelatin 
and  albumen,  it  yields  a precipitate  with  infusion  of  gall  nuts. 

49  • 


578 


PUTREFACTION. 


Tlie  substance  of  the  brain,  nerves,  and  spinal  marrow  differs  from 
that  of  all  other  animal  textures.  The  most  elaborate  analysis  of  cere- 
bral matter  is  by  Vauquelin,  who  found  that  100  parts  of  it  consist  of 
water  80,  albumen  7,  white  fatty  matter  4.53,  red  fatty  matter  0.70, 
osmazome  1.12,  phosphorus  1.5,  and  acids,  salts,  and  sulphur  5.15. 
(Annals  of  Phil,  i.)  The  presence  of  albumen  accounts  for  the  partial 
solubility  of  the  brain  in  cold  water,  and  for  the  solution  being*  coagu- 
lated by  heat,  acids,  alcohol,  and  by  the  metallic  salts  which  coagulate 
other  albuminous  fluids.  By  acting  upon  cerebral  matter  with  boiling 
alcohol,  the  fatty  principles  and  osmazome  are  dissolved,  and  the  solu- 
tion, in  cooling,  deposites  the  white  fatty  matter  in  the  form  of  crys- 
talline plates.  On  expelling  the  alcohol  by  evaporation,  and  treating 
the  residue  with  cold  alcohol,  the  osmazome  is  taken  up,  and  a fixed 
oil  remains  of  a reddish-brown  colour,  and  an  odour  like  that  of  the 
brain  itself  though  much  stronger.  The  two  species  of  fat  differ  little 
from  each  other,  and  both  yield  phosphoric  acid  when  deflagrated  with 
nitre. 


SECTION  VII. 

ON  PUTREFACTION. 

When  dead  animal  matter  is  exposed  to  air,  moisture,  and  a modern 
ate  temperature,  it  speedily  runs  into  putrefaction,  during  which  every 
trace  of  its  original  texture  disappears,  and  products  of  a very  offensive 
nature  are  gerferated.  The  most  favourable  temperature  is  from  60®  to 
80®  or  90®  Fahr.  Below  50®  the  process  takes  place  tardily,  and  at  32® 
it  is  wholly  arrested; — a fact,  which  is  clearly  evinced  by  the  circum- 
stance that  the  bodies  of  animals,  which  have  been  buried  in  snow  or 
ice,  are  found  unchanged  after  a long  series  of  years.  The  necessity 
of  a certain  degree  of  moisture  is  shown  by  the  facility  with  which  the 
most  perishable  substances  may  be  preserved  when  quite  dry.  The  pre- 
servation of  smoked  meat  is  chiefly  owing  to  this  cause;  and,  for  a like 
reason,  animals  buried  in  the  dry  sand  of  Arabia  and  Egypt  have  re- 
mained for  years  without  change. 

It  is  probable  that  when  moisture  and  warmth  concur,  putrefaction  in 
animal  matter  which  has  not  been  heated  to  212®  will  take  place  inde- 
pendently of  atmospheric  influence.  But  when  animal  matter  has  been 
boiled,  and  is  then,  without  subsequent  exposure,  completely  protect- 
ed from  air,  it  may  be  preserved  for  years,  even  though  moist  and  in  a 
temperature  favourable  to  putrefaction.  The  practice  of  preserving 
every  kind  of  food,  both  animal  and  vegetable,  now  a subject  of  exten- 
sive commercial  enterprise,  affords  ample  demonstration  of  this  state- 
ment. The  mode  generally  adopted  is  the  following.  Into  a tin  vessel 
is  placed  any  kind  of  food,  such  as  joints  of  meat,  fish,  game,  and 
vegetables,  dressed  for  the  table;  and  into  the  interstices  is  poured  a 
rich  gravy,  care  being  taken  to  have  the  vessel  completely  full.  A tin 
cover,  with  a small  aperture,  is  then  carefully  fixed  by  solder,  and 
while  the  whole  vessel  is  perfectly  full,  and  at  the  temperature  of  212®, 
the  remaining  aperture  is  closed.  As  the  ingredients  within  cool  and 
contract,  a vacuum  is  formed  if  the  operation  has  been  skilfully  con- 


PUTREFACTION. 


570 


ducted,  and  the  sides  of  the  vessel  are  in  consequence  slightly  pressed 
in  by  the  weight  of  the  atmosphere*  In  this  state  the  vessel  may  be 
sent  to  tropical  climates  without  fear  of  putrefaction;  and  the  most  de- 
licate food  of  one  country  be  thus  eaten  in  its  original  perfection,  in  a 
distant  region,  many  months  or  even  years  after  its  preparation. 

For  reasons  formerly  mentioned,  animal  matters  commonly  undergo 
putrefaction  more  readily  than  those  which  are  derived  from  the  vegeta- 
ble kingdom  (page  454);  but  they  are  not  all  equally  disposed  to  putre- 
fy. The  acid  and  fatty  principles  are  less  liable  to  this  change  than 
urea,  fibrin,  and  other  analogous  substances.  The  chief  products  to 
which  their  dissolution  gives  rise  are  water,  ammonia,  carbonic  acid, 
and  sulphuretted,  phosphuretted,  and  carburetted  hydrogen  gases. 


PART  IT. 


ANALYTICAL.  CHEMISTRY. 


To  enter  into  a detailed  account  of  experimental  and  analytical  chemis- 
try is  altogether  inconsistent  with  the  design  and  limits  of  the  present  work* 
My  sole  object  in  this  department  is  to  give  a few  concise  directions  for  con- 
ducting some  of  the  more  common  analytical  processes;  and  in  order  t» 
render  them  more  generally  useful^  I shall  give  examples  of  the  analysis  o£ 
mixed  gases,  of  minerals,  and  of  mineral  waters. 


SECTION  I. 

ANALYSIS  OF  MIXED  GASES. 


Analysis  of  Air  or  of  Gaseous  Mixtures  containing  Oxygen, — 
Of  the  various  processes  by  which  oxygen  gas  may  be  withdrawn  from 
gaseous  mixtures,  and  its  quantity  determined,  none  are  so  convenient  and 
precise  as  the  method  by  means  of  hydrogen  gas.  In  performing  this  an- 
alysis, a portion  of  atmospheric  air  is  carefully  measured  in  a graduated 
tube,  and  mixed  with  a quantity  of  hydrogen  gas  which  is  rather  more  than 
sufficient  for  uniting  with  all  the  oxygen  present.  The 
mixture  is  then  introduced  into  a strong  glass  tube  called 
Volta’s  eudiometer,  shown  in  the  annexed  wood-cut,,  and  is 
inflamed  by  the  electric  spark,  the  aperture  of  the  tube 
being  closed  by  the  thumb  at  the  moment  of  detonation. 
The  total  diminution  in  volume,  divided  by  three,  indicates 
the  quantity  of  oxygen  originally  contained  in  the  mixture. 
This  operation  may  be  pgriojcmcdiA  a trough,  either  of  water 
or  mercury. 


ANALYSIS  OF  MIXED  GASES. 


581 


Instead  of  electricity,  spong’y  platinum  may  be  employed  for  causing  the 
union  of  oxygen  and  hydrogen  gases;  and  while  its  indications  are  very 
precise,  it  has  the  advantage  of  producing  the  effect  gradually  and  without 
detonation.  The  most  convenient  mode  of  employing  it  with  this  intention 
is  the  following.  A mixture  of  spongy  platinum  and  pipe-clay,  in  the  pro- 
portion of  about . three  parts  of  the  former  to  one  of  the  latter,  is  made  into 
a paste  with  water,  and  then  rolled  between  the  fingers  into  a globular  form. 
In  order  to  preserve  the  spongy  texture  of  the  platinum,  a little  muriate  of 
ammonia  is  mixed  with  the  paste;  and  when  the  ball  has  become  dry,  it  is 
cautiously  ignited  at  the  flame  of  a spirit-lamp.  The  sal  ammoniac,  escap- 
ing .from  all  parts  of  the  mass,  gives  it  a degree  of  porosity  which  is  peett- 
liarly  favourable  to  its  action.  The  ball,  thus  prepared,  should  be  protected 
from  dust,  and  be  heated  to  redness  just  before  being  used.  To  insure  accur- 
racy,  the  hydrogen  employed  should  be  kept  over  mercury  for  a few  hours 
in  contact  with  a platinum  ball  and  a piece  of  caustic  potassa.  The  first 
deprives  it  of  traces  of  oxygen  which  it  commonly  contains,  and  the  second 
of  moisture  and  sulphuretted  hydrogen.  The  analysis  must  be  performed 
in  a mercurial  trough.  The  time  required  for  completely  removing  the 
oxygen  depends  on  the  diameter  of  the  tube.  If  the  mixture  is  contained 
in  a very  narrow  tube,  the  diminution  does  not  arrive  at  its  full  extent  in 
less  than  twenty  minutes  or  half  an  hour;  while  in  a vessel  of  an  inch  in 
diameter,  the  effect  is  complete  in  the  course  of  five  minutes. 

Mode  of  determining  the  Quantity  of  Nitrogen  in  Gaseous  Mixtures. — 
As  atmospheric  air,  which  has  been  deprived  of  moisture  and  carbonic 
acid,  consists  of  ox3’^gen  and  nitrogen  only,  the  proportion  of  the  latter  is  of 
course  known  as  soon  as  that  of  the  former  is  determined.  The  only  me- 
thod, indeed,  by  which  chemists  are  enabled  to  estimate  the  quantity  of  this 
gas,  is  by  withdrawing  the  other  gaseous  substances  with  which  it  is  mixe(L 

Mode  of  determining  the  Quantity  of  Carbonic  Acid  in  Gaseous  Mixtures. 
— ^When  carbonic  acid  is  the  only  acid  gas  which  is  present,  as  happens  in 
atmospheric  air,  in  the  ultimate  analysis  of  organic  compounds,  and  in  most 
other  analogous  researches,  the  process  for  determining  its  quantity  is  ex- 
ceedingly simple;  for  it  consists  merely  in  absorbing  that  gas  by  lime-wate? 
or  a solution  of  caustic  potassa.  This  is  easily  done  in  the 
course  of  a few  minutes  in  an  ordinary  graduated  tube;  or  it  may 
be  effected  almost  instantaneously  by  agitating  the  gaseous 
mixture  with  the  alkaline  solution  in  Hope’s  eudiometer.  This 
apparatus,  as  represented  in  the  figure,  is  formed  of  two  parts: — 
of  the  bottle  A,  capable  of  containing  about  twenty  drachms  of 
fluid,  and  furnished  with  a well-ground  stopper  C;  and  of  the 
tube  B,  of  the  capacity  of  one  cubic  inch,  divided  into  100  equal 
parts,  and  accurately  fitted  by  grinding  to  the  neck  of  the  bot- 
tle. The  tube,  full  of  gas,  is  fixed  into  the  bottle  previously 
filled  with  lime-water,  and  its  contents  are  briskly  agitated. 

The  stopper  C is  then  withdrawn  under  water,  when  a portion 
of  liquid  rushes  into  the  tube,  supplying  the  place  of  the  gas 
which  has  disappeared;  and  the  process  is  afterwards  repeated,  Q 
as  long  as  any  absorption  ensues. 


58^ 


ANALYSIS  OF  MIXED  GASES. 


The  eudiometer  of  Dr.  Hope  was  originally  designed  for  analyzing  air 
or  other  similar  mixtures,  the  bottle  being  filled  with  a solution 
of  hydrosulphuret  of  potassa  or  lime,  or  some  Hquid  capable  of 
absorbing  oxygen.  To  the  employment  of  this  apparatus  it  has 
been  objected,  that  the  absorption  is  rendered  slow  by  the  par- 
tial vacuum  which  is  continually  taking  place  within  it,  an  in- 
convenience  particularly  felt  towards  the  close  of  the  process, 
in  consequence  of  the  eudiomctric  liquor  being  diluted  by  the 
admission  of  water.  To  remedy  this  defect,  Dr.  Henry  has 
substituted  a bottle  of  clastic  gum  for  that  of  glass,  as  in  the 
annexed  wood-cut,  by  which  contrivance  no  vacuum  can  occur. 
From  the  improved  method  of  analyzing  air,  however,  this  in- 
strument is  now  rarely  employed  in  eudiometry;  but  it  may  be 
used  with  advantage  for  absorbing  carbonic  acid  or  similar 
gases,  and  is  particularly  useful  for  the  purpose  of  demonstra- 
tion. 


Mode  of  analyzing  Mixtures  of  Hydrogen  and  other  Inflammable  Gases. 
— When  hydrogen  is  mixed  with  nitrogen,  air,  or  other  similar  gaseous 
mixtures,  its  quantity  is  easily  ascertained  by  causing  it  to  combine  with 
oxygen  either  by  means  of  platinum  or  the  electric  spark.  If,  instead  of 
hydrogen,  any  other  combustible  substance,  such  as  carbonic  .oxide,  light 
oarburetted  hydrogen,  or  olefiant  gas,  is  mixed  with  nitrogen,  the  analysis 
is  easily  effected  by  adding  a sufficient  quantity  of  oxygen,  and  detonating 
the  mixture  by  electricity.  The  diminution  in  volume  indicates  the  quan- 
tity of  hydrogen  contained  in  the  gas,  and  from  the  carbonic  acid,  which 
may  then  be  removed  by  an  alkali,  the  quantity  of  carbon  is  inferred.* 


* It  is  not  easy  to  perceive  how  the  diminution  in  volume  will  indicate 
the  quantity  of  hydrogen  contained  in  the  gas.  If  Dr.  Turner  means  that,, 
in  cases  of  the  mixture  of  free  hydrogen,  either  with  nitrogen  or  air,  explo- 
sion with  an  excess  of  oxygen  will  indicate  the  quantity  of  hydrogen  present 
by  the  diminution  in  volume,  it  being  two-thirds  of  that  diminution,  the  fact 
is  readily  admitted ; but  with  regard  to  the  other  supposed  mixtures,  the 
rule  given  is  obviously  inexact.  Not  to  speak  of  the  case  of  carbonic  oxide, 
which  is  evidently  inapplicable,  as  that  gas  contains  no  hydrogen,  it  will  be 
found  on  examination,  that  where  either  light  carburetted  hydrogen,  or  ole- 
fiant gas  is  mixed  with  nitrogen,  no  conclusion  can  be  drav/n  from  the  diminu- 
tion of  volume;  and  for  this  reason,  that  in  these  combustible  gases,  the  hydro- 
gen exists  already  condensed;  and  besides  it  is  impossible  to  know  beforehand 
how  much  of  the  oxygen  may  be  expended  in  the  formation  of  carbonic  acid.. 

In  the  case  of  a mixture  of  nitrogen  and  light  carburetted  h3^drogen,  the 
experimenter  being  certain  that  no  other  gas  is  present,  it  would  be  easy  to 
ascertain  the  quantity  of  the  latter.  All  that  would  be  necessary  would 
be  to  explode  the  mixture  with  an  excess  of  oxygen,  measure  the  carbon- 
ic acid  formed,  deduce  the  carbon  present  in  it,  and  calculate  how  much 
hydrogen  the  carbon  would  require  to  convert  it  into  light  carburetted  hy- 
drogen. Dy  proceeding  in  a similar  manner,  a mixture  of  nitrogen  and  ole- 
fiant gas  might  be  analyzed. 

Where  the  mixture  consists  of  nitrogen  and  carbonic  oxide,  the  Volume  of 
the  carbonic  acid  formed  will  indicate  the  volume  of  this  oxide. 

If  a mixture  Ikj  supposed  of  nitrogen,  carbonic  oxide,  light  carburetted  hy- 
drogen, olefiant  gas,  and  free  Jiydrogcn,  the  analysis  is  somewhat  compli- 
Ciited.  The  first  step  will  be  the  removal  of  the  olefiant  gas  by  the  method 
of  Dr.  Henry,  by  means  of  chlorine.  The  next  is  to  determine  the  precise 


ANALYSIS  OF  MIXED  GASES. 


583 


An  elegant  mode  of  converting  carbonic  oxide  into  carbonic  acid  gas, 
suggested  by  Dr.  Henry,  is  to  mix  it  with  rather  more  than  its  own  volume 
of  nitrous  oxide  gas,  and  fire  the  mixture  by  the  electric  spark.  The  two 
gases  mutually  decompose  each  other,  and  give  rise  to  nitrogen  and  car- 
bonic acid  gases.  For  each  measure  of  carbonic  oxide,  one  of  carbonic  acid 
is  produced,  one  measure  of  nitrous  oxide  is  decomposed,  and  one  of  nitro- 
gen evolved.  By  employing  a slight  excess  of  pure  carbonic  oxide,  the 
composition  of  nitrous  oxide  inay  be  ascertained.  The  mixed  gases  occupy 
the  same  space  after  deflagration  as  before  it ; and  the  carbonic  acid  gas  oc- 
cupies the  same  space  as  the  nitrous  oxide  which  had  been  present.  (An- 
nals of  Philosophy,  xxiv.  301.) 

When  olefiant  gas  is  mixed  with  other  inflammable  gases,  its  quantity  is 
easily  determined  by  an  elegant  and  simple  process  proposed  by  Dr.  Henry. 
(Page  245.)  It  consists  in  mixing  100  measures,  or  any  convenient  quan- 
tity of  the  gaseous  mixture,  with  an  equal  volume  of  chlorine  in  a vessel 
covered  with  a piece  of  cloth  or  paper,  so  as  to  protect  it  from  light ; and 
after  an  interval  of  about  ten  minutes,  the  excess  of  chlorine  is  removed  by 
lime-water  or  potassa.  The  loss  experienced  by  the  gas  to  be  analyzed,  in- 
dicates the  exact  quantity  of  olefiant  gas  which  it  had  contained. 

This  method  is  not  correct  when  the  vapours  of  the  dense  hydrocar- 
burets  are  present.  Thus,  when  oil  gas  is  mixed  with  chlorine,  the  diminu- 
tion in  volume  arises  from  the  removal  of  the  combustible  vapours  as  well  as 
of  olefiant  gas ; for  the  former  are  equally  disposed  as  the  latter  to  unite 
with  chlorine. 

In  mixtures  of  hydrogen,  carburetted  hydrogen,  and  carbonic  oxide,  the 
analytic  process  is  exceedingly  difficult  and  complicated,  and  requires  all 
the  resources  of  the  most  refined  chemical  knowledge,  and  all  the  address  of 
an  experienced  analyst.  The  most  recent  information  on  this  subject  will 
be  found  in  Dr.  Henry’s  Essay  in  the  Philosophical  Transactions  for  1824. 


quantity  of  oxygen  necessary  for  the  complete  combustion  of  the  residue. 
This  is  ascertained  by  detonating  the  mixture  with  an  excess  of  oxygen,  ab- 
sorbing the  carbonic  acid  formed,  and  analyzing  the  new  residue  (which 
necessarily  consists  of  nitrogen  and  the  excess  of  oxygen)  by  means  of  hy- 
drogen. The  oxygen  in  excess,  thus  ascertained,  being  deducted  from  the 
whole  quantity  employed,  will  give  the  amount  expended  in  the  explosion. 
The  quantity  of  carbonic  a?cid  formed  will  give  the  quantity  of  carbon  in  the 
mixture,  and  this  amount,  together  with  the  weight  of  the  nitrogen,  deducted 
from  the  total  weight  of  the  gas  after  the  removal  of  the  olefiant  gas,  will 
give  the  weight, of'  the  oxygen  and  hydrogen  present.  The  oxygen  in  the 
carbonic  acid  formed,  deducted  from  that  expended  in  the  explosion,  will 
give  the  oxygen  which  has  been  expended  in  the  formation  of  water  ; and 
this  oxygen,  added  to  the  oxygen  and  hydrogen  present  in  the  gas,  will  give 
the  weight  of  the  water  formed.  From  the  weight  of  the  water,  the  hydro- 
gen present  in  it  may  be  inferred,  and  this  deducted  from  the  aggregate 
weight  of  the  oxygen  and  hydrogen  in  the  gas,  will  give  the  weight  of  the 
oxygen  present.  Tliis  oxygen,  by  the  supposition,  must  have  existed  in  the 
carbonic  oxide  ; and  by  calculation,  the  quantity  of  carbon  it  would  require 
to  be  converted  into  that  oxide  may  be  ascertained.  This  carbon  deducted 
from  the  total  carbon  in  the  mixture,  will  give  that  present  in  the  light  cap- 
buretted  hydrogen.  The  carbon  being  ascertained  in  this  gas,  its  hydrogen 
may  be  estimated.  This  hydrogen  deducted  from  the  total  hydrogen  present, 
will  then  give  the  free  hydrogen.  B. 


584 


ANALYSIS  OF  MINERALS. 


1 


SECTION  II. 

ANALYSIS  OF  MINERALS. 

As  the  very  extensive  nature  of  this  department  of  analytical  chemistry 
renders  a selection  necessary,  I shall  confine  my  remarks  solely  to  the  anur 
lysis  of  those  earthy  minerals,  with  which  the  beginner  commences  his 
labours.  The  most  common  constituents  of  these  compounds  are  silica, 
alumina,  iron,  manganese,  lime,  magnesia,  potassa,  soda,  and  carbonic  and 
sulphuric  acids ; and  I shall,  therefore,  endeavour  to  give  short  directions 
for  determining  the  quantity  of  each  of  these  substances. 

In  attempting  to  separate  two  or  more  fixed  principles  from  each  other, 
the  first  object  of  the  analytical  chemist  is  to  bring  them  into  a state  of  solu- 
tion. If  they  are  soluble  in  water,  this  fluid  is  preferred  to  every  other 
menstruum;  but  if  not,  an  acid  or  any  convenient  solvent  may  be  employed. 
In  many  instances,  however,  the  ^substance  to  be  analyzed  resists  the 
action  even  of  the  acids,  and  in  that  case  the  following  method  is  adopted  : 
— The  compound  is  first  crushed  by  means  of  a hammer  or  steel  mortar, 
and  is  afterwards  reduced  to  an  impalpable  powder  in  a mortar  of  agate ; 
it  is  then  intimately  mixed  with  three,  four,  or  more  times  its  weight  of  pot- 
assa, soda,  baryta,  or  their  carbonates ; and,  lastly,  the  mixture  is  exposed 
in  a crucible  of  silver  or  platinum  to  a strong  heat.  During  the  operation, 
the  alkali  combines  with  one  or  more  of  the  constituents  of  the  mineral; 
and,  consequently,  its  elements  being  disunited,  it  no  longer  resists  the  ac- 
tion of  the  acids. 

Analysis  of  Mat  hie  or  Carhonate  of  Lime. — This  analysis  is  easily  made 
by  exposing  a known  quantity  of  marble  for  about  half  an  hour  to  a full 
white  heat,  by  which  means  the  carbonic  acid  gas  is  entirely  expelled,  so 
that  by  the  loss  in  weight  the  quantity  of  each  ingredient,  supposing  the 
marble  to  have  been  pure,  is  at  once  determined.  In  order  to  ascertain 
that  the  whole  loss  is  owing  to  the  escape  of  carbonic  acid  the  quantity 
of  this  gas  may  be  determined  by  a comparative  analysis.  Into  a small 
flask  containing  muriatic  acid  diluted  with  two  or  three  parts  of  water, 
a known  quantity  of  marble  is  gradually  added,  the  flask  being  inclined 
to  one  side  in  order  to  prevent  the  fluid  from  being  flung  out  of  the  vessel 
during  the  effervescence.  The  diminution  in  weight  experienced  by  the 
flask  and  its  contents,  indicates  the  quantity  of  carbonic  acid  which  has  been 
expelled. 

Should  the  carbonate  suffer  a greater  loss  in  the  fire  than  when  decom- 
posed by  an  acid,  it  will  most  probably  be  found  to  contain  water.  This  may 
DC  ascertained  by  lieating  a piece  of  it  to  redness  in  a glass  tube,  the  sides 
of  which  will  be  bedewed  with  moisture,  if  water  is  present.  Its  quantity 
may  be  determined  by  causing  the  watery  vapour  to  pass  through  a weighed 
tube  filled  with  fragments  of  the  chloride  of  calcium,  by  which  the  mois- 
ture is  absorbed. 

Separation  of  Lime  and  Magnesia. — The  more  common  kinds  of  car- 
bonate of  lime  frequently  contain  traces  of  siliceous  and  aluminous  earths, 
in  consequence  of  which  they  arc  not  completely  dissolved  in  dilute  mu- 
riatic acid.  A very  Irequcnt  source  of  impurity  is  carbonate  of  magne- 
sia, which  is  often  jircsent  in  such  quantity  that  it  forms  a peculiar 
compound  called  magnesian  limestone.  The  analysis  of  this  substance, 
so  tar  as  respects  carbonic  acid,  is  the  same  as  that  of  marble.  The  so- 


ANALYSIS  OF  MINERALS. 


585 


paration  of  the  two  earths  may  be  conveniently  effected  in  the  following 
manner.  The  solution  of  the  mineral  in  muriatic  acid  is  evaporated  to 
perfect  dryness  in  a flat  dish  or  capsule  of  porcelain,  and  after  redissolv- 
ing the  residuum  in  a moderate  quantity  of  distilled  water,  a solution  of 
oxalate  of  ammonia  is  added  as  long  as  a preeipitate  ensues.  The  oxa- 
late of  lime  is  then  allowed  to  subside,  collected  on  a filter,  converted  into 
quicklime  by  a white  heat,  and  weighed ; or  the  oxalate  may  be  decomposed 
by  a red  heat,  and  after  moistening  the  resulting  carbonate  with  a strong  so- 
lution of  carbonate  of  ammonia,  in  order  to  supply  any  particles  of  quick- 
lime with  carbonic  acid,  it  should  be  dried,  heated  to  low  redness,  and  re- 
garded as  pure  carbonate  of  lime.  To  the  filtered  liquid,  containing  the 
magnesia,  a mixture  of  pure  ammonia  and  phosphate  of  soda  is  added,  when 
the  magnesia  in  the  form  of  the  ammoniaco-phosphate  is  precipitated.  Of 
this  precipitate,  heated  to  redness,  100  parts,  according  to  Stromeyer,  cor- 
respond  to  37  of  pure  magnesia. 

Tile  precipitation  of  magnesia  by  means  of  phosphoric  acid  and  ammo- 
nia, though  extremely  accurate  when  properly  performed,  requires  a few 
precautions.  The  liquid  should  be  cold,  and  either  neutral  or  alkaline.  The 
precipitate  is  dissolved  with  great  ease  by  most  of  the  acids ; and  Stromeyer 
has  remarked  that  some  of  it  is  held  in  solution  by  carbonic  acid  whether 
free  or  in  union  with  an  alkali.  The  absence  of  carbonic  acid  should,  there- 
fore, always  be  insured,  prior  to  the  precipitation,  by  heating  the  solution 
to  212®  F.,  acidulating  at  the  same  time  by  muriatic  acid,  should  an  alka- 
line carbonate  be  present.  Berzelius  has  also  observed,  that  in  washing  the 
ammoniaeo-magnesian  phosphate  on  a filter,  a portion  of  the  salt  is  dissolved 
as  soon  as  the  saline  matter  of  the  solution  is  nearly  all  removed ; that  is  to 
say,  it  is  dissolved  by  pure  water.  Hence  the  edulcoration  should  be  conu 
pleted  by  water,  which  is  rendered  slightly  saline  by  muriate  of  ammonia. 

Earthy  Sulphates, — The  most  abundant  of  the  earthy  sulphates  is  that  of 
lime,  the  analysis  of  which  is  easily  effected.  By  boiling  it  for  fifteen  or 
twenty  minutes  with  a solution  of  twice  its  weight  of  carbonate  of  soda, 
double  decomposition  ensues;  and  the  carbonate  of  lime,  after  being  collected 
on  a filter  and  washed  with  hot  water,  is  either  heated  to  low  redness  to 
expel  the  water,  and  weighed,  or  at  once  reduced  to  quicklime  by  a white 
heat.  Of  the  dry  carbonate,  fifty  parts  correspond  to  twenty-eight  of  lime. 
The  alkaline  solution  is  acidulated  with  muriatic  acid,  and  the  sulphuric 
acid  thrown  down  by  muriate  of  baryta.  From  the  sulphate  of  this  earth, 
collected  and  dried  at  a red  heat,  the  quantity  of  acid  may  easily  be  esti- 
mated. 

The  method  of  analyzing  the  sulphate  of  strontia  and  baryta  is  some- 
what different.  As  these  salts  are  difficult  of  decomposition  in  the  moist 
way,  the  following  process  is  adopted.  The  sulphate,  in  fine  powder,  is 
mixed  with  three  times  its  weight  of  carbonate  of  soda,  and  the  mixture  is 
heated  to  redness  in  a platinum  crucible  for  the  space  of  an  hour.  The 
ignited  mass  is  then  digested  in  hot  water,  and  the  insoluble  earthy  carbo- 
nate collected  on  a filter.  The  other  parts  of  the  process  are  the  same  as 
the  foregoing. 

Mode  of  analyzing  Compounds  of  Silka,  Alumina^  and  /ron.-^Minerals, 
thus  constituted,  are  decomposed  by  an  alkaline  carbonate,  at  a red  heat,^ 
in  the  same  manner  as  sulphate  of  baryta.  The  mixture  is  afterwards 
digested  in  dilute  muriatic  acid,  by  which  means  all  the  ingredients  of 
the  mineral,  if  the  decomposition  is  complete,  are  dissolved.  The  solu- 
tion is  next  evaporated  to  dryness,  the  heat  being  carefully  regulated 
towards  the  close  of  the  process,  in  order  to  prevent  any  of  the  chloride  of 
iron,  the  volatility  of  which  is  considerable,  from  being  dissipated  in  vapour 


586 


ANALYSIS  OF  MINERALS. 


By  this  operation,  the  silica,  though  previously  held  in  solution  by  the  acid, 
is  entirely  deprived  of  its  solubility;  so  that  on  digesting-  the  dry  mass  in 
water  acidulated  with  muriatic  acid,  the  alumina  and  iron  are  taken  up, 
iu)d  the  silica  is  Icfl  in  a state  of  purity.  The  siliceous  earth,  after  subsid- 
ing, is  collected  on  a filter,  carefully  edulcorated,  heated  to  redness,  and 
wci'jhcd. 

To  the  clear  liquid,  containing  peroxide  of  iron  and  alumina,  a solution 
of  pure  potassa  is  added  in  moderate  excess;  so  as  not  only  to  throw  down 
those  oxides,  but  to  dissolve  the  alumina.  The  peroxide  of  iron  is  then  col- 
lected on  a filter,  edulcorated  earefully  until  the  washings  cease  to  have  an 
alkaline  reaction,  and  is  well  dried  on  a sand-bath.  Of  this  hydrated  per- 
oxide, forty-nine  parts  contrdn  tbrty  of  anhydrous  peroxide  of  iron.  But 
the  most  accurate  mode  of  determining  its  quantity  is  by  expelling  the  wa- 
ter by  a red  heat.  Tliis  operation,  however,  should  be  done  with  care; 
since  any  adhering  particles  of  paper,  or  other  combustible  matter,  would 
bring  the  iron  into  the  state  of  black  oxide,  a change  which  is  known  to 
have  occurred  by  the  iron  being  attracted  by  a magnet. 

To  procure  the  alumina,  the  liquid  in  which  it  is  dissolved  is  boiled  with 
sal  ammoniac;  when  the  muriatic  acid  unites  with  the  potassa,  the  volatile 
alkali  is  dissipated  in  vapour,  and  the  alumina  subsides.  As  soon  as  the 
solution  is  thus  rendered  neutral,  the  hydrous  alumina  is  collected  on  a 
filter,  dried  by  exposure  to  a white  heat,  and  quickly  weighed  after  removal 
from  the  fire. 

Separation  of  Iron  and  ManganeRp. — A compound  of  these  metala 
or  their  oxides  may  be  dissolved  in  muriatic  .acid.  If  the  iron  is  in 
a large  proportion  compared  with  the  manganese,  the  following  pro* 
ecss  may  be  adopted  with  advantage,  ^’o  the  cold  solution  consider 
rably  diluted  with  water,  and  acidulated  with  muriatic  acid,  carbo. 
Date  of  soda  is  gradually  added,  and  the  liquid  is  briskly  stirred  with  a glass 
rod  during  the  effervescence,  in  order  that  it  may  become  highly  charged 
with  carbonic  acid.  By  neutralizing  the  solution  in  this  manner,  it  at 
length  attains  a point  at  which  the  peroxide  of  iron  is  entirely  deposited^ 
leaving  the  liquid  colourless;  while  the  manganese,  by  aid  of  the  free  car- 
bonic acid,  is  kept  in  solution.  The  iron,  after  subsiding,  is  collected  on  a 
filter,  and  its  quantity  determined  in  the  usual  manner.  The  filtered  liquid 
is  then  boiled  with  an  excess  of  carbonate  of  soda;  and  the  precipitated  car- 
bonate of  manganese  is  collected,  heated  to  full  redness  in  an  open  crucible, 
by  which  it  is  converted  into  the  red  oxide,  and  weighed.  This  method  is 
one  of  some  delicacy;  but  in  skilful  hands  it  affords  a very  accurate  result. 
It  may  also  be  em{)loyed  for  separating  iron  from  magnesia  and  lime  as 
well  as  from  manganese. 

But  if  the  proportion  of  iron  is  small  compared  with  that  of  manganese, 
the  best  mode  of  separating  it  is  by  succinate  of  ammonia  or  soda,  prepared 
by  neutralizing  a solution  of  succinic  acid  with  either  of  those  alkalies. 
That  this  process  should  succeed,  it  is  necessary  that  the  iron  be  wholly  in 
the  state  cf*  peroxide,  that  the  solution  be  exactly  neutral,  which  may  easily 
be  insured  by  the  cautious  use  of  ammonia,  and  that  the  reddish-brown  co- 
loured succinate  of  iron  be  washed  with  cold  water.  Of  this  succinate,  well 
dried  at  a temperature  of  F.,  90  parts  correspond  to  40  of  the  peroxide. 
From  the  filtered  liquid,  the  manganese  may  be  precipitated  at  a boiling 
temperature  by  carbonate  of  soda,  and  its  quantity  determined  in  the  way 
above  mentioned.  'I’he  benzoate  may  be  substituted  for  succinate  of  ammo- 
nia in  the  preceding  process. 

It  may  be  stated  as  a general  rule,  that  whenever  it  is  intended  to  preeip- 
Itatc  iron  by  means  of  the  alkalies,  the  succinates,  or  benzoates,  it  isessciv 


ANALYSIS  OF  MINERALS.  587 

tial  that  this  metal  be  in  the  maximum  of  oxidation.  It  is  easily  brought 
into  this  state  by  digestion  with  a little  nitrie  acid. 

Separation  of  Manganese  from  Lime  and  Magnesia. — If  the  quantity 
of  the  former  be  proportionably  small,  it  is  precipitated  as  a sulphuret 
by  hydrosulphuret  of  ammonia  or  potassa.  This  sulphuret  is  then  dis- 
solved in  muriatic  acid,  and  the  manganese  thrown  down  as  usual 
by  means  of  an  alkali.  But  if  the  manganese  be  the  chief  ingredient,  the 
best  method  is  to  precipitate  it  at  once,  together  with  the  two  earths,  by  a 
fixed  alkaline  carbonate  at  a boiling  temperature.  I’he  precipitate,  after 
being  exposed  to  a low  red  heat  and  weighed,  is  put  into  cold  water  acidu- 
lated with  a drop  or  two  of  nitric  acid,  when  the  lime  and  magnesia  will  be 
slowly  dissolved  with  effervescence.  Should  a trace  of  the  manganese  be 
likewise  taken  up,  it  may  easily  be  thrown  down  by  hydrosulphuret  of  am- 
monia, 

Stromeyer  has  recommended  a very  elegant  and  still  better  process  for 
removing  small  quantities  of  manganese  from  lime  and  magnesia.  The 
solution  is  acidulated  with  nitric  or  muriatic  acid,  bicarbonate  of  soda  is 
gradually  added  in  very  slight  excess,  stirring  after  each  addition,  that  the 
liquid  may  be  charged  with  carbonic  acid,  and  a solution  of  chlorine,  or  a cur- 
rent of  the  gas,  is  introduced.  The  protoxide  of  manganese  is  converted  by  the 
chlorine  into  the  insoluble  peroxide,  while  any  traces  of  lime  or  magnesia, 
which  might  otherwise  fall,  are  retained  in  solution  by  means  of  carbonic 
acid.  A solution  of  chloride  of  soda  or  lime  is  in  fact  our  most  delicate  test 
or  small  quantities  of  manganese. 

Mode  of  analyzing  an  Earthy  Mineraly  containing  SilicOy  Iron^  Alum- 
ina,  ManganesCy  Limey  and  Magnesia. — The  mineral,  reduced  to  fine 
powder,  is  ignited  with  three  or  four  times  its  weight  of  carbonate  of 
potassa  or  soda,  the  mass  is  taken  up  in  dilute  muriatic  acid,  and 
the  silica  separated  in  the  way  already  described.  To  the  solution, 
thus  freed  from  silica  and  duly  acidulated,  carbonate  of  soda,or  still 
better  the  bicarbonate,  is  gradually  added,  so  as  to  charge  the  liquid 
with  carbonic  acid,  as  in  the  analysis  of  iron  and  manganese.  In  this  man- 
ner, the  iron  and  alumina  are  alone  precipitated,  substances  which  may  be 
separated  from  each  other  by  means  of  pure  potassa.  (Page  586.)  The 
manganese,  lime,  and  magnesia,  may  then  be  determined  by  the  processes 
above  described. 

Analysis  of  Minerals  containing  a Fixed  Alkali. — When  the  object 
is  to  determine  the  quantity  of  fixed  alkali,  such  as  potassa  or  soda, 
it  is  of  course  necessary  to  abstain  from  the  employment  of  these 
reagents  in  the  analysis  itself;  and  the  beginner  will  do  w'ell  to  devote 
his  attention  to  the  alkaline  ingredients  only.  On  this  supposition,  he  will 
proceed  in  the  following  manner.  The  mineral  is  reduced  to  a very  fine 
powder,  mixed  intimately  with  six  times  its  weight  of  artificial  carbonate 
of  baryta,  and  exposed  for  an  hour  to  a white  heat.  The  ignited  mass  is 
dissolved  in  dilute  muriatic  acid,  and  the  solution  evaporated  to  perfect  dry- 
ness. The  soluble  parts  are  taken  up  in  hot  water;  an  excess  of  carbonate 
of  ammonia  is  added;  and  the  insoluble  matters,  consisting  of  silica,  carbo- 
nate of  baryta,  and  all  the  constituents  of  the  mineral,  excepting  the  fixed 
alkali,  arc  collected  on  a filter.  The  clear  solution  is  evaporated  to  dryness 
in  a porcelain  capsule,  and  the  dry  mass  is  heated  to  redness  in  a crucible  of 
platinum,  in  order  to  expel  the  salts  of  ammonia.  The  residue  is  chloride  of 
potassium  or  sodium. 

In  this  analysis,  it  generally  happens  that  traces  of  manganese,  and 
sometimes  of  iron,  escape  precipitation  in  the  first  part  of  the  process;  and, 


688 


ANALYSIS  OF  MINERALS. 


in  that  case,  they  should  be  thrown  down  by  hydrosulphurct  of  ammonia. 
If  neither  lime  nor  magnesia  is  present,  the  alumina,  iron,  and  manganese 
may  be  separated  by  pure  ammonia,  and  the  baryta  subsequently  removed 
by  the  carbonate  of  that  alkali.  By  this  method  the  carbonate  of  baryta  is 
recovered  in  a pure  state,  and  may  be  reserved  for  another  analysis.  The 
baryta  may  also  be  thrown  down  as  a sulphate  by  sulphuric  acid,  in  which 
case,  the  soda  or  potassa  is  procured  in  combination  with  that  acid;  but  this 
mode  is  objectionable,  because  the  sulphate  of  baryta  is  very  apt  to  retain 
small  quantities  of  sulphate  of  potassa. 

The  analysis  is  attended  with  considerable  inconvenience  when  magnesia 
happens  to  be  present;  beca,use  this  earth  is  not  completely  precipitated  either 
by  ammonia  or  its  carbonate,  and,  therefore,  some  of  it  remains  with  the 
fixed  alkali.  The  best  mode  witli  which  I am  acquainted,  is  to  precipitate 
the  magnesia,  by  phosphate  of  ammonia;  subsequently  recovering  from  the 
filtered  solution  the  excess  of  phosphoric  acid  by  acetate  of  lead,  and  that  of 
lead  by  sulphuretted  hydrogen.  The  acetate  of  the  alkali  is  tlien  brought 
to  dryness,  ignited,  and,  by  the  addition  of  sulphate  of  ammonia,  converted 
into  a sulphate. 

In  the  preceding  account,  several  operations  have  been  alluded  to,  which, 
from  their  importance,  deserve  more  particular  mention.  The  process  of 

▼j  filtering,  for  example,  is  one  on  which  the  success  of  analyses 

Q materially  depends.  Filtration  is  effected  by  means  of  a glass 

funnel  B,  into  which  a filter  C,  of  nearly  the  same  size  and  form, 

made  of  white  bibulous  paper,  is  inserted.  For  researches  of 
delicacy,  the  filter,  before  being  used,  is  macerated  for  a day  or 
' ' two  in  water  acidulated  with  nitric  acid,  in  order  to  dissolve  lim® 
and  other  substances  contained  in  common  paper,  and  it  is  afler- 
^ V wards  washed  with  hot  water  till  every  trace  of  acid  is  removed. 
It  is  next  dried  at  212^,  or  any  fixed  temperature  insufficient  to  decompose 
it,  and  then  carefully  weighed,  the  weight  being  marked  upon  it  with  a pen- 
cil. As  dry  paper  absorbs  hygrometric  moisture  rapidly  from  the  atmos- 
phere, the  filter,  while  being  weighed,  should  be  enclosed  in  a light  box 
made  for  the  purpose.  When  a precipitate  is  collected  on  a filter,  it  is 
washed  with  pure  water  until  every  trace  of  the  original  liquid  is  removed. 
It  is  subsequently  dried  and  weighed  as  before,  and  the  weight  of  the  paper 
subtracted  from  the  combined  weight  of  the  filter  and  precipitate.  The 
trouble  of  weighing  the  filter  may  sometimes  be  dispensed  with.  Some 
substances,  such  as  silica,  alumina,  and  lime,  which  are  not  decomposed 
when  heated  with  combustible  matter,  may  be  put  into  a crucible  while  yet 
contained  in  the  filter,  the  paper  being  set  on  fire  before  it  is  placed  in  the 
furnace.  In  these  instances,  the  ash  from  the  paper,  the  average  weight  of 
which  is  determined  by  previous  experiments,  must  be  subtracted  from  the 
weight  of  the  heated  mass. 

The  tests  commonly  employed  in  ascertaining  the  acidity  or  alkalinity 
of  liquids  are  litmus  and  turmeric  paper.  The  former  is  made  by  digesting 
litmus,  reduced  to  a fine  powder,  in  a small  quantity  of  water,  and  painting 
with  it  white  paper  which  is  free  from  alum.  Turmeric  paper  is  made  in  a 
similar  manner;  but  the  most  convenient  test  of  alkalinity  is  litmus  paper 
reddened  by  a dilute  acid. 


ANALYSIS  OF  MINERAL  WATERS. 


m 


SECTION  III. 

ANALYSIS  OF  MINERAL  WATERS. 

Rain  water  collected  in  clean  vessels  in  the  country,  or  freshly  falleA 
&now  when  melted,  affords  the  purest  kind  of  water  which  can  be  pfbcured 
without  having  recourse  to  distillation.  The  water  obtained  from  these 
sources,  however,  is  not  absolutely  pure,  but  contains  a portion  of  carbonic 
acid  and  air,  absorbed  from  the  atmosphere.  It  is  remarkable  that  this  air 
is  very  rich  in  oxygen.  That  procured  from  snow-water  by  boiling,  was 
found  by  Gay-Lussac  and  Humboldt  to  contain  34,8,  and  that  from  rain 
water  32  per  cent  of  oxygen  gas.  From  the  powerfully  solvent  properties 
of  water,  this  fluid  no  sooner  reaches  the  ground  and  percolates  through  tlie 
soil,  than  it  dissolves  some  of  the  substances  which  it  meets  with  in  its  pas- 
sage.  Under  common  circumstances  it  takes  up  so  small  a quantity  of  for- 
eign matter,  that  its  sensible  properties  are  not  materially  affected,  and  in 
this  state  it  gives  rise  to  springs  tvell,  and  Hver  water,  ^metimes,  on  the 
contrary,  it  becomes  so  strongly  impregnated  with  saline  and  other  sub- 
stances, that  it  acquires  a peculiar  flavour,  and  is  thus  rendered  unfit  for 
domestic  uses.  It  is  then  known  by  the  name  of  mineral  water. 

The  composition  of  spring  water  is  dependent  on  the  nature  of  the  soil 
through  which  it  flows.  If  it  has  filtered  through  primitive  strata,  such  as 
quartz  rock,  granite,  and  the  like,  it  is  in  general  very  pure;  but  if  it  meets 
with  limestone  or  gypsum  in  its  passage,  a portion  of  these  salts  is  dissolved, 
and  communicates  the  property  called  hardness.  Hard  water  is  charac- 
terized by  decomposing  soap,  the  lime  of  the  former  yielding  an  insoluble 
compound  with  the  acid*  of  the  latter.  If  this  defect  is  owing  to  the  pre- 
sence of  carbonate  of  lime,  it  is  easily  remedied  by  boiling;  when  free  car- 
bonic acid  is  expelled,  and  the  insoluble  carbonate  of  lime  subsides.  If  sul- 
phate of  lime  is  present,  the  addition  of  a little  carbonate  of  soda,  by  precipi- 
tating the  lime,  converts  the  hard  into  soft  water.  Besides  these  ingre* 
dients,  the  muriates  of  lime  and  soda  are  frequently  contained  in  spring 
water. 

' Spring  water,  in  consequence  of  its  saline  impregnation,  is  frequently 
unfit  for  chemical  purposes,  and  on  these  occasions  distilled  water  is  em* 
ployed.  Distillation  may  be  performed  on  a small  scale  by  means  of  a re- 
tort, in  the  body  of  which  water  is  made  to  boil,  while  the  condensed  vapour 
is  received  in  a glass  flask,  called  a recipient^  which  is  adapted  to  its  beak 
or  open  extremity.  This  process  is  more  conveniently  conducted,  however, 
by  means  of  a still. 

The  different  kinds  of  mineral  water  may  be  conveniently  arranged  for 
the  purpose  of  description  in  the  six  divisions  of  acidulous,  alkaline,  chalyb- 
eate, sulphurous,  saline,  and  siliceous  springs. 

1.  Acidulous  springs,  of  which  those  of  Seltzer,  Spa,  Pyrmont,  and  Carls- 
bad, are  the  most  celebrated,  commonly  owe  their  acidity  to  the  presence  of 
free  carbonic  acid,  in  consequence  of  the  escape  of  which  they  sparkle  when 
poured  from  one  vessel  into  another.  Such  carbonated  waters  communi- 
cate a red  tint  to  litmus  paper  before,  but  not  after  being  boiled,  and  the  red- 
ness disappears  on  exposure  to  the  air.  Mixed  with  a sufficient  quantity  of 
lime-water,  they  become  turbid  from  the  deposition  of  carbonate  of  lime. 
They  frequently  contain  the  earbonates  of  lime,  magnesia,  and  iron,  in  con- 


• Dr.  Turner  must  here  allude  to  the  margaric  and  oleic  acids,  into  which 
the  oil  used  in  the  fabrication  of  soap  is  converted  by  saponification.  B. 

60 


590 


1 


ANALYSIS  OF  MINERAL  WATER#. 

soquence  of  the  facility  with  which  these  salts  arc  dissolved  by  water  char^*  * 
e^l  with  carbonic  acid. 

I The  best  mode  of  determining"  the  quantity  of  carbonic  acid 

II  is  by  heating"  a portion  of  the  water  ih  a flask,  as  in  the  annexed 

A Iw  %ure,  and  receiving  the  carbonic  acid  by  means  of  a bent  tube, 

111  lip  ^ graduated  jar  filled  with  mercury. 

2.  Alkaline  waters  are  such  as  contain  a free  or  carbonated  alkali,  and, 

consequently,  either  in  their  natural  state  or  when  eoncentrated  by  evapo- 
ration, possess  an  alkaline  reaction.  • 

These  springs  are  rare.  The  best  instance  I have  met  with  is  in  water 
collected  at  the  Furnas,  St.  Michaels,  South  America,  and  sent  to  the  Royal 
Society  of  Edinburgh  by  Lord  Napier.  These  springs  contain  carbonate  of 
soda  and  carbonic  acid,  and  are  almost  entirely  free  from  earthy  substan- 
ces. Of  five  different  kinds  of  these  waters  which  I examined,  the  greater 
part  also  contained  protoxide  of  iron,  sulphuretted  hydrogen,  and  muriate 
of  soda. 

3.  Chalybeate  waters  arc  characterized  by  a strong  styptic  inky  taste, 
and  by  striking  a black  colour  with  the  infusion  of  gall-nuts..  The  iron  is 
sometimes  combined  with  muriatic  or  sulphuric  acid;  but  most  frequently 
it  is  in  the  form  of  protocarbonate,  held  in  solution  by  free  carbonic  acid. 

On  exposure  to  the  air,  the  protoxide  is  oxidized,  and  the  hydrated  peroxide 
subsides,  causing  the  ochreous  deposite,  so  commonly  observed  in  the  vicin- 
ity of  chalybeate  springs. 

To  ascertain  the  quantity  of  iron  contained  in  a mineral  water,  a known 
weight  of  it  is  concentrated  by  evaporation,  and  the  iron  is  brought  to  the 
state  of  peroxide  by  means  of  nitric  acid.  The  peroxide  is  then  precipitat- 
ed by  an  alkali  and  weighed ; and  if  lime  and  magnesa  are  present,  it  may 
be  separated  from  those  earths  by  the  process  described  in  the  last  section. 

Chalybeate  waters  are  by  no  means  uncommon ; but  the  most  noted  in 
Britain  are  those  of  Tunbridge,  Cheltenham,  and  Brighton.  The  Bath 
water  also  contains  a small  quantity  of  iron. 

4.  Sulphurous  waters,  of  which  the  springs  of  Aix  la  Chapelle,  Harrow- 
gate,  and  Moffat  afford  examples,  contain  sulphuretted  hydrogen,  and  9,re 
easily  recognised  by  their  odour,  and  by  causing  a brown  precipitate  with 
a salt  of  lead  or  silver.  The  gas  is  readily  expelled  by  boiling,  and  its 
<|uantity  may  be  inferred  by  transmitting  it  through  a solution  of  acetate  of 
lead,  and  weighing  the  sulphuret  which  is  generated. 

5.  Those  mineral  springs  are  called  saline  which  jdo  not  belong  to  either 
of  the  preceding  divisions.  The  salts  which  are  most  frequently  contained 
in  these  waters  arc  sulphates,  muriates,  and  carbonates  of  lime,  magnesia, 
and  soda.  Potassa  sometimes  exists  in  them,  and  Berzelius  has  found  lithia 
in  the  spring  of  Carlsbad.  It  has  lately  been  discovered  that  the  presence  ' 
of  hydriodic  acid  in  small  quantity  is  not  unfrequent.^  As  examples  of 
saline  water  may  be  enumerated  the  springs  of  Epsom,  Cheltenham,  Bath, 
Bristol,  Bareges,  Buxton,  Pitcaithly,  and  4 oeplitz. 

'J'lic  first  object  in  examining  a saline  spring  is  to  determine  the  nature 
of  its  ingredients.  Muriatic  acid  is  detected  by  nitrate  of  silver,  and  sul- 
phuric acid  by  muriate  of  baryta  ; and  if  an  alkaline  earbonate  be  present,  ^ 
the  precipitate  occasioned  by  either  of  these  tests  will  contain  a carbonate  ' r" 


* 'flic  salt  spring  at  'J’hoodorshallc,  in  Germany,  contains  a considera- 
ble quantity  of  bromine.  See  note,  page  227,  B.  ■; 


ANALYSIS  OF  MINERAL  WATERS. 


591  . 


of  silver  or  baryta.  The  presence  of  lime  and  mag’nesia  may  be  discovered, 
the  former  by  oxalate  of  ammonia,  and  the  latter  by  phosphate  of  ammonia. 
Potassa  is  known  by  the  action  of  muriate  of  platinum.  (Pag^c  295.)*  To 
detect  soda,  the  water  should  be  evaporated  to  dryness,  the  deliquescent 
salts  removed  by  alcohol,  and  the  matter  insoluble  in  that  menstruum  taken 
up  by  a small  quantity  of  water,  and  allowed  to  crystallize  by  spontaneous 
evaporation.  The  salt  of  soda  may  then  be  recog-nised  by  the  rich  yellow 
colour  which  it  communicates  to  flame.  (Pag-e  297'.)  If  the  presence  of 
hydriodic  acid  be  suspected,  the  solution  is  broug-ht  to  dryness,  the  soluble 
parts  dissolved  in  two  or  three  drachms  of  a cold  solution  of  starch,  and 
strongs  sulphuric  acid  gradually  added.  (Page  223.) 

Having' thus  ascertained  the  nature  of  the  saline  ingredients,  their  quan- 
tity may  be  determined  by  evaporating  a pint  of  water  to  dryness,  heating 
to  low  redness,  and  weighing  the  residue.  In  order  to  make  an  exact  ana- 
lysis, a given  quantitj^  of  the  mineral  water  is  concentrated  in  an  evaporat- 
ing basin  as  far  as  can  be  done  without  causing  either  precipitation  or  crys- 
tallization, and  the  residual  liquid  is  divided  into  two  equal  parts.  From 
one  portion  the  sulphuric  and  carbonic  acids  are  thrown  down  by  nitrate  of 
baryta,  and  after  collecting  the  precipitate  on  a filter,  the  muriatic  acid  is 
precipitated  by  nitrate  of  silver.  The  mixed  sulphate  and  carbonate  is  ex- 
posed to  a low  red  heat,  and  weighed ; and  the  latter  is  then  dissolved  by 
dilute  muriatic  acid,  and  its  quantity  determined  by  weighing  the  sulphate. 
TJie  chloride  of  silver,  of  which  146  parts  correspond  to  37  of  muriatic  acid, 
is  fused  in  a platinum  spoon  or  crucible,  in  order  to  render  it  quite  free  from 
moisture.  To  the  other  half  of  the  concentrated  mineral  water,  oxalate  of 
ammonia  is  added  for  the  purpose  of  precipitating  the  lime;  and  the  mag- 
nesia is  afterwards  thrown  down  as  the  ammoniaco-phosphate,  by  means  of 
ammonia  and  phosphoric  acid.  Having  thus  determined  the  weight  of  each 
of  the  fixed  ingredients  excepting  the  soda,  the  loss  of  course  gives  the  quan- 
tity of  that  alkali ; or  it  may  be  procured  in  a separate  state  by  the  process 
described  in  the  forgoing  section. 

The  individual  constituents  of  the  water  being  known,  it  remains  to  de- 
termine the  state  in  which  they  were  originally  combined.  In  a mineral 
water  containing  sulphuric  and  muriatic  acids,  lime,  and  soda,  it  is  obvious 
that  three  cases  are  possible.  The  liquid  may  contain  sulphate  of  lime  and 
muriate  of  soda,  or  muriate  of  lime  and  sulphate  of  soda,  or  each  acid  may 
be  distributed  between  both  the  bases.  It  was  at  one  time  supposed  that  the 
lime  must  be  in  combination  with  sulphuric  acid,  because  the  sulphate  of 
that  earth  is  left  when  the  water  is  evaporated  to  dryness.  This,  however, 
by  no  means  follows.  ‘ In  whatever  state  the  lime  may  exist  in  the  original 
spring,  gypsum  will  be  generated  as  soon  as  the  concentration  reaches  that 
deg-ree  at  which  sulphate  of  lime  cannot  be  held  in  solution.  The  late  Dr. 
Murray*,  who  treated  this  question  with  much  sagacity,  observes  that  some 
mineral  waters,  which  contain  the  four  principles  above  mentioned,  possess 
higher  medicinal  virtues  than  can  be  justly  ascribed  to  the  presence  of  sul- 
phate of  lime.  He  advances^  the  opinion  that  alkaline  bases  are  united  in 
mineral  waters  with  those  acids  with  which  they  form  the  most  soluble 
compounds,  and  that  the  insoluble' salts  obtained  by  evaporation  are  merely 
products.  He,  therefore,  proposes  to  arrange  the  substances  determined  by 
analysis  according  to  this  supposition.  To  this  practice  there  is  no  objec- 
tion; but  it  is  probable  that  each  acid  is  rather  distributed  between  several 
bases  than  combined  exclusively  with  either.  (Page  116.) 

Sea  water  may  be  regarded  as  one  of  the  saline  mineral  waters.  Its  taste 
is  disagreeably  bitter  and  saline,  and  its  fixed  constituents  amount  to  about 


Philosophical  Transactions  of  Edinburgh,  vol.  vii. 


592 


ANALYSIS  OF  MINERAL  WATERS. 


three  per  cent.  Its  specific  gravity  varies  from  1.0269  to  1.0285;  and  it 
freezes  at  about  28.5°  F.  According  to  the  analysis  of  Dr.  Murray,  10,000 
parts  of  water  from  the  Frith  of  Forth  contain  220.01  parts  of  common  salt, 
33.16  of  sulphate  of  soda,  42.08  of  muriate  of  magnesia,  and  7.84  of  muriate 
of  lime.  Dr.  Wollaston  has  detected  potassa  in  sea  water,  and  it  likewise 
contains  small  quantities  of  hydriodic  and  hydrobromic  acids. 

The  water  of  the  Dead  Sea  has  a far  stronger  saline  impregnation  than 
sea  water,  containing  one-fourth  of  its  weight  of  solid  matter.  It  has  a 
fKJCuliarly  bitter,  saline,  and  pungent  taste,  and  its  specific  gravity  is  1.211. 
According  to  the  analysis  of  Dr.  Marcet,  100  parts  of  it  are  composed  of 
muriate  of  magnesia  10.246,  muriate  of  soda  10.36,  muriate  of  lime  3.92, 
and  sulphate  of  lime  0.054.  In  the  river  Jordan,  which  flows  into  the  Dead 
Sea,  Dr.  Marcet  discovered  the  same  principles  as  in  the  lake  itself. 

6.  Siliceous  waters  are  very  rare,  and  in  those  hitherto  discovered,  the 
silica  appears  to  have  been  dissolved  by  means  of  soda.  The  most  remark- 
able of  these  are  the  boiling  springs  of  the  Geyser  and  Rykum  in  Iceland,  a 
gallon  of  which,  according  to  the  analysis  of  Dr.  Black,  contains  the  follow- 
ing substances  ; (Edinburgh  Philos.  Trans,  iii.  95.) 


Soda, 

Geyser. 

5.56 

Rykum. 

3.0 

Alumina, 

2.80 

0.29 

Silica, 

31.50 

21.83 

Muriate  of  soda. 

14.42 

16.96 

Sulphate  of  soda, 

8.57 

7.53 

The  hot  springs  of  Pinnarkoon  and  Loorgootha  in  India  are  analogous  to 
the  foregoing.  A gallon  of  the  water  yields  about  24  grains  of  solid  matter; 
and  the  saline  contents,  sent  to  Dr.  Brewster  by  Mr.  P.  Breton,  I found  to 
contain  21.5  per  cent  of  silica,  19  of  chloride  of  sodium,  19  of  sulphate  of 
soda,  19  of  carbonate  of  soda,  pure  soda  5,  and  15.5  of  water,  (Edinburgh 
Journal  of  Science,  No.  xvii.  p.  97.) 


COMPOSITION  OF  MINERAL  WATERS. 


593 


TABI.E 

Shoiving  the  Composition  of  several  of  the  Principal 
Mineral  Waters,  {From  Dr,  Henryks  Elements,) 

[N.  B.  The  temperature,  when  not  expressed,  is  to  be  understood  to  be 
49°  or  50°  Fahrenheit.] 

1.  Carbonated  Waters. 


Seltzer.  Bergmann. 

In  eaeh  wine  pint. 

Carbonic  acid  - 17  cub.  in. 


Specific  gravity  1.0027. 
Carbonate  of  soda  - 4 grs. 

of  magnesia  5 

of  lime.  - 3 

Chloride  of  sodium  - 17 

29 


Carlsbad  (Temperature  165°  Fahr.) 
Berzelius. 

In  a wine  pint. 

•Carbonic  acid  - 5 cub.  in. 


In  1000  parts  by 

weight. 

Sulphate  of  soda 

2.58714  grs. 

Carbonate  of  soda 

1.25200 

Chloride  of  sodium 

1.04893 

Carbonate  oflime 

0.31219 

Fluate  of  do. 

0.00331 

Phosphate  of  do. 

0.00019 

Carbonate  of  strontia 

0.00097 

of  magnesia 

0.18221 

Phosphate  of  alumina 

0.00034 

Carbonate  of  iron 

0.00424 

of  manganese. 

a trace 

Silica 

0.07504 

5,46656 


Spa.  Bergmann. 

Specific  gravity  1.0010. 
In  each  wine  pint. 


Carbonic  acid  - 13  cub.  in. 


Carbonate  of  soda  - 1.5  grs. 

of  magnesia  4.5 

— of  lime  - 1.5 

Chloride  of  sodium  - 0.2 

Oxide  of  iron  - 0.6 


8.3 


Pyrmont.  Bergmann. 
Specific  gravity  1.0024. 
In  each  wine  ’pint. 


Carbonic  acid  - 26  cub.  in. 


Carbonate  of  magnesia  10.  gis, 

oflime  - 4.5 

Sulphate  of  magnesia  5.5 

of  lime  - 8.5 

Chloride  of  sodium  - 1.5 

Oxide  of  iron  - 0.6 


30.6 


PouGEs.  Hassenfratz^. 


In  each  wine  pint. 


Carbonic  acid 

30  cub.  in, 

Carbonate  of  soda 

10.  grs. 

of  magnesia 

1.2 

of  lime 

12. 

Chloride  of  sodium 

2.2 

Oxide  of  iron 

2.5 

Silica  - « - 

0.5 

— ^ — ' 

28.4 

50* 


594 


COMPOSITION  OF  MINERAL  WATERS. 


Composition  of  Mineral  Waters — Continued, 

11.  Sulphuretted  Waters. 


Aix  LA  Chapelle.  Bergmann. 

Temperature  143°. 

In  each  wine  pint. 

Sulphuretted  hydrogen  5-5  cub.  in. 


Carbonate  of  soda 

of  lime 

Muriate  of  soda 


12.  grs. 
4.75 

5. 

21.75 


Cheltenham,  Sulphur  Spring. 
Brande  and  Parkes. 

Specific  gravity  1.0085. 

In  each  wine  pint. 

Carbonic  acid  - 1.5  cub.  in. 

Sulphuretted  hydrogen  2.5 


Sulphate  of  soda 

of  magnesia 

of  lime 

Muriate  of  soda 
Oxide  of  iron 


23.5  grs, 
5. 

1.2 

35. 

0.3 

65. 


Leamington,  Sulphur  Water. 
Scudamore. 

Specific  gravity  1.0042. 
Sulphuretted  hydrogen,  quantity  not 
ascertained. 

In  each  pint. 

Muriate  of  soda 

of  lime 

of  magnesia 


Sulphate  of  soda 
Oxide  of  iron 


15.  grs. 
7.96 
3.30 
11.60 
a trace. 


Moffat.  Garnet. 

Nitrogen  - 0.5  cub.  in. 

Carbonic  acid  - 0.6 

Sulphuretted  hydrogen  1.2 


Muriate  of  soda 


4.5  grs. 


Harrowgate  Water. 

'New  Wcll^  at  the  Crown  Inn. 
(West,  Quart.  Journ.  xv.  82.) 
Specific  gravity  1.01286  at  69°. 
One  wine  gallon  contains 
Sulphuretted  hydrogen  6.4  cub.  in. 
Carbonic  acid  - 5.25 

Azote  - - 6.5 

Carburetted  hydrogen  4.65 


Also, 

Muriate  of  soda 

of  lime 

of  magnesia 

Bicarbonate  of  soda 


22.8 

735. 

71.5 

43. 

14.75 

864.25 


grs. 


37.86 


Old  Well. 

Sp.  gr.  1.01324  at  60°. 
Sulphuretted  hydrogen  14.0  cub.  in. 


Carbonic  acid 
Azotic  gas 

Carburetted  hydrogen 


Alsa, 

Muriate  of  soda 

of  lime 

of  magnesia 


Bicarbonate  of  soda 


4.25 

8. 

4.15 

30.4 

752.0  grs. 
65.75 
29.2 
12.8 


859.75 


III.  Saline  Waters. 


Seidlitz.  Bergmann. 
Specific  gravity  1.0060. 
In  a pint. 
Carbonate  of  magnesia 
of  lime 


Sulphate  of  magnesia 

of  lime 

Muriate  of  magnesia 


2.5 

0.8 

180. 


4.5 

192.8 


Cheltenham,  pure  saline. 
Parkes  and  Brande. 

In  each  pint. 

Sulphate  of  soda 

of  magnesia 

of  lime 


Muriate  of  soda 


15. 

11. 

4.5 

50. 


80.5 


COMPOSITION  OF  MINERAL  WATERS. 


595 


Composition  of  Mineral  Waters — Continued, 


Leamington,  saline.  Scudamore. 
Specific  gravity  1.0119. 

In  a pint. 


Muriate  of  soda  . 53.75 

of  lime  . 28.64 

of  magnesia  20.16 

Sulphate  of  soda  . 7*83 

Oxide  of  iron  . a trace. 


110.38 


Leamington, Lord  Aylesford’s  spring. 
Scudamore. 

Specific  gravity  1.0093. 

In  a pint. 


Muriate  of  soda  . 12.25 

of  lime  . 28.24 

of  magnesia  5.22 

Sulphate  of  soda  . 32.96 

Oxide  of  iron  . a trace. 


78.67 


Bristol.  Garrick. 

Temp.  74°.  Specific  gravity  1,00077. 
In  each  pint. 


Carbonic  acid  . 3.5  cub.  in. 


Carbonate  of  lime  . 1.5  grs. 

Sulphate  of  soda  . 1.5 

of  lime  . 1.5 

Muriate  of  soda  . 0.5 

of  magnesia  . 1. 


6.0 


Bath.  Phillips. 

Temp.  109°  to  117°.  Sp.  gr.  1.002. 
In  each  pint. 


Carbonic  acid 

1.2  cub.  in. 

Carbonate  of  lime 

0.8 

Sulphate  of  soda 

1.4 

of  lime 

9.3 

Muriate  of  soda 

3.4 

Silica 

0.2 

Oxido  of  iron 

. a trace. 

Bath.  Solid  contents.  Scudamore. 


Muriate  of  lime 

1.2  grs. 

of  magnesia 

1.6 

Sulphate  of  lime 

9.5 

of  soda 

.9 

Silica 

.2 

Oxide  of  iron 

.01985 

Loss,  partly  carb.  of  soda 

.58015 

14, 


Buxton.  Scudamore. 

Sp.  gr.  at  60°.  1.0006.  Temp.  82°. 
In  a wine  gallon. 

Carbonic  acid  . 1.5  cub.  in. 

Nitrogen  . . 4.64 


Muriate  of  magnesia 

.58  grs. 

of  soda 

2.40 

Sulphate'  of  lime 
Carbonate  of  lime 

.6 

10.40 

Extractive  & vegetable  j 
matter  \ 

i 0.50 

Loss 

^ 0.52 

15. 

Or,  according  to  Dr,  Murray’s  views, 

Sulphate  of  soda 

0.63 

Muriate  of  lime 

0.57 

of  soda 

1.80 

of  magnesia 

0.58 

Carbonate  of  lime 

10.40 

Extract  and  loss 

1.02 

15.00 

Matlock  Bath.  Scudamore. 

Temp.  68°.  Sp.  gr.  1.0003. 

Free  carbonic  acid. 

Muriates  and  ) magnesia,  lime,  and 
sulphates  of  ^ soda? 
in  very  minute  quantities  not  yet  as- 
certained. 


16.3 


506 


COMPOSITION  OF  MINERAL  WATERS. 
Composition  of  Mineral  Waters — Continued, 
IV.  Chalybeate  Waters. 


Tunbridge.  Scudamore. 
Specific  gravity  1.0007. 
In  each  gallon. 


Muriate  of  soda 

2.46 

oflime 

0.33 

of  magnesia 

0.29 

Sulphate  of  lime 

1.41 

Carbonate  of  lime 

027 

Oxide  of  iron 

2.22 

Traces  of  manganese,  vc-  i 

gclable  fibre,  silica,  &,c.  < 

Loss 

0.13 

7.61 

Cheltenham.  Brande  and  Parkes. 
Specific  gravity  1.0092. 

In  a pint. 

Carbonic  acid  . 2.5  cub.  in. 


Carbonate  of  soda  . 0.5 

Sulphate  of  soda  . 22.7 

of  magnesia  6. 

of  lime  . 2.5 

Muriate  of  soda  . 41.3 

Oxide  of  iron  . 0.8 

73.8 


BrigiitoIVj.  Marcet. 


Specific  gravity  1.00108. 

Carbonic  acid  gas 

2 J cub.  in. 

Sulphate  of  iyon 

1.80  gra. 

of  lime 

4.09 

Muriate  of  soda 

1.53 

of  magnesia 

0.75 

Silica 

0.14 

Loss 

0.19 

8.50 

Harrogate,  Oddie’s  chalybeate. 

Scudamore. 

Specific  gravity  1.0053. 

In  each  gallon. 

Muriate  of  soda 

300.4 

of  lime 

22. 

of  magnesia 

9.9 

Sulphate  of  lime 

1.86 

Carbonate  of  do. 

6.7 

of  magnesia 

0.8 

Oxide  of  iron 

2.40 

Residue,  cliicfly  silica 

.40 

344.46 


APPENDIX. 


TABLE  I. 


*rABLE  of  Chemical  Equivalents^  Atomic  Weights,  or  Proportional  Num-’ 
bers,  Hydrogen  being  taken  as  Unity. 

In  preparing  the  following  tabular  view  of  the  atomic  weights,  I have 
chiefly  consulted  the  table  published  by  Dr.  Thomson  in  his  First  Princi- 
ples of  Chemistry,  and  by  Mr.  Phillips  in  the  new  series,  10th  volume,  of 
the  Annals  of  Philosophy.  F'rom  the  full  account  already  given  of  the  Laws 
of  Combination  and  of  the  Atomic  Theory,  it  will  be  superfluous  to  describe 
the  uses  of  the  table.  The  only  explanation  required  on  this  subject  relates 
to  the  ingenious  contrivance  of  Dr.  Wollaston,  called  the  Scale  of  Chemical 
Equivalents.  This  useful  instrument  is  a table  of  equivalents,  compre- 
hending all  those  substances  which  are  most  frequently  employed  by  che- 
mists in  the  laboratory;  and  it  only  differs  from  other  tabular  arrangements 
of  the  same  kind,  in  the  numbers  being  attached  to  a sliding  rule,  which  is 
divided  according  to  the  principle  of  that  of  Gunter.  From  the  mathemati- 
cal construction  of  the  scale,  it  not  only  serves  the  same  purpose  as  other 
tables  of  equivalents,  but  in  many  instances  supersedes  the  necessity  of  cal- 
culation. Thus,  by  inspecting  the  common  table  of  equivalents,  we  learn 
that  88  parts,  or  one  equivalent  of  sulphate  of  potassa,  contain  40  parts  of 
sulphuric  acid  and  48  of  potassa;  but  recourse  must  be  had  to  calculation, 
when  it  is  wished  to  determine  the  quantity  of  acid  or  alkali  in  any  other 
quantity  of  the  salt.  This  knowledge,  on  the  contrary,  is  obtained  directly 
by  means  of  the  scale  of  chemical  equivalents.  For  example,  on  pushing 
up  the  slide  until  100  marked  upon  it  is  in  a line  with  the  name  sulphate  ot 
potassa  on  the  fixed  part  of  the  scale,  the  numbers  opposite  to  the  terms  sul- 
phuric acid  and  potassa  will  give  the  precise  quantity  of  each  contained  la 
100  parts  of  the  compound.  In  the  original  scale  of  Dr.  Wollaston,  for  a 
particular  account  of  which  I may  refer  to  the  Philosophical  Transactions 
for  1814,  oxygen  is  taken  as  the  standard  of  comparison;  but  hydrogen  may 
be  selected  for  that  purpose  with  equal  propriety,  and  scales  of  this  kind  have 
been  prepared  for  sale  by  Mr.  Boswell  Reid,  of  Edinburgh. 


Acid,  acetic,  . 50  or  51 

c.  Iw.*  . 59  or  60 

arsenic,  (a.  38  + ox. 

20  Berz.)  . 58 


Acid,  arsenious,  (a.  38  -J-  ox. 

12  Berz.)  • 50 

benzoic  . 120 

boracic,  (b.  8 -f-  ox.  16)  24 


♦ c means  crystallized,  w,  water;  and  the  numeral  before  w expresses  the 
number  of  equivalents  of  water  which  the  crystals  contain. 


598 


APPENDIX. 


Acid,  boracic,  c.  2w.  . 42 

bromic,  (b.  78.26  + 

40Berz.  ) . 118.26 

carbonic,  (carb.  6 -|- 

ox.  16)  . 22 

chloric,  (chi.  36  + 
ox.  40)  . 76 

chloriodic,  (chi.  72  -f- 
iod.  124)  . 196 

chlorocarbonic,  (chi.  36 

-j-  carb.  oxide  14)  . 50 

chlorocyanic,  (chi.  36 

cyan.  26)  . 62 

chromic,  (chr.  32  ox- 
20)  . 52 

citric,  . 58 

c.2w.  . 76 

coliimbic,  . 152 

fluoboric,  . ?68 

fluosilicic,  . ?26.86 

formic,  . 37 

g'allie,  . 63  or  64 

hydriodic,  (iod.  124  -}- 

hyd.  1)  . 125 

hydrohromic,  (b.  78.26 

+ hyd.  1)  . 79.26 

hydrocyanic,  (cyan.  26 

■4-hyd.  1)  . 27 

hydrofluoric,  . 19.86 

hyposulplmrous,  (s.  32 

+ ox. S)  . 40 

hyposulphuric,  (s.  32  -{- 

ox.  40)  . 12 

iodic,  (iod.  124  -f-  ox. 

40)  . 164 

malic,  (Liebig)  . 57 

manganeseous,  . ?52 

mang-anesic,  , 60 

rnolybdic,  72 

muriatic,  (chi.  36  + 

hyd.  1)  . 37 

nitric,  dry,  (nit.  14  -f-  ox.  . 

40)  . 54 

nitric,  liquid  (sp.  gr.  1.5) 

2w.  . 72 

nitrous  (nit.  14  -|-  ox.  32)  46 

oxalic,  . 36 

c.  3vv.  . 63 

perchloric,  (chi.  36  -[-  ox. 

56)  . 92 

phosphorous,  (p.  15.71 
ox.  12)  . 27.71 

phosphoric,  (p.  15.71  -j- 
ox.  20)  . 35.71 


Acid,  saccholactic,  . 104 

sclenious,  (sel.  40  -f"  ox. 

16)  . 56 

selenic,  (sel.  40  -f-  ox.  24)  64 

succinic,  50 

sulphuric,  dry,  (s.  16  4-  ox. 

24)  ^ . 40 

sulphuric,  liquid,  (sp.  gr, 

1.8485,)  Iw.  . 49 

sulphurous,  (s.  16  4-  ox. 

16)  . 32 

tartaric,  . 66 

c.  Iw.  . 75 

titanic,  . 48, 

tungstic,  (t.  96  -f-  ox.  24)  120 

uric,  ' . 72 

Alcohol,  (ol.  gas  14  aq. 

vap.  9)  , . 23 

Alum,  anhydrous,  . 262 

c.  25w.  ‘ ..  487 

Alumina,  .18 

sulphate,  . . 58 

Aluminium,  . 10 

Ammonia,  (nit.  14  + hyd. 

3)  .17 

Antimony,  . 44 

chloride,  (ant.  44  chi. 

36)  . 80 

iodide,  (ant.  44  4-  iod. 

124)  . 168 

protoxide,  (ant.  44  -f-  ox. 

8)  . 52 

deutoxide,  (ant.  44  -|-  ox. 

12)  .56 

peroxide,  (ant.  44  + ox. 

16)  . 60 

sulphuret,  . . 60 

Arsenic,  . . 38 

sulphuret,  (realgar)  . 54 

sesqnisulphuret*  (orpi- 

ment)  . . 62 

persulphuret,  (a.  38  + 

s.  40)  . . 73 

Barium,  . . 70 

chloride,  . . 106 

iodide,  . . 194 

protoxide,  (baryta)  . 78 

peroxide,  . . ?86 

phnsphurct,  . . 85.71 

sulphuret,  . . • 86 

Bismuth,  . . 72 

chloride,  . . 108 

iodide,  . . 196 

oxide,  . . 80 


1 proportional  of  arsenic  and  1 sulphur. 


APPENDIX.  59^ 


Bismuth,  phosphuret, 

87.71 

sulphuret, 

88 

Boron, 

8 

Bromine,  (Berz.)  . 

78.26 

Cadmium, 

56 

chloride, 

92 

iodide, 

180 

oxide. 

64 

phosphuret. 

71.71 

sulphuret. 

72 

Calcium, 

20 

chloride. 

56 

iodide,  , 

144 

protoxide,  (lime) 

28 

phosphuret. 

35.71 

sulphuret. 

36 

Carbon, 

6 

bisulphuret,  (carb.  6.  -j- 
s.  32) 

38 

chloride. 

42 

perchloride,  (carb.  12 
-|-  chi.  lOS)  . 

120 

oxide. 

14 

phosphuret. 

21,71 

Cerium, 

50 

protoxide,  (cer.  50  4” 
ox.  8) 

58 

peroxide,  (cer.  50  -\-  ox. 
12) 

62 

Clilorine, 

36 

hydrocarburet,  (chi.  36. 

4-  ol.  gas  14) 

50 

protoxide,  (chi.  36  -\~ 
ox.  8) 

44 

peroxide,  (chi.  36  4” 

ox.  32) 

68 

Chromium, 

32 

protoxide. 

40 

Cobalt, 

26 

chloride,  . 

62 

iodide,  . 

150 

protoxide,  (cob.  26 ‘ 4" 
ox.  8) 

34 

peroxide,  (cob.  26  4" 
ox.  12) 

38 

phospliuret. 

41.71 

sulphuret. 

42 

Columbium, 

Copper,  (32  Thomson.) 

144 

64 

chloride. 

100 

bichloride. 

136 

iodide. 

188 

protoxide. 

72 

peroxide. 

80 

phosphuret, 

79,71 

sulphuret. 

80 

bisulphuret. 

96 

Cyanogen,  (carb.  12  4~ 
nit.  14) 

26 

bisulphuret,  (cyan.  26 

4-  s.  32)  . 

58 

Ether,  (ol.  gas  28  4"  aq. 

• 

vap.  9) 

37 

Fluorine, 

18.86 

Glucinium,  * 

18 

Gluciua, 

. 26 

Gold, 

200 

chloride. 

236 

bichloride. 

272 

iodide. 

324 

protoxide,  (g.  200  4” 
ox.  8) 

208 

peroxide,  (g.  200  4” 
ox.  24) 

224 

sulphuret,  (g.  200  4" 
s,  48) 

248 

Hydrogen, 

1 

arseniuretted,  - . 

39 

carburetted,  (carb.  6 4" 
hyd.  2) 

8 

bicarb,  (ol.  gas)  carb.  12 
+ hyd.  2) 

14 

seleniuretted. 

41 

sulphuretted,  . ^ 

17 

bisulphuretted. 

33 

Iodine,  . ' 

124 

Iridium,  (Berz.) 

99 

Iron, 

' 28 

chloride,  (ir.  28  4"  chi. 

36) 

64 

perchloride,  (ir.  28  + 
chi.  54) 

82 

iodide. 

152 

protoxide,  (ir.  28  4" 
ox.  8) 

36 

peroxide,  (ir.  28  4“  ox. 

12) 

40 

sulphuret. 

44 

bisulphuret,  ' . 

60 

Lead, 

104 

chloride. 

140 

protoxide,  (1.  104  4" 
ox.  8) 

112 

deutoxide,  (1.  104  4“ 
ox.  12) 

116 

peroxide,  (1.  104  4" 
ox.  16) 

120 

phosphuret. 

119.71 

sulphuret,  . . 

120 

Lithium, 

10 

chloride. 

46 

iodide. 

134 

oxide,  (lithia) 

18 

sulphuret, 

26 

600 

APPEKDIX. 

Magnesium,  > 

chloride, 

12 

Phosphorus,  carburet, 

21.71 

48 

sulphuret,  » 

31.71 

oxide,  (magnesia) 

20 

Platinum,  (Berz.)  . 

about  99 

sulphuret. 

28 

chloride, 

135 

Manganese, 

28 

bichloride. 

171 

chloride,  (m.  28  -f"  ehl. 

protoxide. 

107 

36)  . 

64 

deutoxide. 

115 

perehloride,  (m.  28  + 

sulphuret. 

115 

ehl.  144) 

172 

bisulphuret, 

131 

protoxide,  (m.  28  -f- 

Potassium, 

40 

ox.  8) 

36 

chloride, 

76 

deutoxide,  (m  28  4-  ox. 

iodide. 

164 

12)  . 

peroxide,  (m.  28  + ox. 

40 

protoxide,  (potassa) 
peroxide,  (p.  40  -f-  ox. 

48 

16)  . 

44 

24)  . 

64 

sulphuret. 

*44 

phosphuret. 

55.71 

Mercury, 

200 

sulphuret. 

• 56 

protochloride,  (calomel) 

236 

Rhodium,  (Berz.) 

about  52 

bichloride,  (corros.  sub.) 

272 

protoxide. 

60 

iodide. 

324 

peroxide,  (r.  52  4-  ox. 

biniodide. 

448 

12)  . 

64 

protoxide, 

208 

'Selenium,  . . . 

40 

peroxide. 

216 

Silica, 

16 

sulphuret. 

216 

Silicium, 

8 

bisulphuret. 

232 

Silver, 

110 

Molybdenum, 
protoxide,  (m.  48  -f- 

48 

chloride,  . 

146 

iodide. 

234 

ox.  8) 

56 

oxide,  ' . 

118 

deutoxide,  (m.  48  -f- 

phosphuret. 

125.71 

ox.  16) 

64 

sulphuret. 

126 

peroxide  (molybdic  acid) 

Sodium, 

24 

(m.  48  + ox.  24) 

72 

chloride. 

60 

Nickel, 

26 

iodide. 

148 

chloride,  . • . 

62 

protoxide,  (soda) 

32 

iodide. 

150 

peroxide,  (s.  24  -f-  ox. 

protoxide,  (n.  26  + 

12)  . 

36 

ox.  8) 

34 

phosphuret. 

39.71 

peroxide,  (n.  26  -f~ 

sulphuret. 

40 

12) 

38 

Strontium, 

44 

phosphuret. 

41.71 

chloride. 

80 

sulphuret, 

42 

iodide. 

168 

Nitrogen, 

14 

protoxide,  (strontia) 

52 

bicarburet,  (cyanogen) 

26 

phosphuret. 

59.71 

chloride,  (n.  14  chi. 

sulphuret. 

60 

144) 

158 

Sulphur, 

chloride. 

16 

iodide,  (n.  14  + 

52 

372) 

386 

iodide. 

140 

protoxide,  (n.  14  + ox. 

phosphuret. 

31.71 

8)  . 

22 

Sulphuretted  hydrogen. 

17 

deutoxide,  (n.  14  + ox. 

Tellurium,  (Berzelius) 

32 

16)  . 

30 

chloride. 

68 

Oxygen,  . 

8 

jk  oxide. 

40 

Palladium,  (Berz.) 

about  53 

Tin, 

• chloride,  . ' , 

58 

oxide, 

Phosi)horus,  (Berz.) 

61 

94 

15.71 

bichloride. 

130 

chloride. 

51.71 

protoxide. 

66 

bichloride. 

87.71 

deutoxide, 

74 

Tin,  phosphuret,  . 

sulphuret,  . ^ 

bisulphuret, 

Titanium, 

protoxide, 

deutoxide  (titanic  acid) 
Tungsten, 

deutoxide,  (brown) 

(t.  96  4-  ox.  16) 
tritoxide  (tungstic  acid) 
(t.  96  -}"  ox.  24) 
Uranium, 
protoxide, 
deutoxide, 

Water, 

Yttrium, 

oxide,  (yttria)  . 

Zinc, 

chloride, 

oxide, 

phosphuret, 

sulphuret. 

Zirconium, 

Zirconia,  t 

Salts, 

Acetate  of  alumina, 
c.  Iw. 
ammonia, 
c.  7w. 
baryta, 
c.  3w. 

cadmium,  (c.  2w.) 
copper,  (acid  50 
perox.  80)  . 
c.  6w.  (com.  verdi- 
gris) 

binacetate, 
c.  3w.  (distilled  ver 
digris)  , 
subacctate, 
lead, 
c.  3w. 
lime, 

magnesia, 
mercury,  (c.  4w.) 
potassa, 
silver, 

strontia,  (c.  Iw.) 
zinc, 
c.  7w. 

Arseniate  of  lead, 
lime, 

magnesia. 


appendix. 

601 

73.71 

Arseniate  of  potassa. 

106 

74 

binarseniate,  (c.  2w.)  . 

182 

.90 

silver. 

176 

32 

soda,  . t 

90 

40 

binarseniate,  (c.  4w.) 

184 

48 

strontia. 

110 

96 

Arsenite  of  lime. 

78 

potassa, 

98 

112 

soda. 

82 

silver. 

168 

120 

Carbonate  of 

208 

ammonia. 

39 

216 

sesquicarb.(acid  33  -j- 

224 

am.  17  + w.  9) 

59 

9 

bicarbonate  (Iw.) 

70 

34 

baryta. 

100 

42 

copper,  (acid  22 

34 

perox.  80) 

102 

70 

iron,  (acid  22  -f-  protox.  36) 

58 

42 

lead. 

134 

49.71 

lime. 

50 

50 

magnesia. 

42 

22  or  25 

manganese. 

58 

30  or  33 

potassa, 

70 

bicarbonate,  . 

92 

c.  Iw. 

101 

soda. 

54 

68 

c,  lOw. 

144 

77 

bicarbonate,  (c.  Iw.) 

85 

67 

strontia. 

74 

130 

zinc. 

64 

128 

Chlorate  of  baryta. 

154 

155 

lead. 

188 

132 

mercury, 

284 

potassa. 

124 

130 

Chromate  of  baryta, 

130 

lead, 

164 

184 

mercury, 

260 

180 

potassa. 

100 

bichromate,  . 

152 

207 

Muriate  of  ammonia, 

54 

210 

baryta,  (c.  Iw.) 

124 

• 162 

lime,  (c.  6w.) 

119 

189 

magnesia. 

57 

78 

strontia,  (c.  8w.) 

161 

70 

Nitrate  of  ammonia. 

71 

294 

baryta. 

132 

98 

bismuth,  (c.  3w.) 

161 

168 

lead, 

166 

111 

lime. 

82 

92 

magnesia. 

74 

. 155 

mercury,  (acid  54  + 

170 

protox.  208  + w.  18) 

280 

86 

potassa, 

102 

78 

silver, 

172 

51 


602 


APPENDIX. 


Nitrate  of  soda,  . 
strontia, 

Oxalate  of  ammonia, 
c.  2w. 
baryta, 
binoxalate, 
cobalt, 
lime, 
nickel, 
potassa, 
c.  Ivv. 
binoxalate, 
c.  2w. 

(juadroxalate, 
c.  7w. 
strontia, 
binoxalate, 

Phosphate  of  ammonia, 
(c.  2w.) 
baryta, 
lead, 
lime, 

magnesia, 
soda, 
c.  12|vv. 

Sulphate  of  alumina, 
alumina  and  potassa, 
c.25w.  (alum) 
ammonia,  (c.  Iw.) 


Sulphate  of  baryta,  . 118 

copper,  (acid  40  + pcrox.80)  120 
bipersulphatc,  . lOO 

c.  lOw.  (blue  vitriol)  . 250 

iron,  . . 76 

c.  7w.  (green  vitriol)  139 

lead,  . . 152 

lime,  . . 68 

c.  2w.  . . 86 

lithia,  (c.  Iw.)  . , 67 

magnesia,  (c.  7w.)  . 123 

mercury,  (acid  40  -|- 

perox.  216)  . 256 

bipersulphate  (acid 

80  + perox.  216)  296 

potassa,  . . 88 

bisulphate,  (c.  2w.)  . 146 

soda,  . . 72 

c.  lOw.  . . 162 

strontia,  . . 92 

zinc,  . . 82 

c.  7w.  . . 145 

Tartrate  of  lead,  • . 178 

lime,  . . 94 

potassa,  . . 114 

bitartrate,  . . 180 

c.  2w.  (cream  of  tartar)  198 

antimony  and  potassa, 

(c.  3w.)  (tartar  emetic)  363 


86 

106 

53 

71 

114 

150 

70 

64 

70 

84 

93 

120 

138 

192 

255 

88 

124 

70.71 

113.71 

147.71 

63.71 

55.71 

67.71 

180.21 

58 

262 

487 

66 


APPENDIX, 


603 


TABLE  11. 


TABLE  of  the  Elastic  Force  of  Aqueous  Vapour  at  different  Tempera- 
tures^ expressed  in  Inches  of  Mercury. 


Temp. 

Force  of  Vapour. 

Te.mp. 

Force  of  Vapour. 

Temp. 

Force-of  Vapour. 

Dalton. 

Ure. 

Dalton. 

Ure. 

Dalton. 

Ure. 

32°  F. 

0.200 

0.200 

79°F. 

0.971 

126^  F 

3.89 

33 

0.207 

80 

1.00 

1.010 

127 

4.00 

34 

0.214 

81 

1.04 

128 

4.11 

35 

0.221 

82 

1.07 

129 

4.22 

36 

0.229 

83 

1.10 

130 

4.34 

4.366 

37 

0.237 

84 

1.14 

131 

4.47 

38 

0.245 

85 

1.17 

1*170 

132 

4.60 

39 

0.254 

86 

1.21 

133 

4.73 

40 

0.263 

0.250 

87 

1.24 

134 

4.86 

41 

0.273 

88 

1.28 

135 

5.00 

5.070 

42 

0.283 

89 

1.32 

136 

5.14 

43 

0.294 

90 

1.36 

1.360 

137 

5 29 

44 

0.305 

91 

1.40 

138 

5.44 

45 

0,316 

92 

1.44 

139 

5 59 

46 

0,328 

93 

1.48 

140 

5.74 

5.770 

47 

0,339 

94 

1.53 

141 

5.90 

48 

0,351 

95 

1.58 

1.640 

142 

6.05 

49 

0.363 

96 

1.63 

143 

6.21 

50 

0.375 

0.360 

97 

1.68 

144 

6.37 

51 

0.388 

98 

1.74 

145 

6.53 

6.600 

52 

0.401 

99 

1.80 

146 

6.70 

53 

0.415 

100 

1.86 

1.860 

147 

6.87 

54 

0.429 

101 

1.92 

148 

7.05 

55 

0.443 

0.416 

102 

1.98 

149 

7.23 

56 

0.458 

103 

2.04 

150 

7.42 

7.530 

57 

0.474 

104 

2.11 

151 

7.61 

58 

0.490 

105 

2.18 

2.100  ' 

152 

7.81 

59 

0.507 

106 

2.25 

153 

801 

60 

0.524 

0.516 

107 

2.32 

154 

8.20 

61 

0.542 

108 

2.39 

155 

8.40 

8.500 

62 

0.560 

109 

2.46 

156 

8.60 

63 

0.578 

110 

2.53 

2.456 

157 

8.81 

64 

0.597 

111 

2.60 

158 

9.02 

65 

0.616 

0.630 

112 

2.68 

159 

9.24 

66 

0.635 

113 

2.76 

160 

9.46 

9.600 

67 

0.655 

114 

2.84 

161 

9.68 

68 

0.676 

115 

2.92 

2.820 

162 

9.91 

69 

0.698 

116 

3.08 

163 

10.15 

70 

0.721 

0.726 

117 

3.00 

164 

10.41 

71 

0.745 

118 

3.16 

165 

10.68 

10.800 

72 

0.770 

119 

3.25 

166 

10.96 

73 

0.796 

120 

3.33 

2.300 

167 

11.25 

74 

0.823 

121 

3.42 

168 

11.54 

75 

0.851 

0.860 

122 

3.50 

169 

11.83 

76 

0.880 

123 

3.59 

170 

12.13 

12.050 

77 

0.910 

124 

3.69 

171 

12.43 

78 

0.940 

125 

3.79 

3.830 

172 

12.73 

604 


APPENDIX, 


Table  //.  continued. 


Temp. 

Force  of  Vapour. 

Dalton. 

Ure. 

m^F. 

13.02 

174 

13.32 

175 

13.62 

13.550 

176 

13.92 

177 

14.22 

178 

14.52 

179 

14.83 

180 

15.15 

15.160 

181 

15.50 

182 

15.85 

183 

16.23 

184 

16.61 

185 

17.00 

16.900 

186 

17.40 

187 

17.80 

188 

18.20 

189 

18.60 

190 

19.00 

19.000 

191 

19.42 

192 

19.86 

193 

20.32 

194 

20.77 

195 

21.22 

21.100 

196 

21.63 

197 

22.13 

198 

22.69 

199 

23.16 

200 

23.64 

23.600 

201 

24.12 

202 

24.61 

203 

25.10 

204 

25.61 

205 

26.13 

25.900 

206 

26.66 

207 

27.20 

208 

27.74 

209 

28.29 

210 

28.84 

28.880 

211 

29.41 

212 

30.00 

30.000 

213 

30.60 

214 

31.21 

215 

31.83 

Ts“mp.  ' 

Force  of  Vapour. 

Dalton. 

Die. 

216®  F. 

32.46 

33.400 

217 

33.09 

218 

33.72 

219 

34.35 

220 

34.99 

35.540 

221 

35.63 

36.700 

222 

36.25 

223 

36.88 

224 

37.53 

225 

38.20 

39.110 

225 

38.89 

40.100 

227 

39.59 

228 

40.30 

229 

41.02 

230 

41.75 

43.100 

i231 

42.49 

;232 

43.24 

233 

44.00 

234 

44.78 

46.800 

235 

45.58 

47.220 

236 

46.39 

i237 

47.20 

238 

48.02 

50.300 

239 

48.84 

240 

49.67 

51.700 

241 

50,50 

242 

51.34 

53.600 

243 

52.18 

244 

53.03 

245 

53.88 

56.340 

246 

54.68 

247 

55.54 

248 

56.42 

60.400 

249 

57.31 

250 

58.21 

61.900 

251 

59.12 

63.500 

252 

60.05 

253 

61.00 

254 

61.92 

66.700 

255 

62.85 

67.25 

256 

63.76 

257 

64.82 

69.800 

258 

65.78 

Temp. 

Force  of  Vapour. 

Dalton. 

Ure. 

259®F. 

66.75 

260 

67.73 

72.300 

261 

68.72 

262 

69.72 

75.900 

263 

70.73 

264 

71.74 

77.900 

265 

72.76 

78.040 

266 

73.77 

267 

74.79 

81.900 

268 

75.80 

269 

76.82' 

84.900 

270 

77.85 

86.300 

271 

78.89 

88.000 

272 

79.94 

273 

80.98 

91.200 

274 

82  01 

275 

83.13 

93.480 

276 

84.35 

277 

85.47 

97.800 

278 

86.50 

279 

87.63 

101.600 

280 

88.75 

101.900 

281 

89.87 

104.400 

282 

90.99 

283 

92.11 

107.700 

,284 

93.23 

285 

94.35 

112.200 

286 

95.48 

|287 

96.64 

114.800 

288 

97.80 

289 

98.96 

118.200 

290 

100.12 

120.150 

291 

101.28 

292 

102.45 

123.100 

293 

103.63 

294 

104.80 

126.700 

295 

105.97 

129,000 

296, 

107.14 

297 

108.31 

133.900 

298 

109.48 

137.400 

299 

110.64 

300 

111.81 

139.700 

301 

112.98 

APPENDIX. 


605 


Table  IL  continued. 


Temp. 

Force  of  Vapour. 

Temp. 

Force  of  Vapour. 

Temp. 

Force  of  Vapour. 

Dalton. 

Ure. 

Dalton. 

Ure. 

Dalton. 

Ure. 

302^  Y. 

114.15 

144,300 

310®  F. 

123.53 

161.300 

318®F. 

132.72 

303 

115-32 

147.700 

311 

124.69 

164.800 

319 

133.86 

304 

116.50 

312 

125.85 

167.000 

320 

135.00 

305 

117.68 

150.560 

313 

127.00 

321 

136.14 

306 

118.86 

154.400 

314 

128.15 

322 

137.28 

30r 

120.03 

315 

129.29 

323 

138.42 

308 

121.20 

157.700 

316 

130.43 

324 

139.56 

309 

122.37 

[1317 

131.57 

325 

140.70 

m 


APPENDIX. 


TABLE  III. 


Dr.  Ure’s  TABLE,  showing  the  Elastic  Force  of  the  Vapours  of  Alcohol, 
Ether,  Oil  of  Turpentine,  and  Petroleum  or  Naphtha  at  different  Tem^ 
peratures,  expressed  in  Inches  of  Mercury. 


pother.  1 

Alcohol  sp,  gr.  0*813. 

AIcoliol  sp.  gr.  0.813. 

1 Petroleum. 

Teni  p. 

Force  of 
Vapour. 

Temp, 

P'orce  of 
Vapour.  - 

Temp, 

Force  of 
Vapour. 

Temp. 

Force  of 
Vapour, 

34° 

6.20 

32° 

0.40 

193.3° 

46.60 

316° 

30.00 

44 

8.10 

40 

0.56 

196.3 

50.10 

320 

31.70 

54 

10.30 

45 

0.70 

200 

53.00 

325  ' 

34.00 

64 

13.00 

50 

0.86 

206 

60.10 

330 

36.40 

74 

16.10 

55 

1.00 

210 

65.00 

335 

38.90 

84 

20.00 

60 

1.23 

214 

69.30 

340 

41.60 

94 

24.70 

65 

1.49 

216 

72.20 

345 

44.10 

104 

30.00 

70 

1.76 

220 

78.50 

350 

46.86 

105 

30.00 

75 

2.10 

225 

87.50 

355 

50.20 

no 

32.54 

80 

2.45 

230 

94.10 

360 

53.30 

115 

35.90 

85 

2.93 

232 

97.10 

365 

56.90 

120 

39.47 

90 

3.40 

236 

103.60 

370 

60.70 

125 

43.24 

95 

3.90 

238 

106.90 

372 

61.90 

130 

47.14 

100 

4.50 

240 

111.24 

375 

64.00 

135 

51.90 

105 

5.20 

244 

118.20 

140 

56.90 

‘ 110 

6.00 

247 

122.10 

Uil  01  lurpentine. 

145 

62.10 

115 

7.10 

248 

126.10 

Temp. 

Force  of 

150 

67.60 

120 

8.10 

249.7 

131.40 

Vapour. 

155 

73.60 

125 

9.25 

250 

132.30 



160 

80.30 

130 

10.60 

252 

138.60 

304° 

30.00 

165 

86.40 

135 

12.15 

254.3 

143.70 

307.6 

32.60 

170 

92.80 

140 

13.90 

258.6 

151.60 

310 

33.50 

175 

99.10 

145 

15,95 

260 

155.20 

315 

35.20 

180 

108.30 

150 

18.00 

262 

161.40 

320 

37.06 

185 

116.10 

155 

20.30 

264 

166.10 

322 

37.80 

190 

124.80 

160 

22.60 

326 

40.20 

195 

133.70 

165 

25.40 

330 

42.10 

200 

142.80 

170 

28.30 

336 

45.00 

205 

151.30 

173 

30.00 

340 

47.30 

210 

166.00 

178.3 

33.50 

343 

49.40 

180 

34.73 

347 

51.70 

182.3 

36.40 

350 

53.80 

185,3 

39.90 

354 

56.60 

190 

43.20 

357 

58.70 

360 

60.80 

362 

62.40 

APPENDIX. 


607 


TABLE  IV. 


Dr.  Ure^s  TABLD  of  the  Quantity  of  Oil  of  Vitriol,  of  sp,  1.8485, 
and  of  Anhydrous  Add,  in  100  Parts  of  dilute  Sulphuric  Acid  at  dif-^ 
ferent  Densities, 


Liquid. 

Sp.  Gr. 

Dry. 

Liquid, 

Sp.  Gr. 

Dry. 

Liquid- 

Sp.  Gr. 

Dry, 

100 

1.8485 

81.54 

66 

1.5503 

53.82 

32 

1.2334 

26.09 

99 

1.8475 

80.72 

65 

1.5390 

53.00 

31 

1.2260 

25.28 

98 

1.8460 

79.90 

64 

1.5280 

52.18 

30 

1.2184 

24.46 

97 

1.8439 

79.09 

63 

1.5170 

51.37 

29 

1.2108 

23.65 

96 

1.8410 

78.28 

62 

1.5066 

50.55 

28 

1.2032 

22.83 

95 

1.8376 

77.46 

61 

1.4960 

49.74 

27 

1.1956 

22.01 

94 

1.8336 

76.65 

60 

1.4860 

48.92 

26 

1.1876 

21.20 

93 

1.8290 

75.83 

59 

1.4760 

48.11 

25 

1.1792 

20.38 

92 

1.8233 

75.02 

58 

1.4660 

47.29 

24 

1.1706 

19.57 

91 

1.8179 

74.20 

57 

1.4560 

46.48 

23 

1.1626 

18.75 

90 

1.8115 

73.39 

56 

1.4460 

45.66 

22 

1.1549 

17.94 

89 

1.8043 

72.57 

55 

1.4360 

44.85 

21 

1.1480 

17.12 

88 

1.7962 

71.75 

54 

1.4265 

44.031 

20 

1.1410 

16.31 

87 

1.7870 

70.94 

53 

1.4170 

43.22 

19 

1-1330 

15.49 

86 

1.7774 

70.12 

52 

1.4073 

42.40' 

18 

1.1246 

14.68 

85 

1.7673 

69.31 

51 

1.3977 

41.58' 

17 

1.1165 

13.86 

84 

1.7570 

68.49 

50 

1.3884 

4:0.77 

16 

1.1090 

13.05 

83 

1.7465 

67.68 

49 

1.3?  88 

39.95 

15 

1.1019 

12.23 

82 

1.7360 

66.86 

48 

1.3697 

39.14 

14 

1.0953 

11.41 

81 

1.7245 

66.05 

47 

1.3612 

38.32 

13 

1.0887 

10.60 

80 

1.7120 

65.23 

46 

1.3530 

37.51 

12 

1.0809 

9.78 

79 

1.6993 

64.42 

45 

1.3440 

36.69 

11 

1.0743 

8.97 

78 

1.6870 

63.60 

44 

1.3345 

35.88 

10 

1.0682 

8.15 

77 

1.6750 

62.78 

43 

1,3255 

35.06 

9 

1,0614 

7.34 

76 

1.6630 

61.97 

42 

1.3165 

34-25 

8 

1.0544 

6.52 

75 

1.6520 

61.15 

41 

1.3080 

33.43 

7 

1.0477 

5.71 

74 

1.6415 

60.34 

40 

1.2999 

32.61 

6 

1.0405 

4.89 

73 

1.6321 

59.52 

39 

1.2913 

31.80 

5 

1.0336 

4.08 

72 

1.6204 

58.71 

38 

1.2826 

30.98 

4 

1.0268 

3.26 

71 

1.6090 

57.89 

37 

1.2740 

30.17 

3 

1.0206 

2.446 

70 

1.5975 

57.08 

36 

1.2654 

29.35 

2 

1.0140 

1.63 

69 

1.5868 

56.26 

35 

1.2572 

28  54 

1 

1.0074 

0.8154 

68 

1.5760 

55.45 

34 

1.2490 

27.72 

67 

1.5648 

54.63 

33 

1.2409 

26.91 

608 


APPENDIX. 


TABLE  V. 


Dr,  Ure^s  TABLE  of  the  Quantity  of  Real  or  Anhydrous  Nitric  Acid 
100  Parts  of  liquid  Acid  at  different  Densities, 


Specific 

Gravity. 

Real  acid 
in  100  parts 
of  the  liquid. 

specific 

Gravity. 

Real  acid 
in  100  parts 
of  the  liquid. 

Specific 

Gravity. 

Real  acid 
in  100  parts 
of  the  liquid. 

1.5000 

79.700 

1.3783 

52.602 

’ 1.1895 

26.301 

1.4980 

78.903 

1.3732 

51.805 

1.1833 

25.504 

1.4960 

78.106 

1.3681 

51.068 

1.1770 

24.707 

1.4940 

77.309 

1.3630 

50.211 

1.1709 

23.910 

1.4910 

76.512 

1.3579 

49.414 

1.1648 

23.113 

1.4880 

75.715 

1.3529 

48.617 

1.1587 

22.316 

1.4850 

74.918 

1.3477 

47.820 

1.1526 

21.519 

1.4830 

74.121 

1.3427 

47.023 

1.1465 

20.722 

1.4790 

73.324 

1.3376 

46.226 

1.1403 

19.925 

1.4760 

72.527 

1.3323 

45.429 

1.1345 

19.128 

1.4730 

71.730 

1.3270 

44.632 

1.1286 

18.331 

1.4700 

70.933 

1.3216 

43.835 

1.1227 

17.534 

1.4670 

70.136 

1.3163 

43.038 

1.1168 

16.737 

1.4640 

69.339 

1.3110 

42.241 

1.1109 

15.940 

1.4600 

68.542 

1.3056 

41.444 

1.1051 

15.143 

1.4570 

67.745 

1.3001 

40.647 

1.0993 

14.346 

1.4530 

66.948 

1.2947 

39.850 

1.0935 

13.549 

1.4500 

66.155 

1.2887 

39.053 

1.0878 

12.752 

1-4460 

65.354 

1.2826 

38.256 

1.0821 

11.955 

1.4424 

64.557 

1.2765 

37.459 

1.0764 

11.158 

1.4385 

63.760 

1.2705 

36.662 

1.0708 

10.361 

1.4346 

62.963 

1.2644 

35.865 

1.0651 

9.564 

1.4306 

62.166 

1.2583 

35.068 

1.0595 

8.767 

1.4269 

61.369 

1.2523 

34.271 

1.0540 

7.970 

1.4228 

60.572 

1.2462 

33.474 

1.0485 

7.173 

1.4189 

59.775 

1.2402 

32.677 

1.0430 

6.376 

1.4147 

58.978 

1.2341 

31.880 

1.0375 

5.579 

1.4107 

58.181 

1.2277 

31.083 

1.0320 

4.782 

1.4065 

57.384 

1.2212 

30.286 

1.0267 

3.985 

1.4023 

56.587 

1.2148 

29.489 

1.0212 

3.188 

1.3978 

55.790  ! 

1.2084 

28.692 

1.0159 

2.391 

1.3945 

54.993  I 

1 1.2019 

27.895 

1.0106 

1.594 

1.3882 

1.3833 

54.196  i 
53.399  1 

1 1.1958 

1 

27.098 

1.0053 

0.797 

APPENDIX. 


609 


TABLE  VI. 


TABLE  of  Lowltz  showing  the  Quantity  of  Absolute  Alcohol  in  Spirits  of 
different  Specific  Gravities, 


]O0  Parts . 

Sp.  G 

•avity. 

100  Parts. 

sp.  Gravity. 

100  Parts. 

Sp.  Gravity. 

Ale. 

Wat. 

At  68° 

At  60° 

Ale. 

Wat. 

At  68° 

At  60° 

Ale. 

Wat. 

At  68° 

At60« 

100 

0 

0.791 

0.796 

66 

34 

0.877 

0.881 

32 

68 

0.952 

0.955 

99 

1 

0.794 

0.798 

65 

35 

0.880 

0.883 

31 

69 

0,954 

0.957 

98 

2 

0.797 

0.801 

64 

36 

0.882 

0.886 

30 

70 

0.956 

0.958 

97 

3 

0.800 

0.804 

63 

37 

0.885 

0.889 

29 

71 

0.957 

0.960 

96 

4 

0.803 

0.807 

62, 

38 

0.887 

0.891 

28 

72 

0.959 

0.962 

95 

5 

0.805 

0.809 

61 

39 

0.889 

0.893 

27 

73 

0.961 

0.963 

94 

6 

0.808 

0.812 

60 

40 

0.892 

0.896 

26 

74 

0.963 

0.965 

93 

7 

0.811 

0.815 

59 

41 

0.894 

0.898 

25 

75 

0.965 

0.967 

92 

8 

0.813 

0.817 

58 

42 

0.896 

0.900 

24 

76 

0.966 

0.968 

91 

9 

0.816 

0,820 

57 

43 

0.899 

0.902 

23 

77 

0.968 

0.970 

90 

10 

0.818 

0.822 

56 

44 

0.901 

0.904 

22 

78 

0.970 

0.972 

89 

11 

0.821 

0.825 

55 

45 

0.903 

0.906 

21 

79 

0.971 

0.973 

88 

12 

0.823 

0.827 

54 

46 

0.905 

0.908 

20 

80 

0.973 

0.974 

87 

13 

0.826 

0.830 

53 

47 

0.907 

0.910 

19 

81 

0.974 

0.975 

86 

14 

0.828 

0.832 

52 

48 

0.909 

0.912 

18 

82 

0.976 

0.977 

85 

15 

0.831 

0.835 

51 

49 

0.912 

0.915 

17 

83 

0.977 

0.978 

84 

16 

0.834 

0.838 

50 

50 

0.914 

0.917 

16 

84 

0.978 

0.979 

83 

17 

0.836 

0.840 

49 

51 

0.917 

0.920 

15 

85 

0.980 

0.981 

82 

18 

0.839 

0.843 

48 

52 

0.919 

0.922 

14 

86 

0.981 

0.982 

81 

19 

0.842 

0.846 

47 

53 

0.921 

0.924 

13 

87 

0.983 

0.984 

80 

20. 

0.844 

0.848 

46 

54 

0.923 

0.926 

12 

88 

0.985 

0.986 

79 

21 

0.847 

0 851 

45 

55 

0.925 

0.928 

11 

89 

0.986 

0.987 

78 

22 

0.849 

0.853 

44 

56 

0.927 

0.930 

10 

90 

0.987 

0.988 

77 

23 

0.851 

0.855 

43 

57 

0.930 

0.933 

9 

91 

0.988 

0.989 

76 

24 

0.853 

0.857 

42 

58 

0.932 

0.935 

8 

92 

0.989 

0.990 

75 

25 

0.856 

0.860 

41 

59 

0.934 

0.937 

7 

93 

0.991 

0.991 

74 

26 

0.859 

0.863 

40 

60 

0.936 

0.939 

6 

94 

0.992 

0.992 

73 

27 

0.861 

0.865 

39 

61 

0.938 

0.941 

5 

95 

0.994 

72 

28 

0.863 

0.867 

38 

62 

0.940 

0.943 

4 

96 

0.995 

71 

29 

0:866 

0.870 

37 

63 

0.942 

0.945 

3 

97 

0.997 

70 

30 

0.868 

0.872 

36 

64 

0.944 

0.947 

2 

98 

0.998 

69 

31 

0.870 

0.874 

35 

65 

0.946 

0.949 

1 

99 

0.999 

68 

32 

0.872 

0.875 

34 

66 

0.948 

0.951 

0 

100 

1.000 

67 

33 

0.875 

0.879 

I 33 

67 

0.950 

0.953 

i 

610 


APPENDIX. 


TABLE  VII. 


TABLE  showing  the  Specific  Gravity  of  Liquids,  at  the  Temperature  of 
55°  Fahr,  corresponding  to  the  Degrees  of  Baumh^s  Hydrometer, 


For  Liquids  lighter  than  Water. 


Deg. 

Sp.  Gr. 

Deg. 

Sp.  Gr. 

Deg. 

Sp.  Gr. 

Sp.  Gr. 

Deg. 

Sp.  Gr 

10  = 

=1.000 

17= 

.949 

23  = 

.909 

29= 

.874 

35a=3 

.842 

11 

.990 

18 

.942 

24 

.903 

30 

.867 

36 

.837 

12 

.985 

19 

.935 

25 

.897 

31 

.861 

37 

.832 

13 

.977 

20 

.928 

26 

.892 

32 

.856 

38 

.827 

14 

.970 

21 

.922 

27 

.886 

33 

.852 

39 

.822 

15 

16 

.963 

.955 

22 

.915 

28 

.880 

34 

.847 

40 

.817 

For  Liquids  heavier  than  Water. 


Deg. 

Sp.  Gr. 

Deg. 

Sp.  Gr. 

Deg. 

Sp.  Gr. 

Deg. 

Sp.  Gr, 

Deg, 

Sp.  Gr 

0 = 

:1.000 

15=1.114 

30= 

:1.261 

45  = 

:1.455 

60  = 

:1.717 

3 

1 020 

18 

1.140 

33 

1.295 

48 

1.500 

63 

1.779 

6 

1.040 

21 

1.170 

36 

1.333 

51 

1.547 

66 

•1.848 

9 

1.064 

24 

1.200 

39 

1.373 

54 

1.594 

69 

1.920 

12 

1.089 

27 

1.230 

42 

1.414 

57 

1.659 

72 

2.000 

GENERAL  INDEX 


A 

Acetates,  459 
Acetous  fermentation,  523 
Acidifying  principle,  400 
Acids,  animal,  539 
definition  of,  400 
nomenclature  of,  108 
vegetable,  457 
Acid,  acetic,  457 
acetous,  457 
amylic,  505  ^ 

amniotic,  542. 

antimonic  and  antimonious,  360 

arsenic,  348 

arsenious,  345 

auric,  385 

benzoic,  469 

boletic,  472 

boracic,  199 

bromic,  230 

butyric,  capric,  caproic,  545 
camphoric,  471 
carbazotic,  474 
carbonic,  177 
caseic,  566 
ceric,  491 
chloric,  212 
chloriodic,  225 
chlorocyanic,  267 
chlorocarbonicj  216 
chlorochromic,  353 
chlorous,  210 
cholesteric,  546 
chromic,  352 
citric,  467 
columbic,  358 
cyanic,  264 
cyanous,  265 
ellagic,  470 
crythric,  541 
ferrocyanic,  269 
ferruretted  chyazic,  270 
fluoboric,  235 
fluochromic,  353 
fluoric,  234 
fluosilicic,  320 
formic,  542 
fulminic,  266 
gallic,  470 


Acid,  hippuric,  542 
hircic,  545 
hydriodic,  221 
hydrobromic,  229 
hydrochloric,  206 
hydrocyanic,  260 
hydrofluoric,  233 
hydroselenic,  255 
hydroxanthic,  273 
hyponitrous,  168 
hypophosphorous,  197 
hyposulphuric,  190 
hyposulphurous,  189 
igasuric,  472 
indigotic,  474 
iodic,  223 
iodous,  224 
kinic,  473 
lactic,  542 
lampic,  496 
lithic,  539 
malic,  468 

manganesic  and  manganeseous 
327 

margaric,  485,  514 
meconic,  473,  478 
mellitic,  472 
molybdic,  354 
molybdous,  355 
moroxylic,  472 
mucic,  472 
muriatic,  206 
nitric,  170 
nitro-muriatic,  210 
nitrous,  1 68 
oleic,  485, 514 
oxalic,  461 
oxymuriatic,  203 
pectic,  473 
perchloric,  213 
phocenic,  545 
phosphatic,  197 
phosphoric,  193 
phosphorous,  196 
prussic,  260 
purpuric,  541 
pyrocitric,  467 
pyroligneous,  457 
pyromalic,  468 


612 


INDEX. 


Acid,  pyromucic,  472 
pyrophosphoric,  195 
pyrotartaric,  4G4 
pyro-uric,  541 
rheumic,  472 
rosacic,  541 
saccholactic,  472 
sebacic,  545 
selenic,  201 
selcnious,  201 
silicic,  319 
silicofluoric,  321 
sorbic,  472 
stearic,  514 
suberic,  473 
succinic,  471 
sulphonaplithalic,  249 
sulphuric,  186 
sulphurous,  184 
sulphuretted  chyazic,  271 
sulphocyanic,  271 
sulphovinic,  495 
tartaric,  464 
titanic,  367 
tungstic,  355 
uric,  539 
zumic,  473 
Adipocire,  546 
Aeriform  bodies,  15 
Affinity,  chemical,  109 
table  of,  110 
elective,  single,  110 
elective,  double,  112 
disposing,  150 
quiescent  and  divellent,  112 
by  what  causes  modified,  114 
measure  of,  119 
Agedoite,  516 
Air,  atmospheric,  155 
Alabaster,  415 
Albumen,  534 

vegetable,  514 
incipient,  564 
Alcohol,  491 
Algaroth,  powder  of,  359 
Alizarine,  511 
Alkali,  volatile,  238 
Alkalimcter,  434 
Alkalies,  definition  of,  401 
native  vegetable,  475 
decomposition  of,  by  galvanism, 
99 

Alloys,  397 
Aloes,  bitter  of]  474 
Althea,  483 
Alum,  416 
Alumina,  311 


Aluminium  audits  oxide,  309 
Amalgams,  396 
Amalgam,  ammoniacal,  155 
Amber  and  its  acid,  488 
Ambergris  and  ambreinc,  547 
Ammonia,  238 

solution  of,  239 
character  of  the  salts  of,  238 
Ammoniarct  of  copper,  419 
Amnios,  liquor  of,  567 
Amidine,  503 
Analysis  defined,  IG 
Analysis,  proximate  and  ultimate,  of 
organic  substances,  455 
of  minerals,  584 
of  gases,  580 
of  mineral  waters,  589 
Animal  chemistry,  532 

proximate  principles,  532 
substances,  analysis  of^  455 
oils  and  fats,'  543 
heat,  556 
fluids,  547 

Antimony,  regulus  of,  crude  antimo- 
ny, 358 
oxides  of,  359 
chlorides  of,  360 
sulphurets  of,  36 
golden  sulphuret  of,  362 
glass,  crocus,  and  liver  of,  361  > 
alloys  of,  397 
tartarized,  466 
Anthracite,  500 
Aqua  regia,  210 
Arbor  Dianas,  383 
Saturni,  374 
Archil,  511 

Argentine  flowers  of  antimony,  359 
Arrow  root,  505 
Arseniates,  430 
Arsenical  solution,  431 
Arsenic,  344 

compounds  of  oxygen  with, 
345 

tests  of,  in  mixed  fluids,  346 
alloys  of,  397 
chloride  of  349 
sulphurets  of,  350 
Arsenites,  430 
Asparagin,  516 
Asphaltum,  499 
Atmospheric  air,  155 
analysis  of,  580 
weight  of,  155 
Atom,  what,  129 

Atomic  theory,  Dalton’s  view  of, 
129 


INDEX. 


613 


Atomic  theory,  Berzelius’  view  ofj 
137 

weights,  table  of,  597 
what,  130 

Atropa,  483 

Attraction,  chemical,  15,  109 
cohesive,  14 

terrestrial,  or  gravity,  14 
Aurum  musivum,  339 
Azotic  gas,  154 

Bdllc»ns,  146 
Balsams,  489 
Barilla,  435 
Barium,  301 

oxides  ofj  301 

chloride  and  sulphuret  of,  302, 
303 

Barley,  malting  of,  527 
Barometer,  correction  ofj  for  the  ef- 
fects of  heat,  32 
Baryta,  301 

Basis,  in  dyeing,  what,  508 
Bassorin,  517 

Battley’s  sedative  liquor,  477 
Baurne’s  hydrometer,  degrees  o5  re- 
duced to  the  common  stand- 
ard, 610 
Bell  metal,  397 
Benzoates,  470 
Bile  and  biliary  calculi,  561 
Bismuth  and  its  oxide,  365 
magistery  of^  365 
chloride,  bromide,  and  sulphu- 
ret of,  366 
alloys  of,  397 
Bitter  principle,  519 
Bituminous  substances,  498 
Black  dye,  512 
Black  drop,  479 
Black  lead,  333 
Bleaching,  206 
powder,  306 
Blende,  335 
Blood,  547 

Blowpipe,  with  oxygen  and  hydro- 
gen, 148 

with  oxygen  gas,  148 
Blue,  Prussian,  448 
dyes,  508 

Boa  constrictor,  urine  of,  539 

Boiling  point  of  liquids,  57 

Bones,  576 

Borates,  432 

Borax,  433 

Boracite,  433 

Boron,  198 


Boron,  chloride  of,  217 
Brain,  analysis  of  the,  578 
Brass,  398 
Brazil  wood,  511 
Bromates,  426 
Bromine,  226 
Bronze,  397 
Brucia,  480 
Butyrine,  545 
Butter,  545 

of  antimony  361 

C 

Cadmium,  336 
oxide  of,  337 
Caffein,  517 
Calamine,  335 
Calcium  and  oxide  of,  305 
chloride  of,  306 
Calcination,  279 
Calculi,  urinary,  573 
biliary,  562 
salivary,  559 
Calomel,  379 
Caloric,  19 

communication  of,  20 
radiation  of,  23 
effects  of,  28 
expansion  produced  by, 
in  solids,  30 
in  liquids,  31 
in  gases,  34 
specific,  43 

capacities  of  bodies  for,  43 
of  fluidity,  51 

sensible  and  insensible,  44 
latent,  44 
sources  of,  68 
quantity  ofi  in  bodies,  55 
Calorimeter,  45 
Calx,  279 
Camphor,  486 
Camphorates,  472 
Cannon  metal,  397 
Canton’s  phosphorus,  308 
Caoutchouc,  489 
Capacity  for  caloric,  43 
Carbon,  174 

compounds  ofj 

with  hydrogen,  240 
‘ nitrogen,  259 
chloride  of,  214 
sulphuret  of,  272 

Carbonates,  general  properties  of- 
433 

particular  description  of, 
434-438 
52 


614 


INDEX. 


Carbonic  acid,  177 
oxide,  181 

(^arbosulphurets,  273 
Carburelted  hydrogen,  241 
Carmine,  511 
Cartilage,  576 
Caseous  matter,  564 
oxide,  515 

Cassius,  purple  powder  of,  386 

Cassava,  505 

Catechu,  513 

Cathartin,  517 

Caustic,  lunar,  424 

Cerate,  491 

Cerin,  491 

Cerium  and  oxides,  364 
Cerulin,  510 
Ceruse,  438 
Cetine,  546 
Chalk,  437 

Chameleon  mineral,  326 
Charcoal,  174 

animal,  or  ivory  black,  1 74 
Cheese,  564 

Chemical  affinity  or  attraction,  109 
action,  changes  which  accom- 
pany it,  113 

Chemistry,  definition  of,  16 
organic,  17 
inorganic,  17 
nomenclature  of,  108 
Chinoidea,  480 

Classification  of  chemical  substan- 
ces, 16 

Chlorates,  general  characters  of,  425 
of  potassa  and  baryta,  425 
Chloric  ether,  245 
acid,  2l2 

Chloride  of  boron,  217 
bromine,  231 
carbon,  214 
cyanogen,  266 
iodine,  225 
lime,  306 
nitrogen,  213 
phosphorus,  216 
soda,  298 
sulphur,  215 
Chlorides,  metallic,  281 
Chlorine,  203 

and  hydrogen  (muriatic  acid), 
206 

and  oxygen,  210 
protoxide  of,  211 
peroxide  of,  211 
nature  of,  217 
Chloriodic  acid,  225 


Chlorocarbonic  acid,  216 
Chlorophyle,  520 
Cholesterine,  546 
Chromium,  351 

compounds  of,  with  oxygen,  352 
Chromate  of  iron,  431 
Chromates,  431 
Chrome  yellow,  432 
Cinchona  bark,  active  principles  of, 
479 

Cinchonia,  479 

Chyle,  563  » 

Cinnabar,  381 
Citrates,  468 
Coke,  500 
Coal,  499 
gas,  250 
Cobalt,  340 

oxides  of,  341 

Cocculus  indicus,  principle  of,  482 

Cochineal,  511 

Cohesive  attraction,  14  • 

Cohesion,  14 

influence  of,  over  chemical  ac- 
tion, 114  ' 

Cold,  artificial  methods  of  producing, 
53,  61 

Colocyntin,  519 
Colouring  matter,  507 
Colours,  adjective  and  substantive, 
508 

Columbium  and  its  acid,  357,  358 
Combination  defined,  16 
laws  of,  121 

Combining  proportions  explained,  122 
Combustion,  143 
theories  of,  143 
spontaneous,  484 

Composition  of  bodies,  how  deter- 
mined, 16 

Conductors  of  caloric,  20 
Congelation,  51 
Cooling  of  bodies,  28 
Copal,  488 
Copper-nickel,  342 
Copper,  369 

oxides  ofl  370 
chlorides  of,  371 
sulphurets  of,  372 
ammoniaret  of,  41 9 
alio  vs  of  397 

aminoniacal  sulphate  of,  419 
sheathing,  preservation  of,  99 
Cork,  517 

Corrosive  sublimate,  378 
(yorydalin,  482 
Coumarin,  487 


INDEX. 


615 


Cream  of  milk,  564 
tartar,  465 

Oocus  of  antimony,  361 
Cryophorus,  61 
Crystallization,  404 
of  salts,  404 
water  of,  403 
Curcuma  paper,  512 
Curd,  564 
Cuticle,  577 
Cyanogen,  259 
Cyanuret  of  chlorine,  266 
bromine,  268 
iodine,  268 

red,  of  iron  and  potassium,  447 
Cyanurets,  286 
metallic,  286 
Cynopia,  483 
Cystic  oxide,  575 

D 

Decomposition,  simple,  110 
double,  112 
Decrepitation,  403 
Deflagration,  279 
Deliquescence,  402 
Delphia,  483 
Derosne,  salt  of,  478 
Destructive  distillation,  455 
Detonating  powders,  425 
Dew,  formation  of,  27 
Diamond,  176 

Differential  thermometer,  37 
Digesting  flask,  590 
Dippel’s  oil,  543 
Disenfecting  liquid,  298 
Dragon’s  blood,  488 
Dutch-gold,  398 
Dyes,  507 

E 

Earths,  289,  309 
Ebullition,  57 
Efflorescence,  403 
Egg  shells,  577 
Eggs,  566 
Elaine,  485 
Elastic  gum,  489 

Elasticity,  its  effect  on  chemical  af- 
finity, 117 

Elective  affinity,  109 
Electricity,  73 
Electrical  machine,  77 
Electro-magnetism,  102 
Electro-negative  and  electro-positive 
bodies,  101 


Electro-chemical  theory,  il 
Electrometer,  81 

Elements,  what,  and  how  many,  16 
Emetia,  482 
Emetic  tartar,  466 
Emulsion,  485 
Epsom  salts,  416 
Equivalents,  chemical,  what,  125 
table  of,  597 

Erythrogen,  560 
Essential  oils,  485 
salt  of  lemons,  463 
Ether,  494 

acetic,  muriatic,  hydriodic,  497, 
498 

hydrobromic,  498 
chloric,  245 
nitrous,  497 
pyro-acetic,  458 
sulphocyanic,  498 
sulphuric,  494 
Ethiops  mineral,  381 
per  se,  377 
Euehlorine,  211 
Eudiometer,  160 
Hope’s,  581 
Volta’s,  580 
Evaporation,  60 
cause  of,  62 
limit  to,  63 
Expansion,  29 

of  solids  by  heat,  30 
liquids  by  do.  31 
gases  by  do.  34 
Extractive  matter,  51 9 
Eye,  humours  of,  567 

F 

Farina,  503 
Fat  of  animals,  543 
Feathers,  577 
Fecula,  503 
Fermentation,  520 
Ferrocyanates,  446 
Fibre,  woody,  506 
Fibrin,  533 
Filter,  588 

Fire-damp  of  coal  mines,  242 
Flame,  242, 243 
Fixed  oils,  484 
Flask  for  digesting,  590 
Flesh  of  animals,  577 
Flint,  319 

Flowers  of  sulphur,  184 
Fluidity  caused  by  caloric,  50 
Fluoric  acid,  234 
fluoboric  4cid,  235 


616 


INDEX. 


Fluoborates,  433 
Fluosilicic  acid  gas,  320 
Huosilicates,  322 
Fluorine,  232 
Fluor  spar,  444 
Flux,  white  and  black,  465 
Food  of  plants,  530 
Freezing  mixtures,  54 

in  vacuo,  Leslie’s  method,  61 
Frigorific  mixtures,  table  of,  54,  55 
Fulminating  gold,  385 
mercury,  265 
platinum,  389 
silver,  266 
Fulminic  acid,  266 
Fuming  liquor  of  Libavius,  339 
Fungin,  517 
Funnel,  588 
Fusion,  51 

watery,  403 
Fusible  metal,  397 
Fustic,  512 

G 

Galena,  372 
Gallates,  471 
Gall-nuts,  512 
Gall-stones,  562 
Galvanic  battery  or  trough,  89 
arrangements,  84,  88 
Galvanism,  84 
effects  of,  94 
chemical  agency  of,  96 
electrical  agency  of,  94 
connexion  of,  with  magnetism, 
102 

theories  of  its  production,  90 
Gases,  67 

condensation  oi^  67 
law  of  expansion  of,  35 
conducting  power  of,  22 
formula  for  correcting  the  effects 
of  heat  on,  35 
specific  caloric  of,  45 
their  bulk  influenced  by  mois- 
ture, and  the  formula  for  cor- 
recting its  effect,  64 
mode  of  drying,  67 
Gas  from  coal  and  oil,  250 
Gastric  juice,  660 
Gelatin,  536 
Germination,  526 
Gilding,  397 
Glass,  319 

expansion  of,  by  heat,  31 
antimony,  361 
Glauber’®  salt,,  414 


Gliadinc,  516 
Glucina,  313 
Glue,  536 
Gluten,  515 
Glycerine,  485, 514 
Gold,  384 

oxides  of,  385 
chlorides  of,  386 
fulminating  compound  of,  385 
sulphuret  of,  387 
alloys  of,  398 
mosaic,  339 

Golden  sulphuret  of  antimony,  362 
Gong,  Indian,  397 
Goulard’s  extract,  460 
Gouty  concretions, 540 
Graphite,  333 
Gravel,  urinary,  573 
Gravitation,  14 

Gravity,  effect  of,  on  chemical  actiom 
120 

specific,  modes  of  determining, 

106 

Growth  of  plants,  528 
Gum,  505 

elastic,  489 
Gum-resins,  489 
Gunpowder,  422 
Gypsum,  415 

H 

Hair,  577 

Harrowgate  water,  594 
Hartshorn,  spirit  of,  238 
Heat,  animal,  556 

intense,  how  generated,  148 
Hematin,  511 

Hiccory,  wild  American,  512 
Hircine,  545 

Homberg’s  pyrophorus,  41 7 
Honey,  503 
stone,  472 
Hoofs,  577 
Hordein,  505 
Horn,  577 
lead,  375 
silver,  383 

Humours  of  the  eye^  567 
Hydracids,  salts  of,  438 
Hydrates,  nature  of,  150 
Hydriodates,  441 , 

Hydro,  in  what  manner  employed, 

150 

Hydrocarburet  of  chlorine,  245 
bromine,  246 

iodine,  245  0 

Pydrocyanates,  445 


INDEX. 


617 


Hydrogfen,  146 

deutoxide  of,  151 
arseniuretted,  349 
carburetted,  241 
and  carbon,  new  compounds  of, 
246 

phosphuretted,  256 
potassuretted,  295 
seleniuretted,  255 
sulphuretted,  252 
telluretted,  369 
with  metals,  289 

Hydrometer,  Baume’s,  degrees  of,  re- 
duced to  the  oommon  stand- 
ard, 253 

Hydrosulphuric  acid,  253 
Hydrosulphurets  or  hydrosulphates, 
444 

Hygrometer,  65 
Hyperoxymuriates,  425 
Hypophosphorous  acid,  197 
Hyponitrous  acid,  236 
Hyposulphurous  acid,  189 
Hyposulphuric  acid,  190 

I 

Ice.  See  Water. 

Imponderables,  16 

influence  of,  over  chemical  ac- 
tion, 120 

Incandescence,  71 
Indigo,  508 
acid  of,  474 
resin  of,  474 
Indigogene,  511 
Ink,  471 

sympathetic,  341 

Insolubility,  influence  of,  on  affinity, 
115 

Inulin,  518 
lodates,  426 
Iodic  acid,  223 
Iodide  of  nitrogen,  225 
Iodides,  metallic,  282 
Iodine,  220 

and  hydrogen — hydriodic  acid, 

221 

and  phosphorus,  226 
and  sulphur,  226 

Ipecacuanha,  emetic  principle  of, 
482 

Iridium,  393 
^ron,  328 

oxides  of,  331 
chlorides  of,  332 
sulphuret,  phosphurct,  and  car- 
burets of,  333 


Isinglass,  536 
Ivory  black,  174 
Jelly,  animal,  536 
vegetable,  506 

K 

Kermes  mineral,  362 
Kelp,  435 
King’s  yellow,  351 

L 

Labarraque’s  soda  liquid,  298 
Lakes,  508 

Lamp  without  flame,  496 
safety,  242 
Lampblack,  488 
Lard,  543 
Latent  heat,  52 
Lateritious  sediment,  541 
Laws  of  combination,  121 
Law  of  multiples,  124 
Lead,  372 

oxides  of,  373 
chloride  of,  375 
iodide  and  sulphuret  of,  375 
phosphuret  and  carburet  of,  375 
alloys  of,  397 
Lemons,  acid  of,  467 
essential  salt  of,  463 
Leyden  jar,  80 

Libavius,  fuming  liquor  of,  339 
Ligaments,  577 
Light,  68 

chemical  effects  of,  70 
Light,  heating  power  of,  69 
magnetizing  power  of,  71 
modes  of  determining  its  inten- 
sity, 72 
Lignin,  506 
Lime,  305 

water  and  hydrate  of,  305 
milk  or  cream  of,  305 
chloride  of,  306 
phosphuret  of,  308 
stone,  437 

Liniment,  volatile,  485 
Liquefaction,  50 

Liquids,  expansion  ofj  by  heat,  32 
conducting  powers  of,  22 
Liquorice-root,  sugar  of,  503 
Litharge,  374 
Lithia,  300 
Lithates,  540 
Lithium,  300 
Litmus,  511 
paper,  588 

Liver  of  antimony,  361 


61i8 


INDEX. 


Liver  of  sulphur  (hepar  sulphuris) 
284 

Logwood,  511 
Luna  cornea,  383 
Lunar  caustic,  382 
Lupulin,  518 
Lymph,  567 

M 

Madder,  511 

Magistery  of  bismuth,  365 
Magnesia,  308 
Magnesium,  308 
Magnetism,  electro,  102 
Malachite,  438 
Malatcs,  469 
Maltha,  499 
Malting,  527 
Manganese,  322 
oxides  of,  323 

chloride  and  sulphuret  of,  327^ 
328 

fluoride  of,  328 
Manganesiates,  327 
Manna  and  mannite,  503 
Marble,  437 
Massicot,  374 
Mattter,  properties  of,  13 
Meconic  acid,  473, 478 
Medullin,  518 
Membranes,  577 
Mercury,  376 
oxides  of,  377 
chlorides  of,  378 
cyanuret  and  sulphurets  of,  389 
iodides  of,  380 
fulminating,  265 
muriate  of  (corrosive  sublimate) 
378 

submuriate  of,  (calomel)  379 
Metallic  combinations,  395 
Metals,  275 

general  classification  of,  289 
properties  of,  275 
table  of  discovery  of,  275 
specific  gravity  of,  276 
fusibility  of,  278 
reduction  of,  280 
combustibility  of,  279 
compounds  of, 
with  chlorine,  281 
iodino,  282 
bromine,  282 
[sulphur,  283 
selenium,  286 
cyanogen,  286 
phpsphorus,  288 
hydrogen,  289 


Meteoric  stones,  329 
Milk,  564 
Milk,  sugar  of,  539 
Mindererus’s  spirit,  459 
Mineral  chameleon,  326- 
Mineral  tar,  499 
pitch,  499 

Mineral  yellow,  375 
Mineral  waters,  analysis  of,  589 
Minium,  374 
Molasses,  502 
Molybdates,  354 
Molybdenum,  354 

compounds  of,  with  oxygen, 
354 

sulphuret  of,  355 
Mordant,  508 
Morphia,  476 
Mother  of  pearl,  577 
Mucilage,  506 
Mucus,  568 

Mutiples,  law  of  combination  in, 
124 

Muriates,  439 
Muriatic  ether,  498 
Muscle,  577 

converted  into  fat,  546 
Mushrooms,  peculiar  substance  of, 
517 

Myrica  cerifera,  wax  from,  490 
Myricin,  491 

N 

Nails  of  animals,  577 
Naphtha,  498 

from  coal  tar,  248 
Naphthaline,  248 
Narcotine,  478 

Neutral  salts,  characters  of,  401 
Neutralization,  113 
Nickel,  342 

oxides  of,  343 

Nitrates,  general  characters  of,  421 
particular,  descriptions  of,  42 1 
to  424 
Nitre,  422 
Nitric  acid,  179 
oxide,  165 

Nitrites,  general  characters  of,  424 
Nitrogen  gas,  154 
protoxide  of,  163 
deutoxide  of,  165 
Nitrous  acid,  168 
gas,  165 
oxide,  163 
Nomenclature,  108, 


INDEX. 


619 


O 

Oil,  Dippel’s  animal,  54S 
of  vitriol,  186 
of  wine,  495 
gas,  250 

Oils,  animal,  543 
fixed,  484 

volatile,  or  essential,.  485 
Ointment,  491 
Olefiant  gas,  243 
Olive  oil,  484,  485 
Olivile,  518 

Opium,  active  principle  of,  476 
Organic  chemistry,  453 

substances,  character  of,  453 
Orpiment,  350 
Osmazome,  577 
Osmium  and  its  oxide,  392 
Oxalates,  462 

Oxalic  acid,  crystallized,  composi- 
tion of,  462 
Oxidation,  141 
Oxide,  cystic,  575 
xanthic,  575 
Oxides,  what,  142 

nomenclature  of,  108 
Oxygen,  140 

Oxy-hydrogen  blowpipe,  148 
Oxiodine,  224 
Oxymuriatic  acid,  203 
Oxymuriate  of  potassa,  425 

P 

Palladium  and  its  oxide,  390 

Pancreatic  juice,  559 

Paper,  preparation  of,  for  tests,  588 

Papin’s  digester,  58 

Particles,  integrant  and  component,  15 

Patent  yellow,  375 

Pearls,  577 

Pearlash,  434 

Pericardium,  liquor  of  the,  567 
Perspiration,  fluid,  of,  569 
Petroleum,  499 
Pewter,  397 
Phenecin,5l0 
Phlogiston,  143 
Phosgene  gas,  216 
Phosphates,  general  characters  of,  427 
particular  description  of,  427  t;o 
429 

Phosphatic  acid,  197 
Phosphorescence,  72 
Phosphoric  acid,  193 
ether,  495 

Phosphorous  acid,  196 
Phosphorus,  191 

with  oxygen,  193 


Phosphol’us,  oxides  of,  198 
with  chlorine,  216 
with  iodine,  226 
Canton’s,  308 
Phosphurets,  metallic,  288 
Phosphuret  of  lime,  308 
Phosphuretted  hydrogen  gas,  255 
Photometer,  72 
Picromel,  561 
Picrotoxia,  482 
Pinchbeck,  398 
Piperin,  518 
Pitchblende,  362 
Pitch,  mineral,  499 
Pit-coal,  499 
Plants,  growth  of,  528 
food  of,  530 
Plaster  of  Paris,  415 
Plasters,  488 
Platinum,  387 

chlorides  and  oxides  of,  388 
sulphuret  of,  389 
alloys  ofi  398 
fulminating,  389 
Plumbagin,  519 
Plumbago,  333 
Pluranium,  394 
Pollenin,  518 
Polycroite,  512 
Potassa,  292 
tests  of,  295 
Potash,  292 
Potassium,  291 
oxides  of,  292 

Potassium,  chloride  and  iodide  of,  295 
with  hydrogen,  sulphur,  and 
phosphorus,  295,  296 
Potato,  starch  of,  504 
Precipitate,  red,  377 
Precipitation  explained,  114 
Pressure,  influence  of,  on  the  bulk  of 
gases,  107 

Proportions  in  which  bodies  com- 
bine, 121 

Proportional  numbers  defined,  125 
table  of, 

Prussian  blue,  448 
Prussiates,  445 
Prussiate  triple,  446 
Purple  powder  of  Cassius,  386 
Purpurate  of  ammonia,  541 
Pus,  568 
Putrefaction,  524 
Putrefactive  fermentation,  524 
Pyrites,  iron,  333 
copper,  372 
Pyroacetic  ether,  458 
Pyroxilic  spirit,  507 


620 


INDEX. 


Pyrometer,  40 

Pyrophorus  of  Homberg,  417 

Quantity,  its  influence  on  affinity, 
118 

Quercitron  bark,  512 
Quicklime,  305 
Quicksilver,  376 
Quills,  577 
Quinia,  479 

R 

Radiant  heat,  23 
Rays,  luminous,  68 
calorific,  69 
chemical,  71 
Realgar,  350 
Red  lead,  374 
dyes,  511 

Reduction  of  metals,  280 
Regulus  of  antimony,  358 
Rennet,  564 

Repulsion  opposed  to  cohesion,  29 
Resins,  487 
Resin  of  copper,  371 
Respiration,  552 
Retinasphaltum,  499 
Rh^in,  519 
Rhodium,  391 
oxides  of,  391 
Rhubarbarin,  519 
Rhutenium,  394 
Rochelle  salt,  465 
Rouge,  511 
Rusting  of  iron,  330 

S 

Saccharine  fermentation,  520 
Safety  lamp,  242 
Safflower,  Ml 
Saffron,  512 
Sago  and  salep,  505 
Sal  ammoniac,  439 
Salifiable  base,  40 1 
Saliva,  559 
Salt,  common,  297 
of  sorrel,  463 
petre,  422 
spirit  of,  208 

Salts,  general  remarks  on,  400 
nomenclature  of,  108,  109 
classification  of,  401 
affinity  of’,  for  water,  402 
crystallization  of,  402 
double  and  Iripple,  404 
Sanguinaria,  483 


Sarcocoll,  518 

Saturated  solution,  what,  118 
Saxon  blue,  510 
Scale  of  equivalents,  597 
Scheele’s  green,  347 
Sea  water,  591 
Secreted  animal  fluids,  559 
Sealing  wax,  488 
Sediment  of  the  urine,  573 
Seignette,  salt  of,  465 
Selenic  acid,  201 
Selenite,  415 
Selenious  acid,  201 
Selenium,  200 
oxide  of,  201 

Seleniuretted  hydrogen,  255 
Seleniurets,  metallic,  286 
Serosity  and  serum,  548 
Serous  membranes,  fluid  of,  567 
Shells,  577 
Silica,  319 
Silicates,  319 
Silieated  alkali,  319 
Silicium,  317 
Silk,  577 

Silver  and  its  oxide,  381,  382 
chloride  of,  383 

iodide,  cyanuret,  and  sulphuret 
of,  383,  384 

fulminating  compounds  of,  265, 
383 

alloys  of,  398 
Skin,  577 
Smalt,  340 
Soap,  485,  514 
Soda,  297 

tests  of,  297 
Sodium,  296 

oxides  of,  297 
chloride  of,  297 
Solania,  483 
Solar  rays,  69 
Solder,  397 

Solids,  expansion  of,  by  heat,  29 
liquefaction  of,  50 
conducting  power  of,  20 
specific  caloric  of,  48 
Solution,  118 
Sorrel,  salt  of,  463 
Spar,  Iceland,  437 
fluor,  444 
heavy,  415 
Specific  gravity,  106 
caloric,  43 

Speculum  metal,  398 
Spectrum,  prismatic,  69 
Spelter,  335 


INDEX. 


m 


spermaceti,  543 
Spirit,  proof,  492 
of  wijie,  491 

pyroxylic  and  pyroacetic,  507 
Starch,  503 
Starkey’s  soap,  486 
Steam,  temperature  of,  58 
elasticity  of,  59 
latent  heat  ofi  60 
engine,  principle  of,  59 
Stearine,  485,  514 
Steel,  334 

new  alloys  of,  398 
Strontia,  303 
Strontium,  303 

oxides  and  chloride  of,  303,  304 
Strychnia,  480 
Suberin,  517 
Succinates,  471 
Suet,  543 
Sugar,  501 

of  lead,  460 
of  grapes,  502 
of  liquorice,  503 
of  milk,  539 
of  diabetes,  539 
Sugar  candy,  502 

Sulphates,  general  characters  of,  413 
particular  description  of,  414  to 
426 

Sulphites,  sulphuretted,  189 
general  characters  of,  420 
Sulphocyanates,  449 
Sulphur,  183 

balsam  of,  486 
compounds  of, 
with  oxygen,  184 

chlorine,  215  ' 

carbon,  272 
selenium,  274 
Sulphurets,  metallic,  283 
Sulphurous  acid,  184 
Sulphuretted  hydrogeu,  252 
Sulphuric  acid,  186 

table  of,  607 
ether,  494 

Supporter  of  combustion,  142 
Surturbrand,  499 
Sweat,  569 
Synthesis  defined,  16 

T 

Tallow,  514 
Tannin,  512 

artificial  formation  of,  514 
Tanno-gelatin,  513 
Tantalum,  35.7 


Tapioca,  505 
Tar,  mineral,  499 
Tartar,  cream  of,  465 
soluble,  465 
emetic,  466 
Tartrates,  465 
Tears,  568 
Teeth,  576 

Telluretted  hydrogen  gas,  369 
Tellurium  and  its  oxide,  368 
Temperatures,  what,  42 
Tenacity  of  different  metals,  277 
Tendons,  577 
Thermometer,  37 
differential,  37 

formula  for  converting  the  ex' 
pression  of  one  into  another, 
39 

register,  41 

Thermometers,  graduation  of,  39 

Thorina,  315 

Tin  and  oxides  of,  338 

chlorides  and  sulphurets  of,  339 
alloys  of,  397 
Tincal,  433 

Titanium  and  its  compounds  with 
oxygen,  366, 367 
Tombac,  398 
Trona,  436 
Treacle,  502 
Trough,  galvanic,  113 
Tungsten  and  its  compounds  with 
oxygen,  355 
Turpeth  mineral,  419 
Turmeric,  a dye,  512 
paper,  512 
Turnsol,  511 
Turpentine,  oil  of,  486 
Type,  metal  for,  397 

U 

Ulmin,  517 

Ultramarine,  298 

Uranium  and  oxides,  362, 363 

Urates,  540 

Urea,  537 

Urine,  569 

Urinary  concretions,  573 
V 

Vacuum,  boiling  in,  58 
evaporation  in,  61 
Vanadium,  394 
Vaporization,  56 
cause  of,  56 

Vapour,  dilatation  of,  56 
density  of,  56 


INDEX. 


1 


m 

Vapour,  elastic  force  of,  58 
latent  heat  of,  60 
limit  of,  63 
table  of  the  elastic  force  of,  603 
Vegetable  acids,  457 
alkalies,  475 
extract,  519 
jelly,  506 
chemistry,  455 
substances,  455 
Vegetation,  528 
Veratria,  481 
Verdigris,  460 
Verditer,  438 
Vermilion,  381 
Vinegar,  457 
Vinous  fermentation,  521 
Vitriol,  blue,  419 

green  and  white,  417,  418 
oil  of,  186 

Volta’s  eudiometer,  580 
pile,  89 

Volta,  theory  of,  90 
Volumes,  theory  of,  133 

W 

Water,  composition  of,  149 
properties  of,  150 
expansion  of,  in  freezing,  33 
latent  heat  of,  51 
boiling  and  freezing  point  of,  39 
solubility  of  gases  in,  151 
of  crystallization,  403 
rain,  snow,  spring,  well,  river, 
589 

of  the  sea  and  the  Dead  Sea,  592 


Waters,  mineral,  589 

acidulous,  alkaline,  chalybeate, 
sulphurous  and  siliceous,  5H9 
saline,  590 
Wax,  490 
Welding,  329 
Wheat  flour,  503 
Whey,  564 
White  lead,  438 
White  copper,  398 
Wine,  quantity  of  alcohol  in,  494 
oil  of,  495 

Wires,  tenacity  of,  277 
Woad,  508 
Woody  fibre,  506 
Wool,  577 

X 

Xanthic  oxide,  575 
Xanthogen,273 

Y 

Yeast,  516 

Yellow,  mineral,  or  patent,  375 
king’s,  351 
chrome,  432 
dyes,  512 

Yttria  and  its  base,  314 

Z 

Zaffre,  340 
Zero,  absolute,  55 
Zymome,  516 
Zinc,  335 

oxide  and  chloride  of,  335»  336 
sulphuret  of,  336 
Zirconia  and  its  base,  316 


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